Soil Blockers vs Seed Trays

The cheapest honest way into soil blocking: it makes the same 2 inch block the expensive tools make, and it costs about what a few packets of seed cost.

The usual objection to soil blocking is the entry price, and it is a fair one: the famous tools cost more than several years of plastic trays. This removes the objection. It presses four two-inch blocks, it comes with the seed pins, and it costs very little.

Two inches is the right size to start with. It holds enough mix to carry a tomato or a brassica from sowing to planting out without potting on, and it is the size every soil blocking article you will read assumes you are using.

What you give up against a machined tool is refinement. Cheaper presses flex slightly, release a little less cleanly, and are less tolerant of a mix that is marginally too dry. In practice that means a few more failed blocks while you learn how wet the mix should be -- which you have to learn anyway.

Buy this to find out whether you like the method. If you make three hundred blocks next spring and still like it, that is the point at which a better tool starts to earn its money.

Skip it if: you will be making hundreds of blocks a season. A budget press is a fine way to learn the technique and a tiring way to run a production line.

The reference tools, sold as a nesting pair: 3/4 inch micro blocks to germinate in, 2 inch mini blocks to grow on in, and the inserts that let one drop into the other.

Ladbrooke is the name behind the modern soil blocker, and this is the pair of tools the method was designed around rather than a copy of them. The Micro 20 makes twenty three-quarter-inch blocks at a press; the Mini 4 makes four two-inch blocks with a recess sized to take one.

That pairing is the actual argument for spending this much. In February, bench space under lights and warmth on a heat mat are the two things in shortest supply. Germinating in micro blocks means twenty seedlings occupy the footprint four would, and only the ones that actually came up get promoted into a full-size block. Nothing is wasted on a seed that never germinated.

Potting on becomes a non-event, which is the part people underrate. The micro block drops into the recess in the mini block. There is no tugging a seedling out of a cell, no root torn away from mix, no check to growth. University of Minnesota Extension's warning about seedling roots growing together and being injured at transplanting simply does not arise.

The honest counter-argument is the price. If you sow two trays each spring, a budget press makes an identical two-inch block for a fraction of this. The set earns its money on volume and on the years you keep using it.

Skip it if: you only ever sow a tray or two. This is a long-term tool set at a price that only makes sense if you will use it every season.

The single most space-efficient way to germinate seed indoors: twenty blocks per press, in roughly the bench area four standard blocks would take.

Space under lights is the real constraint on indoor seed starting, and this tool attacks it directly. Twenty three-quarter-inch blocks occupy about the area four two-inch blocks do, which means a single heat mat germinates several times as much seed.

The workflow it enables is worth describing. You sow everything into micro blocks, keep them warm and damp, and after a week or so you know exactly which seeds came up. Only those get promoted into full-size blocks and only those occupy the expensive real estate under the lights. The dud seed never cost you anything but mix.

The discipline it demands is watering. A block this small has very little reservoir, and a warm room will dry it out in a day. Bottom water in a solid 1020 tray, keep a dome or a cover over it until germination, and do not plan a weekend away during the first fortnight.

On its own it is a specialist tool. Bought alongside a two-inch blocker it changes how the whole February bench works, which is why the sets usually make more sense than the individual presses.

Skip it if: you are not going to pot the seedlings on within a couple of weeks. A 3/4 inch block is a nursery, not a home.

The familiar six-cell pack, made thick enough to survive being emptied and refilled for years rather than cracking the first time you push a seedling out.

If the complaint about trays is that they crack, split and end up in a landfill after one season, the answer is not necessarily to stop using trays. It is to buy ones thick enough to survive.

Six-cell inserts are the format most gardeners already think in, and they map neatly onto how a home garden is actually planted: six tomatoes, six peppers, six brassicas. Each cell holds a single seedling, which is precisely what University of Minnesota Extension recommends -- divided containers with one seedling each, so roots do not grow into one another and get injured at transplanting.

The extra-strength plastic matters at one specific moment: when you push a root ball out from underneath. Thin packs split along a corner the first or second time you do it. These flex and spring back, which is the difference between a consumable and a tool.

The maintenance is not optional. Extension's advice for reused containers is to sterilize them by soaking in a bleach or disinfectant solution for thirty minutes. Skip that and reusable trays become a way to carry last year's damping-off into this year's seedlings.

Skip it if: you sow one tray a year. The economics only work if you reuse them season after season, which is also the only way the plastic case closes.

High-density plug trays with enough depth to be useful: seventy-two cells in a standard footprint, which is the tray-side answer to a micro blocker.

A 72-cell plug tray is the tray world's answer to the micro blocker: the way to germinate a great many seeds in the space one flat occupies. For anyone who grows ten varieties of tomato or sows successions of brassicas, that density is the whole point.

Depth is where these differ from the cheap ones. Most 72-cell trays are barely an inch and a half deep, which is enough to germinate and not much more. At a little over two and a third inches there is real root room, so the window between germination and potting on is weeks rather than days.

The trade is the same one every small cell makes: little reservoir, fast drying, and a hard deadline. Leave a 72-cell tray a fortnight too long and you will be pulling out plugs that have wound round themselves, which is the root-bound failure that soil blocks are designed to avoid.

Bottom water them in a solid 1020 flat rather than watering over the top. Small cells wash out, and surface watering is also how damping off spreads along a tray.

Skip it if: you grow only a handful of plants. Seventy-two cells of one crop is a market garden's problem, not a backyard's.

Thick enough to pick up full without folding, which is the entire complaint about cheap trays and the reason these cost more.

Anyone who has carried a cheap 1020 tray full of wet compost knows the failure mode: it folds in the middle and the seedlings go on the floor. Heavy-gauge trays do not do that.

The 1020 name is a standard footprint, roughly 10 by 20 inches, and it is worth sticking to. Every humidity dome, heat mat, cell insert and shelf is built around it.

Buy a couple of solid, undrained trays alongside the drained ones. A solid tray underneath lets you water from below, which is gentler on small seedlings than watering from above and keeps the leaves dry.

Skip it if: you start one tray a year. The economics only work once you are reusing them season after season.