pruning faq’s

Q. I am a beginner at pruning. Any basic tips?

A. At a minimum, follow this basic regimen: Take out the three D’s anytime they occur. The D’s are dead, damaged and diseased wood—and why wouldn’t you want to do this? (Some people say there are five D’s: dying and deformed being added to the list.)

Take out all suckers and “water sprouts” as often as required. This means that mess at the base of a grafted shrub or tree that looks like a thicket of shoots surrounding the trunk.

It also means those things that shoot straight up vertically off a branch at a 90-degree angle or thereabouts from the branch, very common on fruit trees, say, or old magnolias. Look at the architecture of these shoots: If you left them on, what would they turn into? Nothing very useful, or well-engineered. Remove.

Similarly, if anything’s thinner than a pencil or turning inward in a way that looks like trouble, off with its head. Rubbing against another branch is no good, either. (Those are probably all in the D called deformed.)

Q. When do I prune flowering shrubs? It’s so confusing.

A. Each May and June I’m asked, “Why didn’t my lilacs bloom?” only to find out in the next sentence that the questioners had literally nipped the plants in the (flower)bud with late summer, fall, winter or earliest springtime pruning, long after the new year’s blossoms had been set.

Early bloomers flower on old wood. Go out and look at a forsythia or a lilac in winter or early spring: Unless you pruned in summer or fall, you’ll see flower buds already in place, dormant but there. If you prune them off, it won’t flower that year. Make sense? It will not harm the plant to prune extra-early, but why not enjoy the blooms first?

Generally speaking, if you want flowers next year, don’t prune spring-blooming shrubs and trees more than a month or so after they finish blooming, meaning not from late spring or earliest summer, or again until after the next spring’s bloom cycle. After they’re finished flowering, prune immediately.

Woody plants that flower late in the season, such as Hydrangea paniculata, bloom on new wood. Again, go out and look. You don’t see any flower buds in early spring, do you? Discovering where on the stems and when the plant creates its flower buds will help direct your pruning efforts.

Major rejuvenation pruning, when required, I do in spring, to allow the plant the entire season to recover. Sometimes I wait selfishly until after bloom; sometimes I sacrifice bloom in the name of getting the job done asap. One time I never prune (except the 3-D’s, above) in my cold-winter zone: in fall. I don’t want new growth to sprout and then get hit by blasts of cold. Avoid undertaking rejuvenations late in the season.

Q. What is the three-step cut for removing heavy branches?

A. Pruning of heavy limbs is a three-step process, to prevent bark on the trunk from tearing. The first cut is always an undercut (A), made no more than halfway through the branch from underneath. Next, an uppercut (B), from the top, just slightly farther out on the limb from the undercut, will leave a stepped-off stub.

If the limb is still very heavy and long, repeat the first two steps until you have still less weight. Then begin the final cut (step C) near the trunk, a one-step cut from above or below, depending on what angle suits the tree best. Make this just outside the branch-bark collar or ridge, which on many trees is a visibly raised spot where trunk and limb tissue meet. Never cut into the collar; but never leave a big stub, either. The tree will heal itself without wound paint; just leave the collar intact. (Illustration from the National Arbor Day Foundation.)

Q. When and how do I prune my overgrown viburnums?

A. With Viburnum pruning, less is more. Please don’t think of my favorite genus of shrubs (and great bird plants, too) as hedge material to shear and mutilate. The protocol:

Usually viburnums need relatively little pruning, assuming you planted the right species and cultivar in the right-sized space. Most of the pruning I’ve had to do on viburnums was because I didn’t leave enough room for the plant to reach its eventual size. I have cut several to the ground or thereabouts in very early spring, when they simply got too big, but better space planning is much preferable.

Even the lightest pruning, the removal of spent flowers called deadheading, isn’t needed with most viburnums, since what you want is fruit after the flowers (unlike all that deadheading with lilacs, for instance, to prevent messiness).

If a little fine-tuning or gentle re-shaping is required, I time my cuts right after bloom. That gives the plants time to regrow and potentially set blooms, even, for the following year (depending on how far down I cut on which kind). Cut back judiciously to just above a node with each clip of the shears so the plant can make new shoots in a somewhat natural-looking style. Do not try topping or shearing viburnums halfway!

Of course always look for suspiciously vertical new shoots that jut from the base or up from existing branches and remove.

Q. When and how do I prune fruit trees?

A. Fruit-tree pruning is an exception among early bloomers: With apples and the like, including ornamentals like crabapples, what you’re working toward isn’t as much the pretty flowers as an architecture and openness that can carry and ripen maximum fruit. I prune in late winter, knowing those are apple blossoms-to-be I am cutting off.

Every year, remove all the water sprouts or suckers—thin, whip-like wood that juts straight up from the main limbs but could never support any fruit—with a folding saw or running shears.

Then there’s the hard part: taking out big branches. Step back and evaluate the tree, or even better take pictures and digitally “black out” the branches you think the tree would eventually be better without. How does it look now, “without” them?

The basic idea is to open the center to allow light and air circulation, and also to lower the crown if possible. Never remove more than one-third of the tree’s live wood in any year. It will take at least three years, therefore, to accomplish what you imagine when you “pruned” the expendable parts of the tree out of the snapshot.

When removing large branches, first reduce the weight of the limb by cutting off half of it. See the 3-step cut answer, above.

