Here in Boston, over the next week I'm going to start seed for various species of Penstemon in pots which I'll cover with window screen and leave outside. To prepare, I went to Agway and bought 50 lbs of pea gravel, 50 lbs of Turface, 10 lbs. chicken grit (maybe I should get turkey grit instead?) and 10 lbs crushed oyster shells. I also have regular potting mix that I would use for my regular non-Penstemon east coast species.
Can someone suggest what combination of these materials I should use to start my seeds in? I have some east coast penstemon (P. laevigatus, canescens, pallidus, calycosus), some midwesterners (gracilis, cobaea, grandiflorus) and a good number of some of the dryland westerners that I know I'm taking a serious risk with. I think I can plant the easteners in regular potting soil, but the others will need some combination of the others. Thanks for any help.