The Right Way to Prune Hydrangeas, Roses, and Boxwoods

·5 min read
Photo credit: IAN HOOTON/SPL - Getty Images
Photo credit: IAN HOOTON/SPL - Getty Images

You planted some beautiful shrubs, but now you’re not sure what to do. It seems like a lot of pressure! When should you prune them? What if you cut off too much? What happens if you don’t prune? “Most shrubs have an elegant, natural form, and there’s no harm in letting them do their own thing,” says Stephanie Hirvela, horticulturist with Spring Meadow Nursery. “Pruning is not a health issue but more about aesthetics. For example, you can trim a boxwood into a certain shape or remove spindly growth so that a rose bush blooms more vigorously.” Of course, you also should prune to remove dead or broken limbs.

One way you shouldn’t use pruning? To control the size of a plant. Save yourself (and the plant!) some grief and read the plant description or label to learn its mature size before you buy. “Don’t plant a shrub where you plan to prune to keep it small,” says Hirvela. “Pruning shouldn’t be used as height control because that’s not sustainable for you or the plant.” That’s because as the plant makes a bigger root system, which is the engine to fuel growth, all that energy has to go somewhere. You lop off the top but the plant keeps pushing new growth, so you’re constantly fighting to keep it in check. If you have a small space, look for dwarf varieties that have been bred to stay compact.

Here’s what else you need to know about pruning the most popular shrubs:

How do I prune hydrangeas?

This is where pruning gets a little tricky: You absolutely need to know what kind of hydrangea you have or you’ll risk cutting off the flower buds! There are two main types: Hydrangeas that bloom on new wood (or this year’s growth), so they create their flower buds after they begin to leaf out; and those that bloom on old wood, or last year’s growth, so they create their buds the previous season. If you’re not sure what kind you have, consult your local nursery or university coop extension service (find yours here), or wait for flowering, which will provide a few more clues about type.

New wood hydrangeas include panicle, also known as peegee, and smooth, also known as Annabelle, types. These types of hydrangeas can be pruned back by about 1/3 their size in early spring, says Hirvela. Also, trim off spindly branches or branches going sideways. Pruning now also allows you to deadhead old blooms from last season at the same time.

Old wood hydrangeas include oak leaf, big leaf, mountain, and climbing types. “These all set flowers the previous season, so the buds are already present in spring,” says Hirvela. “Do not prune these types in spring or you will remove the flowers! This is a free pass not to have to prune.” Once these types have leafed out, it’s fine to remove any dry, skeletal blooms from last year or branches that have died back.

How do I prune roses?

No matter what type of rose you have, the rules are the same: “The ideal time to prune is in early spring as the leaves first emerge,” says Hirvela. “That’s because the plant hasn’t expended energy yet on buds you’re just going to cut off.” Same as new-wood hydrangeas, using a pair of hand pruners, snip off about 1/3 of the total size of the plant. Take off any dead woody growth with loppers. There’s no fancy way to do it; just trim straight across each stem. The old-school advice to cut on a 45-degree angle is not recommended, says Hirvela. It’s better to minimize the size of the wounds (through which a plant loses moisture) with a straight cut because a smaller surface area heals more quickly.

If you didn’t get around to pruning before your rose leafed out, you still can prune, but you’ll delay the appearance of flowers by a few weeks. If you’re not sure if it’s too late in the season or you’re worried about lopping off buds, skip pruning this year. The plant won’t die. In fact, a general rule for pruning any shrub is that when in doubt, don’t prune! Even if you didn’t prune your rose, it’s fine to snip off spent blooms, called deadheading, throughout the season if you like a neater appearance.

How do I trim boxwoods?

Boxwoods come in many different natural forms including round, columnar, and pyramidal, so you really don’t have to trim them at all. But if you’re trying to create a classic hedge or impose a specific shape, the best time to prune is in early spring, as the new growth emerges but before it hardens off and becomes woody, says Hirvela. That means the new leaves are a brighter green color, soft and flexible (you should almost be able to pinch them off with your fingers). Then snip off only the new growth because if you go too deep, you’ll cut into the old woody growth and create holes. Yes, the shrub will recover in time, but it’s not the nicest look to have a big, old gap in your hedge.

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