Seed-Starting & Transplanting
woman sowing seeds into seed trays

Seed Starting Flats, Trays, Domes & Pots—Comparison Charts

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Seedling Flats

To incorporate our seedling flats into your growing system, first identify which flat best accommodates your crop using the chart below. Typically, the larger the seedling, the larger the cell you will need to allow for proper root development. Those crops that will be in flats for longer may benefit from being started in 20-row flats and “potted up” into plug flats. Seedlings can also be started in, or transplanted into, plug inserts or pots.

Seed Starting Flats Comparison Chart

Table 1. Seedling Flats Comparison
Product Name Recommended Crops Cell Size
20-Row Seed Flats—Save space by starting seeds in one flat and transplanting into cell trays after germination.
20-Row Crops that take longer to germinate and grow (e.g., peppers, eggplant, perennial herbs, lisianthus) 9 ¾” L x ⅞” W x 1 ¼” D
Plug Flats—The standard compact design for efficiently growing seedlings.
50-Cell Artichokes, cucumbers, melons, ornamental grasses, peppers, squash, Tomatoes 1 ⅞” Square x 2 ⅜” D
72-Cell Basil, broccoli, cabbage, flowers, herbs, kale, swiss chard 1 ½” Square x 2 ¼” D
128-Cell Chicory, delphinium, fennel, lettuce, lisianthus, onions, shallots, stock 1 ⅛” Square x 1 ⅞” D
200-Cell Flowers and herbs (small–seeded, e.g., alyssum and chamomile) 1 3⁄16” Square x 1 ⅜” D
Pro-Tray—Round cells.
24-Cell Cucumber, eggplant, melons, pumpkin, squash, tomatoes, and large-seeded herbs and flowers. Diameter (top) 2 ⅓" x Diameter (bottom) 1 ⅘" x 2 ⅓” D
38-Cell Basil, cabbage family, peppers, other veggies, herbs, and flowers. Diameter (top) 2 ¼" x Diameter (bottom) 1 ½" x 2 ⅓” D
Air-Pruning—Promotes healthy root growth.
72-Cell Basil, broccoli, cabbage, flowers, herbs, kale, swiss chard 1 ⅜" x 1 ⅜" x 2 ¼" D
Six-Packs—Great for seedling sales.
Jumbo Plug Inserts Tomatoes, peppers, broccoli, kale, lettuce, greens (for bunching), Flowers, Herbs 2” L x 2 ¼” W x 3 ¼” D
6-Cell Tray Inserts Basil, broccoli, cabbage, flowers, herbs, kale, swiss chard. 1 1⁄2"(L) x 1 ½"(W) x 2 ¼" D
SureRoots® Deep Plug Flats—Promotes deeper root development.
SureRoots® 50-Cell Sweet peas, asparagus, perennials, and crops with a taproot or that are sensitive to root disturbance 2” Square x 5” D
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Support Trays

Use the chart below to select the right tray for your needs. Deep “1020” trays without holes serve as water reservoirs, carry trays for seedling flats and inserts, and are ideal for most seed-starting applications. Shallow trays are excellent for microgreens production. Mesh trays support seedling flats and soil blocks and are best for any application where water drainage is beneficial.

Support Trays Comparison Chart

Table 2. Support Trays Comparison
Product Name Description Depth
Solid Trays without holes—For bottom watering.
Microgreens Reservoir Durable and reusable. 1 ⅛”
Polypro Endurance Shallow Speed Strong, durable polypropylene trays with "bumpers" that make it easier and faster to center and align soil blocks when using Johnny's Soil Blockers. Also great for any shallow tray application. 1 ⅛"
Lightweight Shallow Ideal for bottom watering. 1 ¼”
Polypro Shallow Shallow polypropylene trays with deep channels drain away excess water. Ideal for bottom watering, soil blocking, and microgreens production 1 ¼”
Polypro Endurance Deep Johnny’s thickest wall trays. Developed to endure the most rigorous commercial grower applications. 2 ¼”
Lightweight Deep Ideal for bottom watering. 2 ½”
Solid Trays with holes—For drainage.
Microgreens Growing Durable and reusable. 1 ⅛”
Lightweight Shallow Perfect for microgreens and shoots production. Has holes for drainage. 1 ¼”
Polypro Shallow Durable polypropylene shallow trays with holes for drainage. Available in colors for color-coded production. 1 ¼”
Lightweight Deep Standard 1020 tray. Seed straight into tray or use for extra support. Has holes for drainage. 2 ½”
Mesh Trays—for supporting seedling flats and soil blocks in any application where water drainage is beneficial.
Polypro Mesh Shallow Tight mesh polypropylene design with reinforced ribbing for extra durability. 1 ¼”
Heavyweight Mesh Provide easy transportation and extra support for seedling flats. 2½”
Medium Weight Mesh Provide easy transportation and support for seedling flats. 2½”
Polypro Mesh Deep Durable trays for support and drainage. 2½”
Soil Block Propagation These wide-mesh bottom trays are ideal for soil block propagation. 2½”
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Humidity Domes

