Seed Trays (5 Things To Know & Answers To Common Questions)

You might use a seed tray if you are starting your own plants from seed instead of buying established plants. There are a few things you should know to make sure you use seed trays to their full potential.

So, what do you need to know about seed trays?  A seed tray is a container used to germinate seeds. A standard size seed tray is 1020 (10 inches long by 20 inches wide), but other sizes exist (such as 1010). Ideally, a seed tray has drainage holes and separate cells to make it easier to transplant seedlings into larger pots or into your garden.

Of course, the seed tray you choose will depend on your needs. If you only have a few dozen plants to start, you might want to use smaller 6-cell or 12-cell trays.

In this article, we’ll talk about seed trays and some of the key things you need to know about using them. We’ll also answer some common questions about seed trays.

Let’s get started.

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What Is A Seed Tray?

A seed tray (or seed starting tray) is a container for growing plants from seed. Seed trays are usually made of plastic, although they can be made of biodegradable material (such as coconut coir).

seed tray
A seed tray is used to sow multiple seeds at once – sometimes dozens or hundreds in a single tray!

A seed tray is used to sow multiple seeds at once. Some seed trays are split into cells, and each separate cell is used to grow its own plant from seed.

Ideally, a seed tray will have drainage holes in the bottom of each cell to prevent soggy soil and drowned seeds. A humidity dome can also help to keep soil moisture at the ideal level for seed germination (you can learn more about humidity domes here).

After germination, seedlings grow in the seed tray until they get big enough to transplant. You can either transplant them into larger pots to continue growing indoors, or you can transplant them into the soil of your garden or greenhouse.

repotting plants
When seedlings outgrow their cells in a seed tray, you can repot them (shown here) or transplant them into the greenhouse or garden.

You can also use a seed tray (either with or without cells) to grow microgreens. Check out this article for more information on how you can use seed trays.

A seed tray can hold from 6 seeds to over 1000 seeds – it all depends on which one you choose. The ideal seed tray size will depend on your planting needs.

(If you want to buy seed trays, you can find some from True Leaf Market).

How Big Should Seed Starting Trays Be?

A seed starting tray should be as big as you need to fit all of your plants, plus some margin for error. For example, if you want 90 plants and the seed germination rate is 90%, then you probably want a 100-cell tray (which will give you about 90 plants).

seed tray
Leave a margin for error when planning your seed tray capacity. For example, at a 90% germination rate, you will need about 10% more cells than you think.

A standard size seed tray is called “1020”, which means 10 inches long by 20 inches wide. Usually, a seed tray is slightly longer than 10 inches on the length and 20 inches on the width.

In addition to standard size seed trays, you can find other sizes, including 10×10 and 13×26:

  • A 10×10 is a square tray that is 10 inches long by 10 inches wide (half the size of a standard 1020 tray).
  • A 13×26 is a square tray that is 13 inches long by 26 inches wide (30% larger than a standard tray in both dimensions, and almost 70% larger in terms of area).

You can find lots of different 1010 and 1020 seed trays with different numbers of cells. The more cells there are for a given tray size, the smaller each cell will be.

empty seed tray
A seed tray should be 2 to 3 inches deep. Any deeper and you may have trouble with drainage and damp soil. The seed tray above has no individual cells.

As far as depth: a seed tray should be 2 to 3 inches deep. Any deeper and you might have trouble with drainage, which can lead to damping off of seeds or seedlings.

Damping off is caused by mold/fungi that kills seeds and seedlings – you can learn more about it (and how to prevent it) here.

What Are The Best Seed Trays?

The best large seed trays are Proptek seed trays. They are very sturdy and they have lasted for several seasons.

Jon in garden with seed tray
Me in the garden with a Proptek seed tray and lots of seedlings, ready to go.

They don’t crack apart in sunlight like other thinner seed trays, and they are sturdy enough to take some weight on top of them, if necessary.

Proptek trays are great for starting lots of seeds at once if you start huge crops of tomatoes, onions, peppers, etc. from seed.

The only downside is that you have to buy them in bulk (for example, 10 trays). If that isn’t a problem, you can find Proptek trays at the Greenhouse Megastore:

You can find even more seed tray options and sizes on the Proptek website.

IYou can also find lots of seed tray options from True Leaf Market.

Remember that you don’t have to use separate trays for each seed variety (or for each plant). You can start different plants and varieties in one tray.

However, you do need to keep the soil in the tray at a temperature that will allow all of the seeds to germinate. With the exception of a few plants like okra and pumpkins, most seeds will germinate just fine at a soil temperature of 75 degrees Fahrenheit (24 degrees Celsius).

seedlings in seed tray
A soil temperature of 75 degrees Fahrenheit (24 degrees Celsius) will work great for germinating most vegetable seed varieties.

