Why do my pots dry out so quickly?

Once a pot is fully rooted, most of its volume is root rather than compost, so its water reservoir shrinks even though its size has not changed. This is why a container that was fine in June needs daily attention in August.

Step by step

1. Check whether it is root-bound.Slide the plant out. A solid mass of roots with little compost visible means the reservoir has gone. Potting on one size, or root-pruning and refreshing the compost, restores it.
2. Go up a pot size.Volume rises steeply with diameter, so one size up is often a big change in drying time. Two sizes up at once risks compost staying wet at the edges.
3. Add loam to the mix.A loam-based compost holds water far better than a peat-free multipurpose, and rewets easily if it does dry. Roughly a third loam in the mix is a good balance.
4. Reconsider the material.Terracotta breathes and dries fastest, especially unglazed. Glazed ceramic, plastic and metal hold moisture longer. Thin black plastic in sun heats the rootball as well.
5. Mulch the surface.25mm of gravel, slate or bark on the compost surface substantially cuts evaporation and stops the surface capping. It also stops splashing when you water.
6. Leave a watering gap.Fill to about 25mm below the rim so water pools and soaks in rather than running over the side. Pots filled to the brim are effectively unwaterable.
7. Group pots together.Clustered pots shade each other's sides and raise humidity between them. Moving the most demanding into the middle of the group works well.
8. Move them out of the wind.Wind takes more water out of a container than sun does. A pot on an exposed corner or a balcony dries several times faster than the same pot against a sheltered wall.
9. Water properly when you do.Until it runs freely from the base, then stop. A splash that wets the top 20mm evaporates by lunchtime and trains roots to stay at the surface.
10. Rewet compost that has gone hydrophobic.If water runs straight through and out, stand the pot in a bucket or tray of water for half an hour so it takes up water from below.

Tips

• Wind dries pots faster than sun. Shelter is worth more than shade.
• Water running straight out of the base means the compost is dry, not wet.
• A 25mm gravel mulch on a pot is the cheapest change with the biggest effect.

Common mistakes

• Filling pots to the rim with compost — There is nowhere for water to sit while it soaks in, so most of it runs over the edge and the rootball stays dry. Leave a clear 25mm gap.
• Watering little and often — It wets only the surface and encourages shallow rooting, which makes the plant even more vulnerable. Water thoroughly, less frequently.

If it doesn't work

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