For the seed block recipe that is.
Typically seed block recipes utilize peat and vermiculite, two things I don’t normally use and I can’t say I’m that fond of incorporating into my garden experiment at this point. I would rather use coconut coir from the perspective of pH, cost, and sustainability. Unfortunately they are not a one to one substitute when it comes to seed blocks. Mainly because peat is more… sticky. But I’m still hopeful it can be done.
I started experimenting last night. Equal parts coir and compost, with some greensand as a mineral additive.
They didn’t look too bad (sorry I know it’s pretty dark in the picture). However, there seems to be a fundamental flaw with multiple possible causes.
I should have sifted the compost to make it finer and eliminate the big pieces. I had hypothesized that these would help as a replacement for the vermiculite… I know a bit of a stretch… but they just make it too crumbly. That’s when wet, I don’t think that will get better as it dries. The big chunks also keep it from getting a good form. The blocks should be pretty much a solid square and this is more of a marshmallow cube; kind of rounded on the corners.
I went ahead and put some seeds in a few of these to see how they handle a plant growing in them, but I think most will be scrapped.
I think for the next swing I’ll try sifting the compost. I don’t like to throw too many variables in at once, so I’ll avoid making any other changes, but in the meantime, we’ll see how these go.
The Jones Garden Blog 
Nice post. Thanks for sharing your discovery.
Jones, I always thought that seed blocks were the way to go with starting seeds but the block maker is so expensive that I just can’t bring myself to get one. I’d say you are probably correct in assuming the blocks will begin to crumble apart as they dry out. I’m just curious as to why you don’t like the use of peat and vermiculite. I know that peat is a somewhat non renewable resource as it takes a century or two for nature to make peat.
Have a great day with the seed blocks.
Well, when you use peat you have to balance the pH back out. More additives to the seed blocks and in precise amounts. Either that or you need to test the whole mixture to see where your pH is at. I don’t really like to mess with testing (although it would probably be good to do every once in a while). Vermiculite… that one just makes me nervous. The whole asbestos thing… combined with the fact that it isn’t in it’s natural state when it is useful for gardens… I don’t know. It just doesn’t sit right. I’d rather skip it.
This is a great idea I plan to now use in the spring. I cannot believe the price demanded for such a simple device. There is a definite money making opportunity there.
Wow! What a clever idea!