I don't know what the recommended mix is, but what I've been using has worked well for me: approx. 3/4 Whitney Farms potting soil, 1/4 Gardener and Bloome soil building compost. The seedlings have loved it...in fact, I germinate the seeds in Whitney Farms before separating and transplanting into their own containers

To be honest, Penny, I don't think they're too picky about potting soil! They've thrived in any that I've used. Lately, I've been buying a brand at Albertson's, because it's inexpensive (I think the brand was Carpinito Bros.)

I always use a very gritty mix for germination, 2grit, 1peat, 1loam the seedlings simply fall out of this mixwithout damaging the roots. Thereafter I use a humous rich mix if potting, adding feed in liquid form on a regular basis rather than having rich soil in a pot. If planting out: a very rich soil with lots of organic matter, I dig in about 100 litres of farmyard compost(2 sacks) per square yard, making sure that this is dug into the soil in the second spit, ie about 10-20" deep. They love it!!

Cheers Greenmanplants