Advice
RHS Help & Advice
Container maintenance
Containers need frequent watering and adequate nutrients. Unlike border soil, water cannot flow in from the sides of containers or from below to replace that used by plants. This means that the plant depends on the gardener providing adequate water and nutrients.
The bigger the leaf area, the more water is needed. Windy and sunny conditions increase the amount of water lost from foliage.
If it is not possible to water often enough to keep the compost moist, move containers to a more sheltered, shadier spot. And try adding water-retaining gels.
On the other hand overwatering is very damaging. If water is not draining out freely, check the drainage holes for blockage and assess compost structure. Composts lose their structure over time as the organic components decay, becoming soggy, dense and lacking in air spaces. Shrubs and trees that stay in a pot for months or years are especially vulnerable.
When it is no longer convenient to repot them every year into a bigger pot, they should be repotted in the same pot annually. Use fresh compost, after removing up to one-third of existing compost and roots.
Compost can only hold a certain amount of fertiliser. Adding more in the growing season tops up nutrients.
Use a balanced liquid fertiliser when growth needs to be encouraged and a high potassium one (such as a tomato feed) to encourage flowering when growth is good. Alternatively, add a controlled-release fertiliser at planting time.
In wet weather, keep the bottom of the pot out of the water by standing pots on ‘feet’.