Mini Soil Block Mix

Making Mini Soil Block Mix

When making soil blocks to start your seeds, getting the mix right is the first key to success.  We have been doing soil blocks for several years and over time we have refined our mix to allow for the best germination outcome possible. It is also the most affordable method for us.  As we often state, this is what works for us on our farm. There are many ways to make a mix for the mini soil blocker and we are offering this post and video as an option.

Farmer Tony goes over the recipe that we use for our mini soil block mix.  Here it is in the printed form:

We use a 3 gallon pail as equaling 1 part.  The finished mix using this recipe and our 3 gallon measuring pail is about 5 cubic feet and will make about 30 1020 trays of 300 blocks per tray.

4 parts of peat moss sifted

2 cups of limestone

1 part perlite plug grade

2 cups calphos

2 cups greensand if you can get it OR

2 cups basalt rock powder (not both)

2 cups worm castings

1 parts compost sifted

Feels like I am writing a recipe down and actually it is a recipe.  A recipe that successfully creates little soil blocks that hold up and create the perfect medium for soil germination.

Photos of the parts for clarity

Mini Soil Block Mix

Peat Moss that we sifted

Mini Soil Block Mix

Mini Soil Block Mix

Limestone on the right with Calphos on the left

Mini Soil Block Mix

Perlite  plug grade

Mini Soil Block Mix

Activated Bio Char mixed with basalt, worm castings and bread flour that has composted for 4 weeks

Mini Soil Block Mix

Sifted Compost

View our video on the process to learn more follow the link below:

How we make soil mix for our 3/4" miniblocks

So there it is, our mix for making 3/4" mini soil blocks.  I have many flowers to seed in the coming days so this batch is a good start. Stay tuned for more videos on our other mixes and using our soil blockers.  Time for another round of snapdragons, oh how I wish they were bigger seeds, where ARE my glasses????

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Until next time....

4 thoughts on “Making Mini Soil Block Mix”

  1. Hi Martha:
    When you get biochar in its raw former it needs to be bioactivated to reduce its PH to neutral and balance it within minerals and nutrients so that when it is applied as an amendment it’s ready to go. We accomplish this by mixing 4 parts raw biochar with 1 part worm castings, 1 part basalt rock powder and .25 parts bread flour. We compost this for about 3-4 weeks. The worm castings are rich in soil microbes and fungi. To continually feed these guys during composting we add additional protein/carbohydrates which is the bread flour. Hope this makes sense and thanks for reading our blog!

  2. Hi, in your video you mention that you wouldn’t use this recipe for the larger soil block mixes as it will be too dense for them. What is changed for the larger block mix? Also, how did you decide how much activated biochar to use? From looking at your supply info it seems you’re buying biochar. For people making their own they could keep it slightly more granular instead of grinding it to a powder. Could it then replace the perlite altogether? And finally, if you live in an area of very alkaline soil, could you skip the lime altogether (we never add lime to our garden soil).

  3. In our larger blocks we reduce the peat content and increase the compost component.( see the main menu for a link to our soil block mixes). We use the bio-char at a volume of 1% of total volume for mini’s and 3% for the large blocks. We did this by experiment and it seemed to get the best results. If you use homemade bio-char crush it into the smallest possible pieces and then go through the activation process( see main menu for soil mix links for explanation). Using raw bio-char will raise the PH and will lockup minerals in the block and interfere with plant growth. Smaller pieces of biochar will allow a more even distribution in your mix and will go through the activation process much better. The amount of lime we add to the block mix is used to stabilize the mix near a neutral PH. Peat is by nature somewhat acidic. The balanced PH helps with nutrient availability in the block and will probably have no negative impact on your alkaline soil as the block is neutral or still very slightly acidic. As for replacing the perlite with bio-char my feeling is that the variable sizes of perlite evenly distributed keep the block from getting too dense. Perlite by its nature is neutral in its affect on nutrient availability. By using larger chunks of bio-char in its place you may not have been able to adequately activated it completely and my thoughts are you may get inconsistent results. In addition you would be dramatically increasing the percent Bio-Char in the mix from 3% to 25% when using the same voume as the perlite in your mix. For us perlite is cheap filler compared to the either making our own or purchased biochar and since perlite is produced here locally its the best fit for us.

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