How and when to rejuvenate old shrubs, prune hydrangeas
Caning plants, such as this newly pruned redtwig dogwood, are perfectly suited for rejuvenation. Credit: Dreamstime
Last week, I wrote about selective pruning, an important maintenance practice used to remove broken, damaged and diseased branches from trees and shrubs. Selective pruning is used to improve their shape, control their size and increase air circulation to discourage disease. But there’s another, more severe, method of pruning — rejuvenation pruning — and if it’s warranted, now is the ideal time to undertake the task.
Rejuvenation pruning is the extreme cutting back of (otherwise healthy) overgrown or underproductive shrubs. The method should be used when shrubs have become overgrown, present with a wide open area in their centers or simply have declined and are failing to thrive, fruit or flower. The goal is to force the plant to replace older, weaker stems and less productive branches with fresh, new, vigorous ones. It’s drastic, but when all is said and done, it will be like having a brand-new plant.
Do not attempt rejuvenation pruning on needled evergreen shrubs. They should never be pruned beyond their needles, that is, cuts shouldn’t be made on bare wood. Likewise, do not completely cut down shrubs that grow from a single trunk. Rejuvenation pruning is intended for caning shrubs, those that send up multiple stems straight from the ground.
To rejuvenate your shrubs and bushes, you have three options:
1. Sever the entire plant by cutting it down to the soil line. This method requires a certain level of intestinal fortitude because, let’s face it, it can be nerve-wracking to cut a mature plant to the ground. Waiting for it to grow back while looking at a gap in your landscape isn’t pleasant either, and the time it takes to grow back can vary widely, according to the type of shrub. But this method will provide the most uniform results.
2. Prune all the branches to unequal heights in one session. Begin by removing broken, crisscrossed and diseased branches at their bases, then stand back and visualize the overall size and shape you’d like, and prune each remaining stem or branch, some long and others shorter, making each cut above an outward-facing lateral branch or bud. It’s from these buds that new, outward growth will be stimulated.
3. Remove one-third of the plant’s branches each year over the course of three years, starting with the oldest, least productive. This is the least severe method, as well as the least intrusive to your landscape, but you have to remember to follow through and complete the second and third phases over the next two years.
Hydrangea arborescens cut to the ground in late winter or early spring. Credit: Missouri Botanical Garden
Rejuvenation pruning is well-suited for caning plants such as:
- Beautyberry
- ‘Burning bush’ Euonymus
- Choke berry
- Cotoneaster
- Forsythia
- Lilac
- Purple sandcherry
- Redtwig dogwood
- Rose of Sharon
- Viburnum
Hydrangea pruning guidelines
There are five species of hydrangeas, each with its own requirements. Take heed, as pruning at the wrong time will risk a bloomless season.
Hydrangea macrophylla (mopheads and lacecaps): Prune in late summer, as soon as the flowers fade, but never after September. Remove weaker stems from the base of the plant, being careful to retain several stems of old wood, which will produce buds for next year's flowers. You can prune now, too, but it will cost you flowers this year.
Hydrangea arborescens ‘Grandiflora’ (smooth hydrangea): Cut to the ground in late winter/early spring. If the plant survived the winter nicely, however, and you'd like it to grow better, do a light selective pruning, cutting branches to varying heights.
Hydrangea paniculata Grandiflora (panicle hydrangea; Peegee): Simply remove spent flowers; thin or cut back last year's growth in late winter/early spring.
Hydrangea quercifolia (oak-leaf hydrangea): Remove dead wood at the base of the plant in early spring.
Hydrangea anomala petiolaris (climbing hydrangea): Unruly vines can be shortened in summer. Otherwise, pruning is seldom necessary.
The right tools
The best pruning tool for the job depends on the size of the stems or branches to be cut:
•Use hand pruners for stems up to one-half inch in diameter.
•Use lopping shears for stems between one-half and one-inch in diameter.
•Use a pruning saw for stems with a diameter of one inch or larger.
