As gardeners, we know how to care for our perennial gardens in spring and summer, but late fall can be a tricky time preparing plants for winter. We know that fall cleanup and winter preparations are necessary, but knowing when to mulch, how much to prune or how to deal with dry soil can be confusing. Mostly established through trial and error, this system will help perennials survive the winter in unpredictable Zone 5 climate.

CUT BACK PLANTS SELECTIVELY
The key to perennial garden fall cleanup, and successful growth the following spring, is determining which plants to cut back and which to leave standing. Many perennials are herbaceous; they die back to the ground every year. Plants such as astilbe, bee balm, hosta, daylily, and peony are examples of herbaceous perennials. Once frost hits, the top growth of these plants turns brown or black, and the plants enters dormancy. Use hand pruners to cut off the dead stems and leaves at ground level, then remove the debris, eliminating places for harmful organisms to overwinter. Cutting back this dead material improves the garden’s winter appearance and clears the way for new growth in spring.

Other perennials, such as black-eyed Susans, Hollyhock Zerbina, and Shasta daisies, are semi-herhaceous. The stems and upper foliage of these plants die back, but their base foliage stays green through the winter. Cut off the dead material but leave 2 or 3 inches of green foliage at the base. Perennials that are truly evergreen and those with a woody framework are two groups of perennials that should never be never pruned at the end of the season. On plants such as such as pinks and creeping phlox, snip off old flower stalks and leggy growth, but leave the rest alone. Cutting these plants to the ground in fall is usually fatal since when conditions allow, they photosynthesize throughout the winter. When new growth begins to emerge in early spring, cut out the damaged foliage to make way for new growth, then prune plants for shape.

Perennials with a woody framework, called subshrubs, include artemisia, butterfly bush, lavender, and Russian sage. Subshrubs have exposed growing points, called leaf buds, all along their woody stems. Don’t cut these plants back in the fall or you’ll be removing the leaf buds for next season. Wait until you see new leaves expanding along the stems in spring, then cut the stems back to healthy wood, leaving 6 inches remaining above the ground.

Consider which plants to leave standing because their seedheads provide food for birds or for structural interest. Upright sedums such as Sedum ‘Autumn Joy’ and ornamental grasses are classic examples of plants that add visual interest to the winter garden. Perennials that provide seed for birds include purple coneflower, Joe Pye weed, and sunflowers.

TO COVER OR NOT TO COVER?
In general, remove leaves from most sun-loving perennials, and add leaves to your shade gardens as mulch. As a rule, sun-lovers require good soil drainage. A heavy blanket of leaves will trap moisture and can lead to rot over the winter. Remove leaves from plants like artemisias, catmint, chrysanthemum, lavenders, Shasta daisies, thymes, and yarrows.
Provide some extra protection anything planted after the first of August. These plants haven’t formed a mature root system, so giving them a 3-4 inch layer of compost when the ground has frozen protects them from frost heaving. Compost provides an insulating blanket through the winter and gradually breaks down to improve soil structure and feed plants.

PROVIDE WATER AND WIND PROTECTION
Winter watering is critical to evergreen plants that continue to photosynthesize when it’s cold. When the soil is dry, plants can’t take up enough water to compensate for moisture lost through their leaves. Good soil drainage is critical to successfully overwintering perennials. There aren’t many plants that tolerate cold, waterlogged soil for any length of time as roots and crowns will rot and die. To promote good drainage in our clay-based soil, add lots of organic matter when digging a new bed, and replenish it annually by top dressing with compost in mid-spring. Perennials should not go into winter with completely dry roots. If rainfall is in short supply, continue to water all perennial beds until the ground is frozen. Fall and winter watering is very important to evergreen perennials through the cold months. If the soil is too dry, the roots can’t take up enough moisture to compensate for what they lose from their leaves. This is especially true on windy days when cold gusts increase moisture loss. During January and February, keep a hose handy to spot-water evergreen perennials if the ground thaws and we are short on natural moisture.

DON’T NEGLECT EARLY SPRING CHORES
When new growth begins to emerge, it’s time to begin pulling leaves back from perennials. However, don’t remove all the mulch at once, take it off gradually by removing about one-third of the material at a time. This gives the new growth time to adjust to increased light and wind and acclimate to extremes in temperature. Keep the mulch nearby, so if killing frost is forecast plants can quickly be re-covered.

Early to mid-spring is also the time to finish dealing with the woody subshrubs left standing over the winter. Once you see new leaves emerging along the stems, cut back artemisia, butterfly bush, lavender, and Russian sage to about 6 inches from the ground or by about one-third. Take care not to prune too hard because cutting into the old wood may kill the plant. While you’re on your knees doing these chores, it’s always a pleasure to see the winter-dormant perennials pushing up through the ground, emerging from their long winters nap with renewed vigor.

Robin Milliken is a Landscape Specialist and Master Gardener
The Master Gardener appears monthly in The Olathe Daily News.
© H&R Lawn and Landscape

Links to other monthly columns: