With the indoor seed starting season right around the corner, and direct planting soon to follow, I figured it was a good time to share how to start seeds indoors. When starting your own seedlings as long as it is done correctly, it can save you tens to hundreds of dollars. Not only that, but you’ll also have healthier plants, and increased options for varieties since you choose the seeds!
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This is a complete guide on how to start seeds indoors. I have started just a few seeds indoors and up to hundreds! But to tell you the truth, after many years of starting seeds indoors, I have completely moved away from this practice. I explain this more in detail later in this blog post. But it basically comes down to the fact that I start everything in an unheated outdoor tunnel now.
It took me 14 years of gardening before I purchased one, and before that I started seeds indoors. I explain below some of the things that no one tells you about indoor seed starting, like when it is a good idea and when you should look into other options.
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Indoor seed starting is the process of germinating and growing seeds indoors in a soil medium. The basic concept is the same as outdoors, you need seeds, light, soil and water in order for them to grow.
Indoor seed starting is a way to get to a harvest more quickly than direct sowing outdoors, in most cases. This is due to the fact that seeds germinate best at certain soil temperatures.
If you try to start a tomato seed in the ground in March and the ground is cold, along with the air temperature still getting below freezing occasionally, that tomato seed wouldn’t sprout until the conditions were right. It could be a few weeks to a few months depending on your climate.
However, if you were to plant that same tomato seedling indoors, with a heat mat, creating the optimal soil temperature, it would sprout quickly and get started growing. In theory, it will save you time to get to harvest because you’ve done the germination and the sprouting indoors.
And yet the time you spend growing the seedlings indoors will not directly save you that exact same amount of time outdoors. The reason for this being that seedlings grown indoors need to have time to get used to the amount of light that is outdoors, and the elements like wind. This is called hardening off.
In addition to hardening off a seedling, you also need to transplant. When transplanting, the seedlings go through some shock, called “transplant shock”. Even a small amount of transplant shock, will set back the plant in growth for several days if not more. So both these factors would lead to a certain amount of lag behind a plant that is directly sown in the ground.
But overall, starting seeds indoors can allow you to mimic optimal soil conditions and temperature, thus getting a head start on growing.
Larger plants that are transplanted into the ground means the plants can be spaced exactly with little to no thinning involved.
When you don’t need to remove excess plants, you save money on the seeds and you save time, because you don’t need to go back and remove extra plants.
Another reason to start seeds indoors would be to get ahead of the weeds. You can weed just prior to planting, then transplant large plants into the ground. This practice allows you to easily seed where your crops you want to grow are and where the weeds are.
When weeding can be done without as much effort, it is more likely to get done in the first place. Anything that makes it easier and faster for you to weed is a good thing!
They also sell large kits HERE and HERE. But I would discourage it. If you are starting a large amount of seedlings indoors each year, in my opinion it would be wiser to invest your money in an outdoor seed starting setup like a small greenhouse, unheated tunnel, or high tunnel. For the cost of a large all in one kit, you could buy an entire caterpillar tunnel (almost!).
Are indoor seed starting supplies worth the money? Like every project, there is some upfront costs to get the equipment. The idea is that over time, you’ll pay it off with the savings you reap, and then save money every year there after. If you know you won’t use the materials long enough to make back the money you spent, then by all means, buy transplants from someone else!
First off, I want to share when it makes sense as a gardener to start seeds indoors. When I say “makes sense”, I’m referring to if it is worth your time and energy to start them indoors. I haven’t heard many people talk about this but it is very important. Here are my two criteria for if It makes sense to start seeds indoors.
Let me explain the why behind reason #1. When I bumped up my garden size, I increased the number of plants I would grow indoors. Specifically what comes to mind is tomatoes, starting 20 tomatoes indoors is no biggie, but if you get up to 120 tomatoes like me, it starts to get crazy.
First off, you need to have enough lights to grow that large amount, you need to have extra shelving, and you need to have a ton of extra time to maneuver all of them around when it comes time to harden them off. If you’re starting other seedlings too like peppers, herbs, flowers, it adds even more time, lights, shelving. You get the idea.
A crazy mess of indoor started plants that are being acclimated to the outdoors. It was WAY too much to move inside and out for two weeks. Tomatoes outgrew the indoor lighting and got leggy. After this experience, we started seeds in the caterpillar tunnel. It was amazing!Any mess ups, like not enough space under lights and not watering sufficiently can lead to weak plants. When you have a lot to manage, it becomes more difficult to keep ideal conditions.
It is not my intent to discourage indoor seed starting, merely to point out when it makes sense to do so. The alternative would be either direct sowing seeds or seed starting outdoors in a greenhouse, high tunnel, caterpillar tunnel, or any smaller covered area, even in recycled plastic milk jugs or cloches (winter sowing).
