The Ornamental Garden in October

October rivals anything that spring has to offer in terms of beauty, color, and interest in the ornamental garden.  Masses of late blooming perennials, shrubs with brightly hued berries, and the vibrant fall foliage on many trees and shrubs collectively provide a truly glorious gardening experience.  Meanwhile, this month is a particularly busy time for gardeners.  So let’s get started on that “to do” list.

PLANT, DIVIDE, AND TRANSPLANT

• Plant spring flowering bulbs now that soil temperatures are dropping into the 60s or below. For a succession of color throughout spring, plant a variety of early, mid- and late season bulbs starting with the earliest snowdrops and ending with late blooming tulips and alliums.  Tip: Some gardeners have a reaction similar to contact dermatitis when handling tulip, daffodil, or hyacinth bulbs.  As a precaution, wear gardening gloves when handling bulbs or wash your hands with cool water and soap immediately after planting.
• Plant cool-season annuals such as snapdragon, calendula, Iceland poppy, sweet alyssum, stock, and larkspur. Seeds sown in fall of cool-season annuals will bloom about two weeks earlier than spring-planted seeds.  Transplants of other cool-season annuals, such as pansies and violas, are generally easy to find in local garden centers.  For best results, they need to be well established in the soil before freezing winter weather sets in.
• Divide overcrowded perennials such as daylilies, yarrow, coreopsis, shasta daisy, and Stachys (lambs’ ears). Water them in well so that they become well established before winter, but hold off on mulching them until after the first hard frost to help prevent frost heaving.
• Plant deciduous trees and shrubs before the ground freezes and keep them well watered until they become dormant.   Think about planting trees and shrubs that offer multi-seasonal interest. A few suggested trees to consider include maple (Acer), black gum (Nyssa sylvatica), dogwood (Cornus), or sourwood (Oxydendrum arboretum).   Some suggested shrubs for multi-seasonal interest include Virginia sweetspire (Itea virginica), oakleaf hydrangea (Hydrangea quercifolia), fothergilla (Fothergilla gardenii), blueberry (Vaccinium spp.), red-twig dogwood (Cornus spp.), or spicebush (Lindera benzoin).   For tips on how to prepare the planting site and care for trees and shrubs while they are becoming established, see Virginia Cooperative Extension (VCE) Publication 430-295, Tree and Shrub Planting Guidelines.  Also, check the National Weather Service’s Climate Prediction Center for long-term forecasts so that you can time the planting before a rain is predicted to fall.

