Soil Block Seeding

I am a soil block devotee.

Three years ago, I got tired of starting seeds indoors in cell plug trays. Each cell was tiny, black inside, and hard to clean. Tiny cell holes meant that seedlings were crammed together and hard to remove when transplant time came.

I read articles by the early guru of organic farming, Eliot Coleman who, in the 1970s fretted over his less-than-vigorous seedlings. A visit to Europe introduced him to soil block making.  Soon he had a British company create a sturdy metal soil blocker device. He then devised his own recipe for a seedling soil mix.

The advantages of soil blocks? The blocks are large with a plastic dibble inside and each cell stamps a round depression in the center of the soil block, into which a single seed is planted. I have found that the seedlings are straighter and more vigorous from the day of germination. Best of all, the roots are not confined by the plastic sides and bottom of the cell plugs and spread out naturally. Without becoming rootbound, they naturally air prune. When it comes time to transplant the seedlings, each soil block is large and easy to maneuver into a transplant pot for growing on in and hardening off.

The variables are 1) how many soil blocks you want to make at once and 2) what you use as your seedling soil block recipe. Commercial growers have the option of up to 72 blocks with a stand-up machine!  At home, our options are 1, 4, 5, 10, or 20 cell soil blockers.

I use a 5-cell soil blocker refilled twelve times which creates 60 soil blocks for my tray. I reuse the tray I bought with the original cell plug and tray combo. I can reuse the dome that came with the system while the seedlings are germinating and while using heating mats to warm the bottom of the tray.

Seedling soil block recipes abound. Many use peat moss, which should be sifted before using for soil blocking. Eliot Coleman published his original soil block recipe in his book, The New Organic Grower: A Master’s Manual of Tools and Techniques for the Home and Market Gardener. Peat-free soil block mixes are available.

Intending to make my own seed blocker mix, I was challenged by finding ingredients such as greensand (glauconite) mined from the ocean bottom for a fertilizer that provides iron; colloidal phosphate adding phosphorus; and dolomitic lime for calcium and magnesium. Blood meal is readily available. I located a retailer (no longer selling products) that had these four ingredients in a mix. I use Fruition’s DIY Seed Starting Mix Recipe.

Recipe

Combine and set aside

10 quarts well-sifted peat

10 quarts fine compost

Separately combine; (mixture will average 1 cup of ingredients)

1 part greensand

1 part fine grade colloidal phosphate

1 part blood meal

½ part dolomitic lime

Mix well and add 7 quarts of perlite.  Combine the two dry mixtures and divide into two 5-gallon buckets.  Add water to a dishpan before you form the soil blocks. Prepare your soil block trays. Mine are made of sturdy plastic, have no drainage holes, and came with a fitted clear dome.

The soil blocks should never dry completely. Add water to the block bottoms, not from the top.

Use a large plastic dishpan to mix some of the soil with a moderate amount of water. Make a section of soil about 4-5” tall and long in the pan. Place the soil blocker above the soil and insert straight down firmly, wiggling back and forth to pick up the maximum amount of soil in the blocker.

Turn the blocker upside down and firmly press the soil into each block to fill it up. There will still be a ragged surface so take a putty knife and press more soil into the block holes while smoothing the surface. Pack as tightly as you can. Every flake of soil mixture counts to create a square even block.

Turn the blocker right side up. Move it over the tray and press the blocker lever down hard to create your row of side-by-side blocks. The dibble holes are ready for seed planting. Experts differ as to whether to place a tiny bit of soil over the seeds. I have not needed to.

Label your seeds or rows. I tape the labels to the edge of the tray, then place the dome on the tray and set the tray on a heating mat.

 

 

Soil Block Resources:

Discovering Soil-Block Making, Eliot Coleman https://www.johnnyseeds.com/growers-library/methods-tools-supplies/seed-startingtransplanting/eliot-coleman-discovering-soil-rKL7D

Soil Blocking in Five Easy Steps, Petra Page-Mann

https://smallfarms.cornell.edu/2021/04/soil-blocking-in-five-easy-steps/

Soil Blocking: Good for Your Plants and the Environment, Margaret Roach https://www.nytimes.com/2025/02/26/realestate/gardening-soil-blocking.html

Making Soil Blocks, Penn State Extension Master Gardener Program, 2019

Jim Kasten

https://extension.psu.edu/programs/master-gardener/counties/susquehanna/penn-state-mastergardener-articles/making-soil-blocks