Your potting soil mix for old roses
Q for those of you who grow your antique roses in pots. I'm talking here about smaller but more or less mature roses grown in 20" or larger ceramic, clay or poly pots, not the bands and baby pots used for immature plants.
What potting mix do you prefer? I'm not a big fan of the bagged garden store potting mixes, neither the fluffy stuff with perlite nor the 'organic' stuff, at least, not used on their own. The 'organic' stuff is heavy and drains poorly; while the fluffy stuff is light but also tends to get saturated and has at best zero nutrient value for the roses. So I've been mixing up my own. The last couple of years I have been mixing the bagged, commercial potting fluff with pine bark mulch or better yet, pine bark fines (more finely ground bark), in differing proportions. The pine fines aren't overly heavy and seem to keep the pots draining a bit better, whiling providing acidic and organic component. The roses seem to like it.
I used to just throw mushroom compost into the wooden whiskey half barrels that I used to grow a pair of SDLM, just right on top of my standard potting mix, but every once in a whileI had to lift the plants out and scoop out those barrels because the mushroom compost tended to inhibit drainage.
What do you use? Anybody mix compost or other organic matter into their potting mix? I found a really light weight bagged compost product this summer that I used when I transplanted a few things. It wasn't the standard manure. Wish I could remember what it was composed of, or at least the tradename. It was very light and rather coarse, so might be pretty good for pot culture. And the plants responded well to it.