Pruning tips to keep flowering shrubs blossoming for years

Deciduous shrubs — those that lose their leaves each winter — are always sending up new stems at or near ground level. This makes them forgiving plants to prune. New growth, wherever needed, can eventually correct any mistakes. Still, there’s no reason to butcher these plants.

Forsythia is one of many deciduous shrubs that look their best with their stems rising up in a clump from ground level to create an informal, graceful fountain of foliage and flowers. The way to maintain this graceful appearance is by “renewal pruning.”

RENEW YOUR SHRUB

With renewal pruning, work with the plant’s natural growth habit. Every year, remove old, decrepit stems that no longer flower well to make way for exuberant, young ones. And if these young stems are elbowing each other for space, remove some of them also.

The tools that help achieve graceful form in these shrubs are not hedge shears but a lopper and hand-held pruning shears, perhaps also a small pruning saw.

When to prune is dictated by a plant’s blooming season. Prune early flowering shrubs right after their spring show is over. If you were to prune now, you’d be pruning off many stems that were going to bear flowers.

Reserve your late-winter pruning enthusiasm for shrubs that flower from summer on.

HOW MUCH PRUNING? IT DEPENDS

Variations in the growth habits of deciduous shrubs dictate the degree of renewal pruning needed.

Those that can handle a lot of pruning include red-osier dogwood, Russian sage, butterfly bush, St. John’s wort, and other shrubs whose newest shoots are the ones that carry the best flowers or, in the case of red-osier dogwood, the brightest red or yellow stems. These shrubs also tend to send up many new shoots from ground level each year.

Shrubs whose newest shoots put on the best show are the easiest to prune: Simply lop the whole plant completely to ground level each year. This admittedly drastic pruning keeps them from becoming congested at their centres, and stimulates the season’s flush of lanky, new stems.

Shrubs whose best show is on stems that are 1 year old — common ninebark, flowering almond, rambling roses, kerria, and pussy willows grown as shrubs for their catkins — require slightly less severe pruning. Prune these shrubs by lopping to the ground all flowering stems, that is, those that are a year old, right after they finish their show.

Stems of forsythia as well as those of lilac, mockorange, clethra, honeysuckle, shrub roses, and weigela keep bearing flowers even longer, so can remain a few years before needing to be cut away to make room for younger stems. Use your lopper or saw to first cut some of the oldest stems right to the ground, or to low, vigorous side shoots. These few quick cuts quickly and easily rid the plant of decrepit wood, make way for young wood, and reduce the plant’s height and width.

Next, with hand shears, go for the young sprouts at ground level. Cut to the ground any that are spreading too far out from the base of the plant or that crowd too thickly.

It’s impossible to prescribe how long to leave an older stem, or to say how many new stems to leave each year. Such details depend on the soil and the nature of the plant, as well as how high and how wide you want it to grow.

Finally, the easiest plants to prune are witch hazel, cotoneaster, enkianthus, PeeGee hydrangea, climbing roses, tree peonies and many viburnums. All these shrubs are reluctant to send up new sprouts from ground level, and the relatively permanent framework of branches that they build up typically puts on a good show year after year. This growth habit means you can prune these shrubs rarely, or not at all.

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