TACKLE GENERAL FALL GARDEN CLEAN UP TASKS

• Clean up all flower beds. Remove all weeds, twigs, spent annuals, and other debris from flower beds.   However, if you’re a bird lover, leave some seed-bearing perennials in place. Echinacea (coneflower), Rudbeckia (black-eyed Susan), ornamental grasses, and other plants, such as sunflowers, will provide food for the birds this winter as well as sanctuary for overwintering beneficial insects.  Wait until late winter or early spring to cut them back before new foliage emerges.
• Not sure which perennials to cut back and which to leave standing over the winter? Some plants should be cut back for aesthetics and to prevent the overwintering of pests and diseases.  The best time to do this is after a couple of killing frosts.  If the weather continues to stay warm in October and the plants are still producing flowers, this task may need to wait until November.  Here’s a brief selected listing of perennials to cut back in autumn and why:
  • Achillea (yarrow) – Cut back to induce new basal growth, which helps protect the plant crown in winter.
  • Aquilegia (columbine) – Cut back to control leaf miners.
  • Baptisia (false indigo) – Unless you like the dark seed pods, cut the plant back for aesthetics. The foliage turns black after frost and is unattractive.
  • Bearded Iris – Cut back to prevent overwintering fungal disease and iris borers.
  • Corydalis – Cut back to contain the plant and to keep it from spreading.
  • Crocosmia – Cut back for aesthetics.
  • Hemerocallis (daylily) – Unless you have an evergreen variety, remove dead foliage and dried flower stalks for aesthetics and to help contain daylily rust (fungal disease).
  • Hosta – Cut back for aesthetics. Foliage turns to a mushy mess with the first hard frost.
  • Iris domestica (blackberry lily) – May be cut back in either spring or fall. Leave standing until spring if you want the interesting seed heads to add interest to the winter landscape.   Cut back now if you want to avoid harboring overwintering borers or if you want to keep the seeds under control.
  • Monarda (beebalm) – Cut back to control the spread of powdery mildew.
  • Phlox paniculata (garden phlox) – Cut back to prevent the spread of fungal diseases and to prevent the plant from dropping seeds in the garden.
• While many perennials need to be cut back in the fall for aesthetics and pest/disease control, there are advantages to leaving some perennials in place until late winter or early spring before the new foliage emerges. So it’s OK, in fact desirable, to leave some dormant foliage and stems in place over winter. A major reason is that the old foliage helps protect the crown of the plant over the winter months. Another good reason is that many beneficial insects overwinter in the dead stems and foliage as eggs or pupae and then hatch out in the spring. Here’s a brief selected listing of perennials that may be left standing and why:
  • Agastache — The stems help protect the crown of the plant over winter and also provide habitat for overwintering beneficial insects.
  • Amsonia – The foliage helps protect the crown of the plant during the winter. Also, fallen leaves often catch in the plant’s standing stalks and provide extra protection to the crown.
  • Aster novae-angliae (New England aster) – The foliage and stems on this late-blooming perennial help protect the crown and add texture and interest in the winter landscape.
  • Bergenia (pigsqueak) – The evergreen leaves turn shades of purple and deep red and provide interest in the winter garden.
  • Chrysanthemum – The foliage and stems help protect the crown over winter.
  • Echinacea – The seedheads provide food for birds as well as texture and interest in the winter landscape.
  • Gaillardia (blanket flower) – This plant may be cut back in either spring or fall. The seedheads provide food for the birds over winter.  If you don’t want the plant to re-seed, cut back in autumn.
  • Helleborus – The foliage remains green over winter, which adds texture and interest to the garden. However, it will look unsightly by late winter, at which point it should be carefully cut back before the new spring growth emerges.
  • Tall Sedum – The browned seedheads look attractive in the winter and the hollow stems provide overwintering sites for beneficial insects.
• Dig up the bulbs or roots of tender perennials such as canna, dahlia, caladium, Alocasia (elephant’s ear), tuberose, and gladiolus and prepare them for winter storage. These bulbs are either not hardy to USDA Zone 7 or are only marginally hardy. This task is easier if you wait until after a light frost blackens the foliage.  Cut off all the foliage, then carefully dig up the roots so that you don’t damage them.  Inspect them and discard any that appear diseased or soft.  Allow the roots to dry thoroughly, clean off soil, and pack loosely in peat moss or vermiculite in open baskets or cardboard boxes.  Store in a cool, dry, dark, frost-free location over the winter.  Don’t forget to label the bulbs so that you can easily identify them next spring.
• Mark where late emerging perennials are planted so that you don’t damage them next spring when you begin working in your flower beds. Asclepias (milkweed), Platycodon (balloon flower), Baptisia (false indigo), and some ferns are examples of late emerging perennials.
• Bag all diseased foliage and stems from peonies, garden phlox, or roses and dispose of the debris in the trash. Do not add it to the compost pile.  This will reduce the overwintering of botrytis blight, mildew, and other fungal spores.
• Remove cool-season weeds, such as chickweed, dandelion, wild onion, plantain, and white clover. A few minutes spent pulling these weeds from flowerbeds now will save you many hours of work next spring.
• Protect water features from the accumulation of falling leaves and other debris. Spread netting over the water feature and secure it to keep the leaves out of the water. Remove the leaves from the netting as they accumulate.
• Shred or chop fallen leaves and compost them or save them to use as mulch on next year’s garden. If you’re new to composting, check out VCE Publication 426-703, Making Compost From Yard Waste. For additional information on mulching and composting leaves, see The Garden Shed’s October 2018 Tasks and Tips for the Ornamental Garden in October.
• Have a soil test done this fall if you haven’t had one done in the past two or three years. Soil amendments, such as lime, manure, compost, and chopped leaves, are best added to flower beds in the fall.  But don’t amend until after you get the results of the soil test. For additional information on soil testing, see VCE Publication 452-129, Soil Sampling for the Home Gardener.
• Leave seed heads in place for annuals that you want to self-seed or just scatter the mature seeds where you want them yourself. Some of the annuals and biennials that reseed themselves include cleome, cockscomb, cosmos, foxglove, hollyhock, larkspur, money plant, sweet William, forget-me-not, Shirley poppy, zinnia, four-o-clock, marigold, vinca (Madagascar periwinkle), and impatiens.
• Take preemptive action to prevent deer damage to the bark or branches of young or newly planted trees and shrubs. In fall and winter, male deer rub or scrape against young trees for two reasons: (1) to rub the summer velvet from their horns and (2) to mark their territory as a way to attract female deer and warn other male deer away. Wrap vulnerable tree trunks with a physical barrier such as wire or plastic mesh tree guards, chicken wire, or woven wire fencing. This will protect the trees while allowing them room to grow.

