Nitty Gritty on Soil Blocking

My first year of flower farming I was looking for every and any way to accomplish four goals:

1) Grow amazing and healthy flowers

2) Grow flowers on a super tight budget

3) Save space

4) Add to the earth’s health, not deplete it. 

One of the ways I felt I could accomplish all fours goals was through soil blocking.



Soil blocking, what is this you speak of?  Well, it’s exactly what it sounds like.  You are making compressed blocks of soil, this is in lieu of using flimsy plastic seedling trays that crack after a single use.  Soil blocking was frontiered in the US by Eliot Coleman.  He has all kinds of books and videos that go into the benefits of soil blocking.  He is pretty incredible, if you would like to learn more about organic and sustainable gardening his books are awesome and Youtube videos even more so!


Compressing soil into a little brick sounds counterintuitive to use for little seedling roots.  I would agree.  That is why you don’t use any-plain-'ol potting soil, there are specific soil mixes you can purchase or recipes to make your own.  The main difference between seed starting mix and soil blocking mix is the amount of perlite.  In soil blocking, you need a lot of perlite.  This will allow the soil to drain and those tiny roots to penetrate the soil block and thrive.



Benefits to soil blocking:

1) Economical: not needing to reinvest in seedling trays.  The initial investment in soil blockers can be quite a bit but if you are starting a lot of seeds year after year they will return your investment!  Snag some cafeteria trays from a local restaurant supply store and you are set. 


2) Lessened transplant shock:  Even plants that typically do not do well transplanted can thrive with a soil block.  The idea is that the roots are pruned by the air.  Once the roots hit the air, they stop growing, until the plants are transplanted into the garden or bumped up to the next size soil block.  This inhibits the plant to become root-bound.  By the plant not being root bound, when time to transplant, they the roots aren’t tampered with.  This lessens transplant shock that will allow your plants to not skip a beat, they won’t be sad and will simply continue to thrive.


3) Storage: it doesn’t take much space to store a couple soil blockers and some trays!  If you live in a small house, storing tons and tons of seedling trays may be overwhelming. If you are limited on space for storing trays, you most likely are also limited on shelf space in the greenhouse. You can fit a lot more tiny soil blocks than the traditional seedling trays.



4) Let yourself become a kid again: You get to play in the mud!  Revisit you childhood and lets get to making mud pies, but really, they look more like brownie bites...



What you need:

Soil blockers in your desired size

Soil block mix

Trays of some sort (such as cafeteria trays or even small cookie sheets)

Dome lid


First thing you need to do is invest in some soil blockers.  I originally purchased mine from Johhny Select Seeds but since then, I have found some much less expensive with good reviews on Amazon and will provide the link to those at the bottom of this post .  They have many different sizes.  I opted for the ¾” soil blocker and the 2” soil blocker.  I did wind up getting a bigger size but found that really, the first two were more than sufficient.  The neat thing about soil blocks is that they are like matryoshka dolls, in that each size nestles nicely in the next size.


Once you have your soil blockers in hand, it’s time to get the soil.  You can purchase the soil pre made from select vendors.  I personally didn’t want to pay the crazy shipping and in my area, there was not any soil blocking mix available to purchase.  If you use the normal potting soil your soil blocks will not become a block.  So, I opted to follow Eliot Coleman’s soil blocking recipe.  I did make a change in some of the ingredients, based on the availability of what I could find locally. 



Here’s the recipe we threw together:

3 (five gallon) buckets of peat moss or coconut coir

2 (five gallon) buckets of perlite

2 (five gallon) buckets of compost

1 (five gallon) bucket of garden soil

1 cup blood meal

1 cup bone meal

1 cup wood ash

I will throw it out there that I'm not the biggest fan of peat moss, for the reason that it's not the most sustainable product but it is affordable and easily found.  Peat moss is more acidic where coconut coir is neutral.  I've used both and do prefer the coconut coir when I can swing the cost.

The perlite is what will allow drainage and space for the roots to grow.  Plus, the girls love smashing it between their fingers like popcorn!

Oh compost.  It's simply delicious and vital for plants to thrive.  In our area, it's not the easiest to find good quality compost at an affordable rate (I envy the farmer's who pay $14 a yard for GORGEOUS rich compost!).  We opt to make our own and only purchase when absolutely necessary.  To learn more about making your own compost be sure to read my Nitty Gritty Compost Part I and Part II.

