Too Much of a Good Thing - Pruning Big Shrubs
I don’t prune, divide, or plant this time of year, but I do make notes about changes I need to make. Some of my plants are too big. Most of them started off small (many of them were seeds), but they grew. When I started gardening here, it was hard to believe that I would ever have too much of anything, but plants never stop growing: if they aren’t dead, then they are getting bigger. Perennials often get taller (the height listed on the label is part horticulture, part marketing), and they always get wider. Trees get taller and wider, and shrubs increase in every dimension until they become trees or sag under their own weight. Eventually any plant will be too big or overwhelmed by a faster growing plant.
So you can either cut down some plants or let the design disintegrate. I am deciding what plants I want to prune back, divide, transplant, or give up on. Next spring this superabundance will be dormant, so I will be glad I made some notes.
In my front garden, I have too much of several plants, the biggest is a huge shrub, an oak-leaf hydrangea (Hydrangea quercifolia).
This hydrangea is a huge deciduous shrub that has been there for 25 years. It’s a great example of a plant that has a maximum height because its branches sprawl horizontally and they cannot support themselves. The individual branches grow horizontally and vertically from the base and most of them are over eight feet long even though it’s about six feet tall and nine feet wide. It’s getting too big for my front border (which is about 40 feet long and 12 feet wide.) It dominates its area and it’s eating other plants. Honestly, I think it looks fine, but I want it to be part of a mixed border instead of a lone shrub surrounded by a few perennials.
It also has a dead flower issue. If you googled the plant right now, most sites wouldn’t mention the brown flowers or mention how they ‘provide winter interest.’ Unfortunately, they ‘provide winter interest’ starting in August. This border is crammed full of flowers until November, and brown dried flowers are a downer. So I deadhead it, which is a lot of work that needs to be done during the hottest part of the summer. Now, if I reduce the size by a third to four feet tall and six feet wide, it will have about half the number of flowers to deadhead (let me know in the comments if you want to see the math). So even thought cutting it back is a lot of work, it will look better and reduce the deadheading I need to do.
People are afraid to prune, and I don’t think most advice helps: it makes an intimidating task very complicated. My advice: if it’s deciduous and too big - cut it down to twelve inches after it loses its leaves and before the buds break (December to March for most shrubs). My method can be summed up by “don’t worry about it.”
But that’s not when you are supposed to prune it!
Many plants are “supposed to be” pruned at some vague, magical time, like “after flowering” or “fall.” The problem is that “fall” in the Northeast can be September 22 in Delaware or December 20 in New Hampshire and “after flowering” extends from the moment the main flush of bloom is over until a hard freeze. The thing to remember is that most pruning advice is trying to maximize flowering. If you want to control a plant’s size, every now and then you need to sacrifice some bloom. I know that my hydrangea won’t bloom next summer, but I can live with that.
But I don’t want a one foot high shrub!
Don’t worry about it. Your huge shrub has a huge root system and the shrub will grow more than you ever thought possible. The reason why controlling shrub size is so difficult is because it must be cut to a size that is smaller than you want. Even "dwarf” shrubs tend to grow eight to twelve inches once they are really established. That’s why hedges tend to become too high and wide even though they are pruned two or three times a year. It’s far more likely that new shoots will be too tall and you will need to tidy it up to encourage branching. I expect next year’s new branches to be about three or four feet tall by next July.
But I may kill it!
You may, but probably not. If it’s growing well enough that it’s too big, it will be healthy and resilient. If you are really worried about it, you can either cut it back to two feet tall or only cut down half of it (which will leave flower buds on the other half). It may not solve the size issue, but it will give you confidence to prune it again. Given that the plant is too big, it’s a risk worth taking. I have tried to kill shrubs by cutting them back to the ground, and it has never worked.
But you’re supposed to cut back to a leaf node/branch junction/bigger branch!
Whenever possible (and it’s almost always possible) you should prune back to something. I usually cut the shrub back to two feet and then look for auspicious spots to do the final pruning. If you don’t prune back to a branch junction, the remaining stub may die or create a hydra of new branches sprouting all around. Don’t make yourself crazy, both of these problems are easy to fix next summer.
But it will make the shrub sucker!
Suckers are long, thin straight branches that grow from pruning points or from the base or roots. I have found that If a shrub can sucker, it will sucker no matter how you prune it. Suckers are incredibly easy to cut off, so I don’t worry about it.
Right plant right place! You shouldn’t have planted it there in the first place!
I hate the way that phrase is used. It’s not an incantation that will magically make plants stay the appropriate size. It’s sensible advice if you are thinking of planting desert plants in a bog, but it’s also a marketing phrase used to promote new varieties that are supposedly smaller than other varieties. Recently planted plants ALWAYS grow more slowly than their established counterparts. “Dwarf” is a relative term and no one sues a nursery because their shrubs grew too much. It’s also a phrase used to sell larger, more expensive plants, presumably because they are so slow growing that it won’t grow big enough in our lifetime. Some plants are inherited, some places change due to tree growth and hurricanes, and some plants don’t live up to their hype. Anyway, I am not going to rip out a perfectly wonderful plant and replace it with it’s inbred, dwarf cousin.
Late summer is a great time to walk around your garden and see what trees and shrubs need pruning. If you don’t like the way they are dominating the space, they need to be pruned. If they are eating your walkway, they need to be pruned. If it’s smothering plants that you like, it needs to be pruned. If you need to move around it and it keeps hitting you in the face, it needs to be pruned. If you don’t like it but you aren’t prepared to replace it, you need to prune it hard. Don’t let it intimidate you: you need to keep your plants happy, but they should make you happy too.