Wednesday, February 8, 2012

Using Soil Blocks on the Farm

Awhile back we began to look at a number of our processes on the Farm and try to figure out more sustainable practices to use.  One of the biggest areas for us was how we ran our seed starting and transplanting.  We, like most growers, used a variety of plastic plug trays to start and transplant our young seedlings before  we would plant them in the field.  Plug trays although advantageous in  that they provide a clean organized way to start the plants have a number of draw backs that bother us.
  • Plastic begets more plastic!  The plastic plug trays are typically good for one to two seasons before becoming damaged and have to be replaced.  Plastic waste that is difficult to recycle bothers us a lot.
  • Reusing plug trays is time consuming in that each tray has to be washed by hand before being reused.
  • Getting the plants released from the trays for transplanting can be time consuming and most of the time stresses the plants during transplanting.
  • The cell sizes and shapes of the trays are more designed for automated equipment handling rather the manual processes of our small farm.
  • On some plants growing them on to field transplant size allows time for the seedlings to have their roots circle around the inside cell wall of the plug such that they are unnaturally growing towards a tight root ball instead of in a more natural out ward pattern.  This tight root ball pattern most of the time leaves the plant with a poorer root system after transplanting to the field.
So we began to explore the idea of using soil blocks instead.  Although the initial planting process can take a little longer than using a straight plug system due to time spent mixing soil, the quality of the plants for us seems to be much better and it solved all the issues mentioned above.

Using the 3/4" mini soil blocks to seed difficult to germinate plants and then easily transplanting them to larger blocks for growing on actually began to save us time and space in the propagation house.  So that is what I'd like to show you today is a pictorial of transplanting 3/4" mini-blocks to the larger 2" soil blocks process from start to finish.

The first step is to put together the soil blocking formula mix.  We using a simple formula for our 2" blocks.  The base is 8 parts a peat Perlite Promix BX(which comes PH balanced; followed by 5 parts organic compost; 1 part Vermicompost; 2 parts additional Perlite; and 1 part soil(soil is from a fertile bed on our farm)

Mixing the soil block formula
I typically use a big tub and currently we are hand mixing the materials. Once we scale this up we will be using a portable powered concrete mixer to do this faster and in larger batches.

I hydrate the mix to the consistency of a firm mud. Because I'm a weenie here I use warm water to mix..keeps the hands from freezing and is way more comfortable when making a number of trays.
Just note here; before adding the water mix all the dry ingredients together first.  Set some aside in a small bucket to add later if the mix becomes watery.

Showing the consistency of the mix is just about right.


 Like good pasta I like to test the mixes consistency by taking a small handful and throwing it against the side of the mixing tub. If it sticks in a clump its good to go.  If it falls off in crumbs it needs more water; if it slides down its too wet and needs some more dry mix added.

This photo shows the mix is just right!

3 basic blockers we use
 When I started this experiment I purchased the 3 basic size blockers shown. 

The one in red is the 3/4: mini block. It contains 20 individual blocks with a dibbled top. Going counter clockwise the one above the mini blocker is the 1.5" blocker with 5 individual blocks produced with each pressing.  The last one is the 2" blocker with 4 individual blocks produced in each pressing.

The 2" and 1.5" blockers have removal center pins for different sized dibbles or a square dibble which is used for transplanting the 3/4" mini's.

Charging the blocker is simple.  Keeping a bucket of water next to your mixture, dip the blocker in water before each use then immediately plunge it into the soil mix several times till you see a light mixture of mud come through the top.  This tells you the block is full.  If some of the blocks show the mud but others don't re-plunge again until you see it across all the cells.

The next step before putting the block in your tray is to scrap the excess off the bottom of the blocker.  I do this so the soil block sits square when resting in the tray.

These two photos show you the actual formation of the block in the plastic holding tray.  The type of holding tray we use is weaved on the bottom so that the soil blocks when resting on a capillary mat will be able to wick water up.  The standard tray is about 10" wide by 20" long and will hold 50 2" blocks or 84 of the 1.5" blocks.

As I'm filling the tray I occasionally use a straight edge to even up the blocks so the tray can fill evenly.

Viola! A finished tray ready for transplants.  The cool thing about these blocks is the soil mix already has natural compost fertilization for a good start built right into the block.

Today we were transplanting early season Stock. Each 10"x 20" tray of 3/4" mini-blocks contains 300 possible transplants.  Since germination of very few types of seeds is 100% using the mini's to germinate saves space, potting mix and in the long run time by not washing more plug trays then you needed due to empty cells that did not germinate.

