To Prune or Not to Prune

— Written By

It seems there is always the conundrum in the gardening world this time of year about when to properly prune your plants within the landscape. One question you should always ask yourself is why you are wanting to prune in the first place. It is preferable to err on the side of not pruning rather than prune a plant improperly or for no reason at all. There are several basic rules to follow when pruning an ornamental plant. The three “D’s” – Dead, Diseased, and Damaged branches need to be removed whenever you notice them. If a plant has outgrown its intended space, then pruning may be beneficial. However, you should strive to install plants where they have room to reach their mature size. It becomes a futile effort in trying to force a plant that is naturally 6-foot-wide into a 3-foot area of space. There are many plants such as boxwoods and Japanese hollies that are grown for a particular aesthetic attribute where pruning would be warranted. The health of the plant could be another reason for pruning. Pruning allows more air and light to circulate within the canopy which can help decrease potential disease and insect problems from occurring.

Of course, you can’t properly prune without proper tools. You can start by purchasing at least two pairs of hand pruners, one anvil style and the other a by-pass or scissor style. You’ll want to have a pair of loppers that can cut 1-2 inch branches and also a pruning saw. They should be kept sharp and rust free. Use a standard solvent to wipe the blades after each use. It is recommended to disinfect your pruners after each cut especially while pruning roses or fruit trees to prevent the spread of diseases.

Flowering shrubs and trees bloom on one of two types of wood: new growth or old growth. A rule of thumb is any plant that is summer-flowering can be pruned in late winter or early spring prior to bud break. These plants flower on new growth that will develop the current growing season. Some examples are Abelia, Hibiscus, Callicarpa, hollies, roses, and butterfly shrub. Likewise, any plant that is spring-flowering should be immediately pruned after they complete their show of blooms in the spring. These plants bloom on old growth which developed and hardened the previous year. Some examples of these plants are Rhododendron (includes azaleas), blueberry, Forsythia, Viburnum, Barberry, and Magnolia.

Hydrangeas, however, follow a slightly different set of rules. Hydrangeas that bloom on new spring growth are the earliest to flower. These are the smooth and tree hydrangeas – Hydrangea arborescens and Hydrangea paniculata, respectively. Late winter is the perfect time to thin out excessive growth. More severe pruning will produce a smaller plant with larger blooms while not pruning at all will produce a larger plant with smaller blooms. Oak leaf hydrangea or Hydrangea quercifolia bloom on old growth and shouldn’t need excessive pruning. You can, however, remove flower stalks on any hydrangea after blooming to the nearest bud as a way to tidy up the plant. Oak leaf hydrangeas have wonderful peeling bark and brilliant maroon and purple autumn leaves. The big leaf varieties of Hydrangea macrophylla also bloom on old growth. These include both the mophead and lacecap hydrangeas. Any pruning done to these in late winter will remove the flower buds for the summer. If you must prune these only remove half of all the older stems at ground level after flowering. This will encourage new growth and increase the size of flowers the following year. This group of hydrangeas also includes the cultivar of ‘Endless Summer’ which has the ability to bloom on both old and new growth giving it a longer and more floriferous season.

Colby Griffin is the horticulture agent for Edgecombe County Cooperative Extension. If you have any questions about this article or other gardening issues, he can be reached at colby_griffin@ncsu.edu or 252-641-7815.