How to Overwinter Geraniums Indoors Successfully

Gardeners in cold climates (like Zone 4 Iowa or Zone 5 Illinois) often want to save their zonal geraniums (Pelargonium × hortorum) over winter. While possible, it requires mimicking the cool, bright conditions that trigger dormancy without freezing the plants.

Two Reliable Methods

1. Cool, Bright Storage (Best for Healthy Plants)

Keep potted geraniums in a sunny, unheated room or greenhouse at 41–45°F (5–7°C). Water sparingly—just enough to prevent desiccation. Remove dead leaves but avoid cutting main stems, which can stimulate unwanted growth. This method preserves the plant’s structure for a strong spring comeback.

2. Bare-Root Dormancy (Traditional “Paper Bag” Method)

1. Before hard frost, lift plants, shake off soil, and remove most leaves (keep main stems).
2. Air-dry roots for a few days until they wilt slightly.
3. Dust with sulfur to prevent fungal rot.
4. Place in brown paper bags (not plastic) and store in a cool, dark basement at 45–50°F.
5. Mist lightly every few weeks to prevent total desiccation.

This works best for mature, woody-stemmed plants. Soft, green stems may rot.

Critical Success Factors

• Temperature control is paramount—too warm breaks dormancy; too cold kills tissue.
• Fungus prevention via sulfur dusting and good air circulation.
• Light if using the cool-room method; darkness for bare-root storage.

The Royal Horticultural Society provides detailed overwintering guides at rhs.org.uk. With attention to these details, you can enjoy your geraniums year after year.