Soil Blocks to Grow Seedlings
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A soil block is a cube of lightly compressed soil and nutrients that will grow one seedling. When the plant is ready to be transplanted, the entire block is planted into the soil. No root mangling will reduce transplant shock.
When I first began gardening, I purchased transplants from a local nursery and had a difficult time getting the seedlings out of their individual cells. Often times the plants were root bound and suffered from transplant shock because of my mangling.
Once I decided to grow my own transplants from seed and assembled a Grow Light System, using soil blocks for growing seedlings appealed to me. Since the soil block serves as the container and the soil, it is easy to transplant without injuring the roots.
I learned about soil blocks from reading Eliot Coleman’s book, The New Organic Grower. Part of the charm was that the soil blocker was an investment that would be used for many years to come. No need to invest in plastic cell packs that crack and break over time or peat pots that constrict the roots from growing. I also liked that transplanting soil blocks allows the seedlings establish quickly into the surrounding soil with no root damage.
What is a Soil Block?
A soil block is a cube of lightly compressed soil and nutrients that will grow one transplant. I start all my seedlings in soil blocks that I make with a 2-inch Soil Blocker that produces four soil blocks at once.
Soil blockers are the spring-loaded tools that form and compress the soil mixture into blocks. Once ejected, each block has an indentation at the top of the cube to plant your seed. Soil blockers are available different sizes but I use a 2-inch Soil Blocker. Soil Block Makers are available at Amazon and other places online. Seek out the quality Ladbrooke brand and it will last forever.
Benefits of Using Soil Blocks to Grow Seedlings:
- Eliminates the need for plastic cell packs or peat pots. Since the soil block functions as both the container and the soil for starting and growing seedlings, this reduces the need for plastic growing pots.
- Seedlings develop a stronger root system. More oxygen is distributed to the roots since the growing medium is not contained. Roots are also “air-pruned” once they reach the edge of the block. This means that they stop growing rather than winding themselves around the plastic pot seeking nutrients.
- Transplants establish more quickly. Since there is less disruption to the roots, the seedlings are less prone to transplant shock.
Soil Mix for Soil Blocks
Eliot Coleman’s recommended soil block recipe is composed of peat, lime, coarse sand or perlite, fertilizer, compost, and soil.
Just like any recipe, this one can be altered and adjusted to accommodate the ingredients you have on hand. I have experimented with different mixtures and found that as long as the mixture holds together, it will be fine. I have settled on a mixture of organic seed starting mix, screened compost, perlite, and a little all-purpose granular organic fertilizer.
Soil Block Recipe
The ingredients can be easily found at your local garden center. I have linked to sources online for examples.
Use a 10?quart (2.5 gallon) bucket to measure the bulk ingredients and a standard measuring cup for the other ingredients. You can mix and store the soil block mix in a 12 or 15 gallon storage tote and scoop out as needed.
Ingredients for Soil Block Mix
- 1 1/2 buckets peat moss or coconut coir
- 1/4 cup garden lime
- 1 bucket perlite
- 1 cup all-purpose organic granular fertilizer (such as Espoma Garden Tone).
- 1/2 bucket garden soil
- 1 bucket finished compost.
Directions for Soil Block Mix
1. Add peat moss and lime to your large container. Mix thoroughly to combine.
2. Add perlite and organic granular fertilizer. Mix to combine.
3. Add the garden soil and compost. Mix and store until you are ready to use. This recipe makes about 8 gallons of soil block mix.
How to Make Soil Blocks
When you are ready to make your soil blocks. Scoop out the soil mix into a flat container, such as a dishpan. Add hot water and 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.
Once mixed, the soil should look like peanut butter. Add more water, or reserved dry mix to adjust.
To make the blocks, pile the soil mix into a mound that is about double the height of the soil blocker. Then simply plunge the soil block maker into the mixture. Twisting the blocker helps compress the soil and release it from the mixture without sucking out the wet soil back out. Do this three times so cubes are filled tightly.
Scrape off the bottom of the soil block maker with a straight edge, then set the blocker in your seedling tray and release the soil blocks by pushing down on the handle and lifting the blocker.
The blocks should be firm. If the blocks crumble, add more water to the mix. If they slide out easily and fail to hold their shape, add more dry mix.
Plant your seeds directly in the depressions created by the soil blocker. Label the soil blocks using tape on the outside of the tray.
