We made our first batch of our custom seed starting mix today. We have been very happy with the performance of this mix and wanted to share the recipe here for anyone interested. It is a great mix for using soil blocks, but also excels in plug trays, pots, or any container you can think of.
Instructions: (The “cup” is your basic kitchen measuring cup)
Place 15 gallons of peat moss in a large wheelbarrow
Add 1/2 cup limestone and mix
Add 1 cup granular organic fertilizer (We use Fertrell Feed N Grow purchased from Fedco) and mix
Add 5 gallons compost and mix
Add 5 gallons perlite and mix until it looks like this:

This yields about 25 gallons of mix. It has sufficient nutrients to carry almost all of your seedlings to transplant age.
When you are ready to use it, make sure you add water and mix it until it is moist before placing it into the growing container. If placed into the potting containers dry, it will be extremely difficult to get the mix wet enough to support vigorous plant growth.
Happy growing!