Soil Blocks

The keyword used to find this blog today is soil blocks so I will write about soil blocks.

For you SB newbies a soil block is something you start seeds in, like a Jiffy pot™. Soil blocks allow air pruning to happen which lessens transplant shock. To use soil blocks you will need a soil block maker or two (Johnny's Selected Seeds has a wide variety of the makers from tiny to huge). We use the mini blocks and the 2" blocks for our seed starting activities. I see there is now a 4" block maker which would be wonderful for tomatoes.

Next you have to have some sort of soil mix to put in the blocks. I use the recipe in Eliot Coleman's New Organic Grower pps 140-1
basic Mix:
(a bucket = 10 qt)
3 buckets peat moss (which has been screened through a .25" hardware cloth)
1/2 cup lime or wood ash
2 buckets perlite or coarse sand (perlite is my choice, sand tends to erode out of the blocks especially if top watered)
3 cups base fertilizer (a 1:1:1 of green sand, kelp meal (Eliot uses blood meal) and colloidal Phosphate)
1 Bucket soil (It is suggested to get this from last year's garlic area)
2 Buckets Compost (screen this like the peat)

Mix everything together thoroughly

For the mini blocks use this:
16 parts peat
1/4 part colloidal phosphate
1/4 part greensand (do not substitute, if you cannot find greensand leave out)
4 parts compost
Mix thoroughly

Okay, now that you have soil mix for blocks the next thing to do is to add water and mix it up so you have something that resembles brownie dough. it should be wet enough so when you pick it up it will make a ball and a bit of water will drip out of the ball of dirt. In other words, we are looking for a cohesive substance. if it is too dry or too wet the soil blocks will not keep together. The best way to test is to make some wet soil and than start making blocks. If they are not keeping together either add more water (a little at a time) or add more soil mix until you have the right consistency. It would probably be a good idea to make 50 to 100 practice blocks before doing this for real. When you are done with the practice blocks just dump them back into the container you are using to make your mud pies in.

I use an old hotel pan (one of those shallow rectangular stainless steel pans you see on a hot buffet line). I use to manage kitchens and picked up several over the years and they work for us but they are pricey. A plastic tub will work quite well for a small project. But if you are doing a lot of blocks a wheelbarrow is nice or, if you have one, a cement mixer (I have not used one but I have talked to people who do use them and they say it works well).


Okay you have your soil mix the perfect consistency, now all you need is something to put the blocks into. I use seedling flats nested in permanest trays so I can bottom water the soil blocks (if you water from the top even with a very fine mist you will cause erosion and the blocks will not be able to air prune the roots so all the seedling roots will grow together thus making transplanting a real pain for both you and your plants. Air pruning of roots keeps transplanting shock to a minimum). If you do not have permanest trays you can use anything that has a lip and will hold enough water to keep your blocks moist. if you do a lot of your own seedlings permanest trays are a good investment. I think they cost around $8 each.

Now take the block maker and plunge it into the wet soil mix so each cell is completely full. I like to make a mound of soil that is higher than the cells are deep and plunge into that and than I check to make sure the soil is packed, but not too well packed. If the blocks are too dense the roots have a hard time getting established. Now take the full block maker and put it where you want the blocks and depress the plunger and Voilà you have your first soil blocks.

Hint:If you are making 2" blocks to put the mini blocks into do not forget to put the mini block pegs (little plastic cubes that screw into the 2" block maker) into the big blocks so there is a perfectly sized depression in the bigger blocks.

Hint: in a tray of 2" blocks be sure to leave a couple of spaces blank so you have someplace to put in water and this also makes it a lot easier to remove the blocks when it is time to transplant

Hint: When it is time to harden off the seedlings make sure they are in a place where rain cannot get to them or the blocks will melt in the rain. If this means moving the trays inside do it.