As an added bonus, the soil blocks are easy to move around and organize. If a block fails to germinate, it can simply be removed from the tray and recycled. Also, it is easy to know when it is time to transplant the seedling or pot up into larger containers because you will see the roots when they reach the edge of the block.
Out of all the gardening tools and gadgets I have purchased over the years, this soil block maker is one of the most useful. A soil block maker is a great investment that will serve you well for many years.
You May Also Like:
- 10 Steps for Starting Seedlings Indoors
- How to Develop a Seed Starting Schedule
- Vegetable Garden Planning: Mapping the Garden Beds
- Benefits of Pre-sprouting Seeds
- How to Harden Off Seedlings
Don’t the soil blocks crumble after a good watering?
CD, No, the soil blocks do not fall apart. You do need to get the soil mix right and pack the soil block maker firmly as explained in the article above.
Thanks for this!
One question I have about the mix: I know Coleman was primarily growing veggies, not ornamentals, and his recipe called for peat. I had kind of assumed the lime was included in the mix to offset the peat acidity (he suggests mixing the two first, actually).
So if you’re using coco coir instead, and growing ornamentals, is the lime still really necessary? There’s no need to raise the pH, right?
Great article that goes into a lot of details most don’t. Thanks!
Jessica, You are correct. Coconut coir is pH neutral. There is no need to make the adjustment with lime when you use coconut coir. Thanks for your comment. I will update the article to clarify this info.
Will you be getting the 4inch soil blockers ?
Lisa, I don’t see the usefulness of blocking up to the larger 4-inch soil block. It takes a lot of potting mix and effort to make the block. I do pot up tomatoes, peppers, eggplant into larger containers (plastic cups) until it is warm enough to plant outside. I try to time my other crops when sowed in the 2-inch blocks so they can be transplanted into the garden when they have outgrown the soil blocks.
Great post!. Could you share the recipe you use that uses organic seed starting mix, compost, perrlite, and fertilizer? Also can you share what brand of seed starting mix and fertilizer you use? Thank you!
Deb, the recipe for making soil block soil in in the article above. I try to stick to local brands and those vary. If you are using premade seed starting mix, just substitute it for the peat moss or coconut coir, and garden soil. It doesn’t have to be exact. In fact, if I am making a quick small batch, I don’t measure anything.
I have used soil blocks for several years in 3 sizes: the 3/4″ micro, the 2″ mini and the 4″ maxi. The soil recipe I use is very similar to the one here. I have had great success with this method. Most seedlings are started then transplanted to the garden in the 2″ blocks. Some require more time indoors (with my short season I need as much advance growth as is reasonable), and those are transplanted directly to the 4″ block before being transplanted outside. I have mostly stopped using the 3/4″ micro block, as I have found it often unsuccessful and unnecessary. I also use these blocks to start seedlings for my greenhouse, as it allows me to keep one plant growing to harvest while another is getting started. This way I make the most use of my limited space.
Please tell me about the watering for your seed blocks. And do you use trays with holes or without holes? I am going to order one of these soil block makers right now!
Evelyn, I use double trays, one with holes that hold the soil blocks, and one without holes. Watering is easy this way, just add water to the tray and allow the soil bocks to absorb as much as they can, then lift the inner tray and drain off any excess water.
Thank you all for the great tips and inspiration! Winters are long here in Maine especially when one doesn’t participate in outdoor activity until the Robins are pulling worms! 🙂 I may be older but I still enjoy the smell & feel of the cool dirt on my skin!
Suann, I agree, winters are long here in Maine. I love starting seedlings indoors, under lights. It allows me to enjoy digging in the dirt a little.
Thanks so much for this! I am getting ready to start using soil blocks for me farm in Spring. One thing I am not sure about is if I should purchase Johnny’s 512 soil block mix or if I should make the mix myself. In Elliot’s recipe there are a lot of ingredients I am not sure where to get. I was happy to read that you simplified it a bit and it still works. I think using a soil mix like you use will probably be much cheaper, right?
Lee, Yes, it is less expensive to mix up your own soil block mix especially if you are starting a lot of seedlings. The key is to screen out larger chunks so the blocks hold together. For fertilizer, I use Espoma Plant Tone because it is easy to find in the winter. I will also water the plants with diluted fish emulsion to give them a boost if they look like they are struggling.
Good tips, thanks!