ORGANIC ROSE CARE
Are there any plants more loved and feared than roses? Loved for their beauty and fragrance; perceived, sometimes justly, as being difficult to grow. Novice and experienced gardeners alike assume that roses require regular chemical treatments to keep them in peak condition, but this is not the case.
At the Montreal Botanical Garden, rose care has been honed to a fine art. Under the direction of horticulturist Claire Laberge, the six-acre Rose Garden, with nearly 10,000 roses from more than 1,000 varieties, was recently honoured with the Award of Garden Excellence by the World Federation of Rose Societies. “Yes, it is possible to grow roses organically,” Laberge says. “The first thing to do is to give roses the best possible conditions-six hours or more of sun a day, good aeration, proper watering, good drainage, rich soil and protection from wind. Prune properly and sterilize tools regularly [to prevent the spread of disease]. It's also very important to be curious and observant, being aware of problems as soon as they occur so you can treat them effectively and quickly.”
The Montreal Rose Garden is not yet 100 per cent organic, but the techniques Laberge outlines below have helped move the garden toward that goal.
Blackspot This fungal disease is one of the most common problems, parti-cularly for hybrid tea, floribunda and grandiflora roses. Black or brown round spots appear on leaves in early summer or in September, usually starting in the middle or bottom of the plant; then the leaves turn yellow and drop. Fungal diseases flourish in damp conditions, so to help prevent blackspot, take care not to wet leaves when watering your roses. Laberge recommends inspecting leaves every day or so from late May to June and, at the first sign of fungus, treat plants weekly with either a mixture of potassium bicarbonate or sodium bicarbonate (two grams per litre of water plus 10 millilitres of Safer's soap) sprayed liberally on leaves. Remove affected leaves immediately and dispose of them, but don't put them in the composter. In fall, remove and dispose of fallen leaves from around the plant, then mulch heavily to prevent spores from becoming airborne.
Powdery Mildew Another fungal infection, powdery mildew appears as a white or grey dusting on the leaves, beginning at the top of the plant then spreading. Plants that have limited air circulation or are drought-stressed are more susceptible; the disease usually appears in mid- to late summer. To help prevent powdery mildew, water deeply once a week in the morning (so any moisture on leaves has time to dry) in spring through summer, and keep plants well spaced and pruned for good air circulation. Because powdery mildew primarily attacks new shoots, Laberge recommends not applying nitrogen fertilizers after the end of July. If the fungus does appear, wash off spores with a spray of water on both sides of the leaves every week or spray on a baking soda solution (two grams per litre of water).
Aphids These pests attack soft, new tissue and suck sap from the plant. Keep an eye out for infestations, particularly in June when roses are putting on a lot of new growth. The tiny insects can be black, green or red. Aphids are easy to deal with organically: apply a strong blast of water to plants early in the day to knock them off. Laberge also suggests interspersing rose plants with alliums and marigolds, good companion plants that help repel aphids.
Spider Mites Like aphids, spider mites suck plant juices. Tell-tale signs of infestation are yellow speckles on leaves and webbing on their undersides. Spider mite outbreaks tend to occur in hot weather. A strong spray of water, applied to both sides of leaves in the morning, will reduce infestations. Laberge points out that spider mites love dirt on the undersides, so avoid splashing soil onto foliage when watering.