Shrubs don’t need as much pruning: remove any winter damage and cut four- or five-year-old branches to the ground to stimulate new growth from the base.
For both types, cut out suckers appearing from the roots in any season; American plums, for example, produce veritable jungles of them. You may also have to thin the fruit during years of heavy production to keep the branches from breaking under their weight. Thin when the fruit is still small, then again as they grow if the branches start to bend. To thin, simply pull off excess fruit with a twisting motion, leaving one plum per cluster.
Each autumn, rake up fallen leaves and fruit, which can harbour insects and diseases. Then apply a seven- to 10-centimetre-thick layer of compost or organic mulch to 30 centimetres beyond the tree’s canopy, adding a slow-release or organic fertilizer beforehand if the soil is naturally poor (usually a rapidly decomposing mulch will supply all necessary nutrients). Don’t work amendments in, as this could damage the roots. Studies show plums do best without root competition, so keep the area free of grass and weeds.
If you’re looking for a few new trees for a home orchard, or even if you want a tree or shrub that can do double-duty as an ornamental, consider plums. They’re well worth the small amount of space they take up and, when properly cared for, will provide pretty blooms and bushels of delicious fruit each year.
Here are some of the most common plum problems and how to treat them:
Symptom: black growths on branches.
Treatment: buy disease-free stock. Apply sulfur spray every two weeks from early spring to mid-June: stop temporarily when the plum is in bloom. Cut off knot 10 to 15 centimetres below its base, sterilizing pruning shears between cuts. Burn or bury prunings. Remove wild plums and cherries within 200 metres.
Symptom: Ripe fruit rots. Most common on Japanese plums; frequent during rainy summers.
Treatment: Prune to improve air circulation. Remove and destroy infested fruit. Remove fallen leaves and fruit. Apply compost or mulch.
Symptom: Crescent-shaped incisions on fruit; fruit falls prematurely.
Treatment: Spray with insecticidal soap at petal fall and seven to 10 days later. To prevent, apply Surround, an organic kaolin clay that repels insects (follow package directions). Pick up and destroy fallen fruit.
Mites and thrips, for example
Treatment: Spray with dormant oil in late spring. Spray with insecticidal soap when insects are seen. Don’t apply while tree is in bloom, as this may kill pollinators.