Cold Stratification: The Key to Unlocking Seed Germination

What is cold stratification?

What is cold stratification?  Ι   Why do some seeds need cold stratification?  Ι   When is the best time to stratify seeds?  Ι   Do all seeds need cold stratification?   Ι  Seed stratification process  Ι   Which seeds need stratification?

What is cold stratification?

The name “stratification” was used because seeds used to be layered (stratified) between two layers of moist soil and then exposed to cold. Some gardeners refer to stratification as cold treatment.

Why do some seeds need cold stratification?


Seed dormancy is a state in which the seed is unable to germinate to prevent it from breaking dormancy during the harsh winter season. This is a survival tactic that increases its chances of survival by preventing the seed from germinating until conditions are right.

During cold stratification, seeds undergo a series of physiological changes that lead to the breaking of seed dormancy. These changes include a decrease in abscisic acid levels, a hormone that inhibits seed germination, and an increase in gibberellin levels, a hormone that promotes seed germination. This shift in hormone balance signals to the seed that conditions are now favourable for germination, allowing enzymes to be activated that break down stored nutrients and initiate the process of growth and development.

In addition, seeds requiring cold stratification often possess a hard, impermeable outer shell that prevents water and gases from passing through, making it difficult for the seed to absorb the necessary nutrients for germination. When these seeds are exposed to cold, moist conditions, water is able to penetrate the seed coat, causing it to imbibe and initiate physiological changes that lead to germination. This process is known as imbibition and plays a crucial role in the activation of enzymes that break down stored nutrients, to provide energy to the embryo.

Exposure to the cold, moist winter environment helps to break down the seed coat, allowing the seed to absorb water and other necessary nutrients that activate enzymes and trigger germination.

When is the best time to stratify seeds?

Wintertime is the ideal time to begin stratification, and then the seeds will be ready to plant when spring arrives.

  • Northern hemisphere: January – February
  • Southern hemisphere: June – July

Obviously, seeds could be sowed directly into the ground or pots during winter, but weather conditions can be unpredictable. Also, some climates may not have a cold or wet enough winter to trigger germination, in other cases, the winter may be so wet that the seeds rot.

Do all seeds need cold stratification?

No, seeds from warm climates don’t need stratification, however, some seeds require scarification, which is a process in which the seeds are buffed to weaken the outer shell, allowing water in to trigger the natural sprouting process.

Do you put cold stratification seeds in the fridge or freezer?

Cold stratification seeds are typically placed in a refrigerator. Seeds should not be placed in a freezer for cold stratification, as freezing temperatures can damage or kill the seeds. Instead, the ideal temperature range for cold stratification is typically between 0 and 10°C (32 to 50°F), which can be achieved in a refrigerator or other cool, but not freezing, environment. It’s important to research the specific requirements of the plant species you are working with to determine the optimal temperature and duration of cold stratification.

Seed stratification process


There are several to cold stratify seeds, we will cover the most simple stratification method, known as ‘moist seed stratification‘.

What you will need:

  • Seeds
  • Paper towel
  • Sandwich bag
  • Marker pen
  • Spray bottle
  • Water
  • Refrigerator (set to 1 – 4°C)


  1. Mark the sandwich bag with the name of the seeds and the date.
  2. Carefully moisten the paper towel with a spray bottle, the paper should be damp but not saturated.
  3. Lay the seeds in a thin layer on the paper towel, and fold the paper towel over the seeds to help keep the seeds moist
  4. Put in the refrigerator for 30 – 90 days (until outside temperatures warm up)

Monitor the seeds daily to make sure the medium remains moist. If any seeds sprout during stratification, pot them up and keep them in a warm location inside if it is cold outside. Remove seeds that have developed mould.

Note: Some seeds may require a warmer temperature (up to 10°C) than the temperature of a refrigerator. In this case, they can be stored in a basement.

Which seeds need stratification?