Since switching over to outdoor seed starting I’ve noticed a huge jump in the health of the plants right off the bat, so it is now my preferred method. I do realize, however, that it is not ideal for some of you! There is definitely no “one size fits all” in seed starting. I’ll talk more about outdoor seed starting in my next blog post, but for now, back to how to start seeds indoors.
My number one advice tip for when to start seeds indoors is DO NOT begin indoor seed starting too early! This is a huge mistake among new gardeners. Plants started too early can become leggy, root-bound, or flowering transplants can cause stunting and reduce early production.
The best time to start seeds indoors will often be stated by your seed packet. Personally, I always lean toward the shorter of the time frames.
Black Cherry Tomatoes at harvest!For example, on black cherry tomatoes from the Baker Creek Heirloom Seeds website it says:
“Growing Tips: Start indoors 6-10 weeks before last frost. Heat mat helps to warm soil and speed germination.”
I would never, ever start tomatoes ten weeks early, they may be flowering by then. I would start them six weeks before I plant to transplant them. Which is actually a week or two past my last frost!
This is my personal opinion, obviously, you can start your tomatoes whenever you wish 🙂 I have a longer season, so I don’t have to worry about not getting a harvest if I plant them too late.
If you don’t know your average last frost you can find it out HERE. Keep in mind, it is an average, not an absolute. You could still get frost after that date, but it’s easy to keep an eye on it with the weather forecast being about 14 days in advance.
As I mentioned, I love using soil blocks for starting seeds indoors. It is not for everyone though, so below I’ll tell you how to start seeds in both cell trays and soil blocks.
Some seed starting soil mixes come with a “wetting agent” on them allowing you to easily moisten them after sowing seeds. If your soil mix doesn’t include this, you must wet down your mix prior to putting it in the tray!
The reason behind this is that most soil mixes are made with peat moss. When peat moss is dry, it is hydrophobic, meaning it repels water. The best way to get peat moss in a soil mix wet all the way through is to moisten it in a container and mix it around until it is all moist, almost like mixing cake batter!
This is pretty straight forward but some tips I would add are to make sure all the edges of the tray get the same amount as the middle, and that they are filled completely to the top.
Add a depression to the soil will help your seeds to germinate. The depth of the hole definitely matters! Check your soil packet and see how deep the seed needs to go.
If you feel unsure, I would go more towards too shallow rather than too deep.
Southern Exposure Seed Exchange has a good general guide that says:
“Seeds need air as well as water to germinate. Sow no deeper than 3 to 4 times the diameter of the seed or in the case of oblong seed no deeper than 1 to 3 times the length of the seed.”
I cover any seed that is sown at a quarter inch or more with indoor seed starting soil mix. Some people prefer vermiculite since it is lighter. But vermiculite is just one more thing to buy and to be honest, I get just as good of results from covering with moistened soil mix.
Anything that should be surface sown, like lettuce, I do not cover with anything. You’ll need to keep these seeds moist at all times. And I said moist, not soaking so a fine mist of water sprayed a few times will do.
Some seed trays come with plastic covers or you can cover a seed tray with plastic wrap, in order to keep the moisture in. With every good thing, comes the ability for it to become something bad too.
The intention is to use these only until the very first seed is emerging. Don’t wait until they all emerge. Take the cover off ASAP when you see the emergence of a seedling. Any longer and you’ll increase the risk of fungal diseases, especially damping off. This fungus will kill the seedlings, usually at the soil surface it will turn brown and die.
I use a cover with I am surface sowing seeds like lettuce.
I rarely use a cover if I have covered the seedling with the soil mix. I would especially not use it if you are sowing peppers, tomatoes, or any other nightshades, which are prone to fungal diseases.
If you didn’t pre moisten your soil in step #1, make sure all the soil is moist at this point. It should not be soaked. Hopefully, whatever tray you chose has holes in the bottom to prevent overwatering 🙂 Then place it under grow lights.
An important word about lights, if using fluorescent lights, the lights should literally sit within 2 inches of the tray. This will prevent the seedlings from getting leggy.
LED grow lights are a different story. Some are very intense and need to be placed farther away from the seedlings. You’ll need to experiment with trial and error here since all LED lights are not the same. If the seedlings turn white they are getting too much exposure, if they have long stems and look light they are reaching toward the light they are not getting enough light.
Usually, most people will not put the light close enough. Start close and work your way away from the trays if needed.
It’s always best to mimic nature with gardening. So 12-14 hours with lights on, the rest of the day, lights off! Get a timer to plug your lights into and it will make your life easier 🙂
For seeds that require a higher soil temperature for germination, add a heat mat underneath the tray. Usually anything categorized as a summer crop like tomatoes and peppers should use a heat mat.
