大象传媒

GQT reaches new heights with a programme at The Roof Gardens in Kensington, London. Eric Robson is in the chair with panellists Anne Swithinbank, Matthew Wilson and Bunny Guinness taking the questions.

Bunny explores the history and structure of The Roof Gardens, Kensington and Matthew visits a project at London's Southbank Centre where roof gardening is being used as ecotherapy for people who have suffered from homelessness.

Produced by Victoria Shepherd
A Somethin' Else Production for 大象传媒 Radio 4.

Q: I'm going to leave London in the next ten years. If I could choose to move anywhere in the UK on the basis of soil quality and local climate, with an aim to grow a wide range of species, where would be best to move to?
A: The Roseland Peninsula in Cornwall is very mild and sheltered and can grow huge oak trees. It has an acid soil and can grow a large variety of plants including Camellias and palms. However, you will never really satisfy all species so you would be best to choose a smaller selection of plants that would grow well together and find a climate and soil that suits them best.

Q: I was told when I planted a prairie garden that it would be three years weeding, then sit back and enjoy. It is now the fourth year and no sign of the weeding stopping. What can I do to get the grasses and perennials to spread and bulk up?
A: You can do it in less than three years. The main thing is to get the soil right before you put the plants in, so if you planted into a huge seed bank of weeds it will be hard to eliminate them. The best way to do it is to plant from seed at a really high-density, which will stop weeds being able to grow and you can remove the few that do get through. After four years you should have lots of material that you can divide, so you should be bulking up. As we're moving into the autumn it's the ideal time for dividing flowering perennials, but leave the grasses until spring. You could also give the weeds competition with a cover crop of direct-sown annuals sown in the autumn such as Aquilegia, Nigella, Eschscholzia and even some of the cornfield weeds like Agrostemma.

Q: Does the panel have any tips to mitigate obtrusive traffic noise from the road by our back garden? We already have a 6ft (1.8m) wooden fence and a 10ft (3m) conifer hedge.
A: To be honest the conifer hedge won't do a lot. You can buy soundproof fencing that has a high insulation factor, but you need to make sure you place it correctly and it can be worth contacting a sound engineer to help with this. Running water works by deflecting the sound. A compact hedge on a bank can also help. Using plants to try and baffle the noise of large roads is generally unsuccessful because you need the plants to be very dense and most people have not got space. Creating something like a water feature in the foreground is a good way to distract your attention!

Q: My daughter wanted to grow and apple tree. People said she wouldn't get any apples unless it was grafted. After about 20 years we got lots of apples, but it is now too tall to reach the apples. If it could be cut down to about 6ft (1.8m), would we kill it? If not, how long will it live for? It's about 45 years old.
A: Apple trees will produce apples if grown from seed and it will also grow upwards very quickly. If you cut it down to 6ft (1.8m) it is likely to be too brutal and you won't get healthy growth, but just lots of thin water shoots. You could do a prune in January/February when the worst of the weather's gone, then follow up by pruning in early summer to remove growth tips. You could then summer prune it heavily to reduce the vigor and it should grow back. You may have a few years without apples but they should return. Finally, you could ask someone to create a dwarfing stock for you from a graft.

Q: Can you tell me why every houseplant I have dies on me?
A: Positioning is key. Most houseplants like good but not direct light, so finding somewhere not in harsh sunlight but not in a dark corner is the first step. You need to make sure you analyze where is best for each plant individually. You also need to make sure you get the watering right. Most of them need to feel as though they're almost drying out at the surface of the compost before you water again. You can water from the top, but be careful not to over water. Houses that are hot and dry with central heating generally don't help houseplants.