by Webster Arboretum

Cold Stratification

Before you pop those seeds in a pot, you might check and see if your seeds need a bit of a chill first.

As unpleasant as those cold winter nights can be, they provide many seeds with the signals they need to begin the germination process.

Cold stratification is done to imitate the moist, chilly winter weather that triggers a seed to sprout. Most perennial plant seeds require a combination of cold and damp to germinate.

Common varieties that require cold stratification for spring planting:
(Varieties in bold are native to Central and Western, New York.)

  • Agrimony (Agrimonia@) – 30-60 days
  • Angelica (Angelica atropurpurea) – dry stratify#
  • Apple (Malus domestica) – 90-120 days
  • Arnica (Arnica spp.) – 30-74 days
  • Artichoke (Cynara cardunculus) – 30-44 days
  • Asparagus (Asparagus officinalis) – 21-30 days
  • Aster (Aster spp.) – 30-60 days
  • Basket of Gold (Alyssum saxatile) – 30-44 days
  • Bee Balm (Monarda didyma) – 21-30 days
  • Bellflower (Campanula spp.) – 30-44 days
  • Black Eyed Susan (Rudbeckia hirta) – 30-60 days
  • Bluebell (Phacelia spp.) – 60 days
  • Blueberry (Vaccinium spp.) – 30-120 days
  • Borage (Borago officinalis) – 30-44 days
  • Boxwood (Buxus sempervirens) – 30-60 days
  • Bugbane (Cimicifuga spp.) – 90-120 days
  • Butterfly Bush (Buddleia davidii) – 21-30 days
  • Cardinal Flower (Lobelia cardinalis) – 30-60 days
  • Catmint (Nepeta) – 14-30 days
  • Catnip (Nepeta cataria) – 14-30 days
  • Chamomile (Matricaria chamomilla) – 30-74 days
  • Cherry (Prunus spp.) – 90-120 days
  • Cohosh, Black (Actaea racemosa) – 60-90 days
  • Columbine (Aquilegia spp.) – 21-30 days
  • Comfrey (Symphytum officinale) – 30-60 days
  • Coneflower, Purple (Echinacea purpurea), Prairie (Ratibida) – 30 days
  • Cranberry (Vaccinium spp.) – 30-120 days
  • Delphinium (Delphinium spp.) – 14-30 days
  • Dianthus (Dianthus spp.) – 14-21 days
  • Dogwood (Cornus*) – 90-120 days
  • Edelweiss (Leontopodium alpinum) – 21 days
  • Elderberry (Sambucus spp.) – 60 days
  • Fireweed (Chamaenerion angustifolium) – 30-44 days
  • Forsythia (Forsythia x intermedia) – 30-90 days
  • Foxglove (Digitalis) – 14-30 days
  • Gentian (Gentiana**) – 60-90 days
  • Geranium (Geranium***) – 30-60 days
  • Ginkgo (Ginkgo biloba) – 30-90 days
  • Goldenrod (Solidago spp.) – 30-60 days
  • Goji Berry (Lycium barbarum) – 30-60 days
  • Good King Henry (Blitum bonus-henricus) – 60-74 days
  • Grapes (Vitis labrusca) – 90-120 days
  • Hawthorn (Crataegus) – 120 days
  • Hollyhock (Alcea rosea) – 90-120 days
  • Hyssop (Agastache spp.) – 30 days
  • Iris (Iris spp.) – 60-90 days
  • Ironweed (Vernonia gigantea) – 60-90 days
  • Joe Pye Weed (Eupatorium spp.) – 30-60 days
  • Kiwi Fruit (Actinidia spp.) – 30-60 days
  • Lady’s Mantle (Alchemilla Mollis) – 21-30 days
  • Larkspur (Delphinium exaltatum, Delphinium tricorne) – 14-30 days
  • Lavender (Lavandula spp.) – 7-30 days
  • Lemon balm (Melissa officinalis) – 7-44 days
  • Licorice (Helichrysum petiolare) – 14-30 days
  • Lilac (Syringa vulgaris) – 40-60 days
  • Lousewort, Canadian / Wood Betony (Pedicularis canadensis) – 30-90 days
  • Lupine, Wild Blue (Lupinus perennis) – 30-60 days
  • Magnolia (Magnolia spp.) – 60-90 days
  • Marshmallow (Althaea officinalis) – 30-44 days
  • Marsh Marigold (Caltha palustris) – 60-112 days
  • Milkweed (Asclepias spp.) – 30-60 days
  • Mock Orange (Philadelphus coronarius) – 30-60 days
  • Mugwort (Artemisia vulgaris) – 14-30 days
  • Mulberry, Red (Morus rubra) – 90 days
  • Mullein (Verbascum spp.) – 30 days
  • Oak, English (Quercus robur) – 90 days
  • Ox Eye Sunflower (Heliopsis helianthoides) – 30-60 days
  • Pawpaw (Asimina triloba) – 70 days
  • Peach (Prunus persica) – 60 days
  • Pear, European (Pyrus communis) – 60 days
  • Peony (Paeonia spp.) – 60 days
  • Persimmon, American (Diospyros virginiana) – 60-120 days
  • Phlox, Garden (Phlox paniculata) – 60 days
  • Poppy, Oriental (Papaver orientale) – 21-30 days
  • Primrose (Oenothera biennis) – 14-42 days
  • Raspberry (Rubus idaeus, Rubus occidentalis) – 60-120 days
  • Rhododendron (Rhododendron spp.) – 30-60 days
  • Rosemary (Rosmarinus officinalis) – 14-44 days
  • Rose, Wild (Rosa spp.) – 60 days
  • Sage, White (Salvia apiana) – 14-30 days
  • Self Heal (Prunella vulgaris) – 30 days
  • Serviceberry (Amelanchier spp.) – 90-120 days
  • Shooting Star (Dodecatheon meadia / Primula meadia^) – 30-90 days
  • Skullcap (Scutellaria lateriflora) – 30 days
  • St. John’s Wort (Hypericum**^) – 28-42 days
  • Sunflower, perennial (Helianthus*^^) – 30-60 days
  • Sweet Flag / Calamus (Acorus calamus) – 30-60 days
  • Sweet William (Dianthus barbatus) – 30-74 days
  • Tansy (Tanacetum vulgare) – 14-30 days
  • Thyme (Thymus genus) – 14-44 days
  • Trumpet Vine (Campsis radicans) – 30 days
  • Valerian (Valeriana officinalis) – 14-21 days
  • Vervain (Verbena hastata, V. urticifolia, V. simplex) – 30-60 days
  • Wintergreen (Gaultheria procumbens) – 30-72 days
  • Wisteria (Wisteria spp.) – 30-90 days
  • Witch Hazel (Hamamelis virginiana) – 60-120 days
  • Yarrow (Achillea spp.) – 14-30 days
  • Yucca (Yucca filamentosa) – 30-90 days

