I'm pretty sure I found all of these and even if I didn't I'm not going spelunking in Darkfall Cave again unless I have too. Is there another way to get a Poison Bloom so I can plant it in my Garden (In Hearthfire)? Basically, I'm asking if they regrow, or if theres another area to find them, buy them, or obtain them.

I'm guessing they only prosper in dark caves. Worth a try though.
Just don't hang around if you disturb a plant because they emit a poison gas.

Pretty sure I cleared out the only cave where they are said to grow though.. I checked to see if they regrew awhile back and they hadn't.. So I think I'm screwed...

You can't even plant yellow mountain flowers in Hearthfire (all base game mountain flowers can be planted) so I wouldn't hold my breath on being able to plant poison bloom, especially considering the little animation it does when taking them.
I also tried planting gleamblossom with no luck.

Also, poison bloom should respawn after 10 days of not entering Darkfall Cave.

Dangit.. I was worried about.. I was hoping they found a way around that kinda stuff... But I'll check Darkfall Cave again in a bit, thanks.

I'm pretty sure it respawns. Give it some time.

I had an mod in Obilvion who let you plant plants and make fields. I made multiple rows with Harreda as they has excellent properties
It actually killed an guard then I was around level 20.

What animation?

If you go near poison bloom but don't pick it up the plant shakes a bit then opens up, causing some poison to be released. It also opens up, but without releasing poison, if you pick it quickly. I just mentioned that because it makes it a fairly unique plant. You don't just press the use button and it disappears.

You cannot plant anything added by Dawnguard in any garden in Hearthfire, and the blooms do not seem to respawn for you to collect more, so if you used them all, you can get no more.