Flower · Saxifragaceae
When to sow astilbes
Feathery plumes over divided foliage, for damp shade where little else flowers. The one thing it will not tolerate is drying out, and a single hard wilt marks the leaves for the rest of the season.
First worthwhile crop
Year 2
After planting, not after sowing.
Hardy in USDA zones
3a to 8a
Winter cold sets the limit here, not the calendar.
Frost tolerance
Very hardy
How much cold the plant itself will take.
Those weeks become real dates once you name a place.
Timing, in frost-relative terms
Nothing about a standing crop is sown to a calendar. Once planted, astilbes stay in the ground for years, so the question is not when to sow but whether your winter is survivable and your planting window is open. Both answers come from your frost dates.
- Expect a first worthwhile crop in year 2 after planting.
- Hardy in USDA zones 3a–8a.
Getting the timing right
Plant dormant crowns in autumn or early spring, at soil level, in ground that stays reliably moist. Mulch after planting. In a dry summer it needs watering as a matter of routine rather than in emergencies.
Frost tolerance
Hardy to -35C and needs winter cold to break dormancy. Drought, not frost, is what kills it; a plant in dry shade will fail in its first summer.
Classified as very-hardy, with damage expected below -35°C (-31°F)-31°F (-35°C).