making soil blocks

among the new methods that we’ve implemented at work, one of the best changes made has been the switch to soil blocks over plug flats.  soils blocks have some major advantages  – they also have some major disadvantages.  soil blocks have a greater growing space, which makes for more robust plants.  plants also don’t get pot bound like they do in plug flats, they hit the side of the block and stop growing, and they don’t really on plastic pots, so you don’t have all those pots hanging around or using all that oil to make the plastic.  as disadvantages, blocks take up more room, take longer to make, require special tools and need special containers to hold them.  but overall the benefits far outweigh the drawbacks.

my friend kido and i struggled though trying to get the blocks just right, and while it was fun to work together trying to figure out how to make blocks, i think i would have really benefited from a visual add, which is why this post seems especially important to me.

the recipe for this comes from elliott coleman’s new organic grower – which has an excellent section on soil blocking

step one: mix peat and lime

the peat

this is a half batch recipe which still makes a lot of soil mix.  mix 1.5 – 5 gallon buckets with 1/4 cup of crushed limestone.  you can substitute coconut coir for the peat moss, but it does have to be treated differently, since it has to have water added to it in order rehydrate it.  i prefer peat moss.

step 2. mix in perlite and fertilizers

mixing perlite

add one 5 gallon bucket of perlite, 1/2 cup of greensand, 1/2 cup blood meal, and 1/2 cup of soft rock phosphate.  you can substitute coarse sand for the perlite. mix throughly.

step 3: add compost and soil

soil and compost added

add one 5 gallon bucket of sifted compost and half a  5 gallon bucket of sifted soil and mix throughly.

step 4: add water

adding water

how much water to add?  more than you would guess.  by comparison to usual potting mix it needs to start out much wetter.  i compare it to having more of the consistency of mud pies – maybe a little bit less wet than that, but in this case making it a little too wet is a better than too dry – as blocks will break apart otherwise. mix the water in throughly, and check from time to time the moisture level – it needs to wet enough that when you squeeze it hard, you should be able to get some water to drip out.

final mixing

the mix will look pretty dark, more so than your regular potting mix.  spend plenty of time chopping up and mixing, you don’t want any big chunks.

step 5: the soil blocker

the soil blocker

with the soil fully mixed, it’s time to introduce the soil blocker.  this guy makes 4 – two-inch blocks.  blockers come in a variety of sizes from much smaller to much larger.  they are available from a couple of sources, but most folks i know have obtained them from johnny’s selected seeds.  they are not the cheapest thing, but i think you will find the cost well worth the expense.  we have a larger floor blocker that makes 20 blocks at a time, but i’m still working out the kinks on using it.

we start seedlings in germination trays and then prick them out in the blocks.  other methods have you starting with mini blocks that you then insert into the large block that has a dibble the same size as the mini block. i didn’t have much luck with this – i think mainly because i failed to make a fine enough mix for the mini blockers to hold together.  in order to be able to prick out the seedlings, we made a minor modification to the blocker adding wire nuts to act as a dibble.

inside the soil blocker with wire nuts

step 6: the dip

the dip

very important and a step folks seem to forget is the dip – when i dip, you dip, we dip – before making a batch of blocks dip the blocker completely in water and then shake off excess water.  this helps to make sure the blocks slide out nicely of the blocker. make sure to do this each time you make a new set of blocks.

step 7: pressing the soil in.

pushing the blocker into the soil mix

with a good amount of pressure press the blocker into the soil pile all the way down to the work surface forcing the soil into the blocker.  do this 3 or 4 times to make sure it is full and well packed.  this does require a decent amount of pressure working too light will get you loose soil blocks.  after filling the blocker i turn the blocker a 1/4 turn on the work surface in order to scrap of the excess soil. sometimes this is not enough to get a flush surface at the bottom and i will scrape the bottom with the edge of a small piece of lumber.

step 8: releasing the soil block

pushing the blocks out into the tray

place the blocker on the surface of the tray, rather than trying to drop the blocks out of the blocker from above the work surface. slowly push down on the plunger, and pull up on the handle.  rather than doing this in one swift motion i’ve found a couple of shorter pushes seems to work better.  let the block natural come out guiding the blocker up as the blocks come out.

after the block comes out i use the side of the blocker to tighten up the blocks so there is less space between them.  in addition to making them take up less room i think it helps to keep them from breaking apart as you prick out.

a finished box of blocks

don’t they look cute?  the box i use is reused from another project, i don’t think i would build these wooden boxes for blocks again, but they do work decently well.  when these boxes finally rot away i’ll replace them with ones with hardware cloth bottoms.

at some point in the future i’ll do a full post of pricking out, but for now i just wanted to show a couple of photos so you would see how the blocks work. in the above photo you can see the germ tray that we are pricking out from.

pricking out basil

this is basil that is getting pricked out.  i carefully grab a hold of the leaf and using a chopstick guide the young basil seedling into the hole. pricking out is basically a fancy word for transplanting young plants from a small tray to a pot or soil block.

soil blocks with basil pricked out into it.

this basil will be ready to go outside in about 6 weeks from now.  special thanks to the delicata for taking photos and for sharing good conversation while we spent the afternoon making soil blocks, pricking out, and helping folks find transplants.


4 responses to “making soil blocks

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  4. Pingback: blocking workshop at detroit farm and garden | little house on the urban prairie

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