Now Is The Time For Summer Pruning

It’s that time in the growing season when the days begin to get shorter, and for some plants it’s a time of slowing down. For many plants it’s also a time when a plant’s physiology begins to change, and actions you take in the garden now can affect plants for the rest of the growing season—and in some cases for seasons and years to come.The practice of summer pruning, for which there’s a short window of opportunity, has to be completed in the next few weeks. If done on many trees and shrubs later in the season, pruning can result in winter damage. But summer pruning, now, on annuals, and pruning done a few weeks ago on some perennials (which we refer to, respectively, as “deadheading” and “pinching”), can prolong blooming and create bushier plants with denser flowering habits. There can be a bit of a trade-off on the annuals, though, as the pruning removes some of the immature buds, but it will force these plants to re-bud and continue to flower for weeks or even months going forward.

Deadheading was an art practiced by most gardeners before the advent of hybrid annuals that are “mules” whose reproductive future was not tied to their producing seeds. Annuals such as zinnias, marigolds and petunias that are straight species and not hybrids usually go through a period of heavy flowering, their goal in life being to flower and set seed for the next generation. When we intercede and remove the flowers before they set seed, the plant’s genetic program for survival tells it to grow more flowers, in the hope of producing more seed. Deadhead the petunia flower or the marigold flower, and the plant would grow a new flower.

On modern hybrids, though, the blooming is almost continuous, until Mother Nature (temperature and shorter day length) shuts the plants down. But, in the meantime, these modern bedding plants will bloom for weeks and weeks and weeks without the need for deadheading.

All you need to know is if your plant is a species or a hybrid. Heirlooms are almost always species and will benefit from deadheading, and any of the older varieties of petunias, zinnias, marigolds and other bedding plants will benefit from deadheading.

Most perennials, on the other hand, don’t benefit from deadheading, because they are more seasonal in their blooming patterns. You can deadhead a columbine all you want, but that won’t promote more flowering, and you can pinch every single little heart off a bleeding heart, but that won’t make it bloom longer.

Geums and many salvias can be cut back to promote an extended or second blooming period, albeit not as profuse. Nepetas or the catnips often grow leggy by mid-July, and many of them can be sheared (which is pruning en masse), and this often results in a second bloom later in the summer.

Another plant that you can get several weeks more blooming time out of is the species Echinacea, the old-fashioned ones. One such variety is E. purpurea Magnus, which is grown from seed and is a selection from the species purpurea. This is still my favorite cone flower because of its clean and brilliant color, and as the flowers fade, if you pinch them off, new flowers will be produced for about six weeks or more. Let the flowers remain on the plant and create seed and not only will you have a garden full of cone flowers next year but your plants will flower for a shorter time.

Pinching, on the other hand, does something different to a plant. A good example is the garden chrysanthemum, or bedding mum. When these plants are grown en masse in nurseries, they are usually sprayed with a material that causes them to stay nice and short and produce copious numbers of blooms and thus flowers. In our gardens, though, we can’t use these sprays—but there is another practice that accomplishes the same thing.

In late spring and early summer, generally up to the Fourth of July, as you see the buds developing on these mums, they can be pinched out, or rolled off. The result is that this causes an auxin, a plant hormone, to be released down the stem, which causes new shoots and more buds to be produced. Flowering is delayed by a couple of weeks, but you get more flowers and a much fuller plant.

Pinching also can be done to the perennial hibiscus plant when it’s about 6 inches tall. If the tip is pinched, it will cause new side shoots to develop, and two to four times the stems will emerge and flower. The downside, though, is that the resulting flowers, while much more numerous, will be slightly smaller compared to an unpinched and taller plant.

Some also practice pinching or hard pruning back of Montauk daisies to keep them short and tight instead of their natural taller and somewhat sloppy habit.

Trees and shrubs are yet another world. Pruning of spring flowering shrubs, like forsythia, removes next year’s flower buds, so this should have been done weeks ago and should be avoided now. However, some shrubs like azaleas and rhododendrons can be pruned now to promote new growth and for shaping. Neither plant is a fast grower, and pruning a large rhody now will not produce noticeable results in new growth until next year, and filling out can take up to five years, depending on the variety. For this reason, a good eye and the realization that work done now won’t show tangible results for several years should be kept in mind.

Summer pruning on these plants also prevents them from getting leggy as they age and gives them a better and stronger stem and branching structure. Pruning out deadwood in azaleas now allows you to know early next spring exactly where any new winter damage occurs.

Mock orange and weigela are shrubs that are traditionally pruned and shaped after they flower in June, but I suspect that with our long growing season you might be able to shape them now. If you’re timid, however, just prune a small area and make a mental or calendar note to check those spots next year in June to see if they did indeed flower.

Summer pruning also is a good practice for removing diseased or damaged stems and branches on a variety of trees and shrubs. This includes the removal of stems on apples and pears that are showing signs of fire blight infection. The wounds from the pruning have time to heal before the cold weather, and in the case of infections on fruit trees, including crabapples, the removing of branches affected with fire blight can go a long way toward controlling the disease.

I see more and more people planting spireas. Once limited to only a handful of varieties, there are more and different varieties appearing on the market every year, and they are now available in forms as short as 2 feet tall, to full shrubs growing to 8 feet. The flower colors range from a pure white to variations of pinks to near reds, with some having three colors of flowers on the same plant.

Most of the spireas should be pruned for shaping and forcing the growth of new wood around this time of the year, after they’ve flowered, but beware of the variety you have, as some of the new types, like the Double Play series from Proven Winners, will bloom twice in a season. Cutting off the spent flowers is fine, but pruning back beyond these flowers will remove the buds that provide the second blooms a few weeks later. You need to know what variety you have, and that will dictate the pruning regime.

Euonymus and privet can be pruned throughout the summer to retain shape. In the case of privet, several prunings or shearings can take place through the summer, but pruning after early August should be avoided to allow the newly emerging shoots to harden off before winter.

Privet that is not sheared in the summer tend to lose their foliage much earlier in the winter than those that are summer sheared and well watered, and summer-sheared privet often can retain their green foliage well into December, providing privacy and wind breaks into later fall and early winter.

Prune now, with caution—but keep growing!