If you have an area right next to a warm wood stove or heat source in your home, this would work as an alternative. Just make sure you can set up your lighting there too.
A fan mimics a breeze that would naturally be found outdoors. It will help to keep your plants strong and sturdy and also keep fungal diseases at bay.
Again, do not overwater. Ideally, you should be bottom watering the trays to keep them moist after the seedling emerge. I use a wicking mat placed under the soil tray for this. It takes water in a tray and wicks it up under the tray (since 99% of plastic trays have holes this is where the water is soaked in). The CELL TRAYS I like come with this set up. Or you can create your own.
The reason for watering from the bottom is it helps to prevent fungal diseases.
If the soil dries out completely, so will your plants. There isn’t a lot of soil there, so you really need to keep an eye on it!
If you see roots poking out of your trays, or the plants are getting large and crowded, move them to a larger container and add more soil!
This is a critical step to success, the plants will stagnate in growth if you wait too long to pot them up. When in doubt move them to a larger pot size earlier, rather than too late.
Very likely, your seedling will need additional fertilizer until the time they can get outside. My very favorite is a water soluble fish fertilizer. It can be found HERE. Follow the directions for dilution rates. It is very stinky but works so good.
Once outdoor conditions allow you to do so, (warm enough soil and air temperature), it’s time to harden off the seedlings.
This process gets them used to the outside light and air. Slow and steady is the absolute key!
Keep in mind, this is not an exact science unless you get clear skies everyday. If you get a cloudy day, the seedlings will get less light, on a sunny day, they will get tons of light. Watch the weather closely and adjust accordingly.
Most seedlings are placed in the soil at the same depth as the tray. Tomatoes in particular should be buried deep in the soil a few inches away from the first set of leaves, or placed sideways so the stem is parallel with the soil, the leaves still remain above the soil level. Peppers can also be buried slightly deeper, as can corn- if you’ve ventured into growing that in a seed tray.
The process for starting seeds indoors in soil blocks is similar to cell trays, but has some differences. I’ve noted them all below.
When making soil blocks, the only way to make them is to wet down the mix. If the soil is too dry and they fall apart, if the soil is too wet they slip out before you’re able to compress the soil. When in doubt aim towards the more wet side. It should look like brownie mix when it’s the right moisture level
To make soil blocks you need a fairly deep tray or container, 8-12 inches to pile the wet soil and make blocks. I have a very in depth guide on how to do this HERE. Prior to starting, pick the correct dibble (I think that’s what it’s called), it’s a little plastic piece that creates the depth in the block.
Most soil blocks come with the standard size, I believe it’s a 1/4 inch deep but you can buy other sizes too. This works for most seeds but if I’m planting a large seed I have the 1 inch size dibble for the 2×2 soil blocks too.
As for a tray, I build my own wooden ones, using dimensions and instructions from Eliot Coleman’s Book HERE. I also add wicking fabric directly underneath, with an extra few inches and place two trays over a big half sheet baking pan then fill the pan with water and let the fabric sit in it.
A plastic tray can be used too, but they have their issues if your using it for containing soil blocks. The main problem being that most plastic trays don’t have the structure to hold very heavy blocks. They wobble all over the place when you need to carry them.
Wicking fabric is place under blocks, then two trays are placed over a baking sheet filled with water (not pictured), the excess fabric on the edge goes into the water.This doesn’t require much explanation, just get it down in the bottom of the hole 🙂
I cover any seed that is sown at a quarter inch or more with moist indoor seed starting soil mix. Some people prefer vermiculite since it is lighter. I’ve haven’t had great results with it, so I don’t use it anymore.
Anything that should be surface sown, like lettuce, I do not cover with anything. You’ll need to keep these seeds moist at all times. And I said moist, not soaking so a fine mist of water sprayed a few times will do.
You can cover a soil block seed tray with plastic wrap or some kind of clear plastic cover, in order to keep the moisture in. With every good thing, comes the ability for it to become something bad too.
The intention is to use these only until the very first seed is emerging. Don’t wait until they all emerge. Take the cover off ASAP when you see the emergence of a seedling. Any longer and you’ll increase the risk of fungal diseases, especially damping off. This fungus will kill the seedlings, usually at the soil surface it will turn brown and die.
I use a cover with I am surface sowing seeds like lettuce.
I rarely use a cover if I have covered the seedling with the soil mix. I would especially not use it if you are sowing peppers, tomatoes, or any other nightshades, which are prone to fungal diseases.
I do a light misting over the soil blocks with water, then place it under grow lights.
