Fall Garden Cleanup: Prune This, Not That

By David Salman, Founder of High Country Gardens

Fall is well underway and many of us are focused on getting our gardens and landscapes ready for their winter rest. With the effects of climate change already impacting our lives, we no longer have the luxury of gardening just for beauty. We must also plant and care for our landscapes to benefit the creatures that share our environment. We can do this by providing habitat, supported by our plant choices and maintenance methods. Here is some guidance as to which plants need to be cut back in fall or winter and which should be left standing until spring to make your garden and landscape more "habitat friendly."

Read on for tips in all areas of your garden:

• Deciduous Shrubs & Trees
• Leaves
• Ornamental Grasses
• Perennial Plants & Flowers
• Lawns & Meadows

Deciduous Shrubs & Trees

Winter is an ideal time for pruning deciduous plants (woody plants that lose their leaves), because they are dormant.

• Most fruit, flowering, and shade trees all benefit from winter pruning. This will help to remove crossed branches, gently shape their branch structure, and, with shade trees, help to maintain strong non-forked leaders.
• Don't shear the branches of spring flowering shrubs (Forsythia, Lilac, New Mexico Privet, Spirea, Flowering Quince, and others). These shrubs produce flowers on last year's wood, so removing old growth will reduce or prevent flowering. These plants should be pruned immediately after they are done blooming. 
• Summer blooming shrubs like Russian Sage (Perovskia), Spirea (Caryopteris), and Butterfly Bush (Buddleia davidii and hybrids) should be left untrimmed over the winter months.
  • Russian Sage should be cut back hard in mid-spring, leaving stems 12-15" tall. This should be done every spring to keep them blooming heavily.
  • Blue Mist Spirea and Butterfly Bush should be cut back by 1/3 to 1/2 of their height every third year (NOT annually) to re-invigorate the shrubs and encourage blooming.

Leaves 

Don't kick this valuable resource to the curb! Leaves are a valuable resource for soil building and mulching. They also provide habitat for pollinators, such as bumblebees and beetles, beneficial insects, and wildlife. 

• Leaves should be raked from lawns but utilized elsewhere in the landscape. Chopping up leaves will help them break down more easily; rake them and put them through a shredder or use a lawnmower to shred them. They can also be added to your compost pile.
• Use leaves as mulch under trees, shrubs, and evergreens.
• Use chopped leaves to mulch perennial beds and vegetable gardens.
• In wetter climates, it's best not to leave layers of fallen leaves on top of your untrimmed perennials and other flower beds, as they will cause problems with fungus and rot. Instead, chop 'em up and use them as mulch to improve your soil.

Ornamental Grasses

Why leave ornamental grasses standing? There are many reasons to leave these grasses standing over the winter months. Their foliage and seed heads offer texture, movement, and beauty in the winter; they'll be illuminated by the low angled winter sunshine. Plus, many beneficial insects use these grasses to provide protection for overwintering egg masses, larvae, and adult forms. Leaving ornamental grasses standing until late spring gives the insects time for their eggs to hatch and their larvae to change into adults. Birds will also utilize standing grasses as sources for seed and winter shelter. Ground birds, such as quail, will use large ornamental grasses for winter protection.

• Warm-season grasses should be cut back in mid-spring. This will protect the crown of the plant, and encourage new growth as temperatures warm. Warm-season grasses include Little Bluestem (Schizachyrium), Big Bluestem (Andropogon), 'Blonde Ambition' Blue Grama (Bouteloua), Muhly (Muhlenbergia), Switchgrass (Panicum), Maidenhair Grass (Miscanthus), Giant Sacaton (Sporobolus wrightii), and others. 
• Cool-season grasses have evergreen foliage that should not be cut to the ground. Instead, vigorously "comb out" dead leaves with gloved hands and clip off the dead leaf tips in late fall. In early spring, clip off old seed heads from stalks as far down into the foliage as possible to leave room for late spring flowers. Cool-season grasses include Blue Avena Grass (Helictotrichon), Fescue Grass (Festuca), Silky Thread Grass (Nassella) and 'Karl Foerster' Feather Reed Grass (Calamagrostis).
• If the grass plant has a ring of living leaves with a dead center, it's time to divide the grasses to re-invigorate them. This is necessary once every three to five years depending on the species and growing conditions.

Perennial Plants & Flowers 

Why leave perennial plants & flowers standing over winter months? Like ornamental grasses, it's a good idea to leave perennials standing as well. These plants will often provide the same shelter to beneficial insects as the ornamental grasses. 

Seed bearing perennials such as Purple Coneflower (Echinacea), Joe Pye Weed (Eupatorium), Hummingbird Mint (Agastache), Lavender (Lavandula), perennial Sunflower (Helianthus), and others, also provide valuable winter food for songbirds. Additionally, species with stiff stems and ornamental seed heads, such as Yarrow (Achillea), Purple Coneflower (Echinacea), Tall Stonecrop (Sedum), and others with flat or cone-shaped dried flowers, add to the garden's winter beauty.

Plus, perennials are more cold hardy when their stems are left standing over the winter. This is helpful for overwintering perennials that are living at the edge of their cold hardiness zones. For example, when native Sage (Salvia), Hummingbird Mint (Agastache), and Hummingbird Trumpet (Zauschneria) are planted in USDA zones 5 & 6, this will help them survive the winter cold. This is especially true for young plants (in the ground one to two growing seasons).

• Wait until mid-spring to cut back perennials.
• If perennial plants are exhibiting some summer/fall disease or are infested with injurious insects, then in these instances, these damaged plants should be cut back, and scraps thrown away in the trash, not the compost, to prevent the disease or pests from spreading.
• Learn More: Perennial Plant Care In Seasons 1 & 2

Lawns & Meadows

• Native Buffalo Grass and Blue Grama Grass, as well as Dog Tuff lawns, should be given the last mowing in late October.
• Mow the grass high, leaving it at least 4" tall. Never scalp the lawn in the fall, as this weakens it and leaves the stems vulnerable to damage from cold and dry conditions.
• Grass meadows and wildflower meadows, like ornamental grasses and perennials, should also be left standing over the winter. Mow with the mower deck set high in mid-spring.

Banner Image by Saxon Holt, featuring Rabbitbrush (Chrysothamnus), Switchgrass (Panicum virgatum), Silky Thread Grass (Nasella), and Russian Sage (Perovskia).