Provide the perfect environment for germination by covering your flat with a plastic dome that helps retain moisture and warmth. Remove the dome once the seeds emerge to reduce the risk of disease. Use in conjunction with a heat mat for faster, more uniform germination of heat-loving crops. NOTE: Dome rests lightly over the tray and does not form a tight seal.

Humidity Domes Comparison Chart

Table 3. Humidity Domes Comparison
Product Name Height Description Vented
Clear Acrylic Domes 2" Standard humidity dome for germinating seedlings No
Clear Propagation Domes 7" Great healing chamber for newly grafted plants. Yes
NanoDome 7" Humidity dome with groove for resting a grow light. Yes
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Trays, Flats & Domes Compatibility

Trays & Flats Compatibility Cross-Reference Chart

Table 4. Trays, Flats & Domes Cross-Reference Compatibility Chart
Trays
Polypro Endurance Deep Polypro Shallow Polypro Endurance Shallow Speed Lightweight Deep Lightweight Shallow Microgreens Reservoir
Flats 20-Row ✔ ✔ ✔ ✔
Plug Flats (all cell sizes) ✔ ✔ ✔ ✔
Pro-Tray ✔ ✔ ✔ ✔ ✔ ✔
Air Pruning ✔ ✔ ✔ ✔ ✔ ✔
SureRoots® 50-Cell ✔ ✔ ✔ ✔ ✔ ✔
Jumbo Plug Inserts ✔ ✔ ✔ ✔ ✔ ✔
6-Cell Tray Inserts ✔ ✔ ✔ ✔ ✔ ✔
Insert Pots 2 ½" ✔ ✔ ✔ ✔ ✔ ✔
5x5" ✔ ✔ ✔ ✔ ✔ ✔
Support Trays—mesh Polypro Mesh (shallow and deep) ✔ ✔ ✔ ✔ ✔ ✔
Heavyweight Mesh ✔ ✔ ✔ ✔
Soil Block Propagation ✔ ✔ ✔ ✔ ✔
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Humidity Domes Compatibility Cross-Reference Chart

Table 5. Humidity Domes Compatibility Chart
2" Clear Acrylic Domes Nanodome Propagation Dome
Flats 20-Row ✔ ✔
Plug Flats (all cell sizes) ✔ ✔ ✔
Pro-Tray 24 Cell Flats ✔ ✔
Pro-Tray 38 Cell Flats ✔ ✔ ✔
Air Pruning
SureRoots® 50-Cell ✔ ✔ ✔
Support Trays —no holes Microgreens Reservoir Tray
Lightweight (shallow and deep) ✔ ✔ ✔
Polypro Endurance Deep ✔ ✔
Polypro Endurance Shallow Speed ✔
Support Trays —with holes Microgreens Growing Tray
Lightweight (shallow and deep) ✔ ✔ ✔
Polypro Shallow ✔ ✔ ✔
Support Trays —mesh Polypro Mesh (shallow and deep) ✔ ✔ ✔
Heavyweight Mesh ✔ ✔
Soil Block Propagation ✔ ✔ ✔
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Biodegradable & Plastic Seedling Pots

Pots Comparison Chart

Table 6. Pots Comparison
Product Name Dimensions
Biodegradable Fertil Pots—Round
2 ⅓" Round Fertil Pots 2⅓” W x 2⅓” H
3 ⅛" Round Fertil Pots 3⅛” W x 3⅛” H
4" Round Fertil Pots 4” W x 4” H
Biodegradable Fertil Pots—Insert Strips
36 Cell Fertil Pots Strip 1½” W x 2” H
20 Cell Fertil Pots Strip 2” W x 2” H
18 Cell Fertil Pots Strip 2⅓” W x 2⅓” H
12 Cell Fertil Pots Strip 3⅛” W x 3⅛” H
Plastic Pots
Mini 3½” Sq. x 2⅞” D
Maxi 3½” Sq. x 3½” D
Jumbo 5¼” Sq. x 5½” D
Polypro Insert Pots
2½ 2½” W x 3½”H
5x5 5” W x 2½” H
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