Soil blocks are just blocks of soil that have been compressed enough so they don’t fall apart easily. They are a way of having a plant grow in soil without a pot. They are more fragile than a typical six pack in plastic, but once the roots fill the blocks they are surprisingly sturdy.
There are a few reasons to choose soil blocks over pots. The Micro blocker is ideal for small seeds as the little blocks take very little space in your propagator, meaning you can plant three or four times as much as before. And because you don’t have to use plastic pots you also don’t need to buy them or wash them out and put them away.
But probably the best reason is that there is much less root disturbance when you transplant your seedlings. The roots never get root bound. In a pot, by the time the roots have filled out their container there is always a circle of roots at the bottom that you have to untangle before planting on. With soil blocks the roots are air pruned as they grow. There are lots of little root ends at the edge of the block just waiting to grow when they get transplanted. When they are big enough, you can move them on to a bigger block with a cubic hole already prepared to pop them in!
Extensively used by Dutch commercial growers for decades the hand blocker was designed by Englishman Mike Ladbrooke in the 1960’s for the home gardener and small commercial growers.
Help & Resources
There are many help resources available throughout the world (but very few from the UK). A selection of the best is linked below.
Original Soil Blocking e-book by David Treseman
a detailed guide to soil blocking usage and advantages Soil Blocking Ebook by David Tresemer
A wealth of useful information from soilblockguru Jason Beam of Potting Blocks Co USA
Monty Don’s advice on soil block mixture
Using blocks of soil to grow plants is an ancient Mexican technique which has been adapted for the modern home and commercial gardener. A soil block is a compressed unit of compost which holds together negating the need for a pot. As seeds germinate and grow, their roots eventually reach the edge of the block, where they become exposed and ‘air pruned’. This means they stop growing from the tip and develop a branched root system within the block. In a pot these roots would continue to grow and if not potted on or planted out, they can wrap around the inside of the pot causing the plant to become ‘root bound’. A ‘root bound’ plant can suffer poor growth after it has been moved on or planted out.
Monty is trying out soil blocks in his garden and likes to make up his own mix. Here’s the recipe he’s currently using:
1 part garden soil
1 part leaf mould
2 part garden compost
4 parts coir vermiculite mix
You could also use a shop-bought compost – John Innes mixes work best. But you may need to add loam or garden soil (as long as it isn’t too sandy) to help it bind together.
Once you’ve mixed up your compost, make it very wet and mound it slightly on a flat surface. Then wet your soil blocker, push it down into the mix and squeeze out the new soil blocks onto a seed tray or flat wooden tray. It’s important to remember to water soil blocks gently otherwise they can wash away, so if you’re watering from above, try using a fine rose on your watering can or spray. Alternatively, line your trays with capillary matting and dip one end in water – that way, they’ll be able to soak up moisture from beneath.
Eliot Coleman on the benefits of soil blocking
A quick explanation of the benefits of soil blockers by American farmer and educator Eliot Coleman
Eliot Coleman’s soil blocking mix
Note that we have found Coco Coir to be a more successful binder for soil blocks and include a supply of premixed coir and perlite with all of our soil blockers