Eliot Coleman Soil Block Recipe for Starting Seedlings

Growing your own seedlings provides gardeners with an economical and ecological method for starting plants. But the art of raising vigorous young plants goes beyond simply planting seeds in cells or flats. The soil medium itself plays a vital role in getting seeds off to a robust start.

Enter soil blocking – an innovative technique pioneered by farming guru Eliot Coleman. His recipe for the ideal soil block mix allows gardeners to make their own custom blend, optimized for air pruning roots and preventing transplant shock. Let’s explore why Eliot Coleman’s soil blocking method has become a game changer for many growers.

A Soil Built for Speedy Germination and Sturdy Growth

The basic ingredients in Eliot Coleman’s famous soil block mix provide the perfect environment for germinating seeds and nurturing young seedlings. Here’s an overview of the components and why they matter:

  • Peat Moss – Forms the basis of the mix. Its lightness provides exceptional aeration and drainage while helping retain just the right amount of moisture. Peat’s acidic nature must be balanced by adding lime.
  • Lime – Balances the acidity of peat moss, bringing the pH into the optimal range for most plants. Calcium and magnesium in lime benefit plant growth.
  • Perlite or Sand – Creates spaces within the mix for rapid drainage and air circulation to the roots. Prevents compaction.
  • Fertilizer – Supplies essential nutrients to fuel growth of seedlings. A balanced organic fertilizer with nitrogen, phosphorus and potassium is ideal.
  • Garden Soil – Contributes organic matter and beneficial microbes that assist plants with nutrition and disease resistance.
  • Compost – Also provides organic matter, microbes and slow-release nutrition. Compost lightens and loosens the mix further.

The combined qualities of these ingredients check all the boxes for an ideal seed starting medium: lightweight, loose, breathable, fast-draining, nutritious and able to retain just the right amount of moisture. Now let’s look at a typical recipe for Eliot Coleman soil blocks.

A Sample Recipe for Mixing Your Own Soil Block Blend

Making your own soil blocks allows you to customize the ingredients based on what you have available. Here is one example of a recipe from Eliot Coleman’s book The New Organic Grower:

Eliot Coleman’s Soil Block Mix

  • 3 buckets sphagnum peat moss
  • 1/2 cup dolomitic lime
  • 2 buckets perlite or coarse sand
  • 3 cups organic fertilizer (1 cup blood meal, 1 cup colloidal phosphate, 1 cup greensand)
  • 1 bucket good quality garden soil
  • 2 buckets aged compost or humus

Step 1. In a wheelbarrow or large tub, thoroughly mix together the peat moss and dolomitic lime until the lime is evenly distributed. The lime will help balance the acidity of the peat moss.

Step 2. Add in the perlite or sand and mix it in well. Perlite and sand will help provide drainage and aeration.

Step 3. Next add the organic fertilizer, mixing it in completely. The blood meal supplies nitrogen, the colloidal phosphate adds phosphorus, and greensand contributes potassium.

Step 4. Blend in the garden soil, which will provide organic matter and beneficial microbes.

Step 5. Lastly, mix in the aged compost or humus, which will further improve drainage while adding nutrients.

The end result should be a loose, lightweight, fluffy blend that will easily form cohesive blocks yet provide great aeration to plant roots. The lime balances acidity, the perlite/sand create drainage, the fertilizer feeds plants, and the soil and compost supply organic matter. This is the crux of Eliot Coleman’s magical soil block recipe!

Why Soil Blocks Are Game Changers for Starting Seedlings

What makes Eliot Coleman’s soil blocking method so revolutionary is the way the blocks treat delicate young root systems. When seedlings are started in traditional containers like six packs or peat pots, their roots hit the solid side and bottom walls, causing them to spiral and hit a dead end.

Transplanting these bound-up seedlings stresses and stunts their growth as roots must reorient themselves in the garden. Plants started in Eliot Coleman’s open-bottomed soil blocks experience improved vigor and less transplant shock for several reasons:

Air Pruning of Roots

  • With no walls to block roots, they follow air channels to the block’s edges and tips, sensing the open air beyond. Upon hitting open air, root tips “air prune”, forming smaller lateral roots that branch profusely.

No Transplant Trauma

  • Plants slide right out of soil blocks with roots fully intact, avoiding the growth setback caused by disturbing bound-up root balls of regular containers.

Sturdy Stem Development

  • Uncircling roots allow better uptake of water and nutrients, fueling steady, vigorous growth above ground too. Plants grow stocky vs spindly.

Earlier Hardening Off

  • The exposed sides of blocks eliminate moisture retention, allowing seedlings to gradually adapt to lower humidity. This “early training” eases the transition to the dry air and sun of the outdoors.

