Drought: How to Water Less and Water Better

In one minute

During drought, frequent light watering is not always the best answer. The aim is to help plants develop their roots, protect moisture in the soil and reserve water for the plants that genuinely need it. Before watering, it is also important to check any restrictions that apply in your local area.

When the garden needs water

The first signs can sometimes be misleading.

A leaf may droop during the hottest part of the day, then recover in the evening. Conversely, a plant may remain green even though the soil is already very dry deeper down.

Before watering, it is better to check the soil below the surface. A finger, a small trowel or a piece of wood can help you see whether moisture is still present around the roots.

This simple check helps avoid watering out of habit rather than necessity.

Why light watering can weaken plants

Very shallow watering mainly moistens the top few centimetres of soil. Water there is more exposed to evaporation, and roots may remain concentrated close to the surface.

When it suits the plant’s needs and the nature of the soil, deeper watering encourages roots to explore a larger volume of soil.

But one poor rule should not be replaced by another: clay soil, sandy soil, a potted plant, a young tree and a Mediterranean plant established for several years do not need to be watered in the same way.

The right approach is to adapt:

• the amount of water;
• the frequency;
• how quickly the water is applied;
• the area actually being watered;
• the depth the water reaches.

Drip irrigation can reduce losses by delivering water directly near the roots, provided it is set up correctly.

Water at the most useful time

During the hottest hours, some of the water may evaporate before it has penetrated the soil deeply enough.

Morning watering is often preferable: plants have water available before the heat builds, and any foliage that becomes wet has time to dry.

Evening watering can also be useful in some situations, but foliage that stays wet throughout the night may encourage certain diseases. Whenever possible, it is better to water at the base of the plant rather than over the leaves.

During periods of restrictions, permitted watering times may be set locally. In France, measures vary across four levels — vigilance, alert, heightened alert and crisis — and should be checked on VigiEau or with the local authorities.

Mulch: protecting the water already in the soil

Mulching is one of the most effective ways to slow the drying of the soil.

A layer of dead leaves, straw, wood chips or small twigs can:

• reduce evaporation;
• limit temperature fluctuations;
• protect the soil surface from crusting under heavy rain;
• slow the growth of some unwanted plants;
• gradually feed soil organisms.

INRAE notes that covered soil loses less water than bare soil. ADEME generally recommends spreading mulch over the surface rather than digging it in, and avoiding covering the crown or base of plants.

The depth and material should still be adapted to the situation. A layer that is too compact may hinder infiltration, retain excessive moisture or provide shelter for some animals close to vulnerable young plants.

Living soil holds water better

A garden’s resistance to drought does not depend on the watering can alone.

Compacted, bare soil may absorb sudden rainfall poorly. By contrast, soil that is protected, enriched with organic matter and crossed by roots and soil organisms generally develops a better structure.

Compost, decomposed leaves, dead roots and ground-cover plants all contribute to this structure.

The aim is not to create a perfect “sponge”, but to help water enter the soil, move through it and remain available for longer.

Choose plants suited to the place

A plant that is poorly suited to the soil or climate will require more intervention.

Before planting, consider:

• local rainfall;
• the type of soil;
• exposure to wind;
• the amount of sunlight;
• the space available for roots;
• winter temperatures;
• periods of extreme heat.

Local plants, or plants already well adapted to the regional climate, often need less water once properly established. ADEME recommends favouring water-efficient species suited to the local area rather than artificially maintaining plants with very high water requirements.

Lavender, rosemary, rock roses and some sages can suit dry gardens, but only where the soil, climate and winter temperatures are appropriate. A list of “drought-resistant plants” can therefore never replace observation of the site itself.

Young plantings remain vulnerable

A plant known for its drought resistance is not immediately self-sufficient.

While it is establishing, its root system remains limited to the root ball or planting hole. It may need regular monitoring for one or more seasons.

For a young tree, it is better to water a reasonably wide area around the root ball rather than pour all the water against the trunk. Applying water slowly also gives it more time to soak into the soil.

Watering can then gradually be spaced further apart according to root development, weather conditions and the actual state of the soil.

Collect rainwater

Rainwater can be used to water gardens, provided health rules and any local restrictions are respected. It should not be regarded as drinking water.

A water butt or tank connected to a roof can store part of the rainfall for drier periods.

This reserve remains limited, however: it does not remove the need to choose suitable plants, protect the soil or avoid unnecessary watering.