This week Eric Robson chairs Gardeners' Question Time from Stilton in Cambridgeshire with Bunny Guinness, Bob Flowerdew and Matthew Wilson taking the audience's questions.
Produced by Howard Shannon
A Somethin' Else production for BBC Radio 4.
Q: What low-growing, low maintenance, perennials can you suggest for year-round colour in alkaline soil?
A: Clematis Arabella would go well, Geranium Rozanne ('Gerwat') often flowers through to December and is very hardy. Lavender would just need trimming back once a year and would be likely to thrive.
Q: I have a thirty-foot Eucalyptus tree. How big will it grow, will it start to damage surrounding shrubs and should I trim it?
A: They can be very dangerous anywhere near a house, because the branches will often snap-off in the wind. They can also grow to two or three times this height. It is recommended you either remove it or chop it down to ground-level and encourage it to become a shrub.
Q: My tall plum tree has lost most of its medium-height branches through heavy cropping. The top branches are too high to be useful. Is severe-pruning the answer or would this kill it?
A: Given the condition that it is in, your options are limited. Prune one side drastically one year in the middle of summer, and the other side the following year to bring it down to about half its current height. This should provoke a strong flush of growth.
Q: Should you prune blueberries growing in large pots, and if so when is the best time?
A: Blueberries do not need a lot of pruning if grown in a pot because their growth is restricted. However, they do tend to over-crop so you should remove the oldest growth when it is dormant.
Q: I planted a Gleditsia triacanthos 'Sunburst' twenty-eight years ago in my garden and it had grown to be a very large tree. I have brutally trimmed it this year, but what should I do now to make it look more attractive and will it grow again?
A: Gleditsia can take a hard prune, but this one has been very severe. It might grow back, and if it does it will have a huge amount of fresh short spurs. These may be on the trunk as well as the branches and will probably look quite odd. It would be best in this case to remove the tree completely.
Q: I have two Bramley Apple trees which fruit well, but in Autumn when the fruit is picked brown spots are found under the skin. What is the cause and what can I do?
A: It is likely to be Bitter pit which is caused by calcium imbalance or a lack of calcium. Mulch around the trees as this will increase fertility, as well as using fertiliser in the spring time. You could also spray regularly with seaweed solution.
Q: I have a grapevine in my backgarden. How should I prune it and should I feed it? It is currently growing upwards rather than along my pergola.
A: You cannot over-prune an established grapevine. You should remove most of the young shoots back to just stubs around a few inches long, with a couple of buds on them. You can take out old branches completely if there's a new one to replace it. The harder you treat it, the fewer bunches will grow which will encourage the bunches that do grow to swell and taste much sweeter. There is no need to feed a grapevine because in the UK the soils are generally too rich and wet, so keep fertility away from it.
Q: Some plants simply will not grow for me, though they grow like weeds for other people. These include Winter Aconites and Alchemilla mollis. Have the panel any admissions of their own to make?
A: Bunny has previously struggled with the Daisy Erigeron karvinskianus which generally flowers for nine to ten months of the year. Matthew has recently struggled with Rudbeckia fulgida var. sullivantii 'Goldsturm'. And Bob has struggled with getting a crop from many plants even if they grow, including Paw paw Asimina triloba and Lychee from seed.