GARDENING - Box, variegated plants, a new yew, rhododendrons in clay, iris, mimosa

greenspun.com : LUSENET : Current News : One Thread

ET Thorny problems: the mystery of the pyramids (Filed: 18/08/2001)

Helen Yemm on box bushes, variegated plants and the new yew

Box pyramids

I have just bought in two box pyramid trees, and would like some advice on how to keep them in good condition. I plan to keep them in tubs surrounded by seasonal plants, on a west-facing patio. Jill Kent, Walton on Thames, Surrey

MAKE sure your box bushes are kept nicely moist in the summer, but don't feed them much - box looks better and is more dense if it grows slowly.

They would do better on their own in the containers, partly for aesthetic reasons, but also so that they do not have to compete for root space and water.

Indeed, slightly smaller, moveable containers might be better than large tubs, because you may want to turn the pots to catch the seasonal light, or even swap them around each year so that the plants do not lose their all-important symmetry. Trim them in early summer and again in August if necessary. I always use kitchen scissors on small topiary.

There is little you can do about the "box blight" that has devastated some gardens, except keep your fingers crossed and your scissors or shears clean.

If you find a white insect in the shoot tips, it is box sucker and is controlled by clipping, although you can spray it with BugClear.

Reversion aversion

When we replaced our fence, we had to cut a huge, large-leafed variegated ivy right back. It has grown again, but is now plain green. Once it gets over the shock, will it become variegated again? Jean Cooke, Radlet, Herts

It may help to understand that variegated plants are effectively accidents of nature that have been specifically bred to make attractive garden plants - although many people disagree that they are attractive.

Many plants that have been bred to be variegated - from evergreens, such as elaeagnus and euonymus, to fuchsias - try to revert back to their "original" green form at the drop of a hat.

The plain green forms of any plant have leaves that contain more chlorophyll - the substance that turns sunlight into growing power - and are invariably more vigorous than the variegated forms. Thus, once the green breaks through, the entire plant will, over time, revert to its natural green. Your ivy will not become variegated again by itself. You could try cutting out all the green shoots at source - repeatedly if necessary - and letting only the variegated shoots grow.

Or you could start again with a new plant.

A new yew

My three-year-old yew hedge is now nearly 6ft high, putting paid to the idea that yew is slow- growing. I have so far not pruned it. I want the finished hedge to be about 6ft 6in high. Do you have any advice about pruning new yew? Madeleine Field, Marlow, Bucks

It is remarkable how the myth about yew taking forever to grow is stuck in our gardening consciousness. You are right: contented yew grows surprisingly fast.

The thickest and quickest yew hedges are generally planted in a staggered double row, each plant about 2ft apart, and will rapidly make a dense screen.

To encourage yew to develop this wonderful density, you should start trimming it now. Take about 6in off the top, to encourage plenty of soft, new top growth, and perhaps 3in off each side.

For immature hedges, the best time to prune is mid-summer. Fully grown hedges are usually pruned in August.

Rhododendrons in clay

On both economic and environmental grounds, I am wary of following the advice I have been given on how to improve the vigour of my rhododendrons, which are planted in heavy boulder clay - that is, to dig peat into the soil to a depth of about 1ft. Is there an alternative? Colin Brown, Chelmsford, Essex

The best thing for your unhappy rhododendrons is a thick annual mulch of "gardener's gold" - leaf mould.

Rhododendrons are plants of the forest floor, thriving in the dappled shade and rich, rotted leaf litter of deciduous trees, where the soil is cool. So, anything you can do to fool them into forgetting they do not like your clay will help.

Peat was always the traditional mulch for them, but this, while having the correct acidity, does nothing to feed them - and, anyway, we are now much more aware of the environmental impact of peat extraction. Composted bark is similarly "non-foody", but would make a good, moisture-retentive substitute.

Rhododendrons are relatively compact and shallow-rooted plants. Depending on the size and site of your plants, it may be worth digging them up and improving the soil in a wider area with masses of organic matter, before replanting them.

Your clay may be cold or waterlogged in winter, so improving drainage might have an impact on their welfare.

Quick questions . . .

Kenneth Gubbins, from Tonbridge, Kent, wants to know what to do with a clump of December-flowering Iris stylosa (aka Iris unguicularis) that is a little exhausted, having given him loads of pure sky-blue pleasure every winter for the past 20 years.

The entire mass should be lifted in September, and the best rhizomes planted in small clumps a few inches apart, about 1in deep. They are unlikely to flower this year, since they will be resentful of the disturbance - but, Kenneth, a man's gotta do what a man's gotta do.

John M Tuohy emailed to ask advice about his strapping 5ft tall - but non-flowering - mimosa, which, after spending last winter in a pot outside, died back to ground level.

Next winter, bring the pot in out of the cold and wet. I do not know where you emailed from, but unless it was the extreme south and/or you have a particularly sheltered and sunny town garden, it is unlikely that our winters are mild enough and our summers long enough for your mimosa to flower well outdoors. (Cue 50 readers sending me snapshots of their flowering mimosas thriving in Force 10 gales in the Cairngorms . . .)

Write to Thorny Problems, Helenyemm1@aol.com or The Daily Telegraph Gardening, 1 Canada Square, London E14 5DT. Helen Yemm regrets that she can answer letters only through this column.

-- Anonymous, August 21, 2001


Moderation questions? read the FAQ