Maggie's Farm

When asked "When is the best time to prune a (fill in the type) shrub or tree?" my horticulturalist friend replies "When your blade is sharp."

His point is that, even if there are optimal times to do it, it's more important that it just get done sometime. Poor-pruning or neglected ornamental shrubs are not only unhealthy for these hybridized plants but also makes for an eyesore: leggy shrubs, overly-dense shrubs, and hedge-trimmer buzz-cut shrubs. (Hedge-trimmers are for hedges.)

Up here, probably the most common errors are made in neglected or wrongly-pruned hydrangea, lilac, and forsythia. Most people who grow roses know how to care for them (depending on the category of rose.)

And I almost forgot to mention Privet. Here's the way to keep a Privet hedge going forever.

Here's a good primer on pruning lilacs. I advise people to Google "shrub name + pruning" before taking a blade to a plant. Rejuvenating a long-neglected or wrongly-pruned shrub can take a couple of years because drastic correction can kill the plant.

The reason to care about the timing of your pruning is because some ornamentals bloom on the previous year's growth, and some on new growth. For example, the Macrophylla types of hydrangeas bloom on last year's, but Paniculata types bloom on new growth (a good hydrangea pruning site here.) If you prune at the wrong time, you will have no flowers.

This good pruning summary from Texas A&M says this:

Pruning recommendations for most deciduous shrubs consist of thinning out, gradual renewal and rejuvenation pruning. In thinning out, a branch or twig is cut off at its point of origin from either the parent stem or ground level (Figure 8). This pruning method results in a more open plant; it does not stimulate excessive new growth, but does allow room for growth of side branches. Considerable growth can be cut off without changing the plant's natural appearance or growth habit . Plants can be maintained at a given height and width for years by thinning out. This method is best done with hand pruning shears, loppers or a saw, but not with hedge shears. Thin out the oldest and tallest stems first.

In gradual renewal pruning, a few of the oldest and tallest branches are removed at or slightly above ground level on an annual basis (Figure 8). Some thinning may be necessary to shorten long branches or maintain a symmetrical shape.

To rejuvenate an old, overgrown shrub, remove one-third of the oldest, tallest branches at or slightly above ground level before new growth starts.

The general pruning procedure shown for crape myrtle (Figure 9, applies to many large shrubs and small tree species. If a shrub is grown for its flowers, time the pruning to minimize disruption of blooming. Spring flowering shrubs bloom on last season's growth and should be pruned soon after they bloom. This allows for vigorous summertime growth and results in plenty of flower buds the following year.

Dr. Merc wants every Maggie's reader to have the chance to master the fine points of the computer. I want every Maggie's reader to have the chance to be a competent shrub pruner. 

Photo on top: A row of hydrangeas on Isola Bella, with a little rain blurring my lens. Those Italian gardeners prune everything.