Hi Lab: I had whiteflies when I grew herbs indoor in my zone 5a winter. I checked in the container gardening and folks reported putting worm-casting ON TOP prevented whiteflies from hatching from the soil. Worm casting pH is 6.82 (used by U. of Kentucky). Yes, Rugosa hates chemical fertilizer, organics is best.

REGULAR MiracleGro potting soil pH is slightly acidic at 6.5, it has lots of peat moss, which holds moisture on top, MG moisture-control potting soil, neutral pH, holds moisture too long, perfect breeding ground for whiteflies.

The container with Organic potting soil, with composted pine fines, stayed DRIER on top, and drained faster when watered. That had no whiteflies.

Rugosa is known as "beach rose" due to its tolerance of drought, and does well in sandy soil. Keeping the top of soil DRY is the key to whiteflies-prevention. Another approach would be to spread sand on top, or perlite, which dries out faster than peat moss. Constant watering would promote whiteflies (they hatch on moist surface). Once a week watering would be best, to keep the top drier.