SPRING IS COMING, FOLKS! Consequently, if you haven’t winter-sown your flowering perennials yet, you really need to get hopping. For certain seeds (like the cranesbill geranium ‘Rozanne,’ above) require alternating freezes and thaws, or “stratification” in order to germinate well. Here is a list 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, pictured above), 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, pictured above), 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, pictured above), 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!
I hope the above list is useful to you.
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