Stratification, Vernalization, Cold Treatment, call it what you like, the premise remains the same. Much like a tulip or garlic bulb, certain seeds have evolved to require a cold period prior to germination for maximum production. Now you could toss these types of seeds out in the Fall & cross your fingers, that IS an option. It does however leave them exposed to animals, insects and possibly less than favourable conditions. But if you’re looking for a bit more certainty in your plantings, you can easily replicate these needs inside your fridge.
Options for Vernalization
There are options for vernalization such as potting mix, peat moss, perlite, paper towels. Moisten any of these mediums in trays, then bag them or they can go straight into ziplock bags, add the seeds & place them in your fridge anywhere from 2-4 weeks. You can usually check your seed package for the specific time requirements. Be sure that your chosen medium IS moist but NOT drenched, there is a happy medium there. Also, do future you a favour & clearly label the seed variety & date you did them up.
Once your time period is up, remove them from the fridge & place them in a bright, warm spot to stimulate the germination process. Many of these seeds can also be slow to germinate, so when you’re getting your garden plan ready, plan accordingly for these extra steps and time periods.
Experimenting in the Garden
One of my favorite parts of gardening is experimenting, so this year I went with a couple techniques; Potting mix in ice cube trays & ziplock bags with perlite. Both are easy to stack in the back of the fridge & I can reuse the bags & trays again. Then the left over perlite can go straight into the soil mix when potting the seeds up. Zero waste! Using a tray does however save you the added step of separating your seeds out of the perlite, but the trays take up more space. So there is a trade off there.
Wondering if you have some seeds that should be in the fridge right now? Well, there are literally thousands of plants that require the cold treatment, but here is a quick look at 100 common varieties that require or benefit from the process. Happy Planting!
- Abies (fir)
- Acer (maple, most species)
- Aconitum (aconite)
- Alchemilla (lady’s mantle)
- Allium (ornamental onion)
- Amelanchier (serviceberry)
- Aquilegia (columbine)
- Asclepias (milkweed, some species)
- Astrantia (masterwort)
- Baptisia (false indigo)
- Buddleia (butterfly bush)
- Caltha (marsh marigold)
- Caryopteris (bluebeard)
- Cercis canadensis (redbud)
- Chelone (turtlehead)
- Cimicifuga (bugbane)
- Clematis (clematis)
- Cornus (dogwood)
- Corydalis (fumitory)
- Delphinium (delphinium)
- Dicentra spectabilis, now Lamprocapnos spectabilis (bleeding heart)
- Dictamnus (gas plant)
- Dodecatheon (shooting star)
- Echinacea (purple coneflower)
- Eremurus (foxtail lily)
- Eryngium (sea holly)
- Eupatorium (Joe Pye weed)
- Filipendula (meadowsweet)
- Forsythia (forsythia)
- Fragaria (strawberry)
- Fuchsia (fuchsia)
- Gentiana (gentian)
- Geranium (perennial geranium, cranesbill)
- Goniolimon (German statice)
- Helianthemum (rock rose)
- Helianthus (perennial sunflower)
- Heliopsis (false sunflower)
- Helleborus (Christmas rose)
- Hemerocallis (daylily)
- Heuchera (coral bells)
- Hibiscus moscheutos (perennial hibiscus)
- Hypericum (St. John’s wort)
- Iberis (perennial candytuft)
- Ilex* (holly)
- Incarvillea (hardy gloxinia)
- Iris (iris, many species)
- Kirengeshoma (waxbells)
- Knautia (knautia)
- Lathyrus (perennial sweet pea)
- Lavandula (lavender)
- Leontopodium (edelweiss)
- Lobelia (hardy lobelia)
- Lonicera (honeysuckle)
- Macleaya (plume poppy)
- Magnolia* (magnolia)
- Malus (apple, crabapple)
- Mazus (creeping mazus)
- Mertensia (Virginia bluebells)
- Muscari (grape hyacinth)
- Myrrhis odorata (sweet cicely)
- Nepeta (catmint)
- Oenothera (evening Primrose)
- Opuntia* (beavertail cactus)
- Paeonia* (pivoine)
- Penstemon (beard-tongue)
- Persicaria (fleeceflower)
- Persicaria orientalis, syn. Polygonum orientale (kiss-me-over-the-garden-gate)
- Phlox (phlox)
- Physalis (Chinese lantern)
- Picea (spruce)
- Platycodon (balloon flower)
- Primula (primrose)
- Pulsatilla (pasque flower)
- Quercus (red and black oaks)
- Ranunculus (buttercup)
- Ratibida (prairie coneflower)
- Rosa (rose)
- Rudbeckia (black-eyed Susan)
- Sambucus (elderberry)
- Sanguinaria (bloodroot)
- Sanguisorba (burnet)
- Saponaria (soapwort)
- Saxifraga (saxifrage)
- Scabiosa (pincushion flower)
- Sedum (stonecrop)
- Sempervivum (houseleek, hen and chicks)
- Sidalcea (prairie mallow)
- Silphium (cup plant, compass plant)
- Staphylea* (bladdernut)
- Stokesia (Stokes’ aster)
- Syringa (lilac)
- Thalictrum (meadow-rue)
- Tiarella (foamflower)
- Tricyrtis (toad-lily)
- Trillium* (trillium)
- Trollius (globeflower)
- Tsuga (hemlock)
- Vernonia (ironweed)
- Veronica (speedwell)
- Viola (violets)
- Vitis (grape, some species)