There are many youTube videos about them with all sorts of recipes each person swears by (even though they differ greatly from each other). They may be of help to you. Johnny's Seeds has a good one too.

Personally I gave up on them several years back when it became clear that the only way they would work for me was if I used the packaged mixes made specifically for them - too expensive.

Below I linked some of the many discussions about them from over on the growing from Seed forum here. Some experimental recipes are included.

Dave

Here is a link that might be useful: Soil block discussions

Hi VanIsle. Last year was my first go with the soil blockers, too. I couldn't find all the ingredients for the various mix recipes I found online despite a grand search. As I was also introduced for the first time last year to the big bales of Pro-Mix BX potting soil that our local greenhouse uses, I ended up just making a sopping wet mix of that stuff and trying it out. It's too coarse for the mini-blocks, but it holds together perfectly for the 2" blocks. I started all my pole beans in them last year and they even held up beautifully outside, exposed to winds and some light rains before I got them in the ground. I bought a cheap little fogging nozzle that's perfect for watering them gently, too. I used roughly 1.5 bales of the stuff last year. The price from our greenhouse is $28 (taxes incl), which probably isn't cheap, but since it's the best mix available to me here, it's worthwhile for my situation.