An important word about lights, if using fluorescent lights, the lights should literally sit within 2 inches of the tray. This will prevent the seedlings from getting leggy.
LED grow lights are a different story. Some are very intense and need to be placed farther away from the seedlings. You’ll need to experiment with trial and error here since all LED lights are not the same. If the seedlings turn white they are getting too much exposure, if they have long stems and look light they are reaching toward the light they are not getting enough light.
Usually, most people will not put the light close enough. Start close and work your way away from the trays if needed.
It’s always best to mimic nature with gardening. So 12-14 hours with lights on, the rest of the day, lights off! Get a timer to plug your lights into and it will make your life easier 🙂
For seeds that require a higher soil temperature for germination, add a heat mat underneath the tray. Usually anything categorized as a summer crop like tomatoes and peppers should use a heat mat.
If you have an area right next to a warm wood stove or heat source in your home, this would work as an alternative. Just make sure you can set up your lighting there too.
Even with the wicking trays, I put the heat mat under them, it heats water water and in turn heats the soil above when the water is wicked up.
A fan mimics a breeze that would naturally be found outdoors. It will help to keep your plants strong and sturdy and also keep fungal diseases at bay.
Again, do not overwater. Ideally, you should be bottom watering the trays to keep them moist after the seedling emerge. I use a wicking mat placed under the soil tray for this, mentioned in step #2
The reason for watering from the bottom is it helps to prevent fungal diseases.
If the soil dries out completely, so will your plants. There isn’t a lot of soil there, so you really need to keep an eye on it!
If you seed roots poking out of your trays, or the plants are getting large and crowded, move them to a larger container and add more soil!
This is a critical step to success, the plants will stagnate in growth if you wait too long to pot them up. When in doubt move them to a larger pot size earlier, rather than too late.
4×4 soil blockFor soil blocks, I move my 2×2 inch block up to a 4×4 inch block. They take a ton of space and soil but grow so well. An alternative is moving the 2 inch block into a 4 inch plastic pot.
Very likely, your seedling will need additional fertilizer until the time they can get outside. My very favorite is a water soluble fish fertilizer. It can be found HERE. Follow the directions for dilution rates. It is very stinky but works so good.
Once outdoor conditions allow you to do so, (warm enough soil and air temperature), it’s time to harden off the seedlings.
This process gets them used to the outside light and air. Slow and steady is the absolute key!
Keep in mind, this is not an exact science unless you get clear skies everyday. If you get a cloudy day, the seedlings will get less light, on a sunny day, they will get tons of light. Watch the weather closely and adjust accordingly.
Most seedlings are placed in the soil at the same depth as the tray. Tomatoes in particular should be buried deep in the soil a few inches away from the first set of leaves, or placed sideways so the stem is parallel with the soil, the leaves still remain above the soil level. Peppers can also be buried slightly deeper, as can corn- if you’ve ventured into growing that in a seed tray.
The beauty of soil blocks is that they have so much less transplant shock because the roots are air pruned.
Indoor seed starting is a great way to have flexibility in starting many varieties of plants and save money while you’re at it. All you need is the supplies: soil, light, water, seeds, and your time. Starting any seed is a fun process. Keep in mind your circumstances to decide whether or not this method of starting seeds is for you.
Seed starting season is one of my favorite times of the year. It allows me to start gardening indoors several weeks before my garden beds wake up for the year, and it holds the promise of the growing season to come. In this week’s podcast, I am sharing the seed starting essentials for successfully germinating seeds and caring for seedlings.
Seed starting is the perfect cure for cabin fever. Granted, those of you who live farther north than I do probably experience cabin fever more severely than we in Georgia do, but things are dormant outside, and by this time of year, I am craving something green.
My favorite months of the year are April and October, as the seasons are changing, but since I’ve become a seed starter, February has become my third favorite month. I’m not a fan of snow or cold weather, but here in the Atlanta, Georgia, area, February is when I am in the thick of starting edibles, ornamentals and native perennials from seed.
I actually get started even sooner each year, in January. Peppers always take a bit longer to germinate, so those are the first I sow. Already, I have 20 seed flats of peppers up and growing.
Seed starting indoors allows you to enjoy gardening months ahead of when things naturally start occurring outside. In my case, I have an indoor seed starting room that gets completely filled up with seed trays and greenery from February until the seedlings are ready to be moved outdoors.
My seed starting room is a warm, comfortable place to hang out. I spend a lot of time there staring at little tiny seedlings and trying to notice them growing. I check on them as often as every 15 minutes sometimes, because that’s how quickly they can change.
