Monty Don’s gardening tips: Camellias are prone to all manner of problems but …

By
Monty Don

PUBLISHED:

16:30 EST, 5 April 2013

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UPDATED:

16:30 EST, 5 April 2013

Scores of letters arrive in my mailbag each week from many of you, and although I only have space to answer three at a time, I do assure you that each and every one is read.

So I cannot help but note the pattern of the kind of things that you feel are troubling you most in the garden, and one of the questions that recurs again and again at this time of year is about camellias.

They are an enormously popular plant and lots of us grow them, so it is not surprising that they feature, but the problem of sooty mould lands on my desk as regular as clockwork.

So, let me start with solving the mystery of the black, sticky soot that can appear on the surface of camellia leaves.

Camellias are prone to all manner of problems. Don’t fret, says Monty Don, they can be cured…

The ‘soot’ is a mould that is a symptom rather than a cause of the problem.

This is because it grows on the sticky excrement, known as honeydew, dropped from an aphid or scale insect attached to the underside of a leaf above.

The best treatment is to get rid of the honeydew by getting rid of the offending insect, and the best way to do this is to wash the leaves with washing-up liquid and warm water. Spraying the shrub regularly with water from a hose will dislodge any returning insects.

ASK MONTY

Q. My drain has been damaged and I think the roots of my leylandii are to blame. Is there a law on the height of these trees?
Mr J Worthington, Macclesfield, Cheshire

A. A Leyland cypress will have roots that spread about a third to one half its height. However most of these roots will be slender and not very woody so are unlikely to break a drain. The law says an evergreen boundary hedge cannot exceed 2m (6½ft). There is no restriction on individual trees.

Q. My son has blight on the crops in his greenhouse. What can he do?
Mrs Emily Stubbs, Manchester

A. The most important thing is ventilation. Only water in the evening or first thing in the morning and open the greenhouse wide from early in the morning to late evening, trying to keep a temperature of about 12-25°C.

So much for that problem, but although unsightly, it does not deter from the lovely flowers that are at their very best in gardens across the country right now.

Mind you, where I grew up, in Hampshire, camellias were extremely rare because they do not like chalky, alkaline soil, thriving best in an acidic soil with a pH between 6.5 and 5.5.

They like to get their roots into a loose, open soil, so add plenty of compost (although not mushroom compost, which is alkaline) before planting to allow the right balance between water retention and free drainage. If your soil is too alkaline the leaves will start to show distress by turning yellow. If in doubt, a thick mulch with composted pine bark or needles or composted bracken will help maintain the pH balance.

Although most camellias are pretty hardy, and the smaller-leafed williamsii group are especially so as well as having the advantage of dropping their spent flowers rather than leaving them to wither messily on the tree, they should not be planted on an east-facing wall.

This is because the bright sunlight that usually follows a freezing night will thaw the frozen tissues of the flowers and buds too quickly and can destroy them. The same plant can happily be grown on a west-facing wall, which will be just as cold but will thaw much more gradually.

I receive a lot of letters wondering why it is that camellia buds drop off in spring. The reason is usually because the shrub has not had enough water the previous autumn when the buds are forming – this is especially true if they are growing in a container. Give the plant a good soak each week, ideally using rainwater, which is slightly acidic.

The best time to prune camellias is just before the plant starts to grow in spring, which is just as the flowers finish. Train young plants to have one central stem, leaving the first foot or so bare to get ventilation around the bark.

Next year’s flower buds will form on the initial spring growth, and although there might be a second burst of growth during midsummer, this will not produce any more new buds.