Grey alder

Alnus incana

Hardy pioneer alder of cold and dry sites where common alder will not thrive. Fixes nitrogen via Frankia bacteria and improves poor soils.

Hardiness ratings

Grey alder hardiness across the four zone systems
SystemRatingTemperature rangeHow to read it
USDA hardiness zone Zone 2–7 −45.6 °C to −12.2 °C Plant tolerates down to this zone
RHS hardiness rating H7 down to −20 °C Plant needs at least this level of cold tolerance
Canadian plant hardiness zone Zone 2–7 −40 °C to −7 °C Plant tolerates down to this zone
Australian (ANBG) zone Zone 1–5 −15 °C to 10 °C Plant tolerates down to this zone

Growing notes

  • Larval host for the alder kitten moth and the green hairstreak butterfly
  • Fixes nitrogen via symbiotic Frankia bacteria in root nodules — the same actinorhizal mechanism used by sea buckthorn and bayberry
  • More drought tolerant than common alder — succeeds on dry exposed sites where A. glutinosa fails
  • Excellent pioneer for restoring degraded or eroded ground

Categories

Related plants

Cross-check Grey alder against your zones

Reference

Grey alder on Wikipedia