So much happens before your eyes: The transformation from a tiny little seed that you tuck into the soil to a bonafide good-sized seedling six to eight weeks later that goes outside and takes off from there. That’s a lot of growth in a short period of time, and it’s under your watch. You’re noticing the subtle changes from day to day and week to week, and you’re playing a big role in that. You’ll notice if the things you’re doing — or not doing — are resulting in the seedlings having positive or negative changes.
A couple of years back, I started a course in my Online Gardening Academy™ called Master Seed Starting, a comprehensive series of lessons on starting seeds of all types through various techniques and on understanding the many facets of successful seed starting, from light science to maintaining the correct moisture level.
We are now in launch week for Master Seed Starting — enrollment opened on January 25th and continues through January 30th at midnight — and I am simultaneously offering a free live webinar, Seed Basics & Beyond: 9 Things to Know Before You Start Plants From Seed. You can register to join one of the remaining webinar sessions: Thursday, January 26, at noon EST, Friday, January 27, at noon EST and Saturday, January 28, at 10 a.m. EST. Space is limited, so if you would like to join us, don’t hesitate to register.
There is so much to learn about seed starting before you feel like you’ve got a handle on it and know how to troubleshoot and adapt midstream. In this week’s podcast, I distill seed starting down to the basic information you need to feel confident whether or not you take an in-depth course with me or elsewhere. I can get you started here today with some really solid, sound information, and you can go from there at your pace or as your budget permits.
Seed starting really is fun, and you don’t have to be advanced at it to be successful. If you provide seeds with some basic necessities, they’re going to germinate. They’ve got it in their DNA to do that.
Before going any further, I want to remind you that I have a new book out, “The Vegetable Gardening Book: Your complete guide to growing an edible organic garden from seed to harvest.” It’s chock full of insider tips and new-to-you information that will help you step up your gardening game and tackle challenges.
Seed Starting Benefits
A big benefit of starting your own seeds is the opportunity to grow countless varieties that are not sold as seedlings at your local nurseries. When you start your own seeds, you are never at the mercy of what plants the big box stores or garden centers choose to carry.
Also consider the price difference between buying seeds and buying plants. Both seed packet prices and seedling prices are up from what they used to be not long ago, but seed packets continue to offer huge savings compared to seedlings. For pennies on the dollar, you can have your own plants from seed with many more options to pick from. And these days, saving an extra buck is a welcome opportunity.
If you want to learn more, please visit our website Wholesale Propagation Supplies.
You can start anything you want, as long as the variety is suited to your local climate and growing conditions. Order the seeds you want from one of the many reputable seed companies out there that specialize in the niche that you want to focus on.
Raising plants from seed also allows you to take control of how you grow your food and flowers. If you are an organic gardener like me, you can raise plants while confident that organic growing practices were enforced from day one.
You may be thinking about all the things you have to buy to start seeds and if you’ll really save money in the end. I have good news: You can start seeds with items that you already have around the house, with the exception of maybe one or two things that won’t break the bank.
Picking a Place to Start Seeds
When deciding where to put your seed starting trays, there are a few things to consider. Pick a location where the plants will have room to grow once the seeds have germinated. Having outlets nearby is important so you can set up lights as well as any germination mats and timers you decide to use.
Access to water is also important. If your seed starting location is far from a faucet or spigot, you should be comfortable making trips to refill watering cans. And know that a warm place is better than a cold place. People used to recommend the top of the refrigerators as a warm spot for germinating seeds, but if you have a fairly modern refrigerator, it likely won’t get as warm on top as older appliances.
Soilless Mix for Seed Starting
The first thing to think about getting for seed starting is “soil.” Seed starting mix is, in fact, what’s known as “soilless mix.” It’s not like garden soil or dirt — it’s sterile. That means it doesn’t have the microbial life in it that garden soil does. Soil microbiology can be very good, but it can also include pathogens that will kill your seedlings right as they’re germinating. So soilless mix is the way to go when starting seeds.
An 8-quart bag of soilless mix will run you between $7 and $12, and that will fill two 10-by-20-inch seed trays.
The most common soilless seed starting medium is peat moss. There are pros and cons to using peat moss, though it remains the industry standard, especially from a commercial horticulture standpoint. It’s been my go-to source for a very long time, but I recognize the issues that peat moss brings to the table.
To protect peatland and prevent the release of sequestered carbon, England is banning peat sales to home gardeners by 2024. Many U.K. gardeners have already pledged to go peat-free because they share these concerns, including Monty Don, the host of “Gardeners’ World” and a past guest on the podcast. I’ve done a podcast all about the challenges of using peat moss that you can check out if you want to know more about the cons.
As far as the pros, I have loved peat moss because it is easy to work with, clean, inexpensive and readily available.
