Pruning Shrubs, Part 2 - When is the Best Time to Prune?

Pruning your plant at the proper time is the keystone for success. If you prune a flowering shrub at the wrong time of the year, you will probably miss out on that plant’s blooms for that season. While this isn’t the end of the world and the plant will recover to flower again the following year, it is definitely disappointing. The risk of missing out on a season’s worth of flowering is probably the main reason most people fear pruning their shrubs.  The good news is that pruning shrubs at the wrong time of year almost never harms the plant itself.

To determine when to prune a plant without interrupting its bloom cycle, you need to know if your shrub flowers on new wood or on old wood. These two terms get thrown around a lot, but are rarely explained in simple terms. Here’s what they mean:

Flowering on new wood means that a plant does not create flower buds until after growth begins in spring. The new growth – or rather, the new wood – the shrub creates that season will be responsible for developing the flower buds that will open later that year. Plants that flower on new wood typically flower later in the growing season. Some examples of plants that flower on new wood include roses, rose of Sharon, panicle hydrangea, and butterfly bush (photo 'Miss Molly,' at left.)

Flowering on old wood means that a plant forms the flower buds for next year’s blooms during the current year. The buds are carried through winter on last year’s growth – the old wood. After these plants bloom, they begin forming the flower buds for the following year. Plants that flower on old wood typically flower early in the growing season. There is, however, one very important exception to this, and that is bigleaf hydrangea like the Cityline series or the Let’s Dance series. These flower in mid to late summer on old wood. Some additional examples of plants that flower on old wood include forsythia (photo Show Off^®, below right) lilac, and weigela.

Spring is the time to do most of your pruning, but the question is, which part of spring? Plants that flower on new wood can be pruned in early spring, just as the new growth begins. This leaves them plenty of time to recover from pruning and still create flower buds that will bloom that season. The ideal time to do this is after the buds have emerged on the stems, but before they expand. At this point, you can see where the healthy new growth is located, and pruning before the buds leaf out means that the plant doesn’t waste energy on buds you’ll just be cutting off anyway.

Plants that flower on old wood can be pruned immediately after they finish flowering. If you prune before they flower, you’ll remove the flower buds. If you wait too long after they’ve finished blooming, they may not have enough time to create flower buds for next year.

We offer a number of reblooming plants, like Bloomerang^® lilac, Sonic Bloom^™ weigela, and Bloom-A-Thon^® azalea. Reblooming plants are capable of flowering on both old and new wood, so the best time to prune them is immediately after their first wave of bloom, which occurs on the old wood. This allows you to enjoy their spring display and gives them plenty of time to put on new growth for their rebloom. All they require is a light trim after their first bloom to put on new growth, but if you forget to do this, no worries- you’ll still enjoy a great second show!

When you have dead or damaged wood on a shrub, it can be removed any time. Just be absolutely sure it is dead before doing so! It is sometimes tempting, especially in early spring, to look at a plant and assume it is dead or needs to be cut back, but it’s best to put your pruners down and wait to see if any buds emerge. Wood that is damaged can be removed any time too, as can growth that hinders free passage on walkways or makes it difficult to access an area of your yard. When it comes to safety, all of the other pruning guidelines are secondary.

Remember, shrubs do not necessarily require pruning to flower and perform well. If you’re not sure what to do, or you were happy with the plant’s size and performance last year, go ahead and skip the pruning.