Peter Gibbs is in the chair for this edition of Gardeners' Question Time, recorded in Surrey. On the panel this week, tackling horticultural questions from the audience, are Chris Beardshaw, Pippa Greenwood and Bob Flowerdew.
Produced by Howard Shannon
A Somethin' Else production for BBC Radio 4.
Q: How can I grow a Gunnera manicata? I have tried and failed. How long will it take to grow it to around five foot?
A: Gunnera manicata are from South America and therefore like plenty of warmth, sunlight and nutrient-rich wet soil. They grow to the size of the space in which they are planted so to grow a large one you will need a hole of at least a cubic metre in size, and it will take around three to four years if you encourage it with plenty of fresh manure in early Spring.
Q: When buying a climber such as a Clematis, should I cut it free of its plastic binders or not?
A: The plastic binders can be quite ugly and often have a sharp staple holding them in place. You can plant the Clematis and then replace the plastic binder with your own, for example foam-covered wire or wooden clothes pegs. It needs monitoring because, if you leave the binding on too long, it can restrict the growth of the plant.
Q: I have a bed of small and large leaf Bergenias, the small leaf varieties have developed large brown blotches which spread and eventually kill the leaves. Is the plant dying or can I treat it? It only occurs on the small leaf not the large leaf.
A: You can get brown blotches from cold winds or very hot sun and moisture, but you can see some ringing on this leaf which shows that it is a fungal problem. As soon as you see an infected leaf you should cut it off to stop it spreading. You should then mulch well, in April or May, to encourage new growth that should shake off the infection.
Q: I have a Witch Hazel Jelena and last winter it did not carry any flowers, though it did in previous years. What can I do to help it flower?
A: It is not unusual for them to go through a period of growth without flower before they put on any further substantial flowering periods. If all other conditions are good, do not feed it or prune it but leave it to grow and it should be back to full flower within two to three years.
Q: How can I grow celeriac to a decent size?
A: Celeriac needs starting-off inside in the warm with a wet, rich compost. When planted out it needs a rich and moist soil too. Once it gets to the size of a ping-pong ball, pull off the lower/older leaves at the bottom to encourage growth.
Q: How do I sow and grow Meconopsis (the Himalayan poppy) seed?
A: Getting them started is the most difficult thing. Use about five times as many seeds as you want to germinate - many will die-off. Then if you keep the surviving Meconopsis in acid soil with plenty of organic matter, water and dappled shade, you have the best chances of them flowering.
Q: How can I economically grow brassicas? They are attacked by slugs, cabbage white butterflies and pigeons!
A: Use slug traps and salty water to keep the slugs off, and fine mesh netting or fleece to stop the butterfly and pigeons.
Q: In 1960 we planted a bottle garden in a carboy. The bung has not been out for thirty years, but the Tradescantia just carries on. Will it last forever?
A: It is a great example of the way in which a plant is able to recycle because the only external element added to it has been sunlight. It should continue to last as long as it is not put in extreme conditions like strong sunlight.
Mahonia in bloom
Kept in its jar since 1960, this Tradescantia has not been opened to the outside world in thirty years but still continues to thrive!