How to stratify seeds

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 

Read more in How to and Seeds