Any tips?

I know with HF you can build a greenhouse. Can you plant a lot of ingredients in there? Any other tips on getting rare alchemy ingredients? I find the ones that boost destro damage to be hard to come by.

If you do the College quest-line you'll get your own garden with all (I think they're all there) ingredients plus many potions, and the room refreshes periodically so it provides a steady supply. The other tip is that ingredients grow in certain places and locations so get to know where and go foraging with that knowledge.

Items from the Dawnguard DLC don't seem to be compatible with the Hearthfire DLC ingredient wise.

Nightshade and Glowing mushrooms are fairly common.