How to Sow Seeds in Cell Trays

Master Naturalist Sarah Jay is getting ready for seed-starting at her home in Texas. In this piece, she considers seed cells, their use, and the types out there on the market.

Top view of a woman's palm full of seeds over large cell trays filled with soil mixture. Cell trays for starting seeds are rectangular plastic containers with multiple individual cells, each serving as a small compartment for germinating and growing individual seeds. On top of the cell tray is a small garden tool - a spatula.

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The world of seed starting may seem impossibly huge to those new to the practice. This comes as no surprise, as there are so many things to consider! Seed types, starting methods, soil, and trays are all important aspects of growing your crops from seed. 

Seed cells are a standby in that vein, with professional growers using them and sometimes automatic seeding machines to carry out a quick start. While home growers don’t have to automate or mechanize, they can also benefit from using seed cells rather than starter pots. 

That’s what we’re covering today: seed cells! We’ll identify what they are and how to use them. We’ll suggest a few that we love (like our exclusive Epic 16-cell trays) and point out the pros and cons and accompanying tools you can use with yours. 

Seeds Featured In This Article

Caraflex Cabbage

Caraflex Cabbage Seeds

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Caraflex Cabbage Seeds

Tomato

Cream Sausage Bush Tomato Seeds

Our Rating

Cream Sausage Tomato Seeds

Bouquet Dill

Bouquet Dill Seeds

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Bouquet Dill Seeds

Texas Early Grano Bulb Onion

Texas Early Grano Bulb Onion Seeds

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Texas Early Grano Bulb Onion Seeds

Megatron Jalapeño Chile Pepper

Megatron Jalapeño Chile Pepper

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Megatron Jalapeño Chile Pepper Seeds

Little Gem Mini-Romaine Lettuce

Little Gem Mini-Romaine Lettuce

Our Rating

Little Gem Mini-Romaine Lettuce Seeds

What Are Seed Cells?

Close-up of several plastic cell trays stacked on top of each other in a garden against a blurred background. Cell trays are rectangular-shaped containers with multiple small, individual cells, each serving as a separate compartment for planting seeds. They are plastic and black.
Smaller than starter pots, seed cells come in trays with 4 to 128 sections, ideal for nurseries and greenhouse use.

Unlike a starter pot, seed cells are much smaller. They’re often sold as single plastic trays that range from 4 to 128 sections in total.

Each cell is roughly an inch wide and deep in the larger-numbered trays, giving expert growers much more room to start massive amounts of seedlings as needed. This is typically how a nursery grows seeds, and it’s often carried out in greenhouses and indoor starting areas ahead of the growing season. 

In contrast, lower-numbered cell trays like a 4-cell are meant for smaller-batch starting. These trays allow you to start many seed types with different germination times and needs. As different plants grow at different rates, this solution is ideal for the home gardener as it allows you to ensure perfect conditions for each plant type you’re growing.

Benefits of Using Seed Cells

Top view of a seed starter tray with small sprouts. The starter tray is a black plastic container with recessed cells filled with soil. The small sprouts have a pair of tiny, rounded leaves that are bright green.
Cell trays conserve space, provide ease of use, and are long-lasting, making them advantageous.

The obvious benefit here is the conservation of space. You can start many more seedlings in much less space than if you were to opt for a basic plastic or peat starter pot. While there are some great larger cell trays, these still take up much more space than these smaller cells.

The ease of using a cell tray is another advantage. These trays are easy to move around and can be quickly filled with soil. Most are adapted to machines that transplant seeds into the cells faster, too. 

Depending on the material and treatment of the cells, they’ll last a long time. Most trays last several years as long as they aren’t overexposed to the elements and direct sunlight. Some have even been developed to last much longer than that. More on that shortly!

Consider This Before Purchasing Seed Cells

Close-up of a man's hand pulling young paprika seedlings from a seed starter tray. Paprika seedlings display delicate and slender stems crowned with two small, opposite cotyledon leaves and two true leaves. These leaves are lanceolate, bright green, with a glossy texture.
Large cell trays can become root-bound and may require special tools for up-potting.

While a single large tray may be appealing, it can be difficult to pluck out one of your seedlings from a set of 128 cells when they’ve outgrown their one-inch space. If you leave them in the cells, they become root-bound. Therefore, there are special tools and methods for up-potting seedlings when you use these larger trays. 

Another thing to think about: you must transfer seedlings into larger pots if you wait to plant them out until they’re much larger. While you can pop them out of seed cells and plant them directly in the garden, you may opt to continue to shelter them from harsher elements first.

