How to - Seeds

How to stratify seeds

By
Stephen Westcott-Gratton

Trick seeds into germinating by giving them the cold treatment. Illustrations by Shannon Hong

Different species need varying periods of stratification, ranging from one week to several months. Here are typical requirements for some common garden plants.

Chilling periods

  • Fir (Abies spp.): 1 to 3 months
  • Maple (Acer spp.): 2 to 4 months
  • Monkshood (Aconitum spp.): 3 weeks
  • Flowering onion (Allium spp.): 4 weeks
  • Serviceberry (Amelanchier spp.): 3 to 4 months
  • Snapdragon (Antirrhinum majus): 1 week
  • Columbine (Aquilegia spp.): 3 weeks
  • Redbud (Cercis canadensis): 3 months
  • Species clematis (Clematis spp.): 2 to 3 months
  • Dogwood (Cornus spp.): 3 to 4 months
  • Bleeding heart (Dicentra spectabilis): 6 weeks
  • Shooting star (Dodecatheon meadia): 3 weeks
  • Purple coneflower (Echinacea purpurea): 4 weeks
  • Forsythia (Forsythia spp.): 1 to 2 months
  • Hellebore (Helleborus spp.): 4 weeks
  • Daylily (Hemerocallis spp.): 6 weeks
  • Hardy lobelia (Lobelia spp.): 12 weeks
  • Honeysuckle (Lonicera spp.): 1 to 3 months
  • Magnolia (Magnolia spp.): 3 to 6 months
  • Virginia bluebells (Mertensia pulmonarioides): 6 weeks
  • Phlox (Phlox paniculata): 4 weeks
  • Spruce (Picea spp.): 1 to 3 months
  • Primrose, most (Primula spp.): 4 weeks
  • Species roses (Rosa spp.): 4 to 6 months
  • Elderberry(Sambucus canadensis): 3 to 5 months
  • Lilac (Syringa spp.): 1 to 3 months
  • Hemlock (Tsuga spp.): 2 to 4 months
  • Pansy, viola (Viola spp.): 1 week 

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