Sunday, March 13, 2011

Using Soil Blocks for Growing Seedlings

A recent comment from Jeph at “Fresh is Best” has prompted me to share my experience so far with growing seedlings using soil blocks. As I explained to Jeph, I am no expert as this is only my second year of both growing my own seedlings and using soil blocks. However, my overall experience last year was so positive that I will continue to use soil blocks for most of my seedlings this year.

Previous to growing my own seedlings last year, my garden was planted with purchased transplants and direct seeding. I usually do a lot of research on new gardening methods that appeal to me before trying them. So, I had been reading and learning about seed starting and soil blocks for years before deciding to try it myself. 

Once I decided to grow my seedlings from seed, I knew I wanted to invest in a 2-inch Soil Block Maker. I purchased mine last year from Johnny’s Selected Seeds.

The recommended soil block recipe is from Eliot Coleman’s book: The New Organic Grower and a copy was sent with the soil block maker I purchased last year and can be downloaded for the Johnny’s Selected Seeds website.

Last year I had problems sourcing out these ingredients during the winter months. However, most of my research told me that alternative soil mixes have also been used with good results as long as the soil mixture is fibrous enough to hold together through many waterings but allow air to pass through to provide oxygen to the roots and to permit drainage.

The recommend mix is composed of peat, lime, coarse sand or perlite, fertilizer, compost and soil. What I could easily find in January was organic seed starting mix made from approximately 80% peat moss, 19% perlite, and 1% lime. I also had some organic bagged compost on hand and some Plant Tone fertilizer by Epsoma.  So I thought I would mix up a batch and give it a try: “I Played With the Soil Block Maker!” I passed the compost through a piece of hardware cloth into a tote to screen out any lumps before adding it to the mixture.

The test soil blocks retained moisture and held up well to being moved around and organized into different trays. So I proceeded with using this soil block mixture for my spring seedlings. I did fertilize with fish emulsion when the seedlings showed they need it, which was several weeks after germination, then every two weeks until planted in the garden. I had very good results and my seedlings were healthier and stronger than any transplants I had purchased before. When potting up or transplanting to the garden there is no transplant shock since you are not disturbing the roots. The transplants just continue to grow.

The fall seedlings were started in soil blocks made from Pro-Mix Potting & Seeding Mix (Made from Canadian sphagnum peat moss, limestone, perlite, vermiculite, and a wetting agent), screened compost, and a sprinkle of Plant Tone by Epsoma. This will be my second year growing from seed and I am using the Pro-Mix, screened compost, Plant Tone method again for my soil blocks.

I use a dishpan to mix up small batching of soil block mix as needed. I add Pro-Mix and screened compost to the dishpan at a ratio of approximately 3 scoops of Pro-Mix to 1 scoop of screened compost. I sprinkle in a couple of tablespoons of Plant Tone by Epsoma and add water. I mix the soil and water together then I let it sit for a few hours or even until the next day. This gives the mixture ample opportunity to soak up as much water as it can.

Johnny’s has a great video showing how to make the soilblocks: Click here to view.


  1. This is so fascinating. I've never done this method before. Really like it!!

  2. Thanks for this post. I bought a soil block maker back in January but did have time to research the soil mix before it was time to get the seeds started for this year. I will definitely use it next year. I also want to check out the wooden seedling boxes that were shown in the "Grow Biointensive" Videos.

  3. I have been growing my own seedlings for years but have never used soil blocks. From everything that I have been reading, I think that I will try them next year.

    Thanks for the great informative post!

  4. Great work! I love my home made single block maker, though some day I want the one you have. You may have seen my problems with my blocks on my blog. It was my laziness that caused it. I grabbed mostly finished compost and didn't screen it at all. Threw in some vermiculite and water and presto, impromtu soil block mix. The blocks set up nicely, but crumbled later. May have been the worms in it. ROFL. Should work though. Just let them dry out before planting. I refuse to buy potting soil if I have compost. I suppose screening it would be a good idea. ROFL. Great post!

  5. Thanks for posting this. I have been seriously tempted to switch to soil blocks for my seed starting but hesitant because the mixture process seems a little fussy and potentially unforgiving. It sounds like I should just do my homework and go for it. I think I will be asking Santa for the 2 inch block maker for Christmas this coming year. :D

  6. Meemsnyc: I had to invest in seed starting equipment last year anyway since I was starting from scratch. So purchasing the seed block maker seemed smart since I will be using it over and over through the years. I really like the way it works.

    Liisa: Try mixing up a small batch to see how it works. I also loved the wooden boxes in the “Grow Biointensive” videos. Some were 6-inch deep, so I imagine the crops grow just like normal until space opens up in the garden then they continue to mature in a shorter amount of time.

    Robin: I like that I only have the trays to clean every year instead of all the little cell packs. I have always had difficulty getting seedlings out of the cell packs. Transplanting or potting up the soil blocks is really easy. I think it is worth the investment.

    Sinfonian: Experimenting is the only way to really figure things out on our own. I tried using straight seed starting mix and the soil blocks crumbled when watered as well. I also tried using straight compost without sifting and these didn’t hold up well either. So now I sift out the little chunks in the compost before mixing and everything holds together much better. Then when the roots grow, they help hold the block together as well.

    Laura (kitsapFG): I know the mixture will be easy for you to figure out. I bet a few test runs and you will be good to go. You probably already have the components on hand. They worked really well for the tomatoes and peppers. As I mentioned before, potting these up was really easy and there was no transplant shock because the roots are not disturbed.

  7. Soil block are great! I've been using a mix of 1/3 garden mix (from the local landscape's just dirt and compost) + 1/3 peat moss + 1/3 vermiculite and the blocks hold together just fine...they are SO easy to transplant!

  8. Deb Fitz: That sounds like a great mix. There is not right or wrong mix. Just experiment and figure out what works for you. I think the ease of transplanting is the largest benefit to using soil blocks.

  9. The pictures above are like cake. My mouths are getting watery. Oh my God! LOL...

    The soil must not be hard or intact so that the roots can freely grow.

    Thank you so much for this interesting post.

  10. Canadian Sphagnum Peat: The DO look like cake don't they? The soil is compact enough to hold together and withstand watering, but porous enough for water to drain and roots to grow through.