The addition of garden soil may sound alarming, don't seedlings need sterile mix?!  Unless you have a known disease your soil is safe.  You could also substitute this component with additional compost, if you would prefer.  The reason behind the garden soil is that ideally it aids in the shock of the transplant, that way the little plants already have a little taste of what their eventual home will be.  I haven't had a problem incorporating soil from our garden into the blocking mix, plus- I like free components!

The blood meal, bone meal and wood ash can be supplemented with other amendments, as long as the plants get some base nutritional needs.  Some growers prefer not to have fertilizers in the soil for starting seeds, I personally haven't seen a downside and love that I don't need to feed the seedlings for a few weeks, since that's about how long it takes for them to gobble up all the good stuff in the soil mix.  To learn more about plant nutrition be sure to read my post Nitty Gritty on Plant Nutrition


Mixing it up

We toss all the ingredients in the wheelbarrow and mix thoroughly.  Then, we added warm water in the ratio of one part water to every three parts of mix, adding more water as needed.  Why warm water? The warm water will activate all the goodies in the soil to make them readily available for the seedlings.  Plus, it’s cold and my hands get frozen!  Soil block mix needs to be way more wet than your used to.  When seed starting in trays, you want the soil to be damp like a moist sponge.  That’s too dry for soil blocking.  If the mix is too wet, it won’t become a block.  If it’s too dry, the block will crumble.  It’s very much like Goldilocks and the three bears scenario. Throwing the soil to the side of a shed is a fun way to find out if you have your ratios correct, my girls love this part!  If you throw it and it runs down, it’s too wet.  If you throw it and it doesn’t stick, it’s too dry.  If you throw it and the mix stays stuck, it’s just right.  After testing the soil, just spray down the side of the shed with a hose. Not into mud flinging? Then eyeball and just try making the soil blocks!


Making blocks

Once you have your mix ready, its time to play in the mud!  We just used our cement pad to make a nice pile of the soil for the soil blocker.  You want the pile to be about one and a half inches deeper than your soil blocker is high (because it’s going to compress!).  If the pile is too deep, the bottom of your soil blocks won’t be even.  If the pile isn’t deep enough, you won’t have a complete soil block. 


When the pile of mix is ready take your soil blocker, push it down until it hits the ground (or other surface you are working on) and twist back and forth.  Lift the blocker to your tray and push handle to release the soil blocks.  Easy peasy.  Well, not really.  It takes a little practice but it’s well worth it!  Keep a bucket of warm water on hand, in between each batch, submerge soil blocker into the water to rinse.


Using the blocks

Soil blocks made, now you continue to start your seeds as normal.  I like the ¾” soil blocks for small seeds, such as celosia or snapdragons.  The 2” soil blocks are great for sweet peas.  Once you sow the seeds, don’t push the seed into the soil block.  It will most likely break the block, instead sprinkle some soil mix or vermiculite on top, depending on the seed’s germination needs.  Bottom water the soil blocks, but don’t let them get soggy!  It takes a little practice and watching to get watering down.  Soil blocks are great at hanging onto water but if you let them dry out too much, they can be fussy to rehydrate (and your tender seedlings may die a crispy death before you realize it).  In the early stages of germination, I like to lightly mist the top of the soil blocks to keep the seeds hydrated.  You can use a heating mat or whatever system you prefer to use, just like using the seedling trays.



When you see your seedling busting at the seams (literally) then simply bump them up to the next size soil block or harden them off and transplant out.  I do find that sometimes I need to break up the soil block, just slightly, when transplanting out into the growing beds.



That’s about it on soil blocking!  If you are looking for a green alternative to plastic trays, or are looking to save space, soil blocking may be for you!  

If you liked this blog be sure to visit our YouTube channel. Come on with us hand in hand on our journey of turning an unloved patch of dirt into a thriving micro-urban-flower-farm! This isn’t a “how-do” video series but rather more of a “how-we-do” adventure.

Jessica Tulip.jpg

Until next time, I hope you enjoyed the blog and I am looking forward to handing you some blooms soon.



To help you on your soil blocking quest, here are some Amazon links to soil blockers: 



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