It is important to know whether a bush flowers on new or old wood. Once you have determined that a shrub blooms on the previous year's growth (old wood), you know that the correct time to prune it is immediately after it finishes blooming. By contrast, a shrub that blooms on new wood can be pruned much earlier in the year.
This list of shrubs that bloom on old wood is not exhaustive. Instead, the goal has been to include many of the most commonly grown flowering (deciduous) bushes in the northern U.S. and southern Canada. While it is reassuring to consult such lists, you do not need them if you just remember the general rule of thumb:
- Shrubs that bloom in spring flower on old wood and should be pruned just after those blooms fade. They need to be left alone to put on growth during the summer and to set bud for the following spring. If you prune them too late, you miss out on some or all of their flowering next year.
- Shrubs that bloom in summer flower on new wood (produced during the current year's spring season). They are often pruned in late winter or very early spring. This still gives them most or all of the spring to put on growth and set the buds that, come summer, will become flowers.
In some genera, though, not every species can be pigeonholed into the same category. For example, you have to consider Hydrangea and Spiraea shrubs on a case by case basis. You can't say that all hydrangeas flower on new wood or that all spireas bloom on old growth. The gardener finds a similar situation with roses (Rosa spp.), making it difficult to generalize about the best pruning time. Interestingly, some types of hydrangeas fall into both categories; they are called "reblooming hydrangeas."
The advice to prune bushes that bloom on last year's growth immediately after they finish flowering may seem unrealistic to some gardeners. "Immediately" is a harsh word for someone juggling a career, family, social commitments, health issues, and, yes, landscape maintenance.
Mercifully, there is a grace period for pruning. In her book, Caring for Perennials (p.37), Janet Macunovich helps us calculate the grace period: "Give the plant three months of good growing between the time you cut it and when you expect to see it bloom" (although months during which the plant will be dormant do not count). She uses Forsythia as an example. This bush starts blooming in April and finishes blooming in early May. Let's say you do not get around to pruning it until early June. Macunovich assures us that it will still blossom next April, citing the fact that the bush still has "part of June, all of July and August, and at least a little of September" to finish growing and set bud (p.38).
Shrubs That Bloom on Old Wood
This list presents entries in roughly chronological order so that the shrubs that bloom the earliest appear first. Note that a shrub's inclusion on this list does not mean that you necessarily have to prune it every year, but only that, if you do choose to prune it, the ideal time to do so is right after it is done flowering. The focus here is on bushes with showy flowering displays, as opposed to plants that, while technically part of the "flowering shrubs" category, are more often grown for a feature other than flowers. For example, Japanese barberry (Berberis spp.) is known for its foliage and thorns, while Tatarian dogwood (Cornus alba) is valued for the red color of its bark.
Here are some of the most popular shrubs that flower on the previous year's growth:
- Witch hazel (Hamamelis x intermedia)
- Andromeda, or "lily-of-the-valley bush" (Pieris japonica)
- Flowering quince (Chaenomeles speciosa)
- Japanese rose (Kerria japonica)
- Viburnums, such as Korean Spice (Viburnum carlesii)
- Daphne (Daphne x burkwoodii)
- Azaleas such as Rhododendron 'Golden Oriole'
- Rhododendrons (Rhododendron spp.)
- Purple-leaf sand cherry (Prunus x cistena)
- Weigela florida
- Mock orange (Philadelphus coronarius)
- Lilac (Syringa vulgaris)
- Ninebark (Physocarpus opulifolius)