Tuesday 12 November 2019

Diarmuid Gavin: Drought busters

Plant pretty shade and drought-tolerant species to form a moisture-retaining mat beneath trees

Create 'a woodland' using ferns near trees and bulbs
Create 'a woodland' using ferns near trees and bulbs

Despite the occasional rainy week during the summer, our landscape has endured months of drought. Even in wet summers, the rain that falls doesn't always dampen the soil. In places where there is an overhead umbrella or canopy of leaves, moisture is spread too far from the roots of underplanting.

I've a ribbon of birch trees planted in my front garden acting as a curtain of foliage, screening us from the road for six months of the year. The conditions below these trees, despite occasional downpours, could be described as dustbowl. No quantity of rain manages to penetrate the ground and the normal species chosen for places of shade don't thrive. So if you've some of these extreme conditions in your garden, what plants will do well during the summer months with a lack of reliable moisture?

While many plants will grow happily in moist shade, the combination of poor light and dry soil is a real challenge. This could be at the base of conifers, at the bottom of an old wall facing north or under the full canopy of deciduous or evergreen trees in the height of summer. There are ways of alleviating this. Try to improve the soil by adding compost, soil conditioner or well-rotted manure. This will help build a good structure, and the addition of humus material will aid retention of any available moisture.

If you are trying to plant in the ground beneath established trees, be aware of their shallow roots. Use small plants that you can tuck into the gaps between roots. Try to avoid slicing through them with a spade but don't panic if you sever one, as it will most likely regenerate.

As juvenile plants establish themselves, they will find their way around the root system. Choose plants potted in a soil-based compost, as peat dries out very quickly. This can be a challenge because most nurseries and growers use peat-based composts.

Wait until early autumn to plant so new plants can settle in while there is moisture available. Water in well and spread mulch between them. You'll also need to keep an eye on them in summer, and water if you think they're suffering. For best results, install simple irrigation such as laying a seep hose to leak water into the surrounding soil.

What to plant? Choose species that tolerate shade and drought, that will colonise and form a moisture-retaining mat. Epimediums are great - they have attractive foliage and in spring bear pretty delicate flowers; 'Sulphureum' has beautiful yellow blossoms. Cut back dead foliage in spring, taking care not to snip off budding flowers. Vincas or periwinkles are great at forming mats in dry conditions and have an abundance of white or mauve flowers in spring.

Ferns (pictured) go beautifully with trees to form woodland-like gardens but you do need to be careful in your choice, as many ferns require moisture. But some of our native evergreen ferns will do very well in dry shade: Asplenium scolopendrum (hart's tongue fern), Polystichum setiferum (soft shield fern) and Polypodium vulgare (the common polypody). You will still need to water them in until they get established but they are very drought-tolerant once they are - you sometimes see them growing out of walls as well, so they're not fussy about soil requirements.

Bulbs pair well with ferns and I've found the dwarf daffodil 'Tête-à-Tête' and native bluebells very resilient in the dry soil under my birch trees. You may also try Cyclamen hederifolium (ivy-leaved cyclamen) here - not just for the bright flowers but also attractive foliage - and some Anemone nemorosa (wood anemone) bulbs this autumn (give them a soak before planting).

I'd also recommend hardy geraniums such as Geranium phaeum 'Album', which rapidly forms gentle mounds covered in white flowers to brighten up the shadiest spot. G. macrorrhizum are superb at forming clumps in dry conditions - 'Bevan's Variety' will produce lots of pink flowers and remains semi-evergreen over winter. Flower arrangers could also chance popping in some Alchemilla mollis (lady's mantle), whose fresh foliage and sprays of tiny lime green flowers are always a winner and will happily self-seed into available gaps.

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