When temperatures begin cooling off in the fall, it's time to put your perennials to bed for the winter. For the most part, perennials will overwinter just fine in Central Oregon by following these simple steps.
In late fall or early winter, your perennials will start to lose their leaves, die back and go dormant. At this time, cut them back to 6 to 8 inches above ground level. This will allow the stem to hold snow in place, which will insulate your plants from the cold.
You can also wait until spring to cut back perennials if you prefer. However, it's easier to apply mulch in the fall if plants have already been cut back.
Regardless of when you cut back your perennials, you’ll want to mulch them for the winter. For most perennials, you should apply 2 to 5 inches of mulch. You can use any kind of mulching material, such as hemlock mulch, pine post peelings, dried grass clippings, etc.
The mulch serves the dual purpose of holding in winter moisture and insulating the root system. Continuous freezing and thawing cycles can damage root tissue and cause root death. That's why it's best to apply mulch after the ground has frozen lightly. The mulch will keep the ground frozen.
Some perennials, however, do better without winter mulch. These plants don't tolerate wet soils and are susceptible to root rot or losing their centers.
On the other hand, some perennials are very tender and require extra winter mulch—5 inches or more. Below are lists of perennials that do better without mulch and those that prefer extra mulch.
Remember to water your perennials during dry spells when there is no snow cover. Water when the top portion of ground has thawed and can accept water. Water every four to six weeks during these periods.
Keep in mind that your perennials will wake up at different times in the spring. Don’t give up hope if you don’t see signs of life right away!
Perennials that prefer no additional mulch through winter
- Aster, Aster spp.
- Basket of Gold, Aurinia saxatilis
- Black-eyed Susan, Rudbeckia fulgida
- Blanket flower, Gaillardia aristata
- Creeping phlox, Phlox subulata
- Coreopsis, Coreopsis spp.
- Daisy, Shasta daisy, Chrysanthemum spp.
- Daylily, Hemerocallis spp.
- Delphinium, Delphinium spp.
- Dianthus (pinks), Dianthus spp.
- Evening primrose, Oenothera spp.
- Flax, Linum spp.
- Gas plant, Dictamnus spp.
- Gayfeather, Liatris spicata
- Geranium, Geranium spp.
- Geum, Geum spp.
- Germander, Teucrium spp.
- Globe thistle, Echinops spp.
- Grasses (most ornamental grasses)
- Hens and chicks, Sempervivum spp.
- Iris, Iris spp.
- Lamb’s ear, Stachys byzantina
- Larkspur, Delphinium spp.
- Mexican hat, Ratibida spp.
- Pasqueflower, Pulsatilla spp.
- Pearly everlasting, Anaphalis spp.
- Penstemon, Penstemon spp.
- Poppy, Papaver spp.
- Purple coneflower, Echinacea spp.
- Pussy-toes, Antennaria spp.
- Rockcress, Arabis spp.
- Russian sage, Perovskia atriplicifolia
- Salvia, Salvia spp.
- Silvermound, Artemisia schmidtiana
- Soapwort, Saponaria spp.
- Snow-in-summer, Cerastium tomentosum
- Spiderwort, Tradescantia spp.
- Spurge, Euphorbia spp.
- Stonecrop, Sedum spp.
- Sulfur flower, Eriogonum umbellatum
- Sunrose, Helianthemum spp.
- Tansy, Tanacetum spp.
- Thrift, sea pink, Armeria spp.
- Thyme, Thymus spp.
- Valerian, Centranthus spp.
- Yarrow, Achillea spp.
Tender perennials that prefer extra mulch (5 inches or more) throughout the winter
- Ajuga, Ajuga repens
- Bergenia, Bergenia cordifolia
- Chrysanthemum, Chrysanthemum morifolium
- English daisy, Bellis perennis
- False mallow, Sidalcea spp.
- St. John’s wort, Hypericum patulum
- Lavender, Lavandula spp.
- Pincushion flower, Scabiosa caucasica
- Plumbago, Ceratostigma plumbaginoides
- Wallflower, Erysimum spp.
- Armitage, A.M. 2000. Armitage’s Garden Perennials: A Color Encyclopedia. Timber Press.
- Brickell, C., and J.D. Zuk. 1996. A–Z Encyclopedia of Garden Plants. DK Publishing.
- Still, S.M. 1994. Manual of Herbaceous Ornamental Plants. Stipes Publishing.