Seed Tray Cell Size Guide: How to Choose the Right Tray for Different Plants

The right seed tray cell size depends on four things: how quickly the crop grows, how long it will remain in the tray, how much root space it needs, and how closely the grower can manage water and nutrients. Smaller cells increase the number of seedlings per tray, while larger cells provide more growing medium and a wider margin against drying out or becoming root-bound.

As a practical starting point, fast-growing cool-season crops that will be transplanted young can use smaller cells. Tomatoes, peppers, eggplants, cucumbers, melons and other seedlings held for longer generally need larger or deeper cells.

Cell count alone is not enough. A "72-cell tray" from one supplier may not have exactly the same dimensions or cell volume as another. Always compare the individual cell opening, depth, volume, drainage and total tray footprint before making a final selection.

Quick Seed Tray Size Guide

Typical tray density	Relative cell size	Common starting applications	Main advantage	Main limitation
12–24 cells	Large	Cucurbits, large seeds, vigorous seedlings, long holding periods and home propagators	More root space and moisture reserve	Fewer plants per tray and greater media use
32–50 cells	Medium-large	Tomatoes, peppers, eggplants, larger flowers and crops that will remain indoors longer	Good balance between plant space and tray efficiency	Requires more bench space than high-density trays
72 cells	Medium	General vegetable and flower propagation; warm-season seedlings when managed and transplanted on time	Versatile and widely used format	Some crops may require potting up if held too long
105–128 cells	Small-medium	Lettuce, brassicas, herbs, many annual flowers and shorter production cycles	Efficient use of bench space	Faster drying and less room for delayed transplanting
200 cells and above	Small	High-density commercial plug production and crops transplanted very young	Maximum plant count per tray	Requires precise irrigation, nutrition and transplant timing

This table describes relative classes, not universal standards. Cell volume and depth must still be checked because tray footprints and cell shapes vary.

What Does Seed Tray Cell Size Mean?

Seed tray size is commonly described by the number of cells in one tray: for example, 24, 50, 72, 128 or 200 cells. If two trays have a similar overall footprint, the tray with more cells normally has smaller individual cells.

However, cell count is only a convenient label. The specifications that directly affect the seedling are:

• Cell opening: the width available at the top of each cell
• Cell depth: the vertical space available to the root system
• Cell volume: the amount of growing medium surrounding each seedling
• Cell shape: round, square, tapered, ribbed or another profile
• Drainage opening: the size and location of holes at the base
• Tray footprint: the overall length and width and its compatibility with benches, base trays or covers

For accurate comparisons, buyers should request measurements or cell volume rather than relying only on the stated cell count.

Why Does Cell Size Matter?

Larger Cells Hold More Water and Nutrients

Larger cells contain more growing medium, which provides a greater reserve of water and nutrients. This usually makes them more tolerant of small irrigation delays and more suitable for seedlings held for a longer period.

The University of Georgia's commercial transplant guidance notes that larger cells retain more water and nutrients and normally produce stockier plants. The trade-off is that a newly germinated seedling occupies only a small part of that volume, so careless irrigation can leave the medium wet for too long.

Smaller Cells Increase Production Density

Small cells allow growers to produce more seedlings on the same bench area. They reduce the amount of growing medium used per plant and can make tray handling and large-scale transplant production more efficient.

The smaller root-zone volume also changes faster. It can dry rapidly and experience faster shifts in fertility, soluble salts and pH. High-density plug trays therefore require more precise irrigation and nutrition management than large-cell hobby propagators.

Cell Size Affects the Transplanting Window

A seedling can remain in a larger cell longer before its roots fill the available space. A small cell has a narrower transplanting window: delaying planting or potting up can cause roots to circle, growth to slow, or the plug to dry too quickly.

Choosing a cell size is therefore partly a scheduling decision. The relevant question is not only "How large will this plant become?" but also "How many weeks must it remain in this tray?"

How to Choose a Seed Tray Cell Size in Four Steps

Step 1: Estimate the Time From Sowing to Transplanting

Choose smaller cells when seedlings will be transplanted young and on a predictable schedule. Choose larger cells if they must remain protected for longer because of climate, sales timing or production planning.

