Our gardening expert John Stoa answers your queries
Q. My dwarf rhododendron leaves seem to have scorch marks around the edges. What causes this?
The keen gardener likes to grow healthy plants, so in spring we tend to give everything a wee feed with some fertiliser. Whereas this may suit roses and most shrubs, it does not suit rhododendrons, azaleas and heathers. Adding fertiliser can scorch the leaf margins and weaken the plant. If you want to show kindness, give them an annual light mulch of well-rotted leaf mould, or ericaceous compost in early winter.
Q. What is the best variety of pumpkin for kids to grow to get a good lantern?
The variety Hundredweight can produce huge pumpkins, but restrict the fruit to just one per plant if you are going for size. Now is a good time to start sowing seed to get the children involved right from the start. They will need to look after the plants throughout summer, giving them plenty of water and a weekly feed so they will have an immense pumpkin for Hallowe’en.
Q. Do you need to dead head daffodils, tulips and other bulbs once flowering has finished?
To keep your spring bulbs strong so they can continue to flower every year, remove all old flowers after flowering, otherwise they will use up all their energy for seed production, rather than initiating next year’s flower buds. However, many dwarf bulbs such as snowdrops, aconites and crocus come to no harm and regenerate well from their own seed dispersal, so let them seed at will. Be careful with grape hyacinths and bluebells as they can soon colonise your whole garden.
Q. My soil seems to be infected by clubroot. Can I still grow swedes?
Clubroot fungus infects all members of the brassica family including cabbages, cauliflower, turnips, swedes, radish and rocket and lasts in the soil for several years. If we maintain a strict rotation we minimise infection. However, breeders are now producing varieties with resistance to this fungus. The varieties Invitation, Gowrie, Lomond and Marian are all said to be resistant so well worth a try. I grew Invitation last year but was disappointed with size and texture.
Q. Is it possible to have raspberries to eat over a long season?
If you do not have polytunnels, you’ll need to grow a selection of varieties to cover early summer till autumn. Malling Jewel fruits quite early, then you have a choice of Glen Ample, Glen Fyne or the new, outstanding Glen Dee for midsummer. Follow these with Polka or Autumn Treasure which will fruit till the frosts come. Both have bigger fruit and spineless canes than the standard Autumn Bliss.
Q. My pansies in tubs are trying to flower but the leaves seem to be infested with small greenfly. How do you control them?
Pansies are liable to greenfly infestations, but these are easily controlled with an insecticide spray designed for greenfly on roses. Choose a windless dull day and give the leaves a good soaking. Make sure the plants are not allowed to go dry and give a feed once a month.