Mrs Smith of Beaminster in Dorset has asked for advice about choosing trees and other plants that will be able to survive what she calls 'the new climate'. She had been particularly upset by the obvious distress of her Cornus controversa ' Variegata' in this hot, dry summer. I wrote half an answer to her letter last week, stressing that where a plant was situated and how and when it was planted were also important factors in whether it was likely to survive through a period of drought. The nature of the soil itself is critical, as is mulching the ground liberally now, while it is still saturated with autumn rain. If we provide plenty of humus, which acts like blotting paper, the plant will have a reservoir to draw on next summer. If we don't, it won't. Planting in autumn rather than spring and mulching the ground are simple, practical strategies, which are effective. Trying to second-guess nature is not.
Anyone who has holidayed in Italy, Spain, the south of France or Corsica (where we were this summer), sees plenty of evidence of trees and shrubs that survive droughts far more severe than anything we had this last summer. Sweet chestnuts thrive in the mountains in Corsica, growing in rocky, poor soil that seems scarcely capable of supporting a blade of grass, let alone a tree. Australian eucalypts are survivors too, though they are bullies, fast outgrowing the space that gardeners intend for them. They need regular and brutal pruning.
But the problem with Mediterranean plants is that, although they will survive drought, they will not necessarily survive our wet winters, which forecasters say are likely to get even wetter. Masses of grit in the planting hole helps; it provides drainage in winter and forces plant roots to grow a more extensive network to find food and drink in summer.
Cotoneasters are persistent, as are hollies of all kinds. Rhus (the sumach) throws up suckers, which can be a nuisance, but a newly planted Rhus typhina ' Laciniata' with elegantly cut, ferny leaves, looked fresh in our new garden all summer. In autumn, the leaves turned wonderful shades of yellow and orange. The pea tree Caragana arborescens survives in hot dry sites and has yellow pea flowers in late spring. The foliage is like a willow's and if you look for the form 'Pendula', you'll have something that looks like a small weeping willow, the branches usually grafted on to the top of a five-foot stem.
The first shrubs to flag in our garden this summer were the lacecap hydrangeas. The first herbaceous plant to wilt was my favourite loosestrife, Ligularia przewalskii - tall spires of yellow flowers on black stems above jagged, dramatic foliage. In both cases the fault was mine. I was trying to find shade for the hydrangeas (shade being in short supply in our garden) and planted them where they would be sheltered from the sun by coppiced stands of hazel. But I did not prepare the planting holes well enough. They did not have enough blotting paper. And the loosestrife family are known to like ditches and other soggy places. But they grew well without either in our last garden and I thought I could risk them again. All gardeners try to push the bounds of possibility. But even though I did give them masses of humus, it didn't fool them. Sadly, they'll have to go.
But cistus is well used to heat, as are other Mediterranean natives such as lavender and rosemary. I've found the latter more tolerant of winter damp than the former. Greys, such as the shrubby artemisias, round-leaved ballota, the neat, white-flowered Convolvulus cneorum, Dorycnium hirsutus, covered all over with silvery hairs, santolina and senecio will all do well in scorching sun. Brooms, such as the Spanish broom, Spartium junceum, understand it too. The Spanish broom needs some managing, though. Left to itself, it gets tall and leggy. You need to cut it back each spring, trimming only the new, green stems. Like several of these Mediterranean subjects (lavender, for instance), it won't produce new growth if you cut into old wood.
Russian sage ( Perovskia atriplicifolia) also needs hard pruning to look its best. It's not Russian, nor is it a sage; it's an aromatic subshrub from Afghanistan and Tibet that's generally treated like a herbaceous plant. The top growth is best cut down each spring to the base. The stems are greyish-white and the foliage is toothed, coarse, but shows the same grey-white on the undersides of the leaves. It's a useful plant because it performs at the end of summer, producing long wands of misty blue-mauve flowers during August and September. 'Worth a place in the choicest garden for its graceful habit and long season of beauty,' wrote the Edwardian plantsman, William Robinson, who never gave praise where it wasn't due. It was a new arrival when he wrote about it, first introduced into this country in 1904.
Caryopteris is similar in many ways, but more definitely shrub-like, wider, but not so tall as Russian sage. Both like good drainage and do best in full sun. Caryopteris has brighter flowers, particularly in the variety 'Kew Blue'. This is a seedling raised at Kew in 1945, a child of a cross-bred caryopteris raised in the Thirties by Arthur Simmonds at West Clandon in Surrey. Like perovskia, caryopteris needs to be cut hard back in spring.
So there are plenty of plants that can survive drought. As well as the above, Mrs Smith could try abelia, buddleia, ceanothus, elaeagnus, fremontodendron, any of the rock roses (helianthemums), mallows, mock orange - which is surprisingly tolerant of drought - phlomis, potentilla, the gorgeous papery-flowered Romneya coulteri (it romps away when it's happy, but is tricky to establish initially), sage of various kinds and tamarisk. But not all will survive long periods of below-zero temperatures in winter. And not all will struggle through winter wet. That is the key. But we must garden optimistically and in the certain knowledge that whatever the future holds in terms of climate, plants will (in general) be better equipped to cope than we are.Reuse content