How to Make a Simple Soil Blocker

I have long been fascinated with soil blockers.  It seems like such a smart, efficient, and economical way to start seeds, but when faced with the option of purchasing a soil blocker or two or spending the money elsewhere in the garden, the soil blocker never quite made it to a priority in the garden budget.  That changed this winter, when I realized that you could totally make your own soil blocker (of course you can!), and so I’m finally giving it a trial run with some of my seedlings this year.

After posting a photo of my first attempt at making soil blocks for seed starting, a number of you have requested more information on how I made my soil blocker and how it works.  Well, ask and you shall receive!  In today’s post I’ve got the low down on soil blocking and and how to make your own simple soil blocker for less than $2.

How to Make a Simple Soil Blocker | Sweet Domesticity

A simple soil blocker is essentially two parts: a form that you will fill with starting medium and a plunger to compress and eject the soil block.  You could use just about anything that is cylindrical (or could be made cylindrical by cutting out the bottom).  It should also be fairly sturdy and waterproof.  Chances are you have something in your home that would work, but if not, you can purchase the supplies very inexpensively from your local hardware store, which is exactly what I did, and what I’ll describe below.  If you already have some of these supplies (or something similar), I’m confident you’ll be able to adapt these instructions as necessary.

How to Make a Simple Soil Blocker | Sweet Domesticity

I dug through the bins of PVC fittings at the hardware store until I found something that was about as wide, and a little taller than I wanted my soil blocks.  I ultimately ended up with 2″ wide x 2 3/4″ long PVC coupling.  Then I walked over to the “fasteners” section, and picked out the biggest fender washer (the ones with the smaller hole) I could find that would easily pass through the PVC, a bolt that was just a little longer than than the PVC, and a nut to hold the washer in place.  All said and done, I spent 61 cents on the PVC, and 78 cents on the hardware.  

The PVC is pretty much ready to go.  For good measure, wash it up to eliminate the potential for residual factory PVC dust or chemicals to find a way into your soil mix.    To make the plunger, simply thread the washer onto the bolt, all the way down to the head of the bolt, followed by the nut to hold it in place (having the end of the bolt or nut on either side of the washer is what is going to make the little indent in the top of the block). It doesn’t get much easier than that, does it?

The other thing you’ll need to prepare is your seed starting mix.  Blend all of the components together first, then gradually add water to your seed starting medium until it starts to hold together, reserving several scoops of dry mix, just in case it gets too wet and you need to add some dry stuff back in.  Mix it by hand (it’s messy, but effective) until the mix is the consistency of oatmeal.  It should be wet enough that if you squeeze it in your hands and it will hold its shape when you release it, but not so wet that it is dripping or forming mud puddles in the bottom of the bucket.

How to Make a Simple Soil Blocker

Start by putting the soil blocker on a flat surface.  I found that placing it in an old plastic storage container worked really well and it contained the mess.  Fill the cylinder to the top with the wet starter mix.  If you notice a lot of water seeping out from under the PVC, your mix is too wet.

How to Make a Simple Soil Blocker | Sweet Domesticity

Next, take the plunger and push down on the seed starting mix to form the soil block.  It should condense to around half of the original volume (it might be a little more, or a little less, depending on what’s in your starter mix).  It’s okay if a little water seeps out during this process. If it is not condensing well, your mix might be too dry.

How to Make a Simple Soil Blocker | Sweet Domesticity

While still pushing down on the plunger with light pressure (just enough to hold it in and the soil beneath it in place), pull the cylinder up and off of the newly formed soil block.

How to Make a Simple Soil Blocker | Sweet Domesticity

As the plunger is removed from the soil block, you’ll be able to see how the end creates a nice little hole for the seed.

How to Make a Simple Soil Blocker | Sweet Domesticity

Carefully transfer the soil blocks to a drip tray.  If your starter mix is the right consistency, they will hold together and tolerate the move well.  If your soil blocks crumble when you try to pick them up or move them, your soil mix is either too dry, or you are not compacting it enough.  If they are sticking to your work surface, or part of the soil block is coming off with the plunger, your mix is  too wet.

How to Make a Simple Soil Blocker | Sweet Domesticity

The first few soil blocks you make might take a little time and some trial and error to get a good feel for it, but once you get the hang of it, you can really produce them quickly.   The process is a much messier than making newspaper pots, but it is also much faster (and who doesn’t appreciate a little dirt under their fingernails this time of year?).  Once you have finished making your soil blocks, everything can be cleaned up and stored for later use.

How to Make a Simple Soil Blocker | Sweet Domesticity

The key to watering seedlings started in soil blocks is a spray bottle.  I have been adding a very small amount of water to the bottom of the drip tray to prevent them from drying out while on the heat mat and to create a little humidity, but I’ve found that misting the blocks a couple of times a day with a spray bottle is the most effective way to keep the soil blocks hydrated (and on that note, coir appears to be an excellent choice for soil blocks).

This is my first experience with using soil blockers for seed starting, so I’m sure I”ll be learning a trick or two along the way as spring goes on.  Expect to see a follow up post once the seedlings have taken off!

6 Responses to How to Make a Simple Soil Blocker

  1. Amber says:

    Thanks so much for sharing! I bought the compressed coir pellets this year, but I will certainly have to try this out next year – at that price, you can’t really afford NOT to try it!

  2. […] from plastic cells to peat pots to DIY newspaper pots (and even no-container options, like soil blocks), all of which can be held in a large flat tray for watering and […]

  3. SARAH O'NEIL says:

    Hi Maria. I love it. This is so cool and so simple. I love poking about in the hardware store for things that could be used for something I have in my head – completely different from the actual purpose of the item. Thanks for sharing this.
    Cheers Sarah : o )

  4. Gerhard Fries says:

    Thanks for your great gardening tips

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