Drought-tolerant does not mean doing without watering

A drought-tolerant plant may need watering during establishment and may lose ornamental performance when water is very limited. Tolerance when mature, survival, growth and flowering are different levels. Promising a garden with no watering ignores soil, climate, the size of the plant and the establishment period.

Transplanted trees and shrubs depend at first on the rootball and the nearby soil. Only after they have sent roots out into the surrounding volume can they draw on water with greater autonomy.

Mature specimens create immediate impact, but they also require a rigorous establishment programme, adjusted to the season, the species and the dimensions.

A plant can close its stomata, reduce growth, lose leaves or abort flowers in order to survive. If the aim is shade, flower or fruit, the water regime should sustain that function.

Research on ornamentals shows that watering influences floral resources and visitation.

The design should define hydrozones, soil cover, watering depth and criteria for reducing frequency after establishment. Deep watering at longer intervals can be more suitable than wetting the surface every day, depending on the soil.

Monitoring should look at moisture, new shoots, wilting, growth and dieback, avoiding fixed calendars with no reading of the ground.

A mature tree arrives with a crown and a rootball far larger than those of a young plant. The visual benefit is immediate, but so is the potential loss through stress. The volume of water, the frequency of inspection and the protection against wind should be defined for the real specimen.

The reduction in watering should be based on root expansion and on the behaviour of the crown. A fixed calendar of one or two years may be insufficient in difficult soils or excessive in favourable conditions.

The most common mistakes are stopping watering straight after planting; watering little and shallowly; using the expression ‘no water’; and assessing only whether the plant is alive.

At Diaplant, establishment watering is defined by size, rootball, soil and season. The reduction is progressive and depends on real establishment, not just on a reputation for drought resistance.

Low watering is a design goal that is reached after establishment. It is not an automatic property printed in the name of the species.

• Relating the climate envelopes of urban tree species to their drought and thermal tolerance. (2021).
• Functional traits are better than climate niche approach at predicting the vital growth and mortality rates of urban tree species. (2026).
• Plant origin and irrigation influence floral resource value and pollinator attraction to ornamental plants. (2026).