BBC Radio 4’s Gardeners’ Question Time, which is aired on Fridays and Sundays, attracts two million listeners each week — BBC Gardeners’ World has the same number of viewers — and its influence on horticultural spending habits is immeasurable.

But just how prepared are the panellists for the onslaught of questions?

For the first 47 years, the team were shown the questions in advance, but that tradition was dropped in 1994.

Nowadays being a panel member is not for the fainthearted but for those with a depth of gardening knowledge and an incisive grasp of a question.

Regular panellist Anne Swithinbank says: “We don’t get to see the questions ahead of the recording, but they are screened and selected by the producer and chairman. If they weren’t, I suspect it would be how to cope with slugs and snails, how to get rid of ground elder and how to prune wisteria every week.

“We are often asked to recommend plants for specific sites and another common one is why some plants refuse to flower for their owners.

We get asked a lot of questions about grape vines, figs and, strangely, rhubarb.”

Chairman Eric Robson adds: “The most common problems are slugs, snails and the getting rid of them. Female panellists always have the most gruesome methods of killing and disposing of them.”

They’ve been faced with some extremely unusual questions over the years.

Swithinbank recalls being asked: ‘If I was a tree, what sort would it be and why?

And what trees would the other panellists be?’ “I said ‘I suspect I’m more like a spreading shrub with rather jolly flowers, but wishfully thinking, would like to be a tree of heaven – sort of heavenly but rather high maintenance (this tree puts out suckers). Or a pencil-thin Italian cypress (Cupressus sempervirens)’.”

Robson recalls the panel being asked about the effectiveness of grow-lights.

“Unfortunately, the questioner was a prison inmate (we were recording at Leyhill Open Prison) and he wasn’t interested in growing cucumbers.”

Fellow panellist Matthew Biggs said that often the last questions are humorous. He was once asked, ‘What would you save from your burning shed?’ All agree that, however, much gardening knowledge they have, they still get nervous before a live show.

Mr Robson said: “Even after 16 years in the chair, the adrenaline runs before each show. After all, it’s a big responsibility chairing one of the longest running broadcast programmes in the world – 63 years and still going strong.

“As the then controller of Radio 4 said to me when I took over, ‘You realise this isn’t just a job. We’re actually handing you the keys to Middle England’.”

Best of the bunch – Hardy geranium (Cranesbill)

IF YOU want a perennial which is going to give you so much valuable ground cover that weeds won't stand a chance, then the hardy geranium is for you.

These tough perennials come in an abundance of colours, are long-flowering and require very little attention.

Some will live quite happily in dry, shady spots including G macrorrhizum Ingwersen's Variety or G gracile. Among the most rewarding are G Johnson's Blue, which produces masses of blue flowers, while G oxonianum Wargrave Pink bears pretty pink flowers from May to September.

Buy them as young plants in small pots and they will soon grow into sizeable clumps which can be lifted and divided every few years. Good plant partners include those with a strong architectural outline, such as tall alliums, irises and phormiums. Hardy geraniums are generally troublefree, but can be cut back in midsummer if they start to look tatty and may flower again.

What to do this week

● Thin direct-sown seedlings of annuals and vegetables.

● Continue to tie in new shoots of climbers.

● Take semi-ripe cuttings of passion flower and oleander.

● Plant out leeks, self-blanching celery and marrows.

● Plant canna lilies outside.

● If you want extra large rose blooms for cutting, remove any buds developing at the side of the main terminal bloom on each shoot.

● Pick small gooseberries to thin out heavy crops, leaving remaining fruits well spaced out.

● Introduce new fish to your pond and start feeding fish more often as the weather warms up.

● After pruning, give shrubs a generous soak with liquid feed and cover the soil around them with a mulch.

● Apply a nitrogen-rich feed to lawns which are looking pale and sparse.

THREE WAYS TO...diagnose lily problems

1 Lily beetles, which are bright red measuring up to 7mm long, with black heads, appear on lilies from early spring onwards and eat the leaves, flowers and seed pods, effectively ruining plants. In midsummer the orange-red grubs also appear. The best solution is to pick the adults and grubs off by hand.

2 If dark green, water-soaked spots appear on the leaves, which turn brown and die off, withering from the base of the stem upwards, it's likely to be the fungus Botrytis elliptica, which produces spores that are spread on air currents and by rain and water splash. Remove and dispose of infected leaves and the top growth if necessary. Bulbs from infected plants can be kept provided they show no signs of rotting.

3 If the foliage shows yellow mottling and streaking, the plants are stunted and the flower buds fail to develop, it may be due to viruses such as tulip-breaking virus, lily mosaic and lily mottle. There is no control available, so you just have to remove all infected plants and spray against aphids, which may carry the virus.