Paper Towel Cold Stratification

  1. Spread the seeds in a single layer across double layers of damp paper towel. Wring the paper towel out so that it is not dripping wet.
  2. Make sure each seed has good contact with the damp towel.
  3. Insert the damp paper towel into a Ziploc bag or sealed container.
  4. Label the container with the date and seed variety.
  5. Place seeds in the back or bottom of your refrigerator where it is coldest. Do not place your seeds in the freezer.
  6. In most cases, after 30 days your seeds will be ready to be removed from the refrigerator and potted. If seeds start to sprout in the refrigerator, remove them immediately and pot them in a suitable medium until it’s warm enough to plant them outdoors.

Potting Soil Cold Stratification

Instead of the paper towel, you can also dampen a small amount of your favorite potting mix until it can hold together in a ball. Mix the seeds into the mix (approximately 1 part seed to 3 parts soil) and then place them into a ziploc bag at the back of the refrigerator.

^Native but threatened in New York State.

#Dry stratify: Refrigerate dry seeds until use

@Native varieties of Agrimony:Tall Hairy Agrimony (Agrimonia gryposepala), Many-flowered Agrimony (Agrimonia parviflora),Woodland Agrimony (Agrimonia rostellata).

*Native varieties of Dogwood: Red Osier Dogwood (Cornus sericea), Gray Dogwood (Cornus racemosa), Pagoda Dogwood (Cornus alternifolia), Silky Dogwood (Cornus amomum), Round-leaved Dogwood (Cornus rugosa), Bunchberry (Cornus canadensis), Flowering Dogwood (Cornus florida).

**Native varieties of Gentian: Closed Bottle Gentian (Gentiana andrewsii), Meadow Bottle Gentian (Gentiana clausa), Fringed Gentian (Gentianopsis crinita), Cream Gentian / White Gentian (Gentiana alba), Stiff Gentian / Dwarf Gentian (Gentianella quinquefolia).

***Native varieties of Geranium: Wild Geranium / Spotted Cranesbill (Geranium maculatum), Carolina Cranesbill (Geranium carolinianum), Bicknell’s Cranesbill (Geranium bicknellii).

*^Native varieties of St. John’s Wort: Shrubby St. John’s Wort (Hypericum prolificum), Spotted St. John’s Wort (Hypericum punctatum), Pale St. John’s Wort (Hypericum ellipticum), St. Andrew’s Cross (Hypericum hypericoides / crux-andreae), Orangegrass/Pineweed (Hypericum gentianoides). The most prevalent species, (Hypericum perforatum) is not native to Central and Western New York.

*^^Native varieties of Sunflowers: Woodland Sunflower (Helianthus divaricatus), Thin-leaved Sunflower (Helianthus decapetalus), Pale-leaved Sunflower (Helianthus strumosus), Giant Sunflower (Helianthus giganteus), Jerusalem Artichoke / Sunchoke (Helianthus tuberosus), Fewleaf Sunflower (Helianthus occidentalis)