Do I need to water pots in winter?

Winter kills container plants in two opposite ways and people only guard against one. Winter wet drowns things standing in the open. Winter drought kills things that never see rain — an evergreen in a porch, a bay by the front door, a pot tucked against a house wall under an overhang. The plant looks dormant, nobody waters it, and in March the leaves go brown from the tips.

Step by step

1. Work out which pots get rain and which do not.Stand outside during a shower and look. Anything under eaves, in a porch, on a covered balcony, against a wall on the sheltered side, or under a dense evergreen canopy is in a rain shadow and will not water itself.
2. Understand why evergreens are the vulnerable ones.Deciduous plants drop their leaves and lose almost no water. Evergreens keep transpiring whenever the temperature is above freezing, and cold drying winds accelerate it. That is the physiological drought that browns conifers, bay, box and camellias over winter.
3. Check by lifting, every two or three weeks.Tip the pot or lift the rim. A pot that has genuinely dried out feels startlingly light. That is a faster and more reliable check than pushing a finger into cold compost.
4. Water in the morning, on a day that is not freezing.Morning gives the compost the day to drain and the foliage time to dry. Watering in the evening leaves free water in the pot overnight when the temperature drops, which does far more damage than the dryness would have.
5. Water sparingly and let it drain fully.Enough to moisten the rootball, not enough to leave the pot saturated. Never water a pot standing in a saucer in winter, and never water a rootball that is frozen solid — wait for a thaw.
6. Do not water dormant deciduous plants unless they are bone dry.A deciduous shrub or a pot of dormant bulbs needs the compost just moist, no more. Overwatering these through winter is the classic route to root rot and to bulbs that never come up.
7. Reduce the demand rather than increasing the watering.Move rain-shadowed pots out into the open for winter if they are hardy, group them together to reduce wind exposure, and mulch the surface. A pot that catches its own rain looks after itself.

Tips

• Camellias and rhododendrons set next year's flower buds in late summer and drop them if they go dry over winter. A pot of camellia that flowered badly in spring was very often dry the previous November.
• Brown, crisping tips on a potted conifer or bay in February is winter drought and wind burn, not frost damage. Frost damage is usually blackened and soft.
• Snow on a pot is not watering. It sits on the surface, most of it sublimates or runs off the sides, and very little reaches the rootball.

Common mistakes

• Assuming rain does the job — Rain falls at an angle and the plant's own canopy sheds most of it outward. Even a pot in the open can stay dry under a dense evergreen through a wet month.
• Watering everything on a schedule through winter — The pots in the open are already too wet. Winter watering is targeted at specific pots you have identified, not a routine applied to the whole patio.
• Watering when a hard frost is forecast that night — Free water in the compost freezes, expands and damages both roots and pot. Give the pot a full day to drain first.

Questions people ask