Using a very technical set of tools.....2 Popsicle sticks, we begin by lifting the first mini plug out of its germinating tray.  we use the sticks on the first few to open up space without damaging the plants.  Once there is enough room we just use our fingers to pick up the blocks.

These blocks are actually quite sturdy. Once the plant germinates it immediate sends roots throughout the block which just increases its structural strength.

The beauty of the square dibble used in the 2" block is that it is precisely the same size as the 3/4 mini block being transplanted.  So transplanting is simply placing the 3/4" block in the square hole..give it a gentle pressing in and your done!

A just finished tray of Stock transplants

The final tally sitting on the propagating house's capillary mat.  This whole transplant process wasn't much slower then manually transplanting from plugs into another type of plug tray.  In the end we have found that these transplants grow faster with hardly no transplant shock. Aside from a weekly foliar dose of sea kelp/fish fertilizer the only thing to do is keep them hydrated.   As small as these guys are now they should be ready for the field by the end of first week of March.

Our goal over the next year is to move all of our seeding and transplants to the soil block system and reduce our reliance on plastic just a little bit more.   In my next entry I'll discuss the planting of the finished block in the field and talk a little bit more about how we use the 3/4" mini's  and the 1.5" blocks.

As part of our philosophy of keeping what we do transparent to all who follow us or buy from our sustainable farm I'm glad to answer any questions. You can contact me at

Tony Gaetz

We have received a lot of email, asking where to get the block makers.  Johnny's Seeds and carry them now.  At the time of the original post, they were harder to find.  We are so happy folks are interested in giving them a try.  Happy Growing!


  1. I am so impressed, your love for your flowers and the earth will surely reward you with beautiful flowers and a health land for years to follow.

  2. Thank you so much!! Such nice words!

  3. That's really interesting! Thanks for sharing your move away from plastic. Can't wait to pick up some of your stock at the market!

  4. When placing your larger blocks in the tray, it is important to leave space between the blocks and to not cram them in as you show here. This allows for the air pruning of the roots which is a CRITICAL part of why soil blocks are so much better than a pot. It allows the plant to keep growing roots and never get root bound.

    1. Hi Jeremiah;

      Thanks for your insights below. I agree 100% on a looser spacing in the growing tray to allow air pruning on all sides of the block would be optimum. For us though we had to weigh the downsides of tighter spacing versus being able to get as many transplants as needed through our limited propagation house benches before field transplanting. What we found was even though some of the roots of the transplants did leave the block we never grew things on so long so that they grew significantly into the adjacent block. All our blocks are watered via capillary mats with limited overhead spraying. Block integrity is maintained as well as even moisture. Even though this is perhaps not the most optimum these types of transplants showed little field transplant stress and started to grow faster then similar plants grown in standard plastic plugs.

      Thanks again for your comments and I appreciate you reading our blog.

      Best Regards,

      Tony Gaetz

  5. I am definitely trying this next week. Thanks so much for sharing

  6. Hi there, just wanted to thank you for this great post. I have also decided to get rid of the nasty plastic plug trays for my seedlings in my backyard's micro farm and bought the block makers. However, most of the recipes I have found online for making block soil required some pretty obscure and hard to find ingredients: (Glacial rock dust, colloidal phosphate, greensand myccorrizae, organic fairy dust...)

    I'm happy to have found someone with a much simpler recipe that works!

    Thanks again!

  7. see more info on "all things soil blocks" at key word: Potting Blocks

  8. I'm looking to use soil blocks along with capillary mat & heat mats for market garden starts, and am wondering about any lessons you've learned since adopting this system. Did you find the blocks were able to pick up from the capillary mat even through the woven bottom trays? Did you have to bunch up the mat or anything like that to get contact with blocks? Have you been able to use Are you able to use heat mats or are you depending on a heated propagation room? You mentioned limited overhead spraying. Was that because water from the propatation mat was insufficient? Appreciate the feedback.

  9. Sorry, for misstatement above: meant to ask if "water from the capillary mat was insufficient".

  10. Tony and Denise,

    Thanks for all your inspiring posts and pics about soil blocking. We've started blocking most crops this year (we couldn't make cosmos fit in any block), but we are finding sifting peat and compost to be quite inefficient. Have you figured out a technique or sifter design to speed this up?

    Jonathan Leiss

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