Amy - Actually, what I would do in your situation personally is try own-root. If you're afraid that the mites got into your soil, backhoe it out (or shovel..) and replace it with garden soil from a nursery. But I couldn't find anything stating that the mites live in the soil. Then buy own-root roses. They're way more expensive than the the 2/$5, but at least you know that they're gonna make it. Or, I'd order roses from Palatine.. their roses are the best!
