Sure-fire transplants

The transplanted seedlings - cucumbers, gem squash, lettuce, and Swiss chard - that went into my garden last week have delighted me. They have continued their rapid growth without even appearing to pause, indicating that there was no transplanting shock whatever.

There is a reason for this, of course. The seeds were sown in soil blocks, rather than in flats, so that when the young plants were set out in the garden the roots were not disturbed in the slightest degree.

I made the soil blocks (a mixture of soil, peat, and compost) with the aid of a little hand tool that has recently come onto the market.

Recently, I was introduced to soil-block transplanting at the Vermont farm of David Tresemer, who literally threw some 6-inch-tall corn seedlings into little holes in the ground, pulled some soil up around them, and gave them a little water. It was as simple as that. He didn't even bother to press the soil down around the plants.

''There's no need to,'' Mr. Tresemer pointed out, ''when the roots are encased in a block of soil.'' Three weeks later I returned to find the corn knee-high and thriving. They, too, had known no setback.

Dutch horticulturists developed the soil-block approach as an alternative to the peat pot. It involved cheaper materials (soil was an ingredient) and cut down on labor dramatically. Now many other Europeans, particularly the British, use soil blocks extensively.

Large machines turn out thousands of soil blocks an hour - and that's the way it might have remained, had the owner of a small nursery not approached Michael Ladbrook, who runs a small engineering company in Bidford-on-Avon, Warwickshire.

Could the company make a hand-operated blockmaker that a modest-size nursery might use? Mr. Ladbrook responded with a 20-block unit that a worker can use to turn out up to 30,000 blocks a day.

As an amateur gardener, Ladbrook saw the advantages of soil blocks for transplants, so he made a small four-unit blockmaker for himself. Soon, Ladbrook began making the small units for sale.

The soil blocks can be readily pressed out on, say, a wooden board. Each block has a small indentation to accept a seed. I found that by covering the blocks with a sheet of newspaper, topped by plastic to reduce evaporation, brought about quick germination. In my first test I planted 30 blocks to Swiss chard and all but two germinated.

Once up and growing, the seedlings are best watered using a mister or fogging attachment on the end of a hose. Or, as I did, the plywood containing the blocks is placed in a plastic tray and water is poured carefully into the tray to about a quarter of the way up the blocks. This way the seedlings are watered without any noticeable erosion.

These, then, are the advantages of using soil blocks for transplants:

* They are readily made at a modest cost. You can use a commercial seed-starter mix as is (Terralite and Pro-mix are two brands that have been used successfully in tests), or make up a mixture from 50 percent peat moss, 25 percent screened compost, and 25 percent garden soil. If the garden soil is heavy clay, include some sand.

* Seeds germinate readily in the blocks. Some gardeners stack the flat wooden trays of blocks several tiers deep until germination begins. Then the blocks are moved into the greenhouse, cold frame, or straight outdoors in temperate weather.

* Roots stay undisturbed so there is no transplant shock.

* Because the blocks are composed entirely of the growing medium, roots grow freely through the sides of the block and into the garden soil, so that accelerated growth begins immediately.

When making blocks, add water until the soil mix is a little on the sloppy side (no longer stiff). Push the blockmaker into the mixture with a wiggling motion and begin pressing out the blocks.

The narrow space in between each one prevents the roots from growing into a tangled mess. The seedlings may be transplanted once the roots begin to grow out and down the sides of the block.

The hand blockmaker will shortly be made available through several outlets in the United States. For information write to By Hand and Foot Ltd., PO Box 611, Brattleboro, Vt. 05301.