Finally, if you are using plastic trays, they need maintenance, like cleaning and protection from harsh weather in between use. Some trays are not recyclable and will end up in landfills after use. That makes some less eco-friendly than others, and less desirable to more eco-conscious gardeners.

When to Start Seeds In Cells

Close-up of a gardener's hand sowing seeds into a starter tray. The seeds are tiny, flat, round in shape, and yellow in color. The starting tray is plastic, black, with separate recessed cells filled with moist soil.
Seed cells are ideal for space conservation, ease of use, and mechanical sowing.

If you are working with a large amount of seeds, you want to conserve space, and you’d like to offer yourself some ease of use, seed cells are a great option. This is the only viable option to sow your seeds mechanically. 

If you are going to plant out all your seedlings at the same time, cells are a great choice. That means you can take your tray out to the field or garden and transplant all of them simultaneously.

If you use these trays for succession sowing, you’ll have to puzzle out the right timing. This is where a smaller number of cells in a tray may be beneficial. You can use a 16-cell tray to mimic the conditions in a normal 128-cell tray and start a batch of 16 plants once per week. This enables perfect succession timing rather than trying to remember when you started each part of the tray.

The type of seeds you’re growing is important, too. If you’re using reusable cell trays, don’t plant seeds prone to transplant shock or susceptible to damage by root disturbance. Save those for biodegradable pots and cells, or direct-sow those seeds into the garden when the conditions are right. 

3 Types of Seed Cells and How to Use Them

Here are a few types of cell trays and some instructions related to their use. All of these are readily available at many garden retailers. We have some in our shop as well!

Plastic Cell Flats

Epic 16-Cell Seed Starting Trays

Epic 16-Cell Seed Starting Trays
  • Durable and Long-Lasting Construction
  • Eco-Friendly Manufacturing
  • Engineered for Optimal Plant Growth
  • Convenient and Flexible Design
  • Versatile Seed-Starting Solution
View at Epicgardening.com

Many conventional trays are made of flexible plastics that work for a couple of years and then start to degrade. We prefer much more durable models, like our Epic 16-cell tray

The greatest benefit to Epic 16-cell flats is they last longer than biodegradable pots, and they are ready to go every year, unlike soil blocks. They give you lots of room and options for your initial start, and eight of these are designed to fit into a Universal Bottom Tray

This tray has 16 cells and is injection molded BPA-free, recycled plastic. It’s highly durable and doesn’t require more than a wash and protected storage between use. You can expect this tray to last a lifetime. Inside each cell are four internal ribs that prevent root spiraling. 

The bottoms are open, providing air pruning at the lower end and ease of extraction during transplant time. Because eight of these trays fit inside a UBT, removing the cells is much easier than it would be a full tray of 128 cells. It does all this while providing the same number of cells to plant into.

The most beneficial aspect of this tray is that you can remove 16 seedlings at a time for transplanting, care, and even rotation for the best foliage and root development.

With these, all you have to do is fill with your starting mix and plant your seeds. Place them in your starting area and monitor for seedling growth. Then, pop them out to transplant when you’re ready. 

Biodegradable Cells

Recycled Paper Pots

Recycled Paper Pots
  • Eco-Friendly Seedling Growth
  • 100% Recycled, Food-Grade Paperboard
  • Sustainable Manufacturing Practices
  • Biodegradable in Garden or Compost Bin
  • Green Alternative to Plastic or Peat Pots
View at Botanicalinterests.com

Individual cells made of biodegradable cardboard or peat are a great way to reduce some potential pitfalls of standard cell trays. Plant the seeds in them, and when the seedlings are ready to move to the garden, transplant the whole pot directly into the soil when the seedlings are mature enough. You will need an accompanying carrying tray to use these for watering and moving around.

With these, you reduce shock in the transplanting process. You also avoid any disturbance involved in moving the trays around and avoid damaging potentially sensitive roots. There’s no plastic to mess around with and no maintenance. That being said, you will have to replenish these before your next growing season. They are single-use.

Peat pots also get a bad rap at times, as peat is not a renewable resource and only exists in a few parts of the world. It’s such an ecologically important plant. Those concerned about impacts should opt for products from sustainably-managed peat bogs. 

Soil Blocks

Close-up of small-sized soil blocks for sowing seeds. Soil blocks are crafted from a mixture of soil and a binding agent, forming compressed cubes or blocks that serve as individual planting units. These blocks have a crumbly texture and a distinct, earthy color.
Opt for soil blocks for an eco-friendly, no-transplant-shock solution.

