SPRING IS COMING; if you haven’t winter-sown your flowering perennials yet, you really need to get hopping. For certain seeds (including the cranesbill Geranium ‘Roseanne,’ above) require alternating freezes and thaws, or “Cold Stratification,” in order to germinate. Here is a list (compiled, I’ll confess, for my own easy reference as well as yours) of common perennials which need this yin and yang treatment:
Aconitum (Monkshood), Alchemilla (Lady’s Mantle), Alstroemeria (Peruvian Lily), Asclepias (Milkweed), Astrantia (Masterwort), Baptisia (False Indigo), Buddlejah (Butterfly Bush), Caltha (Marsh Marigold), Caryopteris (Bluebeard), Chelone (Turtlehead), Cimicifuga (Bugbane), Clematis, Delphinium, Dodecatheon (Shooting Star), Eremurus (Foxtail Lily), Filipendula (Meadowsweet), Fuchsia, Gentiana (Gentian), Geranium species (Cranesbill Geranium), Goniolimon (German Statice), Helianthemum (Rock Rose), Helianthus (Perennial Sunflower), Heliopsis (False Sunflower), Helleborus (Christmas & Lenten Rose), Heuchera hybrids (Fancy-leaved Coral Bells), Hibiscus (Hardy Hibiscus), Hypericum (St. John’s-Wort), Iberis (Perennial Candytuft), Incarvillea (Hardy Gloxinia), Kirengeshoma (Waxbells), Knautia (Crimson Scabious), Lathyrus (Perennial Sweet Pea), Lavandula (Lavender), Leontopodium (Edelweiss), Macleaya (Plume Poppy), Mazus (Creeping Mazus), Mertensia (Virginia Bluebells), Myrrhis odorata (Sweet Cicely), Nepeta (Catmint), Oenothera (Evening Primrose), Penstemon (Beard-tongue), Persicaria (Fleeceflower), Phlox (all types), Physalis (Chinese Lantern), Platycodon (Balloon Flower), Primula (Primrose, all types), Pulsatilla (Pasque-flower), Ranunculus (Buttercup), Ratibida (Prairie Coneflower), Rudbeckia (Black-eyed Susan, most types), Sanguinaria (Bloodroot), Sanguisorba (Burnet), Saponaria (Soapwort), Saxifraga (Saxifrage), Scabiosa (Pincushion Flower), Sedum (Stonecrop), Sempervivum (Hen-and-Chicks), Sidalcea (Prairie Mallow), Stokesia (Stokes’ Aster), Thalictrum (Meadow-rue), Tiarella (Foamflower), Tricyrtis (Toad-lily), Trollius (Globeflower), Vernonia (Ironweed), Veronica (Speedwell), Viola species types (Violets).
The simplest way to accomplish cold-stratification is to plant seeds in covered containers, and then set them outdoors. This easy program is outlined in my post Winter-Sowing 101. Just be sure to make your plantings sooner rather than later. Don’t wait until the nightly freeze becomes the nightly thaw!
And, I hope you find the above list useful. I certainly do!
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Related Posts:
Winter-Sowing 101
Making a Greenhouse & Sowing Seeds
Kevin, GREAT to have this list. Actually, I've already wintersown my perennials, including the Platycodon mentioned above.
I love the geranium Roseanne! Are you wintersowing it this year?
Very helpful. Thanks!
Samantha – No – I already have two Roseanne's in the Serpentine Garden. I really love them, too. They bloom and bloom here from spring through frost.
Do you think these perennials, if wintersown, will bloom this summer? Or will you have to wait until next year to see the flowers?
Adele – some will bloom this summer; Campanula, for instance. Others may bloom closer to fall, while others sown this winter won't bloom until next year. But that's OK. Gardening has taught me not to hurry!
Kevin, How do you know which seeds require DO NOT COVER, COVER LIGHTLY, NEEDS DARKNESS? By any chance do you have such a list of light requirements?
Welcome, Pippi21. We are talking about winter-sowing outdoors in containers,
right? My own policy with seeds is thus:
Tiny seeds: do not cover. Just press down gently to insure good contact with soil. The only exception here is Delphinium, which I sprinkle with a tiny amount of fine soil. This is habit, not gospel.
Larger seeds: sow 1/8-inch deep, never deeper.
I hope this is helpful to you; if not, kindly let me know! Keep in mind that with winter-sowing, you can generally ignore the directions on seed packets.
Your blogspot is so inspirational and so informative. Thank You for sharing all of your gardening knowledge and experience. Sure wished you were my neighbor or lived in our neighborhood!
Kevin, I am in love with that purple triumph tulip called Purple flag. Do you recall where you ordered it from? It's color is so different and I love its satiny texture. Those Blue Jacket hyacinths have caught my eye too. I write the names of flowers that I love from you blogspot so I can add them to my flowerbeds in 2011/2012. When you go looking at all these bulb and seed catalogs, it is helpful to have the specific names so you don't order the wrong thing. What about the exact variety of those grape hyacinths that you have planted with the Purple Triumph “Purple flag” tulips? Do you realize how many varieties there are in catalogs of this bulb? The colors are either blue or purple and sometimes look the same. You have a good eye for color..
Betty – Those are the same types of muscari I force for indoor bloom. The variety name is Cote d'Azure. They are truly lovely. I'm glad you like the combo — I'm drawn to purples and blues, too!
I am trying my hand at this winter sowing… Some success so far. Assylum, morning glory, and larkspur! Its amazing… I live in zone 6. What are your thoughts on Imperial Star Artichokes???
Patti – Congratulations on winter-sowing success. I was not familiar with the Imperial Star artichoke until I looked it up just now. Thanks to you, I think I’ll add it to my wish list!
Good luck Kevin. I am trying an experiment. I started seeds indoors (on the windowsill) and out on the patio table (winter sowing). The indoor has germinated and sprouted. The outdoor …nothing yet…UGH! I will keep you posted. Thank you for your inspiring articles! Happy seeding!