I'm Never Buying Plastic Seed Trays Again! Soil Blocking Is the Simpler Way to Start Seeds

Every February the seed trays come out – those flimsy plastic cells that crack after a season or two, stack awkwardly, and leave roots tangled in a tight little spiral by transplant time. There’s a better way to start seeds indoors, and it doesn’t involve plastic cell trays at all.

Soil blocking skips the containers entirely. A special metal press compresses a wet soil mix into firm freestanding cubes, and seeds go directly into a small dimple pressed into the top of each block. Starting seeds indoors gets a lot easier when there’s less to clean, sterilize, or eventually throw away.

Why Soil Blocking Works So Well

The big thing soil blocking has going for it is air pruning. When roots reach the edge of a soil block, they hit open air and stop growing outward. Instead of circling and tangling the way roots often do in plastic cells, they branch back inward and build a denser, more fibrous root system. That root structure tends to be better prepared for transplanting than most seedlings coming out of a plastic pot.

Less transplant shock is the usual payoff. Roots that haven’t been circling or cramping don’t need time to untangle and reorient when they hit garden soil. The block goes in the ground, roots start exploring almost immediately, and the seedling barely seems to notice it moved. Gardeners who switch to soil blocking often report stronger, faster-establishing transplants than they were getting from trays.

What You Need to Get Started

The soil blocker itself is the main investment. A 2-inch (5 cm) four-block hand press is the most useful size for general seed starting – tomatoes, peppers, squash, flowers, herbs. A 2-inch soil blocker can pay for itself fairly quickly once you stop buying trays every season. Mini 3/4-inch (2cm) blockers work well for tiny seeds like lettuce and basil that get potted up into larger blocks as they grow. If you want, you can get the whole convenient set here from Amazon. Or you can opt for one of the cheaper ones up above.

The mix matters more than most people expect. Regular potting soil usually won’t hold together well enough – blocks need extra fibrous material to keep their shape. A basic blocking mix is roughly three parts coco coir, two parts compost, one part perlite, and a small amount of garden soil for structure. The mix should feel like very wet oatmeal – dense enough that it holds together when squeezed but still releases cleanly from the press.

Making the Blocks

Too wet and the blocks just turn soft and slump. Too dry and they crumble before you even plant. Getting that moisture level right usually takes a couple tries anyway. But once you’ve squeezed a handful and felt that heavy, wet-oatmeal texture in your hands, you start to recognize when it’s right and can usually repeat it without much trouble.

Press the blocker down firmly into the mix, give it a little twist to pack it in tight, then push the lever so your clean blocks drop out onto the tray. Rinsing the blocker between presses helps if it starts sticking. The blocks should hold their shape right away and sit neatly with clear edges between them. Drop one seed into the small dimple on top of each block, cover it lightly with a pinch of dry mix if it needs darkness, and set the tray somewhere warm.

How to Water Soil Blocks

Watering from the top can disturb small seedlings and sometimes knock seeds loose before they’ve anchored properly. Bottom watering is usually the better option. Pour water into the tray underneath and let the blocks pull it up from below. You’ll see the color slowly shift from lighter to darker as moisture moves through.

These blocks do dry out faster than regular plastic trays, so checking them daily helps. During germination, a humidity dome or plastic wrap over the trays slows evaporation. Misting helps, as well. Once the seedlings come up, remove the cover and keep the blocks moist but never soggy. Shallow seedling trays with a dome from Amazon tend to work well for bottom watering since they hold enough water without drowning the blocks.

Sizing Up and Transplanting

Seedlings started in 3/4-inch (2 cm) mini blocks get potted up into 2-inch (5 cm) blocks once they develop their first true leaves. The 2-inch blocker has a square dibble that creates a pocket the exact size of the mini block – set the smaller block into the larger one and firm the mix around it. Once they outgrow that, you can move to the 4 inch.

Transplanting to the garden is straightforward. Dig a hole slightly larger than the block, drop it in, firm soil around the edges, and water. The block gradually biodegrades into the surrounding soil. Roots grow straight out from the block instead of needing to uncoil and reorient. Whole trays of seedlings can often be transplanted in less time than it takes to pop plants from plastic cells one by one.

What Soil Blocking Doesn't Fix

The learning curve on mix consistency trips people up at first. Blocks that fall apart before seeds germinate are usually too dry. Blocks that sag or lose their shape are too wet. The fix is typically just adjusting water incrementally until the texture feels right – dense, heavy, and just barely holding together.

Soil blocking also doesn’t make sense for every situation. Direct-sow crops like carrots and beans don’t benefit much from the method. Very large seeds like corn or sunflowers that go straight in the ground don’t really need the head start. Where soil blocking shines is with transplants – tomatoes, peppers, eggplant, brassicas, flowers – crops that spend weeks indoors before going outside.

The Real Advantage over Plastic Trays

Less cleaning, no stacking, no cracks, no roots to untangle at transplant time – the advantages of soil blocking go on and on. The mix costs about the same as bagged potting soil, and one blocker will last you for years. Once the method clicks, it’s genuinely faster and tidier than the plastic alternative.

Experienced soil blockers often cut their indoor growing time noticeably compared to traditional seed-starting methods. Since air-pruned roots establish so quickly after transplanting, seedlings don’t always need as many weeks indoors before they’re ready to go. For anyone tired of hauling out the same cracked trays every spring, soil blocking is worth trying at least once.