The one-inch to two-inch versions of these cells are a great option for gardeners who want to skip the trays altogether. They’ve got the same benefits as your biodegradable pots but without the need to replenish. All you need is a soil blocker and a good blocking soil mix, and you’re good to go. No transplant shock!

You will, however, need a carrier tray and a sometimes expensive soil blocker. You also need to clean and dry the blocker between uses, but that’s a simple process. Blockers also last a long time, so purchasing one is a decent investment. There is a slight learning curve, but after a few times of working with blocks, it’s easy to work out any issues. 

To use one of these, make your seed-blocking mix, ensuring it’s solid enough to hold shape and leach some moisture when you squeeze a clump in your hand. Then, use your blocker to shape and press the blocks into a tray. Most blockers have a dibbler that leaves an impression where you can plant the seeds afterward. Sprinkle more mix or some vermiculite over the seeds, and voilà.

Soil blocks dry out faster than the soil that would otherwise be in pots. It can take time to figure out the best watering schedule that will provide enough moisture but not so much that it degrades your blocks. You may also have to up-plant your starts, making other pots or even larger seed blockers necessary. 

Accompanying Seed Cell Supplies

Close-up of a small seed starting tray with a humidity dome on a heat mat and under artificial light. The starting tray is a plastic, black, square-shaped container with recessed cells for planting seeds.
Consider using grow lights, humidity domes, and heating mats for optimal germination.

A bottom tray isn’t completely necessary when using plastic or biodegradable trays, but it helps with watering and transportation. You definitely need a bottom tray for soil blocks, though, as they need a place to sit when your seeds are developing their first foothold. 

Other basic seed-starting supplies like grow lights, humidity domes, and heating mats are great for any of the above options for seed starting. These provide seeds with the light, humidity, and warmth they need to germinate and grow. 

One very important tool to have for plastic cell trays is a widger. You’ll need it to remove the starts from the trays at the time of transplant. Just slip it into the corner of a cell, lever the soil mass out of the tray, and into the new pot or garden ground. If you don’t want to use a widger, consider our Epic trays that allow you to use your finger to pop plants out.

Best Seeds For Seed Cells

Close-up of lettuce seedlings in seedling trays in a greenhouse. Lettuce seedlings exhibit a charming and distinctive appearance characterized by tender, elongated stems and delicate, vibrant green leaves. The leaves are oval, with slightly serrated edges.
Choose your cell size based on the type of seeds you’re likely to plant.

Smaller seeds and those that aren’t sensitive to shock during transplant are great options for seed cells. Wildflowers and perennials are also perfect for cells. When working with larger seeds, opt for larger cells, go with direct sowing, or start in larger starter pots.

  • Lettuce: The minuscule seeds of lettuces, like Little Gem Mini-Romaine Lettuce, benefit from cell starting. Plant in small cells and transplant out when they grow true leaves.
  • Onions: Oversow your onions in seed cells and separate them upon planting or up-potting. This is a great way to get even more out of your harvest, but choose the right onion for your area. In warmer areas, try the short-day Texas Early Grano Bulb Onion.
  • Herbs: Much like lettuce, herbs tend to have tiny seeds that appreciate a smaller starting space. Planting dill directly in the garden (even when it’s a little cold) will yield tons of fragrant frond-like leaves in summer. I prefer to go with Bouquet Dill because of its giant flowers. Dill is also a great attractant for swallowtail butterflies.  
  • Tomatoes: Many gardeners like to start tomatoes in larger cells or pots and let them get nice and big before planting them out. A 16-cell tray start is a great way to get a lot of them going so you can have tons of tomatoes at harvest. You’ll likely need to up-pot if you’re starting seeds early to get a jumpstart on the season. Opt for new and interesting determinate varieties like Cream Sausage Bush Tomato. 
  • Peppers: Capsicum species are just as beloved as tomatoes and require similar care in the starting process. Choose larger cells or up-pot to allow for lots of plant development before transplanting them outdoors. There are tons of pepper choices, too, with nice mid-range options, like Megatron Jalapeño Chile Pepper. 
  • Brassicas: Small seeds make these great for sowing in smaller cells. Try an early sow cabbage variety, like Caraflex Cabbage, for small cabbages with a conical shape and a quick maturation rate.  

Final Thoughts

Seed cells are not a new technology, but there are new and exciting developments in this category of seed-starting that make your life easier. Whatever method you choose, there are things to consider. All have their convenience and modularity factors

Think about the seeds you want to plant, and use that to determine your plan for this upcoming growing season.

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