July 13, 2006

All my dahlias survived this past winter left in the ground, some protected by large, black, plastic, upside-down flowerpots or glass cloches, and others not. I put this down to the fact that I have well-drained soils in my borders, meaning that they are spared their greatest threat: having to stand with their tubers sitting in cold, damp ground over extended periods. Had my soil been clay, no doubt they would have perished. My mixed borders would be all the poorer without them, for the invaluable colour they provide in mid to late summer.

Another most welcome plant is the bamboo phyllostachys for the main reason that it does not rampage about the garden but remains a neat clump. I have the yellow stemmed species Phyllostachys aurea, and the black stemmed P. nigra, both of which have been given the Award of Garden Merit by the RHS. Such plants are listed in the booklet AGM Plants 2004?5, published by the RHS (and available at Wisley Gardens, 01483 211320) or you can read it, fully updated, at www.rhs.org.uk/plants/award_plants.asp. It is invaluable if you’re looking for plants that are of robust constitution, chosen for their ‘outstanding excellence’. However, my P. nigra is not looking at all well despite the fact that it is not flowering, a common cause of fatality among bamboos.

It is growing underneath a black walnut, Juglans nigra. I had heard that walnuts give out some sort of chemical through their roots that deter other plants from growing too near to their base, so I rang the RHS Members Advice Service to verify this. Apparently, the roots and leaves of walnuts contain phytotoxins in the form of juglone, and there exists evidence that these inhibit growth of many plants by impairing their nutrient uptake if they happen to be growing too close by. However, research has revealed that some plants, including dicentra, polygonatum, dryopteris, trilliums and viola, don’t seem to be affected.

This will not deter me from planting walnuts in the future; in fact, I now rather respect them for their ability to dispose of deeper-rooted plants that would otherwise deprive them of nutrients in the soil. They do, in any case, eventually grow into large trees, gaining as much as 100ft in height, and in the case of the common walnut (Juglans regia), 50ft in spread. I’ll only plant a walnut where I can give it plenty of breathing space, as a specimen tree probably surrounded by lawn.

Another thing I have learned is that there are certain ornamental trees that do not like a windy site. Owners of gardens with wonderful views, such as mine, have to pay for panoramic pleasures with gusty knocks. My Liriodendron chinense, having shown signs of ill health last year, gave one last burst with a rather sad display of undersized leaves and has now gone to that great nursery in the sky. But a cherished, rarely grown tree, Toona sinensis, a native of woodland in South-East Asia and Australasia, which Roy Lancaster recommended to me, is faring well. Because I am selling my house shortly, I won’t see its scented, greenish white flowers as it is still a young tree, a six year old. In my new garden, I am going to try T. s. Flamingo which produces vivid pink young leaves in the spring that then turn a creamy yellow before they settle down to light green.

On the subject of wind, my research has come up trumps when it came to the choice of climbing roses for exposed positions. On occasion, the wind blows fiercely because of a tunnel effect between some outbuildings, which I was determined to clothe in roses. Sure enough, the roses Cecile Brünner and Dortmund, bashed about as they are, show no signs of having suffered. The former has pink, double flowers of subtle scent in June and July that seem to have been ‘painted on’ in perfect distribution by a Victorian artist depicting a rural cottage idyll.

Dortmund produces generous amounts of single, strong red, unscented flowers and, if dead headed after the first flush, it bounces back with a similarly showy display in late summer. I agree with the sentiments of many gardeners who say they only grow scented roses, but Dortmund is so obliging in poor soils and exposed sites that it can prove to be a truly welcome friend.

This article first appeared in COUNTRY LIFE magazine on July 6, 2006