Plant of the Month January 2025
GENERAL INFORMATION: Rhododendron ‘P.J.M.’ is one of hardiest rhododendrons. It, and others, were developed by Peter J. Mezitt and his son in the 1930s from crosses between R. carolinianum x R. dauricum var. sempervirens. For more information visit https://www.rhododendron.org/v53n4p195.htm. I love the dark purplish colour to the winter leaves and the spicy smell when you brush against the bush. The winter leaf curl gives us an idea of the outside temperature: no curl, above freezing, slight curl, about -2°C , tightly curled, -7°C or lower.
Common Name: PJM.
Cultivars: 'Aglo' - pink’, Landmark' - near red, 'Olga' - pink, 'Pink Diamond’, 'PJM Compact’, 'PJM Elite’, 'PJM Elite Star’, 'PJM Regal’ and more.
Rhododendron ‘P.J.M.’ - shrub before pruning.
Life Cycle: Small broad-leaved evergreen shrub.
Height: to 2 m high with same width.
Bloom Time: Early May in Toronto.
Flower Colour & Size: Clusters of 4-8 pink funnel shaped flowers about 5cm long, with 4-5 petals and 10 prominent stamens. (Azaleas have 5).
Rhododendron ‘P.J.M.’ flower.
Fruit: Small capsule.
Leaves: Lepidote, (tiny scales on the lower leaf surface), green, leathery, elliptical leaves to 6 cm long, becoming purple in winter. Leaves tightly rolled below -7°C. Aromatic with a spicy smell.
Rhododendron ‘P.J.M.’ - leaves - March.
Rhododendron ‘P.J.M.’ - curled leaves, mid December.
Range: Parents native to Eastern North America and China.
Habitat: Mountainous areas.
CULTIVATION:
Plant: where sheltered from the wind, (especially in winter). Mulch well.
Light: Partial shade. Will tolerate more light in winter.
Soil: Acid loam with plenty of organic material, pH 6 or lower. Will grow in more neutral soil when established. Use sulphur or acidifying fertilizers if base soil is above pH 6.
Water: Well drained moist soil. Preferably use rain water if tap water is alkaline.
USDA Hardiness: Zones 4 and up.
Companion planting: Other acid loving plants and shrubs.
Rhododendron ‘P.J.M.’ - September, with acid loving plants.
Propagation: Carefully removing side stems from base and replant in late spring. Try bending a stem to the ground and layer it. Stem tip cuttings, with 3 or 4 leaves and without a developing flower bud, taken in July and August, before the stems harden, will root easily.
Pruning: Best left alone but if necessary, remove older stems at ground level after flowering. Also remove higher branches if needed to reduce height.
Rhododendron ‘P.J.M.’ - after pruning.
Pest and Diseases: My plant is 30 years old. I have had no problems with it, its offshoots and near relations. Healthy plants will deter aphids, borers, lace bugs, leafhoppers, mealybugs, mites, nematodes, scale, thrips, and whitefly. A poorly-sited plant could be susceptible to crown rot, root rot, leaf spot, rust, and powdery mildew. Leaf scorch can occur in hot sun and root rot may happen in waterlogged soil.
Native Alternatives: Rhododendron carolinianum.
Pollinators: Bees, flies, butterflies, hummingbirds.
Toxicity: All parts are poisonous.
References:
https://www.missouribotanicalgarden.org/PlantFinder
https://plants.ces.ncsu.edu/plants/rhododendron-pjm-group
Text and images supplied by Anna Leggatt (Toronto Master Gardener)