For example, cool-season vegetables such as lettuce and many brassicas are often transplanted younger than warm-season tomatoes, peppers and eggplants. A University of California greenhouse guide uses 128-cell trays for cool-season vegetables intended for transplanting after about one month and 72-cell trays for warm-season crops expected to remain in the tray longer.

This is a useful production example, not a universal rule. Cultivar, temperature, light, nutrition and local planting dates can change the schedule.

Step 2: Consider Seed and Root Characteristics

Large seeds and vigorous seedlings normally need more volume. Crops that produce fast, extensive or sensitive roots benefit from deeper or wider cells, especially if the grower wants to avoid an intermediate potting-up stage.

Smaller seeds do not automatically require small cells. Seed size affects sowing, but the final cell selection should account for the seedling's growth rate and expected holding time.

Step 3: Match the Tray to Irrigation and Growing Conditions

Choose a larger cell if seedlings will be hand-watered, checked less frequently or grown in a warm, dry environment. Smaller cells are more suitable when irrigation is uniform and staff can monitor moisture closely.

Whatever the size, the tray must provide:

• Drainage that removes excess water
• A seed-starting medium with adequate air space
• Even filling without large voids
• Uniform watering across center and edge cells
• Sufficient light and airflow after germination

Step 4: Decide Whether Potting Up Is Acceptable

Starting in small cells and moving seedlings into larger pots can save germination space. It also adds labor, containers, growing medium and another handling step.

If the objective is to sow once and transplant directly to the garden or field, select a cell that can support the full planned indoor growing period. If space is limited and labor is available, a smaller germination cell followed by potting up may be more efficient.

What Seed Tray Size Is Best for Different Plants?

The following recommendations are practical starting ranges. They should be adjusted for the actual cell volume, cultivar, climate and production schedule.

Tomatoes, Peppers and Eggplants

Use medium to large cells when these warm-season crops will remain indoors for several weeks. A 50- or 72-cell format is a common commercial starting point, while home gardeners may prefer 24- or 40-cell propagators for more growing space.

A 72-cell tray can work for tomatoes, but it is not automatically suitable for a long holding period. If roots fill the plug before outdoor conditions are ready, move the seedlings into larger pots.

Lettuce, Cabbage, Broccoli, Kale and Other Brassicas

Small to medium cells are usually suitable because these crops are commonly transplanted at a younger stage. Commercial systems may use 105-, 128- or higher-density trays when irrigation and transplant timing are tightly managed.

Larger cells remain an option for home growers or retailers who want a more forgiving product with a longer usable window.

Cucumbers, Squash, Pumpkins and Melons

Use large, preferably deeper cells and avoid keeping these seedlings confined for too long. These crops grow rapidly and their roots do not benefit from unnecessary disturbance.

Formats with approximately 12–32 larger cells are a useful starting point. Direct sowing may be preferable where the climate and planting schedule allow it.

Onions and Leeks

These can be produced in smaller cells, and some production methods place several seedlings in one cell. The choice depends on whether the crop will be transplanted as individual plants or small groups.

Depth still matters because narrow, deeper cells can provide more root space without using the bench area of a very wide cell.

Herbs

Herbs should not be treated as one group. Basil grows quickly and may be sown as a small cluster, while slow-growing woody herbs may require a longer holding period. Fast herbs transplanted young can use small to medium cells; longer-cycle herbs need more volume or an up-potting plan.

Annual Flowers

Many annuals can begin in 72- to 128-cell formats when transplanted on time. Vigorous varieties, large-seeded flowers and plants intended for a longer retail period benefit from larger cells.

Perennials and Deep-Rooted Seedlings

Select deeper cells based on root architecture and the length of the propagation cycle. Total cell depth may matter more than the number printed on the tray.

Explore our Nursery Trays and Pots for different seed-starting applications.

Is a 72-Cell Tray a Good General-Purpose Choice?

Yes. A 72-cell tray is a practical general-purpose format for many vegetables, herbs and flowers because it balances plant count, root space and growing-medium use. It is especially useful for growers who want one versatile commercial tray rather than several highly specialized densities.

It is not the best choice for every crop. Very fast cucurbits may need larger cells, while commercial lettuce or brassica production may use smaller, higher-density plugs. A 72-cell tray also becomes too small if warm-season seedlings must remain indoors beyond the planned transplanting window.