You can see a table with the time to germination for various vegetable seed types at different soil temperatures here.

If you wish, you can also create a makeshift seed tray out of things you might already have at home – you can learn more here.

How Do You Tamp Down Seeds?

After you fill the seed tray cells most of the way with soil, poke holes (with a pencil or your finger), put the seeds in the holes, and cover them with soil, you might want to press down the soil a little (not a lot!)

Tamping down the seeds (putting pressure on the soil from above) will help to ensure that the seeds get good contact with the soil and the water in the soil. This will encourage germination.

seed trays
After planting seeds and covering them, tamp down the soil to ensure good contact between seed and soil. Don’t overdo it, or you will get compacted soil and lack of air for your seeds!

You can tamp down seeds by pressing lightly with your fingers, or you can use a soil tamper. You will need a small one for cells, or you can use a larger one for an open seed tray with no cells.

Just make sure you don’t press down too hard on the soil. Otherwise, the soil will become compacted, and the seeds may get too much moisture, too little air, or both.

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How Do You Mark A Seed Tray?

To mark a seed tray, you can use anything that you can cut into thin strips that you can write on with a marker. Some ideas include:

  • Strips cut vertically from plastic containers (yogurt, sour cream, etc.)
  • Popsicle sticks (the thicker ones are probably easier to write on).
  • Thin wood pieces (cut as thin as you want, but you will need a saw – be careful!)
Seed Tray Labels
You can cut a plastic container into thin strips to make labels for your seed trays.

Paper doesn’t work well, because it will usually get wet when you water your seed trays. Then the ink will run (or the paper will decay) until you can’t read the label anymore.

Just stick your marker into the soil in one of the cells in the seed tray, near the edge. Then you can see what you have in the tray at a glance.

If you plant more than one seed type in a tray, you could use multiple labels (one for each row or column of cells). You could also just draw a quick sketch in your garden journal and indicate what is planted in each part of the seed tray.

Do Seed Trays Need Sunlight?

For most types of seeds, trays do not need sunlight until after germination occurs. Some exceptions include:

  • Celery
  • Dill
  • Lettuce
lettuce seedling
Lettuce seeds (and some others) do need light to germinate, but many seed types do not.

You can learn more about which seeds need light to germinate here.

Once seeds have germinated, the seedlings will need light to continue growing. Without some type of light source (such as sunlight or grow lights), they will eventually die due to the darkness.

If the light is too dim, you may see your seedlings get leggy (long and thin) as they stretch out upwards to grow towards the light.

Many plants need direct sunlight to thrive (there are exceptions though). You can learn more here.

When To Transplant Seedlings From Seed Trays

There are two times when you will need to transplant from seed trays:

  • 1. When the seedlings outgrow the cells in the seed tray. You can tell this is happening if you see roots growing out of the drainage holes at the bottom of the cells, or if the seedling is “root bound” when you pull it out of its cell. At that point, transplant them into larger individual pot to continue growing.
  • 2. When the weather tells you it is time to move the plants outside. This depends on both the plant type and the last spring frost date in your area (you can find frost dates by zip code or city and state here).
seedlings in seed tray
When your seedlings outgrow the seed tray, it might be time to transplant into larger individual pots, or directly into the garden (weather permitting).

Can Seed Trays Be Recycled?

You can recycle seed trays if they are sturdy enough and if you can get them to last! Unfortunately, a host of issues can damage seed trays, including:

  • UV radiation (from sunlight)
  • freezing with water inside (this can cause cracks when the water expands into ice)
  • rough handling (dropping them, or dropping things on them)
UV radiation from sunlight can do serious damage to certain types of plastic, which is what many seed trays are made from.

Flimsy seed trays might not last more than one season. However, well-made seed trays can last several seasons.

Remember to wash out your seed trays after each season (or each use if you plant in the spring and fall). Use soap and water to clean your seed trays to eliminate any mold or other soil pathogens that might be present.

Otherwise, you could be inviting disease to attack your next crop of seedlings.


Now you know a little more about seed trays, how to choose one, and how to use them. You also know what to do if you want to recycle seed trays to get more use out of them.

I hope you found this article helpful.  If so, please share it with someone who can use the information.

(If you want to buy seed trays, you can find some from True Leaf Market).

You can learn more about bottom watering plants (and why to do it) here.

You can learn about seed starting mix (and how to make it) here.

Check out this article that will help you to figure out how many seeds to plant.

To find books, courses, seeds, gardening supplies, and more, check out The Shop at Greenupside!

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Jon M

Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

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