Trimming Tips And Pruning Posits

It’s that time in the growing season when the days begin to get shorter and, for most plants, it’s a time of slowing down.

It’s also a time when a plant’s physiology begins to change. Some of the 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. When done on many trees and shrubs later in the season, pruning can result in winter damage. But summer pruning now on annuals and weeks ago on some perennials (which we refer respectively as “deadheading” and “pinching”) can prolong blooming and create bushier plants with denser flowering habits.

Deadheading was an art practiced by most gardeners before the advent of hybrid annuals—or “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 a heavy flowering. At that time, their goal in life is 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. For example, 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 shuts the plant 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. Any of the older varieties of petunias, zinnias, marigolds and other bedding plants will benefit from deadheading as well.

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. You can pinch every single little heart off a bleeding heart, but that won’t make it bloom longer.

On the other hand, one species of plant that you can get several weeks more blooming time out of are 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 July 4, 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 type of 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 can also 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.

Another perennial species that responds well to pinching is the achilleas. When pinched young and the plant is reduced to just a few stems, it develops into taller and stronger stems that make great cuts and garden displays.

The same is true of the tall garden phlox

paniculata

. When punched when about 8 inches tall, you end up with multiple branching and smaller flowers. But if half of the emerging stems are cut to the ground early in the season, the result is stronger and taller stems at flowering time with larger flower clusters.

Tuberous dahlias and herbaceous peonies also can have their buds pinched to produce fewer but dramatically larger flowers. Both plants tend to produce two- to three buds per stem. And if the buds are reduced to one bud as soon as they appear, the largest and showiest flowers are produced.

I write about roses with hesitancy, as there are now so many new varieties and so many thoughts on summer pruning on the queen of the summer garden. Again, it’s important to know what variety you have, as pruning a rugosa rose at this time of the year can have disastrous consequences if you want those large, classic, red rose hips come fall.

Deadheading a hybrid tea rose and pruning it back to the last set of five leaves has always been the guild to producing new flowering stems in about five weeks. As always though, diseased stems and canes should always be cut from any rose bush to reduce the chances of further infection and pruning needs to stop in late summer to allow the plant to harden off for the winter.

Trees and shrubs are yet another world. Pruning of spring flowering shrubs, such as forsythia, removes next year’s flower buds so this should be avoided. However, some shrubs, such as the 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. Filling out can take two- to three years. 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.

I’ve also noticed that there is a certain amount of dieback on the azaleas that we grow. This dieback should be pruned out every summer, allowing you to review the plants in the spring to see if continuing dieback is from winter damage or another issue. If you don’t remove the deadwood you never know when the damage occurred.

Summer pruning is also a good practice for removing diseased or damaged stems and branches on a variety of trees and shrubs. 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 to controlling the disease.

I see more and more people planting spireas. Once limited to only a handful of varieties, there are more 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. Some varieties can be deadheaded or even sheered when flowering fades and they’ll rebloom again in several weeks. Some will continue to bloom without pruning through the summer. You need to know what variety you have though and what its pruning needs are.

It’s generally believed that pines should not be summer-pruned as the pruning wound emits ethylene gas, which is known to attract borers to the plant. This is especially true of our native pitch pine and the overplanted Japanese black pine. Best time to prune these is late winter or very early in the spring.

Euonymus and privet can be pruned throughout the summer to retain shape.

In the case of privet, several prunings or sheerings can take place through the summer. Keep in mind that pruning after early August should be avoided to allow the newly emerging shoots to harden off before winter.

Privet that is not sheered in the summer tends to lose its foliage much earlier in the winter than that which is summer-sheered and well watered. Summer-sheered privet can often retain its green foliage well into December, providing privacy and wind breaks into later fall and early winter.

There’s also a lot to be said about the summer pruning of fruit trees, and of course the ever perplexing hydrangeas. But those will have to wait for another column.

Keep growing.