EDAR's verified 72 Cell Seed Starting Tray measures 55 × 29 × 6 cm and uses 72 cells with drainage openings. Those specifications apply to that product only and should not be assumed for every 72-cell tray on the market.

72-Cell vs 128-Cell Seed Trays

Factor	72-cell tray	128-cell tray
Individual cell volume	Normally larger when tray footprints are similar	Normally smaller
Seedlings per tray	Lower	Higher
Moisture buffer	Greater	Lower
Typical holding period	Longer	Shorter
Monitoring requirement	Moderate	More precise
Growing-medium use per plant	Higher	Lower
Common use	General vegetables, warm-season crops and longer schedules	Cool-season vegetables, herbs, flowers and young plug production

Choose 72 cells when plant size and schedule require more root-zone volume. Choose 128 cells when production density is important and the seedlings can be irrigated carefully and transplanted young.

When Should Seedlings Be Moved to a Larger Pot?

Pot up or transplant seedlings when the root system holds the plug together but before it becomes densely crowded. Other signs include:

• Roots circling inside the cell
• Roots extending heavily through drainage holes
• The plug drying much faster than before
• Growth slowing despite suitable light, temperature and nutrition
• Leaves crowding neighboring plants
• The transplant date being delayed beyond the tray's planned holding period

Do not use seedling height alone. Tall, weak growth may indicate insufficient light rather than a need for a larger container.

Tray Specifications Buyers Should Compare

For importers, distributors, retailers and private-label brands, cell count is only the beginning. A complete specification should include:

1. Overall tray length, width and height
2. Number of cells
3. Cell opening dimensions
4. Cell depth and volume
5. Cell shape and taper
6. Drainage-hole dimensions and position
7. Material and material thickness or finished tray weight
8. Wet and dry handling strength
9. Compatibility with base trays, domes, heat mats and filling systems. Seedling heat mat setup and temperature control guide.
10. Nesting height and number of trays per carton
11. Expected reuse or intended single-use positioning
12. Color and branding options
13. Retail pack quantity and packaging format
14. Instructions and plant recommendations supported by the actual cell dimensions

Samples should be tested with the intended growing medium and irrigation method. A tray that stacks well when empty may behave differently after filling, watering, moving and removing the plugs.

Common Seed Tray Selection Mistakes

Choosing Only by Cell Count

Cell counts are not globally standardized. Compare dimensions and volume, not just "72" or "128."

Using Small Cells Without a Transplant Schedule

High-density trays save space only when seedlings can be moved on time. Delays quickly remove that advantage.

Selecting Large Cells but Overwatering Young Seedlings

Large cells contain more wet medium around a small root system. Water according to actual moisture conditions rather than tray size alone.

Ignoring Tray Compatibility

The tray should fit the intended base tray, humidity dome, nursery bench, heat mat, retail package and transport carton.

Using Heavy Garden Soil in Plug Cells

Dense soil can restrict drainage and air movement. Use a growing medium designed for seed starting or propagation.

Final Recommendation

Choose the smallest cell that can support the crop until its planned transplant or potting-up date without creating excessive water stress or root restriction. Fast, young transplants can use smaller cells; vigorous crops and longer schedules need larger or deeper cells.

For home gardeners, 20- to 40-cell propagators provide a forgiving amount of space and are easy to manage. For commercial vegetable and flower propagation, 72-cell trays offer a versatile middle ground. Higher-density trays such as 105, 128 or 200 cells are most effective when irrigation, nutrition and transplant timing are tightly controlled.

Always confirm the actual cell dimensions and volume. The number of cells describes tray density, but the space available to each root system determines how the seedling must be managed.

Need help selecting a seed tray or propagator for your product range? Explore EDAR's nursery trays and seed-starting products, or contact us to discuss cell count, dimensions, materials, packaging and OEM/ODM options.

FAQs

Further Reading

University of Georgia Cooperative Extension: Commercial Production of Vegetable Transplants

University of California sustainable agriculture program: Transplant Production in the Greenhouse

Biodegradable Seed Starter Pots vs Plastic Seed Trays: Which Is Better?