Overview
- German gardening outlets warn that entire root balls can freeze in containers, so wrap pots with jute, fleece or coconut matting and shield them against a house wall.
- Insulate from ground chill by setting containers on wood or Styrofoam, and use a minimum pot diameter of about 30–40 centimeters for better cold buffering.
- Hardiness differs by type: panicle and snowball hydrangeas are generally frost‑tolerant, while mophead/bigleaf and teller forms, including many indoor-bred cultivars, need protection.
- Winter drought is a frequent killer, so check moisture and water moderately only on frost‑free days; if soil is frozen, thaw the pot in a cool garage or cellar before watering and avoid warm water.
- In very cold regions, move pots to a cool, frost‑free space such as a cellar or unheated greenhouse, and consider leaving spent flower heads in place as a protective cap over tender buds.