Q Can you offer advice on my tomatoes which have ‘green back’? I was told it was a lack of potash but adding it doesn’t solve the problem. It affects my ‘Alicante’ and ‘Shirley’ varieties. A ‘Green back’ manifests as hard green areas on the shoulder of the fruits. The causes are insufficient or irregular watering, light levels and/or feeding so ensure a steady supply of all three. Q I have black spot on my roses – even on the ‘Peace’ and ‘Wendy Cousins’ varieties. Could you recommend a good spray? A Weather conditions have been ideal for the black spot fungus this year. I can’t recommend a spray but picking off and burning the leaves, including any that have fallen, is a good idea. Roses recover well so don’t worry too much. Q I have a ten-year-old self-fertile greengage tree on dwarf root stock. Despite following pruning advice, I get no fruit just flowers. Help! A Greengages and plums flower early and are vulnerable to frosts and lack of pollinators. You can’t avoid frosts, but encouraging bees into your garden will help. Make sure the tree is watered, kept weeded and mulched. And be patient! Ten is still very young for a greengage tree.