How do I overwinter tender plants?

Overwintering is about keeping plants alive rather than growing them. They need protection from freezing, very little water, and enough light not to become drawn and weak. Warmth is usually a mistake.

What you'll need

• Frost-free shed, garage or greenhouse (optional)
• Horticultural fleece (optional)
• Dry compost or sand (optional)

Step by step

1. Know what actually needs protection.Check hardiness before lifting everything. Many plants labelled tender survive outdoors in a sheltered spot with a mulch over the crown.
2. Act before the first frost, not after.One frost can kill a tender plant outright. Watch the forecast rather than the calendar, particularly in autumn.
3. Cut back and lift tubers and rhizomes.Dahlias, cannas and begonias. Cut the stems back, lift, dry them off, and store in dry compost somewhere frost-free.
4. Move pots into a frost-free but cool space.An unheated garage, porch or greenhouse. Cool and light beats warm and dark — warmth prompts weak growth the plant cannot support.
5. Water very sparingly through winter.Just enough that the compost does not fully dry out. Overwatering a dormant plant is the most common cause of winter losses.
6. Give as much light as possible.Plants kept warm in the dark produce pale drawn growth and rarely recover. A cold bright windowsill is far better than a warm dark cupboard.
7. Protect plants staying outdoors.Fleece over the top, a thick mulch over the crown, pots grouped together against a wall and raised off the ground on feet.
8. Reintroduce gradually in spring.Harden them off over a week or two, as you would seedlings. Straight outside after months under cover kills them.

Tips

• Take cuttings in late summer as insurance. If the parent plant does not survive, you have replacements, and they take up almost no space.
• Wet plus cold kills far more plants than cold alone. Improving drainage and keeping rain off pots matters more than the temperature.
• Check stored tubers monthly for rot and remove anything soft before it spreads through the whole box.

Common mistakes

• Overwatering plants in winter storage — Dormant plants use almost no water, and wet compost rots the roots. It kills more overwintered plants than cold does.
• Storing them somewhere warm and dark — Warmth prompts growth that the low light cannot sustain, producing weak drawn stems that collapse.
• Waiting until after the first frost — A single frost can kill a tender plant. Move them based on the forecast, not the date.

Questions people ask