Soil blocks provide a sturdy base for seedlings

When I was visiting David Tresemer at his farm in Brattleboro, Vt., one time, the horticultural tool specialist tossed a 10-inch corn seedling to me. It was growing in a small block of soil. As I caught the seedling, barely a crumb of soil fell from the roots. This is hardly the ideal way to treat a seedling, but Mr. Tresemer did it to illustrate a point: Soil blocks, commonly used by European nurserymen for starting seeds, are much sturdier than you might imagine. They're slowly gaining ground here in the United States, and they are catching on as a great way to grow seedlings among home gardeners because of a dandy little soil-block maker invented by Michael Ladbrooke, an English engineer and avid gardener.

I've used the blockmaker for the past few years, and soil blocks have become my favorite way to start seedlings -- for many reasons. Soil blocks are:

Inexpensive. With the right type of soil, rich in well decayed organic matter (humus), or of ``chocolate-cake consistency,'' as Tresemer puts it, you can make the blocks out of straight garden soil. A 50-50 mix of of aged compost (in the final ``soil'' stage) and peat moss also works well. So will most of the potting-soil mixes available at garden outlets. There's also a special blockmaking mix now on the market. I have heard of some growers using a blend of shredded newspaper and garden soil, and I plan to experiment along these lines this season.

Easily and quickly made. With a little practice you quickly recognize the right consistency of the soil-starter mix (as wet as cooked oatmeal but not runny), and thereafter the blockmaker does it all for you. With a little practice, you'll be able to turn out four soil blocks faster than you can fill a single peat pot.

Convenient. You can turn out just as many blocks as you need when you need them. Or you can make a large batch at one time and store them for later use.

Durable. Given the right quality of mix, the block holds its shape from the moment it is formed and resists erosion from anything other than a pelting rain for weeks on end.

In my own experience some unused blocks were left outdoors all summer, and while the rain had umbrella-shaped them by the close of the season, they were still usable. Once the seedlings are up, the roots quickly fill the blocks, making them stronger still -- as Tresemer's toss of the corn seedling illustrated.

Soil blocks have been used by European growers for a couple of decades and the idea only recently moved to the US. But research shows that a highly productive agricultural system, based on soil blocks -- or champines, as they were called -- flourished in Mexico 2,000 years ago.

The Indians grew most of their crops alongside irrigation canals, which provided both water and much of the fertility for the land as well. The farmers of those days would scrape the muck off the bottom of the canal and spread it out in a thick layer on the canal banks. When the mud had partially dried, it would be cut into squares which then became the soil blocks in which seeds were sown or cuttings made.

After transplanting in the fields, the plants grew to maturity largely on the nutrients that came with the soil block. Recognizing the extraordinary fertility of the canal muck, the Indian farmers of the day enhanced it still further by throwing spent plant material into the canals where it was left to rot. Most Mexican farmers have turned to chemical farming during this century, but a few scattered examples of this ancient soil-block agriculture are still found in isolated areas of Mexico today, Tresemer points out.

Modern-day soil blocks are made by first pushing the blockmaker into the mix; then the plunger is depressed, squeezing out the excess moisture. The same plunger then ejects the newly formed blocks, which are immediately ready to receive a seed.

I press out the blocks into a plastic tray and then separate them so that there is a quarter of an inch between each block. This is enough space to prevent adventurous roots moving from one block into another (air pruning is the term used).

If you have a good deal of compost in your mix, the block will contain enough plant nutrients for about 10 days of growth. Thereafter, feed the seedlings with a diluted nutrient solution every time you water. Use at about 1/10 the strength or even weaker of the normal recommendation because you are feeding the plants so frequently.

I set the tray dead level and then pour water gently into one end of the trays, allowing the blocks to soak up water from the bottom. How much water you put in will depend on how many blocks the tray holds. Whatever isn't soaked up after about 15 minutes is excessive.

How frequently you water (every day, twice a day, or every other day) will largely depend on how hot the weather is and how big the plants have grown. A little observation will tell you all you need to know. Don't let the blocks go dry.

Greg and Pat Williams who put out that most informative horticultural newsletter HortIdeas (Gravel Switch, Ky.), water their soil-block seedlings by the wick method. They place the blocks on an absorbent piece of cloth with one end in a pan of water. The absorbent cloth used for diapers, the Williamses have found, works very well.

For most crops you sow one seed to a block. But commercial growers in Europe discovered some time back that perfectly good harvests of onions, leeks, and beets could be obtained by planting three to four seeds to a block. That might seem crowded, but at transplanting time the blocks are simply set out a little farther apart than would be the case for single plants.

The carrot is one vegetable that doesn't do well in blocks. That's because the fine taproot strikes the bottom of the block almost as soon as the leaves are up and immediately starts to fork. On the other hand, the short, stubby carrot varieties can be started in blocks.

While the most common block is a 2-inch-square cube, the full line of Ladbrooke blockmakers enables the gardener to sow seeds in tiny half-inch blocks which drop into the 2-inch blocks, which in turn fit into the 4-inch- square cubes. The 4-inch cubes will take tomatoes through to the flowering stage.

Copies of Ladbrooke's 2-inch blockmaker are being made in Asia, where his patents are ineffective. They are several dollars cheaper than the $18.50 Ladbrooke version (which also includes Tresemer's manual on soil block making and use).

The 2-inch blockmaker copies are listed in several garden supply catalogs. The three Ladbrooke models are available from Green River Tools, Box 1919, Brattleboro, Vt. 05301, the company that also developed the blockmaking compost in collaboration with the Woods End Laboratory of Temple, Maine.