Do pots really need drainage holes?

Drowned roots and dry roots produce the same symptom: a wilting plant. That is the whole reason pots without drainage are so lethal — the feedback is inverted, and a careful owner kills the plant faster than a neglectful one.

What you'll need

• A plastic or terracotta liner pot with holes
• Pot feet, stones or an upturned saucer
• Diamond hole saw and a drill (optional)

Step by step

1. Understand what the hole is really for.It is not just to let water out; it is to let air in behind it. As water drains, air is drawn down through the compost. Roots need oxygen, and that exchange is what supplies it.
2. Check the hole is actually open.Plenty of plastic pots come with the hole only part-punched, and terracotta pots block with compacted compost, moss or roots. Poke it clear before planting.
3. Fill with compost right down to the hole.Crocks or gravel in the base do not improve drainage; because water does not pass from fine compost into coarse gravel until the compost above is saturated, they raise the wet zone rather than lowering it. A piece of mesh over the hole to keep compost in is the only thing worth adding.
4. Raise the pot off the ground.Pot feet, tiles or two slates. A pot sitting flat on paving seals its own drainage hole, particularly once moss builds up. This is the second commonest drainage failure after having no hole at all.
5. Drill a hole if the container allows it.Plastic and metal drill easily. Glazed ceramic and terracotta need a diamond hole saw, run slowly, kept wet, with the pot supported and no hammer action. They still crack sometimes, so accept that risk before you start.
6. Use the liner pot method where you cannot drill.Plant into an ordinary pot with holes that fits inside the decorative one, and stand it on an upturned saucer, a brick or a few stones so its base is clear of anything that collects. Lift it out to water, let it drain, put it back.
7. Tip out whatever gathers in the outer container.Every couple of weeks, and always after heavy rain if it is outdoors. That reservoir is what causes the damage.
8. Use saucers seasonally.In a July heatwave a saucer holds a reserve the plant takes up during the day, and that is useful. From autumn it keeps the base of the pot saturated through months when the plant is barely growing, and that rots roots. Take them away in autumn.
9. Read wilting properly before watering.Push a finger into the compost. Wet compost and a wilting plant means drowned or rotting roots, not thirst. Tip it out and look — healthy roots are firm and pale, drowned roots are brown, soft and smell sour.
10. Cover the hole against pests where it matters.A square of fine mesh over the hole keeps compost in, and keeps slugs, ants and vine weevil from moving in through the base.

Tips

• A pot with no hole is a bog garden, and there are plants for that — but not the ones people usually put in them.
• The single most common drainage fault outdoors is a pot standing flat on a paved surface. Pot feet cost very little.
• Indoors, the liner-pot method is better than drilling in almost every case, because you can water at the sink and let it drain properly.

Common mistakes

• Planting directly into a decorative pot with no hole — Water accumulates in the base with nowhere to go, the roots there die, and the plant wilts as though it needs more water. It is the commonest way houseplants and patio plants are killed.
• Adding gravel to a pot with no hole to create a reservoir — It does not create drainage, only a sump. The saturated zone sits just above the gravel and the roots still sit in it.
• Leaving saucers under outdoor pots over winter — Compost that never drains through a cold wet winter is the classic route to root rot and split terracotta.

If it doesn't work

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