Peat moss has excellent water-holding capacity, and the seeds respond to it very well. There is a small learning curve when first working with peat moss, primarily the need to understand that peat moss is hydrophobic, meaning it does not readily absorb water. Once it does absorb water, it holds that moisture very well for a long time until it dries out completely and is very hard to rehydrate.
Professional seed starting mixes that contain peat moss usually include what’s called a wetting agent, which facilitates water coming into the peat moss. It breaks through the barrier that causes peat moss to naturally repel water. You don’t usually find that wetting agent in off-the-shelf retail bags of seed starting mix, so be prepared to put some effort into hydrating peat-based seed starting mix.
Within a peat moss seed starting mix there may be perlite, which is a natural product that expands the air space, which is good for root development. Perlite looks like little pieces of popcorn or styrofoam, but it’s actually volcanic glass that has been expanded through heat. Alternatively, a mix might contain vermiculite, which has a shiny flat texture and does a great job of retaining moisture. Vermiculite is also a natural product that is expanded by exposure to heat.
An alternative to peat that has been coming on strong in recent years is coir, which is basically finely ground coconut fiber. Many gardeners who are trying to get away from using peat have found coir to be the closest acceptable peat alternative. It looks similar, feels similar and holds water pretty well. If the salt has been removed from coir through a process called buffering, it can work very well as a seed starting medium.
Big-brand off-the-shelf coir products are not buffered, and I have found through extensive trials that they do not perform well as a seed starting medium.
Another downside of coir is that it is shipped a great distance to get on store shelves, plus there is a lot of deforestation going on where coconut trees are planted.
A new product that is gaining in popularity for seed starting is called PittMoss. Made in Pennsylvania, it is a peat alternative made out of recycled paper. The makers of PittMoss have done a really good job over the past few years refining and perfecting it with their soil scientist and putting it through the paces to be that non-peat moss, non-coir seed starting or soil mix alternative.
Last year was the first year I really had a chance to spend some time with it and experiment with it, and I have to tell you, I had some exceptional results. I used the PittMoss product called Plentiful and found to be better than both coir and the peat moss products I usually use. That being said, there is a learning curve if you are used to working with peat or coir because the watering requirements are different. When you do fine-tune how often and how much to water PittMoss, it can be a really impressive alternative.
Seed Starting Containers and Trays
When it comes to picking containers for seed starting, you have nearly unlimited options. There are so many retail products out there, and you can find a well-curated selection at GreenhouseMegastore.com, a one-stop shop where they are offering “The joe gardener Show” listeners 15% off with the code JOEGARDENER at checkout.
Compartmentalized seed starting trays are typically found in a standard size of 10 inches by 20 inches — that’s the industry standard. They come in several types of plastic, from single-use to sturdier plastics that are nearly indestructible.
Some trays have segmented cells, ranging from 128 openings per tray down to 50 or 36 or 18 and so forth. I like the 50-cell seed trays, but I use lots of different sizes all the time. It’s a matter of personal preference and how many seeds you plan on sowing.
I don’t like using single-use plastic, so I am excited this year to have indestructible seed trays from Conor Crickmore’s Neversink Farm in New York. Conor has been a guest on the podcast to discuss market farming, and he’s quite the product inventor. His seed trays come in all different sizes and mimic soil blocking — a technique that provides more airflow to roots. That promotes faster germination and better root development.
Soil Blocking
Soil blocking, traditionally, involves using a metal form to press a soil mix (peat moss or coir, with compost, perlite and lime combined with water and stirred to the consistency of a brownie mix) into 2-inch cubes. The moisture is the binding agent for the first week or two until the roots take over.
The beauty of soil blocks is that when the roots grow to the edge of the block, they stop growing because there’s no more soil to come in contact with. It’s called “air pruning,” and it stops the growth of the roots temporarily and also prevents them from growing in circles inside a container and becoming root-bound.
Soil blocking is a great technique, but time-consuming, which is why I don’t do it as much. If your soil blocker makes four or five blocks at a time and you have 72-cell trays, you’ll be working at it for a while.
Conor’s Winstrip trays are the closest thing to soil blocking there is, and there is a new product on the market called Swift Blocker that produces up to 72 soil blocks at a time. The reviews so far have been great, and I am trying them out myself. If you’d like to see the Winstrip trays in action, check out my recent video working with them in my greenhouse.
If you think you’ll be seed starting for some time, these products I have mentioned will be worth the investment. You get what you pay for, and these will last you a long time.
Upcycled Seed Starting Containers and Trays
If you are looking to save money while seed starting, well, it’s really easy. Anything that can hold about 2 inches of soil and has drainage holes can be used as a seed starting container. Takeout containers with holes punched in them are typically perfect options for seed starting, especially the clamshell-type containers with clear plastic lids. I’ve even used pizza boxes as containers for an experiment on how much I could grow while spending the least amount of money possible.