Q. When and how do I prune my roses?

A. I grow very few roses, but if I grew more in very early spring I’d be on the alert: Many common kinds of roses are pruned when the forsythia blooms. Read how the pre-eminent rosarian of the day, ex-Brooklyn Botanic Garden rose-garden curator Stephen Scanniello, approaches it, in this very complete piece from Newsday newspaper.

Q. My Weigela is messy and out of bounds. How and when do I prune it?

A. Many shrubs, including weigela, hate being cut back part way, and are better pruned thus: Remove a portion of the oldest stems near the base, to allow younger wood to develop fully. Weigela look a mess when cut back at midpoint, as do Buddleia.

If the weigela has really outgrown its space, cut the whole thing to about 12 inches from the ground right after flowering (or earlier spring if you like, skipping the bloom) and it will regrow.

Q. When do I prune butterfly bush, or Buddleia?

A. Off with its head, in earliest spring. Just before the buds want to break, cut the most familiar kind, B. davidii, down to near ground-level. Even though in some gentle winters it seems as if it will break higher up, it will look like a hell of a mess without a hard cutback in a cold-winter zone like mine, trust me.

Q. When do I prune twig dogwoods and twig willows?

A. Grown for their colorful twigs (you can see some of mine in fall with golden crabapple fruit here), these tough creatures in the genera Salix and Cornus can be cut to near the ground every few years if they grow out of bounds, or you can thin selectively, removing some older stems at the base to let new ones come through. If their color isn’t as good anymore, give them a thorough cutback, or stooling, to promote younger more vibrant wood. Prune in late winter or earliest spring if needed.

Q. When do I prune my Hydrangeas?

A. Generally speaking, prune the mopheads (H. macrophylla, the big blue ones) after they bloom in summer, but before they set next season’s buds. How? Cut out the oldest stems to the ground to make room for new ones. This one’s a trickster to normal thinking, because though it blooms relatively late, in most varieties it does so on year-old wood, so it does carry flowerbuds over the winter. Deadheading is always allowed, as flowers fade.

With Hydrangea paniculata, the ‘Pee Gee’ and ‘Tardiva’ and other panicle types, a different thinking: They bloom on new wood. Prune them in spring just before new growth begins or thereabouts. They can be cut back quite hard, and still make new wood that then gets buds and blooms. Or you can skip pruning altogether, if you like.

Where to place your cuts can be confusing on paniculatas. I have had ones I didn’t cut back enough turn to octopuses (octopi?) and really look a mess, and this is inclined to happen on older specimens that have been cut back again and again. I’ve also cut old ones back too hard and had to suffer through some gawky recovery years.

The “secret,” if there is one: To get a good-shaped plant, you will often be cutting back to a mixture of oldest (thicker) wood and younger (last year’s) wood, which is counter-intuitive. The pruned structure will look odd, but try to think only in terms of creating a framework for emerging shoots that will then be topped with flowers. Your cuts indicate to the plant where it should (please) sprout from. Let go of the fact that the wood you’re leaving will be of varying thicknesses, not some perfect-looking architecture.

As for the oakleaf types, H. quercifolia, I either don’t deadhead at all or if they need pruning I do it right after bloom–not later. If they are overgrown, take out some of the oldest stems at the base, as with the blue mopheads. When I used to grow H. arborescens ‘Annabelle,’ I cut her to the ground each year (like the panicle types, she blooms on new wood, so how much you prune is up to you).

Want to hear the contrarian view on hydrangea pruning? As with all gardening, part-art and part-science, here is one, and it’s from a very impressively credentialed individual, Dick Bir of North Carolina State University, whose point of view is summed up here.

Q. How and when do I prune lilacs?

A. Unless the shrub’s in need of rejuvenation, cutting off bouquets of flowers is all the pruning you’ll want to do. I never prune them here in my Zone 5B climate after July 4, and like to finish up earlier.

Most lilacs don’t need much pruning beyond the “musts”, the 3-D’s (top of page). But by doing a little “pruning” (read: cutting bouquets of flowers to enjoy) you do the plant a favor, and prevent the ugly aftermath of lilac-blooming season, those dried-up trusses that persist forever, or so it seems.

Always cut out dead, damaged or diseased wood as it occurs on any shrub or tree, and likewise with suckers that sprout from the base (and may in fact be growing from the rootstock if it’s a grafted plant).

Sometimes an older lilac needs reshaping. Conventional gardening wisdom says any shrubs can be “rejuvenated” over three years by cutting one-third of its oldest stems to the base each year, but I ask this: Look at your lilac (or any other shrubs) carefully. Sometimes you don’t want to reinvent (a.k.a. “rejuvenate”) the thing but just to tweak it, so look and think, and look some more before the saw comes out. I like the way Jeff Jabco of the Scott Arboretum of Swarthmore College explains the various stages of the pruning process—whether the yearly flower-harvesting kind or the more ambitious undertakings.

Q. When and how can I prune Chamaecyparis? They are loose-looking and also outgrowing their spot.

A. To prevent Chamaecyparis and other Cypress Family conifers (including some others with fan-like needles, like Arborvitae and juniper), from getting too big and bulk them up a bit, you can gently head the branches back occasionally. This means snipping off just some of the ambitious tips where the spray-like flattened needles fork, telling the plant gently to redirect its growth into fullness rather than elongation. Note: Never cut back into old wood on a Chamaecyparis or the others mentioned (I was able to find a video that might help describe why and how to prune lightly this way, better than I can here).