Revolutionary as they are, Eliot Coleman soil blocks do require some specific care on the part of the gardener…

Caring for Seedlings in Eliot Coleman Soil Blocks

The open-bottomed nature of soil blocks makes proper watering technique paramount. Follow these tips for success:

Water from the bottom only – Set blocks in trays and add water to tray, letting blocks soak it up from below. Bottom watering stimulates downward root growth.

Keep evenly moist, not saturated – Check blocks daily and add water to trays as needed to maintain even moisture, but don’t overdo it.

Allow to dry out slightly between waterings – Let blocks get nearly dry on top between waterings to prevent damping off disease. Roots will seek water at bottom of blocks.

Make drainage holes in tray – Make sure the trays holding the blocks have drainage holes to prevent waterlogging if you overwater.

Consider a seedling heat mat – Placing trays on a heated mat under grow lights will drive vigorous growth. Maintain 65-75°F temperatures.

Let blocks warm up before planting – Mix up soil blocks a few days before seeding to allow the organic matter to warm up to room temperature.

Handle blocks gently – Don’t crush or compress blocks when moving them. Handle gently to avoid damaging delicate roots.

Following these care tips will help you maximize the air pruning effects and prevent issues like damping off when using Eliot Coleman’s revolutionary soil blocking technique.

Timing from Planting to Transplanting

One huge advantage of soil blocks is they allow seedlings to grow for 4-6 weeks before needing to be transplanted into the garden. Here are some guidelines on timing:

  • Large seeds (beans, corn): 1 seed per block, transplant in 2-3 weeks.
  • Small seeds (carrots, lettuce): 2-3 seeds per block, thin to 1 plant, transplant in 4-6 weeks.
  • Flowers and herbs: 1 seed per block, transplant when 2 sets of true leaves.
  • Seedlings (onions, brassicas): Transplant into blocks when cotyledons appear. Move to garden in 4-6 weeks.
  • Root crops (radish, beets): Sow 2-3 seeds per block. Thin to 1 plant. Transplant before roots hit bottom of block.

Adjust timing based on your climate, growing season length and how quickly each variety grows. But soil blocks generally allow 4-6 weeks of germination and growth before transplanting.

Customizing Your Own Soil Block Recipe

The basic ingredients in Eliot Coleman’s mix can be modified based on what’s available to you. Don’t worry about following an exact soil block recipe. The key is finding the right balance of drainage, moisture retention and nutrition. Consider these substitutions:

  • Instead of peat moss, try coco coir, leaf mold, compost, or worm castings for moisture retention.
  • Substitute vermiculite, rice hulls, or pumice in place of perlite or sand to provide drainage.
  • Mix and match organic fertilizers like alfalfa meal, kelp meal, rock phosphate, etc. based on what you have on hand.
  • Swap homemade compost for purchased compost, or use leaf mold instead.
  • Experiment with adding mycorrhizae or biochar to increase microbial activity.

Part of the fun is tweaking the ingredients to create your perfect soil block blend. Use Eliot Coleman’s recipe as a starting point and adjust components to suit your needs.

Eco-Friendly Soil Blocks – An End to Plastic Flats & Containers

In addition to the benefits for plants, soil blocks provide a more ecologically friendly alternative to plastic six packs, peat pots and other single-use seed starting containers that generate needless waste. Some key advantages of soil blocks:

  • Zero Plastic Waste – No more piles of used seedling flats, six packs or peat pots sent to the landfill every year.
  • Fully Biodegradable – Blocks and any paper trays used decompose back into the soil. Even the wooden block makers can be reused indefinitely.
  • Close Plant Spacing – Block geometry allows you to space plants 2-3 inches apart, reducing wasted space compared to round peat pots.
  • Local & Sustainable Materials – Most ingredients like peat, compost, sand, and fertilizers can be sourced locally.

By starting your own seeds in soil blocks, you can save money while also keeping hundreds of plastic seedling containers out of the waste stream every year. The ecological benefits are enormous.

The Takeaway: Healthier Roots and Happier Gardeners

After reading about the logic behind Eliot Coleman’s soil blocking method, the benefits are clear:

  • Air pruning prevents roots from circling in containers
  • Seedlings slide out of blocks with no transplant trauma
  • Uncircling roots absorb more moisture and nutrients
  • Seedlings grow stocky and strong, ready for the garden
  • Earlier hardening off and no transplant shock
  • Customizable mixes catered to each gardener
  • Zero plastic waste compared to seedling flats

No wonder soil blocking has become a gardening game changer! While it does require learning some new techniques, the perfectly healthy root systems and vigorous, stocky plants are worth the effort. Follow Eliot Coleman’s mix recipe and care tips to experience the soil blocking difference in your own garden. Once you try it, you may never go back to plastic seedling trays again!