In addition to drainage holes, containers need humidity domes. These are transparent covers that will hold moisture in while allowing light through. Light exposure is essential to prevent seedlings from getting stretched and leggy — or spindly, as some people call it.
A lot of seed starting kits come with humidity domes because if the soil dries out too quickly, the seeds may never germinate. But if you are using repurposed containers that don’t have clear covers, you can make your own home with clear plastic wrap.
Once germination is complete, you can remove the covers.
Germination Mats
Germination mats, also known as propagation mats or heat mats, are something I put in the category of nice to have but not need to have.
If the room you are starting seeds in never gets warm enough to heat the soil up to 70° or so, your seeds may never germinate. That’s where germination mats come in. Some mats are thermostat controlled to be dialed into a preferred temperature, while less expensive mats are preset to around 75° and the temperature cannot be changed.
Grow Lights
If you think you don’t need any lights because you have a sunny south-facing window to put your seeds in, I have to disabuse you of that notion. Rare is the case that you’ve got perfect exposure from a south-facing window that gets all-day sun and is going to give you the light that you need for those plants to be sturdy and stout.
Seedlings will stretch for the light if they’re not getting the amount of usable photosynthesis that they need. They must have abundant light to stay compact, and if you’re just relying on a window for that, they’re going to get tall and leggy — and that’s not a desirable outcome.
The good news is, you don’t have to spend a fortune on lights. You can buy a shop light or you might already have a shop light with twin 4-foot-long 40-watt fluorescent lubes that you’ve had around the basement or the garage for a long time. Those light tubes that fit into the fixture probably aren’t going to be as effective as they used to be because over time the less usable light they put out. So you might need to invest in some new light tubes, but that’s really an inexpensive investment.
These days, if you set out to buy new shop lights you’ll probably find LED shop lights that will work a bit better and be more efficient.
If you’re a gadget person like me and appreciate how light frequency can impact a plant’s ability to grow properly, then you’re going to be interested in a more sophisticated lighting system. That typically includes LED lighting, which can be inexpensive. You can spend $20, $30 or so and go up from there into the couple-hundred-dollar range. But again, you get what you pay for. So the more you spend, the more usable light it’s putting out and plant performance will be enhanced. This is a big subject that we go into in great depth in Master Seed Starting.
Racks
Another purchase you may want to make is a really good seed starting rack. I use stainless steel wire baker’s racks that are found at big box stores. They run about $110 or $120 these days. These come on wheels, you can hang lights from them, and they typically hold four standard seed starting trays. I love these, and the seed starters I know who get them feel the same way.
You can use the top of a bookcase or a table if you don’t have room for a rack or don’t want to spend the money right now.
Watering
Once you find the sweet spot in watering, it will come easily to you. But until then, you are probably going to overwater or under water. Overwatered seeds can’t breathe and then die, and under-watered seeds don’t get enough moisture in the seed embryo to start and complete the germination process.
Watering can be time-consuming, so one of the techniques I teach in Master Seed Starting is a self-watering system that I show you how to make. It’s a hands-free way to make sure that your plants get just the water they need without getting too much.
If you look at the top of the seed tray where the sprout emerges and it looks very dry there, that doesn’t necessarily mean that it’s dry all the way down. When you have lights on top, they can generate some heat that can cause evaporation right at the surface of the small cells where the seed starting mix lives and the seed lives. There may still be adequate moisture below the surface — so you can’t judge if your plants need more water just by looking at the surface.
You can water from above, which is called top watering. It just means using your watering can and pouring water back and forth until you feel like you’ve watered it enough. I tend to shy away from that, especially when the seedlings have emerged and they’re still tender. Those drops of water, depending on how finely they’re broken up, can beat up those seedlings a little bit or a lot. And so I like to bottom water, which means allowing the solid tray underneath the cell tray to hold water. The seed starting mix will wick up the moisture through the holes in the cells and will continue to pull it up to the surface.
Reasons Seeds Fail
When seedlings get leggy or spindly, it could be that they are getting too much fertilizer, but the culprit is almost always that they are not getting enough light. The seedlings may need to be closer to the light source, and how close that is depends on the type of light you have.
As mentioned, too much water or not enough water is another common issue.
Going back to why we use sterile seed starting mix, another problem you may encounter is that seedlings can potentially die overnight due to a fungal condition called damping off. The seedlings will be fallen over and the part of the stem right at the soil line will look like is dissolved. This happens most often when using a nonsterile seeding starting medium.
To prevent damping off — in addition to using sterile mix — ensure that air is circulating around the surface of the trays from the time the seeds germinate until a few weeks later. You can do that with a small fan.
