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Drought Tolerant Planting

The summer is fast approaching and if you're still choosing new planting for your garden, it’s important to select plants that work well in this climate here in South West France. Even experienced gardeners can be caught off guard by the extremes of our winters and summers, so don't assume that because a plant worked well in your garden in the UK it will be OK in the Midi Pyrenees.

Over here, the summers are long and dry, so for a low maintenance garden, it’s advisable to select drought-resistant plants, which, after an initial period of being watered-in, can survive without irrigation.

All plants need water, of course. Water is essential to all living things, and in plants it’s required for photosynthesis, when plants convert the sun's energy into molecular energy, taking in sunlight, carbon dioxide and water and producing glucose and oxygen. It's also needed for transpiration, where water and minerals are drawn up through the roots and transported through the xylem vessels of the stem, up to the leaves, where water evaporates through the stomata (small openings in the leaf). Water also keeps plants turgid and erect. Without the endoskeleton or exoskeleton that keeps animals upright, vascular plants rely on turgor pressure to remain rigid and supported, and thus insufficient water results in drooping and wilting.

Drought-tolerant plants have built-in features which allow them to obtain sufficient water during our incalescent summers. A useful indicator is the leaves, and those that are succulent, silver coloured, hairy, small or needle-like are all useful in their own way, and are good indicators of a plant that will cope well with dry growing conditions, maximizing water uptake and minimizing water loss.

Succulents (from the Latin “sucus” - juice, or sap) have fleshy leaves, stems and roots, specially adapted for storing water. Examples include Crassula, Delosperma, Jovibarba, Sedums and Sempervivums. They all cope beautifully with extended hot temperatures and are very easy, low maintenance plants.

Many drought tolerant plants have silver or grey-green leaves, with their light leaf colour absorbing less heat and reflecting the harsh rays of the sun. Silver foliaged plants, such as Achilleas, Artemisia, Cotula, Glaucium and Perovskia, will all thrive in full sun, and their pleasing foliage is versatile in planting schemes as it can both help tone down bold, hot colours, and harmonize with softer, cooler colours.

Some plants have a coating of fine hairs on their leaves or stems, and these trichomes serve to trap moisture around the plant tissues. Salvia verticulata, Stachys byzantina, Sempervivum arachnoideum and Sempervivum ciliosum are popular examples that add sensory appeal to the garden.

Another way for plants to avoid excessive water loss is to have reduced leaf areas, with leaves that are either very small, or long, thin and needle-like. The reduced surface area tempers evaporation brought about by wind and sun, with fewer stomata resulting in less water being lost through transpiration. Such plants include Arenaria, Dianthus, Lavender, Penstemon pinifolius, Rosemary and Thyme.

Of course, is not just about leaves. Plant roots have the vital function of obtaining water from the soil and there are two categories of plant root systems: fibrous roots and taproots.

Fibrous rooted plants have a network of thin, branching roots. They are shallow rooted and obtain surface water. As such, they are more prone to drying out and thus may require additional irrigation. This doesn't mean you have to dismiss all shallow rooted plants though, as some of them possess the leaf qualities previously discussed. Shallow rooting plants such as Sedum, Phlox subulata and Phlox douglasii, can be useful additions to our French gardens, especially in such situations as rocky terrain with poor soil depth, or over a septic tank system, where you would not want to risk root penetration.

Tap-rooted plants have one dominant central taproot, with some lateral secondary and tertiary roots. Tap roots penetrate deep into the ground and can therefore access underground water stores when the surface water is depleted. Plants such as Acanthus, Euphorbia, Poppies and Verbascum all have tap roots and do very well over here, coping with periods of drought.

One thing all drought tolerant plants don't like is excessive water. As the winters here can be very wet it’s important to ensure that your soil has good drainage, drought resistant plants will not survive a winter in clay soils. Drainage can, of course, be improved by digging in plenty of organic matter and horticultural grit. 

 

John and Debbie Wilson

www.lejardindesespiemonts.fr    05 63 64 68 76

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