511 mix for begonias?
I am getting ready to repot some begonias. I posted a couple months ago for help ID'ing a new begonia, which turned out to be don miller. True to what I have read about it, it came with a free bonus of powdery mildew, which spread to my 'Audrey Brenda' and 'Sophie Cecile'. Right as I was getting that under control I had a bad fungus gnat outbreak. I am getting that under control but I think I need to get them in a different mix - currently they are in miracle grow moisture control with added perlite. I was thinking 511 would be a good option for less peat, good water retention but also good drainage.
1) is 511 a good idea, or would anyone recommend a different recipe?
2) should I add the lime, or would that be too alkaline for begonias?
3) I usually feed with Schultz plant food mixed half strength at every watering (sometimes every other) would it need any thing else supplemented?
I have several cuttings rooting currently just in case ;)