Quick verdict
Forty four-cell inserts, 160 cells, each 2.5 by 2.5 inches and 2.8 inches deep with drainage holes and air-pruning slits, eight of which fit a standard 1020 flat. The deep, wide cells grow stronger root systems than shallow 72-cell inserts and the slits stop roots circling. They are thick BPA-free plastic made to be reused for years, and the four-cell format lets you move or pot on a few plants at a time.
Strengths
- Deep 2.8 inch cells with 2.5 inch width for strong roots
- Air-pruning slits and drainage holes in every cell
- Eight inserts fill a standard 1020 tray
- Thick, reusable BPA-free plastic
- Four-cell units move and pot on independently
Weaknesses
- Deep cells use more mix per plant
- Fewer plants per flat than 72-cell inserts
- Needs a solid 1020 tray underneath for bottom watering
The overall YardToolLab Score is out of 100. Section scores are out of 10.
Room for Roots
Shallow 72-cell inserts are fine for lettuce and a nuisance for tomatoes, which hit the bottom in two weeks and need potting on. RooTrimmer’s four-cell inserts are the alternative: cells 2.5 inches square and 2.8 inches deep, with drainage holes and air-pruning slits, eight to a standard 1020 flat. The pack of forty gives 160 cells of thick, reusable BPA-free plastic.
This review is based on the maker’s specifications and on how deep-cell 1020 inserts perform for seed starting generally. We have not used these inserts ourselves.
Depth and Width
Root systems grow down first. A 2.8 inch cell lets a tomato, pepper, brassica or squash seedling build a complete root system before it is transplanted, so it establishes in days rather than sulking for a week. Many gardeners skip a potting-on stage entirely by sowing directly into deep cells. The trade is more mix per plant and fewer plants per flat, 32 instead of 72.
Air Pruning
Slits in the cell walls let roots reach air, which stops the tip and triggers branching behind it. Instead of a spiral of thick roots around the pot wall, the plug comes out as a fibrous mass that grabs the new soil at once. It is the same principle as fabric pots, built into a cheap insert.
Format
Four-cell units are the practical size. Pick up the four tomatoes that are ready and leave the rest; move one unit to brighter light; pot on a few at a time. They stand in a solid 1020 tray for bottom watering, which is how they should be watered, or alone on any waterproof surface.
Build and Reuse
Thick plastic that does not crack when you push a plug out is the difference between a tray that lasts one season and one that lasts ten. RooTrimmer’s inserts are described as heavy duty, and owners of this class of tray treat them as a permanent part of the greenhouse kit. Wash with a mild bleach solution between crops.
Who Should Buy It
- Vegetable gardeners starting tomatoes, peppers, squash and brassicas.
- Anyone tired of potting on from shallow cells.
- Market gardeners wanting durable inserts in quantity.
Common Owner Complaints
Mix consumption and lower count per flat. Both are the cost of root room.
Filling and Sowing
Pre-moisten the mix so it holds together, fill the cells loosely and tap the insert on the bench to settle it rather than pressing, which compacts the plug and slows roots. Sow at the depth the packet gives and cover with vermiculite for even moisture. Deep cells hold enough reserve that seedlings can go two or three days between waterings in cool weather.
Alternatives to Consider
Bootstrap Farmer 6-cell inserts are the premium equivalent. A 72-cell insert suits small-seeded quick crops. Soil blocks from a 2 inch blocker give similar root quality without plastic.
Verdict
For strong, fast-establishing transplants, deep cells with air pruning are the right tool and these inserts supply 160 of them in a 1020 format built to last. Bottom water in a solid tray and skip the potting on.
Full specifications
RooTrimmer 40-Pack Reusable 4-Cell Deep Seed Starter Trays with Drainage and Air-Pruning Slits FAQs
Roots grow down before they grow out. A 2.8 inch cell lets tomatoes, peppers and brassicas develop a full root system before transplant, so they establish faster and need potting on less often.
When a root tip reaches the slit it meets air and stops, and the plant branches new roots behind it. The result is a fibrous root ball instead of a spiral.
Eight inserts fit a standard 1020 flat, 10 by 20 inches. They also stand alone on any waterproof surface.
Thick plastic in this format lasts many seasons. Wash with mild bleach solution between crops.