When seeds never germinate no matter what you do, there could be a few reasons. They may just be too old and no longer viable, or the problem could be they were planted too deeply or not deeply enough. (The correct depth varies from seed to seed.) If the soil temperature is too cool or too warm, that would also explain why the seeds failed to sprout. Different seeds have different optimal soil temperature ranges for germination, and they also have different light requirements. Some seeds need light to germinate while others will only germinate in darkness — but remember that all seedlings need light once they germinate.
The type of seed starting mix you use can also explain why seeds failed to germinate. For example, a heavy mix may be too wet for successful germination.
Timing
I really get going with my seed starting in February because it’s when I am roughly eight weeks out from my last risk of frost in spring. I can’t put anything outside until that frost-free date has passed, and the plants need six to eight weeks of indoor growing time to get up and going.
You can quickly learn the first and last frost dates for your area at almanac.com by typing in your zip code. Then count back from your last frost date to determine when to start your seeds indoors.
I hope you learned a few things from listening to the podcast that will make you feel more confident starting seeds this year. If you haven’t listened yet, you can do so now by scrolling to the top of the page and clicking the Play icon in the green bar under the page title.
What are your seed starting essentials? Let us know in the comments below.
Links & Resources
Some product links in this guide are affiliate links. See full disclosure below.
Episode 083: Gardening Indoors: The Science of Light, with Leslie Halleck
Episode 140: The Successful Journey of a Market Farmer: Conor Crickmore of Neversink Farm
Episode 200: Monty Don: Behind the Scenes of Gardeners’ World, and More
Episode 238: Peat Moss: Examining the Challenges of Its Ongoing Use in the Face of Climate Change
Episode 259: Getting to Know PittMoss, a Peat-free Growing Medium Alternative, with Dr. Charles Bethke
joegardener blog: The Best Soil Temperature for Seed Germination
joegardener.com/seedwebinar – Register for Seed Basics & Beyond: 9 Things to Know Before You Start Plants From Seed
joegardener Online Gardening Academy™: Popular courses on gardening fundamentals; managing pests, diseases & weeds; seed starting and more.
joegardener Online Gardening Academy Master Seed Starting: Everything you need to know to start your own plants from seed — indoors and out. Enroll by January 31.
joegardener Online Gardening Academy Organic Vegetable Gardening: My new premium online course membership opens in 2023. Sign up for the waitlist here.
joegardener Online Gardening Academy Beginning Gardener Fundamentals: Essential principles to know to create a thriving garden.
joegardener Online Gardening Academy Growing Epic Tomatoes: Learn how to grow epic tomatoes with Joe Lamp’l and Craig LeHoullier.
joegardener Online Gardening Academy Master Pests, Diseases & Weeds: Learn the proactive steps to take to manage pests, diseases and weeds for a more successful garden with a lot less frustration. Just $47 for lifetime access!
joegardener Online Gardening Academy Perfect Soil Recipe Master Class: Learn how to create the perfect soil environment for thriving plants.
Earthbound Expeditions: Great Gardens of Italy & France with Joe Lamp’l
joegardener Newsletter
joegardener Facebook
joegardener Facebook Group
joegardener Instagram
joegardener Pinterest
joegardener Twitter
joegardenerTV YouTube
Growing a Greener World®
GGWTV YouTube
Indestructible seed trays from Neversink Farm
Swift Blocker
Seedling Heat Mat 2-pack
Seedling Heat Mat with Digital Thermostat Controller
PittMoss Plentiful
Territorial Seed Company – Our podcast episode sponsor and Brand Partner of joegardener.com
Greenhouse Megastore – Our podcast episode sponsor and Brand Partner of joegardener.com – Enter code JOEGARDENER for 15% off your order
Disclosure: Some product links in this guide are affiliate links, which means we get a commission if you purchase. However, none of the prices of these resources have been increased to compensate us, and compensation is not an influencing factor on their inclusion here. The selection of all items featured in this post and podcast were based solely on merit and in no way influenced by any affiliate or financial incentive, or contractual relationship. At the time of this writing, Joe Lamp’l has professional relationships with the following companies who may have products included in this post and podcast: Rain Bird, Corona Tools, AeroGarden, Milorganite, Soil3, Greenhouse Megastore, PittMoss, Territorial Seed Company, Earth’s Ally, National Wildlife Federation and TerraThrive. These companies are either Brand Partners of joegardener.com and/or advertise on our website. However, we receive no additional compensation from the sales or promotion of their product through this guide. The inclusion of any products mentioned within this post is entirely independent and exclusive of any relationship.
For more information, please visit Reusable Seedling Trays Factory.