Our experts tackle your gardening queries, including chemicals in manure, mollusc-munched cannas and a maggot with the tail of a rat
Anne Swithinbank
A keen fruit, vegetable and house-plant grower, Anne was formerly the glasshouse supervisor at RHS Garden Wisley.
Ashley Edwards
As a head gardener with charity Horatio’s Garden, Ashley enjoys sharing his passion for plants.
Pippa Greenwood
Pippa is one of the foremost experts on pests and diseases. She gardens using organic methods.
Q What can go with summer fowers for a long display?
Ulrika Kuoppa-Jones, Oxfordshire
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ANNE SAYS I prefer to keep my dahlias separate, for a better chance of controlling damage to emerging growth by slugs and snails. You could lift the tubers just after the first autumn frosts and replant the spot with tulips in November. Store the dahlia tubers somewhere frost-free, pot up in spring and plant out at the end of May or beginning of June. Sow zinnias or Cosmos bipinnatus nearby.
Look out now for plants of biennials such as honesty, foxglove and Salvia sclarea to plant in place of annuals that are starting to run out of steam. The biennials will bloom from late spring into summer next year.
Interplanting is a lot of fun, so that instead of an area occupied by one plant type, you’ve mixed it up with perhaps astrantias, autumn-planted Dutch irises or alliums rising through in late May and, a little later, perennial veronicastrums or yellow Rudbeckia maxima.
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ASHLEY SAYS Choose lots of spring bulbs – they don’t take up much space. Snowdrops will herald spring, soon followed by Narcissus ‘Rijnveld’s Early Sensation’ and later Camassia leichtlinii Caerulea Group.
Polemonium ‘Northern Lights’ flowers again if cut back and is compact. If you have a back wall to this area, consider Rosa × odorata ‘Mutabilis’, which can be trained and will provide colour-changing flowers from summer to autumn.
Late-flowering grasses can be added, too – the dead foliage adds structure to the winter garden. Calamagrostis × acutiflora ‘Karl Foerster’ would be a good choice for a small border, with a spread of around 60cm, reaching about 1.8m in height. Rudbeckia ‘Goldsturm’ will put on a fantastic autumn display, the yellow flowers catching the low evening light. For winter, choose slow-growing and graceful Mahonia gracilipes.
Q My well-watered bulb onions are not growing. Why?
Bob Sinclair, by email
A PIPPA SAYS From what I can see t
