Ask the RHS EXPERTS
Mild mildew
Q Can I do anything about the mildew covering my climbing roses and Michaelmas daisies?
A Powdery mildew is common in late summer covering the upper surface of leaves with grey film. Downy mildews have more fluffy spores beneath the leaves. Some roses and Michaelmas daisies are notoriously susceptible to this mildew.
Products with a physical mode of action such as ‘SB Plant Invigorator’ collapse the powdery covering and reduce the severity of attacks. Some gardeners spray their plants with milk or baking soda solution – these can be effective but the milk soon smells and baking soda solution can harm foliage.
Garden fungicides, at this late season, are unlikely to be cost-effective. Rather than rely on fungicides, it is better for the environment to replace susceptible plants with resistant ones.
Aster x frikartii is closely related to Michaelmas daisies and mildew-free, while for roses consider ‘Aloha’ and ‘Malvern Hills’.
WORM WORRIES
Q I’ve heard that worms are a sign of a healthy garden, but I have very few. Should I be concerned?
A As long as your plants are growing adequately, worm numbers are not a cause for concern.
Sandy soils don’t have many worms at the best of times, so perhaps your soil is rather sandy. Adding compost or other rotted organic matter can help, either dug in or, better, applied as mulch. However, plants grow well enough on sandy soil even without worms.
Worms tend not to thrive in acid soils. A test kit from the garden centre will tell you if the pH is below 6 and therefore acidic. Unless you are
