Why autumn is the time to watch the water
After months of irrigation and heat, the soil reaches October with an altered structure: it may be compacted by repeated surface watering or may have lost porosity. The autumn rains, when they arrive, test that structure. Observing at this moment is more informative than doing so in high summer, because rainwater spreads more widely than localised irrigation and shows the real behaviour of a plot.
Observation should be done without haste and over several days. A single day of heavy rain can mislead: what looks like a serious problem may be a one-off accumulation from a storm. It is worth noting which areas remain damp 24, 48 and 72 hours later, and whether the water disappears by infiltration or simply evaporates from the surface. That difference points to very different decisions.
In coastal areas, with soils that are often sandy or contain fill, water can disappear too quickly and fail to reach the roots. Inland, with more clay, the opposite happens. The same rain tells different stories depending on the soil, which is why the reading must be done on site, not by comparison with other gardens.
- Note the time and date of each observation; a simple notebook is enough.
- Repeat the observation after a second rain to separate the one-off from the recurring.
Signs worth recording in the soil
The first sign is the puddle: where it forms, how long it lasts and what shape it has. An elongated puddle beside a kerb suggests a problem with levelling or with the outflow of water; an extensive one in the centre of a flat area may indicate a compacted layer below. Colour matters too: cloudy water that carries fine soil points to erosion, while clear stagnant water usually indicates that the soil is not absorbing.
The second sign is texture in the hand. When you take a handful of damp soil, if it forms a compact ball that does not break apart when pressed, there is a lot of clay or compaction; if it crumbles at once and leaves your fingers sandy, drainage is fast but water and nutrient retention will be low. In both cases the decision changes: in the first, the structure is worked; in the second, organic matter is improved and irrigation adjusted.
The third sign is the plants. Yellow patches on lower leaves, slow growth or roots appearing at the surface can indicate excess water or a lack of oxygen in the root zone. None of these signs, on its own, confirms a diagnosis; their value lies in repetition and in coinciding with the earlier observations.
- Carry out the ball test in three different parts of the garden, not just one.
- Photograph the puddles with a fixed reference point to compare their evolution.
Slopes, edges and the path of the water
Water does not stay where it falls: it follows the slope. Observing where it flows allows you to detect incipient erosion, rills in the mulch or soil piled against walls and trunks. On a plot with a gradient, the low point is usually the dampest and also the most vulnerable to accumulating salts and root diseases. That low point should be identified before planting, because it conditions which species will work there.
Built edges also speak: a path that holds water, a tree basin that is too deep or a wall that blocks surface drainage create problems that are not solved by changing the substrate. Sometimes the solution is as simple as opening a passage or lowering an edge; other times it requires rethinking the levelling. Observation should include those built elements, not only the earth.
In Mediterranean coastal gardens, where irrigation combines with occasional torrential rain, the path of the water also determines where nutrients are washed away. Fast-draining areas become poorer and need more frequent organic inputs. This is a practical consequence of observation, not a theory.
- Draw a simple sketch with arrows showing the path of the water after rain.
- Check whether mulch is piling up against trunks: it can keep moisture in a sensitive spot.
Common mistakes when interpreting what you see
A common mistake is confusing dry soil at the surface with dry soil at depth. After summer, the top layer may look arid while at 20 centimetres the moisture is still high, especially in clay soils. Watering or replanting guided only by the surface leads to excesses. The reverse also happens: soil that drains quickly at the surface may have a compacted layer that holds water further down.
Another mistake is adding sand to improve a clay soil without observing it first. Mixing sand and clay in unsuitable proportions can form a mass harder than the original. Prior observation prevents acting by reflex. It is also common to fill depressions with soil without checking why they formed: if the problem is a blocked outflow, the fill merely moves the puddle.
Finally, there is the mistake of deciding on a single day of intense rain. A garden seen during a storm may look like a disaster; seen three days later, it may have only one low point that can be resolved with a slight change of level. Repeated observation protects against costly and unnecessary interventions.
- Do not fill a depression without first identifying its origin.
- Wait at least 48 hours before assessing a waterlogged area.
Decisions you can take after observing
With the observations noted down, decisions become concrete. If the problem is compaction, the first step is usually to aerate and add well-decomposed organic matter, not to replace the entire substrate. If it is excess water at a low point, it may be enough to raise the planting slightly or create a surface outlet. If drainage is too fast, it is worth choosing adapted species and adjusting watering frequency before adding materials.
Observation also guides plant choice. A corner that stays damp three days after rain is not suitable for species sensitive to waterlogging, however Mediterranean they may be. It can, however, host specimens that tolerate that condition. This reading avoids the mistake of planting and waiting to see what happens, which in gardening usually proves costly.
In the context of Sotogrande and the Costa del Sol, where mild autumns coexist with concentrated rains, the key is to observe before acting and review afterwards. A garden is not diagnosed in one visit: it is read over several days. That discipline, more than any product, is the basis of well-resolved drainage.
- Link each observation to a concrete decision before buying materials.
- Review drainage after each heavy autumn rain and note any changes.