Gardening Guy: It’s Time to Prune Trees and Shrubs | Weekend magazine
By Henry Homeyer
Now your rhododendrons, lilacs and other spring flowers have bloomed and are ready to be pruned. By pruning now, you will not damage the buds that will form later this summer and bloom next spring. This is also a good time to prune conifers like pines and hemlocks if you are trying to control their size.
Let’s start with rhododendrons and azaleas, as many gardeners seem to delay pruning until they block the view out of windows. If you just want to keep your rhododendrons the same size this year as last year, pruning is easy: just look at the color of the stems and cut off the new growth which is bright green. Older shoots are beige or brown.
Make your cuts just in green growth. By doing this, you are leaving a growing point for new growth next spring. Most rhododendrons bloom on old wood, that is, shoots that have arisen the previous year.
But what if you want to seriously reduce the size of your azalea or rhododendron? You can make your cuts further down the stems. Make cuts just above a fork or where branches grow in two or more directions. You will cut off the growth of two or even three years of growth. There are dormant buds on these bare stems, and they will start new growth. The lower you cut the stem, the longer it will take for growth to begin.
Most rhododendrons keep their leaves year round, but many azaleas drop their leaves and sprout new leaves every year. Old leaves of evergreen species will be darker in color than new leaves, making it easy to see new growth. By the time you read this – depending on your climate – some evergreen rhododendrons will have sent new shoots after the flowers have bloomed. In the middle of a cluster of light green leaves, you might see a small, very sharp bud. It is the flower of the next year.
If you want to shape or reduce the size of your shrub and see new leaves and flower buds, you have to make a decision: what is most important? Next year’s flower show or mastery of your shrub? I say (as the Red Queen said in Alice and Wonderland), “Gotta get your head!” Since pruning is so easily carried over to another year, do it now, even if it means sacrificing a few flowers. There should always be more flower buds appearing later this summer.
Lilacs should ideally be pruned two to three weeks after flowering, but it can also be done now. The buds develop during the summer at the end of the branches to flower the following spring.
If your lilacs aren’t blooming as well now as they once did, it may be because the soil’s pH has turned acidic from acid rain or pine needles. You can take a soil sample and send it to your state’s extension service for analysis, but if you only want to know the pH, you can purchase a simple test kit from your local garden center or hardware store.
Lilacs work best with almost neutral (pH 7.0) or slightly higher and more alkaline soil. The soil test or pH kit will tell you how many pounds of lime to add per hundred square feet, but that’s hard to translate into action. So often I just winged it: I add lime around the base of a lilac and pull out three or four feet all around. I measure it in a 1 liter yogurt pot: 1 liter for the small lilacs, two for the large ones. Not precise, but it helps. Do it now – lime takes time to change the pH.
If you have a pine, hemlock, or spruce in your yard or against your house, you would probably prefer it to stay the same size, or at least not towering over the house. It’s easy to do: YOU MUST TRIM NEW GROWTH EVERY YEAR. Just look at the tips of the branches now. You will see that this year’s growth is a slightly different color than the rest of the branch. Just cut that. Do it now, now is the time to do it.
British gardeners – and therefore many American gardeners – love box trees. They love hedges and round, stout balls. Some even create rabbits and other silly sculptures called topiaries. If you have boxwood, they need a light haircut every year in June or July. Never prune them after August, because pruning stimulates new growth and it will be tender, and will turn brown and ugly in the winter.
Prune your boxwood with a good pair of hedge shears. Mine are about 24 inches long, with 9 inch long blades. Don’t use old rusty pairs, buy a good pair like those made by Fiskars or Barnell. Most of the Fiskars tools are of good quality and sold at a reasonable price. I don’t recommend electric hedge shears as they can ruin a shrub for as long as it takes you to sneeze. I like the light shears for big jobs.
When pruning boxwood, remove just a little bit with each cut. You can work quickly, but just take a little at a time to get the exact shape you want and not create holes with a large cut.
Size can be fun. You can create a beautiful piece of art if you take your time and step back to look at it as you go. And if you goof and create an “oops,” well, it’ll all grow back. So go for it!
Henry Homeyer is a professional pruner and gardening consultant living in Cornish Flat, New Hampshire. Contact him with SASE by mail at PO Box 364, Cornish Flat, NH 03746; or send an email to firstname.lastname@example.org.