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by Sandy Patry


Using an individual small block of soil to start and grow each plant, without the use of pots or mass planting flats, was first introduced to me at a COG Ottawa presentation by Eliot Coleman about two years ago. The idea of growing plants in individual small cubes of soil, progressively transplanting to larger blocks and then to the garden with little or no root disturbance was fascinating. ;

At about the same time, I discovered that Michael Ladbrooke, the builder of the small hand blockers used to form the growing blocks, was located in England, about 20 km from the job site I visited every six weeks or so. I visited Michael, acquired a blocker and tried the process. With the success of that test, I acquired a full range of blockers to start the several thousand seedlings my wife Suzanne and I plant each year for our part-time perennial business.

We have become avid users of this technique. Why?


• Space-saving: The compressed soil blocks require no pots and the cubic shapes can be set side by side with only a 2 mm (1/8") air gap left between blocks. Root growth stays within the block and does not cross the air gap to interlock blocks. This means that 220 of the 19 mm (3/4") cubes made by the micro blocker take up only about 0.1 sq. m (1 sq. ft.). Thirty-six of the 2" cubes produced by the mini blocker take up the same space. This is a great advantage when starting seeds indoors and for starting slow-germinating or slow-growing plants like many perennials.


• Efficiency: The planting of one to three seeds per block, depending upon the germination quality of the seed, has a tremendous saving in seed use compared to broadcasting seed in flats. We reduced our seed requirements to one third of our previous use. Blocks allow plants to grow in a controlled mixture of compost and organic fertilizer, conserving these precious commodities compared to general broadcasting in the garden growing area. It is easily possible to make and seed several hundred blocks per day for the home gardener and 4000 or more for the commercial grower. After planting out, there are no pots to collect, wash and store.


• Survivability: Plants grown in blocks are individual and evenly spaced, with each plant receiving the same amount of growing medium. The root system is contained by the air barrier around the cube and does not entangle with other plants or circle the walls of the container. The straight wall of the cube allows more root space than tapered pots or plugs, and the mixture of the ingredients in the block is carefully controlled. This all leads to high survival rates for seedlings since early growth is fast and healthy and root shock from handling is minimized.


• Transplanting: The blocks are self-contained, easily handled within a few hours of being formed, and almost indestructible with normal handling once the root system of the seedling has been established. The blocks can be made with inserts to form transplant depressions the size of the next smaller cube: the micro fits into the mini, which in turn fits into the maxi (4" cube) if desired. The 2" cubes can also be planted directly into the garden. Since the blocks are so stable and the root systems are not intertwined, transplanting is simply a matter of dropping the smaller block into the larger block or directly into the garden and watering the plants in. Since there is no root loss or disturbance, the shock is minimal and the plant does not suffer any setback.

There are three main steps in using the blockers successfully: mixing the soil, forming the blocks, and seeding and transplanting.


• Soil Mix: Much has been written on the mix of soil required to form blocks to grow plants in. When we first started, we searched for some of the obscure items such as greensand but we have found, through our own experience and from talking with other block users in America and Holland, that the "proper" mix is variable. However, it should have the following qualities: be able to hold its shape when free standing; have a good balance of plant nutrients; have reasonable drainage; and have a pH value around 6.2. For blocks 1.5" and larger, we use, by volume, about 30% peat moss, 30% compost or compost/leaf mould mix, 30% garden soil and 10% sharp sand for drainage. Two bushels of this mix will produce approximately 400 of the 2" blocks. We add about two cups of balanced organic fertilizer to this volume and small quantities of lime to adjust pH. Originally we used more peat but found this was not required. In Holland, growers successfully produce millions of plants in blocks using just black muck soil and fertilizer, with no peat or compost. In small 3/4" blocks used for seed starting and initial growth, we add to our regular mix either worm compost which has been screened for removal of large solids or commercial fertilizer-free mixes such as Pro-Mix. Seeds do not require nutrients until they reach their true-leaf stage; then we fertilize with fish emulsion.


• Making Blocks: Mix the dry ingredients together well. We do this in a flat bottomed plastic container such as worm farms come in. Add water until the mixture has the consistency of wet mortar or oatmeal porridge. The most common problem is insufficient moisture in the mix. A handful of the mix when squeezed should ooze out between the fingers.

Push the blocker into the wet mixture, slightly twisting it back and forth. Lift the blocker from the tub and scrape the excess mixture from the bottom of the block using the lip of the tub. Place the blocker on the surface of the flat or tray and release the blocks by holding the ejection handle at the fixed height and pulling up on the main body. [Note: a common problem is pushing down on the ejection handle rather than lifting against it.] Continue to make blocks and eject them side by side with a maximum of 2 mm (1/8") between blocks. Sometimes the blocker will produce poorly formed blocks - don’t despair. Speed and quality quickly improve as you gain experience. Any container can be used to hold the blocks from boards to home- built flats. The flat should not hold more than 150 of the 2" blocks as this is the size and weight limit for comfortable handling by most gardeners. We cut one side off the box/flat for easier in-and-out handling of blocks. We use a lot of grape shipping boxes recovered from the local supermarket as flats - about the right size and price! Blocks can be made any time, stored and used later by just rewetting.


• Seeding Blocks: We generally put one to three seeds per block, depending upon the germination quality of the seed, in order to end with one plant per block. We pick the seed from a flat saucer with the moistened tip of a toothpick.

This method reliably picks up one or two seeds at a time and releases them when touched to the soil block. The tip requires rewetting every 5 to 10 seeds so we keep a small cup of water beside the seed saucer. To cover the seed we use a fine soil screen to sift compost or peat dust over the entire flat - a flour sifter will work quite well. Water the blocks with a fine rose or misting nozzle about every 2 days to keep them moist. We transplant 3/4" blocks into 2" blocks when the plants have two to three sets of true leaves. Plants can be grown in the 2" mini blocks until planted in the garden or transplanted to 4" maxi blocks and grown on to larger sizes. In Holland, many large blocks are never planted in the soil, but plants are grown to maturity in the blocks with liquid nutrients such as fish emulsion. It is best to water the blocks before transplanting or setting out in the garden.

We start plants in different sizes of blocks:


• 3/4" blocks: tomatoes, peppers, eggplant, most perennials, most herbs and annual flowers. We later transplant to 2" blocks.


• 1.5" or 2" blocks: brassica family, peas, corn, lettuce, Chinese greens, spinach, squash, and plant or tree cuttings. Onions and leeks are started and grown with 4 to 5 plants per block and, when set out in the garden, the blocks are planted with the equivalent of 4 plant spaces between them - they grow in these bunches and just push apart from each other with no apparent difficulty.


• 3" or 4" blocks: melons, squash, and large cuttings from trees, house plants and ornamentals. We have grown transplants of tomatoes, eggplants and peppers to maturity in 4" blocks.

Blockers are available for the small- scale gardener in hand-operated sizes of 3/4" x 20 blocks, 2" x 4 blocks, and 4" x 1 block. Blockers are available for larger scale gardeners and growers in hand-operated sizes of 1.5" x 20, 2" x 12, and 3" x 6 blocks. Large scale automated blockers are available for 1.5", 2", and 3" sizes with production rates of 50,000 blocks/hour.

Soil blocks are an interesting and efficient method of growing successful, healthy plants with a considerable reduction in effort and materials. It’s fun to play in the mud!



Sandy Patry is a Master Gardener and a COG Ottawa member. He and his wife Suzanne operate Whitehouse Perennials as a part time business near Almonte, Ontario.



Copyright 1993. Sandy Patry

Reprinted with permission. All rights reserved.

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