Drought doesn’t end when the rain arrives. The soil remembers.

After hot days, rain quickly changes how a place feels. The air is more comfortable, surfaces are wet and the garden looks refreshed. But none of that tells us how much water has reached the roots.

Here, ‘the soil remembers’ is a metaphor for the soil’s existing condition and water reserves. It doesn’t mean that all dry soils repel rain, or that every tree recovers at the same rate.

How much falls, and how much stays

What happens to rain depends on its intensity and duration, the soil, the slope and the surface cover. Some water enters the soil, some runs off and some later returns to the atmosphere. Soil that is already saturated may take in very little additional water. These relationships are explained in the USGS overview of infiltration.

Why this changes the design

Designing a terrace, path or parking space also determines where rain will go. That makes drainage a useful question while the garden layout is still taking shape. Adding another planting bed afterwards won’t, by itself, solve how water reaches the plants.

The design response is to connect surfaces and planting where conditions allow. We need to check how the soil takes in water, where any excess can safely go and how the proposal affects the house, neighbouring sites and existing trees.

Designing for a tree means designing the space its roots will live in.

The canopy and the conditions beneath it

Trees cool through shade and evapotranspiration. These are different mechanisms: shade reduces a surface’s exposure to sunlight, while evapotranspiration transfers water to the atmosphere. The EPA explains both effects of vegetation.

For an individual garden, the question goes beyond which species to plant. We also ask how much room its mature canopy will have, what lies below the surface and how the plant will be cared for during dry periods.

Before drawing the planting beds

• Where does water currently flow from the house and paved surfaces?
• Where does it collect, and where does it disappear quickly?
• What do we know about the soil and existing roots?
• Which parts of the garden are most exposed to sun and wind?

The answers don’t have to lead to a complex system. They may change the position of a path, the size of a planting area or the sequence of work. What matters is that the decision comes from the place.