Perennials Which Require Cold Stratification

February 15, 2013

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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Related Posts:
Winter-Sowing 101
What to Winter-Sow…& When
How’s Your Winter-Sowing Coming Along?
Old House Living: When the Power Goes Out
How to Clean Old Windows

Comments

  1. James says:

    Kevin, GREAT to have this list. Actually, I've already wintersown my perennials, including the Platycodon mentioned above.

  2. Samantha says:

    I love the geranium Roseanne! Are you wintersowing it this year?

  3. Eric says:

    Very helpful. Thanks!

  4. Adele says:

    Do you think these perennials, if wintersown, will bloom this summer? Or will you have to wait until next year to see the flowers?

  5. Samantha – No – I already have two Rozanne’s in the Serpentine Garden. I really love them, too. They bloom and bloom here from spring through frost.

  6. 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.

  7. Pippi21 says:

    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?

  8. Welcome, Pippi21. We are talking about winter-sowing outdoors in containers,
    right? My own policy with seeds is thus:

    Tiny, dust-like seeds: I don’t cover them. I do, however, press them down gently to insure good contact with soil. 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.

  9. Anonymous says:

    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!

  10. Betty819 says:

    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..

  11. 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!

  12. Patti says:

    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???

  13. Patti – Congratulations on your 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!

  14. Patti says:

    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!

  15. Antoniette says:

    I gave winter-sowing a go last winter and had 2 dozen containers out in the backyard in bins. The seeds which did the best were foxgloves and lupines, I had dozens and dozens of them! Some seeds did not germinate, and it could very well be that they were older seed since I was just experimenting. Painted daisies did fabulous as well, so I’m going to plant more seeds this winter. Great January project after the holidays are over and the gardening bug starts to hit!

  16. Jean says:

    Kevin: I checked on my seeds last weekend and saw that my Bachelor Buttons have sprouted. We have had a very warm winter for our zone 6 so I guess I shouldn’t have been surprised. I never thought I would like looking out my window and seeing milk jugs in my garden, but knowing what is going on inside of them makes them quite a lovely sight!! Thank you again for the inspiring ideas!!

  17. Pat Torgrimson says:

    Hi Kevin,
    I have wintersown seeds and put them on my back deck. They are now completly covered in snow. Should I remove some of the snow that they do get some light?

  18. Jean – Congratulations!

    Pat Torgrimson – No need to worry about the snow. Mine, until recently, were buried under a pile of white stuff, too.

  19. Tammy says:

    As I did my annual winter sowing I was trying to figure out which flower seeds benefitted from it and which didn’t. This list is so helpful, Kevin, thank you!

  20. Rosemary says:

    Having no gas stove, I used a hot glue gun (without the gluestick of course) to make the holes in my plastic milk and water bottles for winter sewing. Worked great! My gluegun is the type for hot temp. gluesticks not cold temp glue gun.

  21. Tammy – Nice to hear from you. So glad you found the list helpful.

    Rosemary – Hot glue gun – great idea!

  22. trillium says:

    I’ve been following the directions on the seed packets, planting them however deep they were instructed to be. Will let you know if they successfully grew or not. Great, inexpensive project. I have planted about 75 containers this winter, knowing that if successful, I’ll share some of the plants.

  23. Sandy H says:

    I’ve successfully started some of those, such as lavender and helianthus and rudbeckia, without stratification, so I’d check your seed pack to see if it’s absolutely required if for any reason you’re not thrilled by the idea of winter sowing. The nice thing about almost all those seeds that require it is that they are also busy self-sowers — at this point I mostly just transplant the babies. Sometimes I just throw those seeds where I want them in the garden as soon as there’s bare soil available (larkspur and alyssum work well that way).

    I use winter sowing as insurance. For instance, half my onions get winter sown and half get started in the house. (Usually the winter sowing in the actual garden under the cold frame wins when it comes to size at transplant time, probably because it is less stressed by container crowding if I procrastinate planting. Sometimes it’s also the only part of the crop to avoid damping off, though now that I’ve learned about chamomile tea as a solution for that I tend not to lose much indoors to that either). The only problem this year is that my cold frame is already fully populated by spinach I sowed in December and other greens that have self-sown, so I’m going to have to make room.

  24. Martha says:

    Hey Kevin–you mention perennial asclepias–how about the annual varieties? There are some wonderful ones available now. I grew some last year and saved seeds.
    (These are also great for attracting monarch butterflies and finding the caterpillars.)

  25. debra kohl says:

    do I need to wintersow columbine? thanks.

  26. debra kohl – You don’t have to winter-sow columbine (Aquilegia). But you certain can. I winter-sowed dozens of columbine seeds back in 2010, and to my horror, every seed germinated when spring arrived!

  27. Arianna says:

    Kevin, I’ve been doing “winter stratification” without knowing it by leaving my old seed packets in an unheated garage! This year, in our community garden, at the questions of the children in the area, we are trying this method, with a few differences on pecans! All of the articles promised saplings if done properly. Who knew you could get trees from your nut bowl?

  28. Ivy says:

    Kevin,

    I planted some turnips and mustard seeds in late October or early November and they are looking great! Ilive in the Atlanta,Ga. area I’am thinking that in terms of growing season I
    am a little off is that correct?

  29. Sandra says:

    Hello Kevin,
    Your site is terrific! I have WS for the first time this year– and am very excited, the Malva zebrina has just sprouted. I’ve been writing the name on the outside of the milk jug — in (purple!) nail polish… shows up well, and then I keep a log of when planted, & add the date in permanent marker. It’s been so wet, the perm. marker on my earlier plantings was fading fast.
    Cheers,
    Sandra

  30. Dolores Clifton says:

    Wow, Kevin, stumbling upon your blog a few months ago has been a godsend for me. The valuable info you share has changed my perspective on gardening, even in my high desert area. We range from 7a-5b in this capital of NV… Our state only receives 7.5″ of annual rain. Most all of our water comes from the snow pack in the Sierra’s. Through trial and error, I’ve found many successes, but I’m quite anxious to try your jug method of starting the seeds! It seems I’m usually late for starting them, then planting, whilst waiting for the last frost – we’ll get ours mid-June to July1! I can appreciate how your method really starts hardy, happy, seeds. Oh, I look forward to your weekly wisdom. :)

  31. Kent says:

    I thought ‘Rozanne’ was sterile? You can’t get seeds for it that I know of. Plus, ‘Rozanne’ isn’t pink, as in the pic.

  32. Shelly says:

    Hi
    Thanks for the great site. I’m going to give this a try. My pop bottles are ready to fill and seeds are waiting to be planted. Can I use Shultz potting soil plus for my bottles? It has sphagnum peat moss composted forest products perlite lime and time released fertilizer.
    Thanks. ..wish me luck !

Trackbacks

  1. [...] in your garden. Speedwell needs a period of cold weather to germinate. This process, known as stratification, softens the seed coat so that it splits quickly in the spring when moisture and warm temperatures [...]

  2. [...] of freezing and thawing. The freezing and thawing helps break open the seed coat. Here’s a long list of perennials that require cold stratification, but among those familiar to northern gardeners are perennial [...]

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