Your answer is both. I know, that doesn't help. Pruning in the fall is ideal for many varieties of plants because they are going to sleep instead of waking up. When plants awaken in the spring, they are pushing root and top growth quickly. Some varieties prefer one season or the other and there are many reasons for leaving growth on the plant through winter. That is why it is so confusing and you can't seem to find an easy answer.

So, can you cut in the spring? Yes, you can. Boxwoods can be easily burned by the fluctuating weather we have been experiencing here this year. The new growth is sometimes damaged by cold temps and whipping cold winds. They can also be damaged by exposing previously shaded leaves to hot sun. So, if you can, prune them back when the weather stabilizes a bit. It looks like next week could be good. Don't worry, any damage that they sustain from weather will recover when it flushes growth again a few weeks later. (different varieties of boxwood are more or less likely to be damaged but all will handle a pruning in spring.)

The butterfly bush can also be pruned back now. I have known people who cut them all the way to the ground in spring or fall. They are a resilient plant here. However, my general rule of pruning plants like that is to not cut more than one third it's height for a severe cut-back. It will still bloom well although you may see a bit of reduction in flowers. Remove much of the thin side branches and trim the tops just enough so that they are not drooping over in the rain. Your shrub will look silly until the leaves and new growth flush out.

A nice day followed by several days where the weather looks like it will be in the 60's and 70's with some mixed in rain is ideal. Don't cut your boxwoods while hot sun is beating on them. you will raise the potential for burn. But they will recover.

Cut the butterfly bushes soon before the leaves fully flush out. Also, keep up on removing brown flowers and you will prune as the season continues.

have fun!

Robbie

If you are an iphone user "A Way to Garden" produced a nice free podcast on pruning... I was emboldened to go out and tackle my shrubs this year!

Just an FYI... butterfly bush (Buddleia davidii) is on Pennsylvania DCNR's watch list for invasive plants. Many people have chosen not to plant or sell this potentially ecologically problematic plant, and some have chosen to remove existing plants.

Here is a link that might be useful: DCNR - Butterfly bush

Carrieb - just wondering have you ever seen butterfly bushes gone wild in meadows ? Ocassionally in my garden I have seen a butterfly bush drop volunteers, but not problematic. Only a few times I have seen butterfly bushes growing along road where I assume they have not been planted.
Now I have seen way to many wild bradford pears and would never plant that in my yard.
Just wondering - Mike

To EL - was just wondering if now would be an ok time to prune my boxwoods and butterfly bushes? yes now is the time. If you have not done in the fall - spring is ok -

how about pruning lilac bushes., Mine have gotten so tall but the leaves are mainly at the top to mid height. The bottom third of the bush is bare for the most part. They are just about done blooming and I know you are supposed to prune after blooming but my question is really "How severly can I prune". I would like to keep them at a decent height but also don't want to kill them. Last yr they were exceptional due to the wet spring, this yr they are average. These are the common lilac. Thanks for your advice.

Now is a good time to prune lilac. Usually you remove 1/3 the oldest stems at the ground in order to get new leafy bottom growth plus blooms on top, but the old fashioned are pretty indestructible... You can pretty much cut as much as you want, just if you cut too far back it may be a couple years before you get blooms again

plantman - I have weeded out quite a few butterfly bushes in the gardens I tend in the Philadelphia area. Our Morris Arboretum decided long ago to remove all from their gardens, and no longer sell them at their plant sales (despite people still asking for them.)