Pruning Plants that Bloom in the Spring

(News article for March 13, 2020)

We prune plants for a variety of reasons. Sometimes, we prefer or feel obligated to maintain a certain appearance, such as a raised canopy on a plant that naturally produces growth near the base or a small number of trunks on a potentially multi-trunked plant.

Often, we prune because a plant was put in a place for which it eventually got too large – close to a house, under a window or power line, etc. This type pruning is largely preventable by attention to mature plant size and placement, prior to planting.

One reason to train young trees, particularly, is so that they’ll have good structure and not have the narrow crotch angles and included bark that make branch attachments weak. (If you’ve ever wondered why ‘Bradford’ pear trees tend to break apart in storms, this is why.)

Removing crossing limbs to prevent damage and removing already damaged or diseased parts of plants are other reasons to prune.

When it comes to fruiting plants, we may prune to make picking easier, to increase sunlight penetration and air movement, and to improve fruit quality.

There are several things to consider when deciding if, when, and how to prune. One of the primary considerations regarding when to prune is flowering time and, relatedly, whether a plant flowers on new (current season’s) or old growth.

Ornamental plants that bloom in the late winter and early spring generally bloom on shoots that grew in a previous season. Many of our azaleas, like the southern Indica hybrids (‘Formosa’, ‘George Lindley Tabor’, etc.), are poster children for this. To avoid sacrificing blooms, these should be pruned after flowering.

I’ve been asked how late is too late to prune azaleas. The end of June or first of July are sometimes mentioned as a cut-off dates, after which flower buds are likely to be forming for the following year. However, I don’t know exactly when flower bud formation starts here in southern Louisiana. (This stage of bud formation is something that happens within the plant – not something we can see on the outside of a branch.)

Rather than putting off pruning until the end of the window for doing so, if you need to prune your azaleas, you might go ahead and do it fairly soon after blooms fade. This gives plants more time to recover before weather gets hot.

Other plants that bloom on old growth and should be pruned soon, if needed, include camellias, primrose jasmine, Carolina jessamine, and bridal wreath spirea.

Crape myrtles, chaste trees (vitex), and American beautyberry are examples of the opposite situation. They produce blooms on new shoot growth and so can be pruned in late winter, while dormant, without removing flower buds.

Some groups have species with both types of plants. Among the hydrangeas, mophead or “French” hydrangeas generally bloom on old growth, although there are exceptions (such as the Endless Summer series). Mophead hydrangeas are unusual among the old-growth bloomers in that they bloom relatively late in the season. Oakleaf hydrangeas bloom on old growth as well, while panicle hydrangeas, like ‘Limelight’, bloom on new growth and can be pruned in late winter.

Many roses bloom on new growth, which is why they’re often pruned in late January or early February. There are some roses, though, that bloom once per year on old growth and should be pruned after flowering. These include the Cherokee rose and Lady Banks’ rose.

Let me know if you have questions.

Contact Mary Helen Ferguson.

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Azaleas in bloom in Washington Parish, Louisiana. (Photo by M.H. Ferguson)

3/25/2020 2:48:44 PM
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