DIY Seed Starter Soil Posted on March 9, 2013 by Bizy Bii Reply This is so freakin easy, I couldn’t believe it. Still don’t. 4 parts filtered compost 2 parts sphagnum peat moss 1 part perlite 1 part vermiculite Boom. Sphagnum peat moss and perlite tend to lighten the mix and allow it to drain more quickly. Compost and vermiculite increase moisture retention.