Look at the planter before touching the soil
The first check is visual and tactile. Lift the pot or container, if its weight allows, and check whether water comes out of the bottom hole minutes after watering. If nothing comes out, drainage is compromised. If it runs turbid for a long time, the substrate has probably broken down and become clogged. On terraces in Estepona, with drip irrigation and occasional wind, it is common to find large pots where the top seems dry while the bottom stays wet for days.
Push a wooden stick or cane down to the bottom and look at it when you pull it out: if it comes up with clinging mud, retention is excessive; if it comes out clean and dry along its whole length, the water is not reaching down. Also check the surface crust and any roots showing through the holes. A root circling inside means the volume has become too small. None of these signals is solved by adding fresh substrate on top; they are corrected only by acting on the cause.
- Carry out the test after a normal watering, not after heavy rain.
- Photograph the condition before intervening so you can compare in spring.
Diagnosing the substrate: texture, smell and structure
Substrate is judged with your hands. Take a handful from the middle layer, not the surface, and squeeze it. It should form a ball that breaks apart easily when touched. If it stays compact like modelling clay, the mix retains too much; if it crumbles into fine dust and holds nothing, it is exhausted. Smell helps: healthy substrate smells of damp earth, while a sour or drains-like smell indicates poor aeration and excess water.
Texture is not the only thing. Old substrate can look fine yet have lost its structure: fine particles have filled the pores and air no longer circulates. This explains why a plant watered as often as before begins to yellow. In ceramic pots exposed to autumn sun, the outer part warms while the inside stays cold and damp, which makes the problem worse. Before deciding to replace the whole volume, consider whether aerating the top layer and renewing drainage may be enough.
- Compare substrate from the centre with that at the edge: they usually behave differently.
- If there are earthworms and a fresh smell, the mix is probably still working.
Volume, drainage and watering: three linked decisions
The size of the planter determines the margin for error. A shallow, wide pot dries out sooner than a tall, narrow one of the same volume because it exposes more surface to the air. Conversely, a very deep, narrow pot can keep the base waterlogged. Before changing the substrate, measure the actual volume and compare it with the size of the plant. A one-metre shrub in twenty litres will live under permanent stress, however much it is fed.
Drainage is not fixed by stones in the bottom alone. A thick layer of gravel raises the internal water level and can make matters worse if the hole is small. Better to check that the hole works, tilt the pot slightly and use a mix that drains well from the top. As for watering, do not schedule out of habit: in autumn, with cooler nights, consumption falls. A common mistake is to keep the summer timetable and discover rot weeks later. Adjust according to the weight of the pot and the dampness of the stick.
- Mark the water level in the saucer so you do not confuse rain with irrigation.
- Never fill to the brim: leave two or three centimetres free so you can water without overflowing.
Renewing the substrate without repeating mistakes
When renewal is due, the most common mistake is reusing old soil mixed with a little fertiliser. If the structure has collapsed, fertiliser will not correct the lack of air. Another mistake is filling the pot with very fine universal substrate, which compacts with watering and wind. On the coast, a mix with coarse materials that maintain porosity is preferable, with the proportion adapted to the type of plant: a herb and a potted citrus do not need the same thing.
When repotting, untangle circling roots and remove dead ones. Do not press the soil down hard: let the water settle it. Water once and wait a few days before watering again, watching how the plant responds. If yellow leaves appear at the base, check drainage before adding more water. This approach of observing before acting saves substrate, avoids losses and suits gardening in Sotogrande, where many terraces share wind and salinity. The key is not a recipe but reading the signals of each planter before deciding.
- Keep a sample of the old substrate in a bag to compare texture the following year.
- Do not fertilise a newly repotted plant until you see new growth.