I can't seem to get my butterfly bushes to become "bushy". They end up being tall and slender and only about 2 feet across. They are healthy looking and have lots of blooms but don't look like a rounded bush like the pictures. I live in zone 5 so they get cut to 12in in the winter...is that the problem?
Do you deadhead them? That's one way both to encourage more flowers and to keep them bushier and more compact. As each bloom fades, I cut back that branch a little below the bloom, and then I'll typically get a couple more little branches and then blooms coming out from that spot.
If that still hasn't helped, then one other thing you could try is in the spring after they've grown a bit, prune them back about halfway, that may stimulate more branching (but it'll delay flowering a bit if you do that). If that doesn't do it either, then the answer may be that in climates like yours where they die back every winter, you can't get the form that you want. Here they don't die back so you can get them pretty much whatever shape you want. Or it could be as your plant gets older, it'll send up more shoots from the base each year which will make it bushier. I have to say though when I have newly planted BB's (which I imagine are somewhat equivalent to yours that have to start fresh every year) if I am good about deadheading them they are nice and bushy. I don't just take off the flower, I cut back a bit of the branch that the flower came from too, maybe that's what makes the difference. Or maybe it's the particular cultivars that I have ('Dartmoor' is one of my favorites)
ecrane3 is definitely right. Prune it back and different cultivars grow differently.
Butterfly Bush does excellent up here in PA. I have cut back 8' tall well established shrubs too 2' above the ground in the spring and it grew back to 6' with no problem that year. Just let it get established a little more.
Mine definitely does better getting cut short in early spring, instead of fall. I neglected to cut it back one fall, and was really surprised how much fuller it grows when the branches are left on over the winter. Around here it's almost "semi-evergreen". It still has leaves on it now. But this is a different zone here, so maybe a different story.
I cut mine back in the spring and by the end of the season, it is gigantic - about 7 feet tall and 5 feet wide. I cut it down to about 2 or 3 feet tall (mostly because I got lazy the previous fall!). I had originally gotten the plant as a small twig that my mother in law gave me and I never thought it would grow but it's made it through 2 summers and counting.
Different colours have different growth habits, too - here, the yellow and the white are much larger bushier plants than any of the purples, both when left unpruned, or pruned down to 12" in early spring.
Are you fertilizing it with nitrogen? Too much of that might make it tend to grow too tall and leggy. I wait until mine is beginning to set buds and then give it something like Bloom Booster. I also mulch mine early in the spring with compost.
Hey. Mine always leafs out in fall and keeps it's tiny silvery "leaf buds" all winter. Then it blooms in summer. It's not in full sun, but it blooms steadily (not heavily though) and I deadhead as described above. I've never pruned it and it's getting kinda big. If I trim now, will it affect this summers blooms.? Increase or decrease? Does it bloom on new growth?