[maxjohnson]

I use partial compost in my grow bags (up to a third) and don't over water, so it doesn't wash out very much. Personally I mix slow release fertilizer thoroughly with the mix.

If you use peat heavy type of potting mix, yes you want to add lime and check the pH. It depends on what you buy. ProMix use sphagnum moss which is more pH neutral. I like potting mix that has well aged coconut coir.