Wilde side

Kim Wilde answers your gardening questions.

How can I save my roses from black spot? By mid-season they’ve lost lots of leaves, despite spraying and removing the diseased ones. Our soil is light and gravelly with limited sun.
The dreaded black spot strikes again, just like Snow White’s evil stepmother, jealous of the rose’s beauty. The fungus is most common where the air is pollution-free, and overwinters on stems and fallen leaves, ready to infect early in the season. Since spraying seems ineffective, try a more organic approach. Hard prune infected bushes this spring, and burn the prunings. Improve poor soil with organic matter, which helps retain soil moisture and strengthens plants. A mulch of leaf mould can deter disease spores, reduces evaporation, suppresses weeds and improves the soil. Roses usually need sun; black spot thrives in darker, damper conditions, so your aspect is against you.

I make compost for my shady garden (damp in winter, dry in summer). But in the past two years, loads of moss has built up. Is my compost the culprit?
It’s unlikely that the compost is behind your problem. You could choose (as the Japanese do) to enjoy moss as an easy-going alternative to grass. It needs little watering, no mowing or fertiliser, and stays lush all year. If you’re not convinced, you must change the conditions that encourage it. Moss killer is only a temporary solution. Common causes are waterlogging, underfeeding, over acidity, shade, drought and sandy, free-draining soil. How about pruning shrubs and trees to get more light into the garden? Prevent moss on the lawn with good aeration, drainage and soil fertility, and not scalping it when mowing. Drive a fork into the lawn at regular intervals for aeration, and rake to stop thatch choking out new growth. Feed in spring and late summer.

My Euphorbia mellifera is not flourishing. It is kept indoors and watered regularly (but not over-watered). The leaves develop, then die rapidly.
I am a euphorbia fan. Although there are indoor species, such as E. pulcherrima (poinsettia), the evergreen shrub E. mellifera (honey spurge) is for outdoors and unsuited to being a houseplant. It is hardy in milder regions, but can be grown in a pot and overwintered in a frost-free greenhouse. Planted in well-drained, sandy soil in a sheltered, sunny spot, it should form a large shrub (2m x 2.5m) with honey-scented flowers in late spring.