Q. My oleander shrubs are overgrown. When and how severely can they be pruned?
A. The best time to prune oleanders is late winter just before new growth occurs (late February to early March). Oleanders flower on current season’s growth. So, if you prune just before new growth occurs, you’ll still get flowers. However, severe pruning (removing 1/3 or more of the plant), may result in the oleander not flowering for several years.
Pruning severely causes a plant to put all of its energy into recovering the lost growth at the expense of producing flowers. This is particularly true if you severely prune and then fertilize with a high nitrogen fertilizer, including fertilizing the lawn grass that is in close proximity to the oleanders. But sometimes the need to severely reduce a plant’s size overrides the need for flowers. When a plant becomes too large for its location, the problem really goes back to planting the wrong plant in the wrong place.
Even though we may not know the mature size of a plant when we plant it, the plant is only doing what it is genetically designed to do. Oleanders can grow to a height of 10 to 18 feet with a spread of 10 to 15 feet.
Q. I have a holly bush that has grown too large. Can I trim it back severely and have it recover? I also have large azaleas that I trimmed back last year but they’re overgrown again. Can I trim them back severely again and have them recover?
A. Hollies and azaleas generally respond well to severe pruning. And, they probably will recover. But, as you’ve experienced with your azaleas, genetically plants are designed to grow to a certain height. When you prune to reduce their height, they will regain the growth, again and again. So, you may have a regular job on your hands in pruning these plants every year or so to maintain the desired height.
The problem really goes back to the wrong plant in the wrong place. It’s a good idea to find out how large a plant grows (both in height and spread) before planting it. To plant a plant that is designed to grow ten feet in height where you need a plant that only grows three feet in height can result in having to constantly prune.
Finally, to prune for the sake of reducing the height may result in fewer berries in the case of the holly, if it’s a female plant, and fewer flowers in the case of the azalea. Eventually, you may decide to remove these overgrown plants and replace them with smaller maturing ones.