Anemone Anemone spp.
Anise hyssop Agastache foeniculum
Angelica Angelica archangelica
Arnica Arnica montana
Artichoke Cynara cardunculus
Asparagus Asparagus officinalis
Balloon flower Platycodon grandiflorus
Barrenwort Epimedium spp.
Bellflower Campanula spp.
Black cohosh Actaea racemosa
Black-eyed Susan Rudbeckia hirta
Blanket flower Gaillardia aristata
Bloodroot Sanguinaria spp.
Blue star Amsonia spp.
Borage Borago officinalis
Brussels sprouts Brassica oleracea var. gemmifera
Butterfly bush Buddleja spp.
Butterfly weed Asclepias tuberosa
Catchfly Silene spp.
Catnip Nepeta spp.
Chamomile Matricaria chamomilla
Chinese lantern Physalis alkekengi
Clematis Clematis spp.
Common boneset Eupatorium perfoliatum
Common mallow Malva sylvestris
Common milkweed Asclepias syriaca
Coral bells Heuchera spp.
Creeping thyme Thymus serpyllum
Delphinium Delphinium spp.
Echinacea (coneflower) Echinacea spp.
False indigo Baptisia spp.
False sunflower Heliopsis helianthoides
Foxglove Digitalis spp.
Fuchsia Fuchsia spp.
Geum Geum spp.
Globe flower Trollius spp.
Globe thistle Echinops spp.
Goldenrod Solidago spp.
Great burnet Sanguisorba officinalis
Hardy plumbago Ceratostigma spp.
Helen’s flower Helenium spp.
Hellebore Helleborus spp.
Hibiscus Hibiscus spp.
Hollyhock Alcea spp.
Hyssop Agastache spp.
Indian pink Spigelia spp.
Joe-Pye weed Eupatorium maculatum
Lady’s mantle Alchemilla spp.
Lavender Lavandula spp.
Lemon balm Melissa officinalis)
Licorice Glycyrrhiza glabra
Lilac Syringa spp.
Lobelia (cardinal flower) Lobelia spp.
Loosestrife Lysimachia spp.
Lupine Lupinus spp.
Marshmallow Althaea officinalis
Masterwort Astrantia spp.
Meadowsweet Filipendula ulmaria
Milkweed Asclepias spp.
Monkshood Aconitum spp.
Oxeye sunflower Heliopsis helianthoides
Pansy Viola tricolor var. hortensis
Pasque flower Plusatilla vulgaris
Peony Paeonia spp.
Perennial flax Linum perenne
Peruvian lily Alstroemeria spp.
Phlox Phlox spp.
Plantain lily Hosta spp.
Poppy Papaver spp.
Primrose Primula vulgaris
Red hot poker Kniphofia spp.
Rosemary Rosmarinus officinalis
Sage Salvia officinalis
Sea holly Eryngium spp.
Skullcap Scutellaria spp.
Speedwell (Veronica) Veronica spp.
Spiderwort Tradescantia spp.
Spring adonis Adonis vernalis
Spring corydalis Corydalis solida
St. John’s Wort Hypericum perforatum
Sweet cicely Myrrhis odorata
Swiss chard Beta vulgaris subsp. cicla)
Sweet woodruff Galium odoratum
Tansy Tanacetum spp.
Thyme Thymus vulgaris
Tickseed Coreopsis spp.
Toad lily Tricyrtis spp.
Valarium Valeriana officinalis
Viburnum Viburnum spp.
Violet Viola spp.
Whirling butterflies Gaura lindheimeri
Wild garlic Allium ursinum
Wild indigo Baptisia tinctoria
Winter aconite Eranthis hyemalis
Wintergreen Gaultheria procumbens
Yarrow Achillea millefolium


Is cold stratification really necessary?

Some seeds will germinate even without stratification, but stratification can increase the germination rate. I have sown a number of cottage plant seeds without stratification. My foxgloves from last year self-sowed and I have a large collection of baby foxgloves in the garden. However, if you have purchased cold climate seeds that should be stratified, it is recommended.

Some plant species, particularly those native to colder climates, have evolved to require the moist, cool conditions of winter to break their dormancy and initiate germination in spring. By exposing the seeds to a period of cold stratification, which mimics these natural conditions, the germination process can be jump-started for these species.

Therefore, if you have purchased seeds of plants that require cold stratification, it is always advisable to follow the recommended stratification period and conditions for optimal germination.


  • Cold stratification is a simple process of exposing seeds to a period of moist, cool conditions in order to break their dormancy and promote germination.
  • The process of cold stratification mimics the natural conditions that many plant seeds would experience in the wild during winter when cold temperatures and moisture help to prepare the seeds for spring germination.
  • By properly cold-stratifying seeds, gardeners can increase the germination rate of seeds.
  • Cold stratification can be achieved by placing seeds in a moist medium, such as sand or vermiculite, or a damp paper towel and placing them into a refrigerator or other cool location for a period of time ranging from several weeks to months.

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