MANAGE AUTUMN INSECT PESTS

Irises are susceptible to a variety of pests and diseases.  One of the most annoying is the iris borer, which is the larvae of the brownish-looking nocturnal Miller Moth (Macronoctua onusta).  The moth lays its eggs on old iris leaves and flower stalks in autumn.  The larvae hatch in late spring and tunnel into the leaves on their way down to the rhizome.  The damage they cause makes the rhizome susceptible to bacterial soft rot.  Iris borer eggs that overwinter on dead foliage are the source of infestation each spring.  To break the life cycle of this pest, remove dead leaves from rhizomes in autumn to prevent any eggs from surviving over the winter months.

Inspect your evergreen trees and shrubs for bagworms.  Bagworm eggs overwinter on evergreens such as junipers, spruce, hemlock, and arborvitae as well as many other trees.  Pick off and burn any egg cases that you find. This may be done from fall until spring. See VCE Publication ENTO-351NP on Bagworm for additional information.

PREVENT UNINVITED WINTER HOUSE GUESTS 

Around mid-October, the adult Lady Beetle (or Ladybugs as they are more commonly known) begins moving out of the garden and into nooks and crannies under tree bark, leaves, or other sheltered spots that will afford them protection from winter’s cold weather.  As they search for winter lodgings in earnest, they often enter our homes through tiny cracks around windows, doors, attic vents, or any other opening available to them.

The Brown Marmorated Stink Bug is another insect that often tries to overwinter in your home. Fortunately, the stink bug population seems to have dissipated somewhat over the past few years.  However, if you see them gathering on the south or west-facing side of your house, chances are very good that they will try to seek entry into your home for the winter.

Insects aren’t the only creatures seeking a warm place to spend the winter.  Rodents often look for entry points into the home.  To prevent access, seal all potential entry points.  Leaving the garage door up is an open invitation to a mouse or rat.  Make sure there’s no food available to attract them such as grass seed, bird seed, and seeds that you’ve saved from your garden.

ACCLIMATE HOUSEPLANTS

If you didn’t bring your houseplants indoors at the end of September, definitely get them indoors this month.  The longer they stay outside, the harder the transition to the indoors will be for them.   Once they are indoors, keep a close watch on them for spiders, spider mites, white fly, scale, mealy bug, and other unwanted hitchhikers.  These pests may not show up for days or even weeks after you’ve moved the plants indoors.

Houseplants may go through a period of adjustment to lower light levels.  If they are getting sufficient water but dropping leaves, they may not be getting enough light.  If that’s the case, try relocating them to a brighter location.

ENJOY THE AUTUMN LANDSCAPE AND PONDER WHY LEAVES CHANGE COLOR

As you work on your October gardening tasks, take time out to enjoy the view. As the days have shortened and temperatures cooled, the vivid colors of autumn have transformed the landscape. The transformation starts in the cooler, higher elevations and gradually spreads to the warmer, lower-lying valleys. Meanwhile, the veins that transport fluids into and out of leaves gradually close off at the base of each leaf.  The clogged veins trap sugars in the leaf, which promotes the production of anthocyanins.

Three types of pigments are involved in autumn color:

• Chlorophyll, which gives leaves their green color, is present in the chloroplasts of leaf cells throughout the entire growing season.
• Carotenoids, which produce yellow, orange and brown colors, are also present in the chloroplasts of leaf cells throughout the growing season but are masked by chlorophyll. Once the leaves stop producing chlorophyll, the carotenoid pigments become visible.
• Anthocyanins, which produce reds, pinks, and purples, are typically not present during the growing season. Anthocyanins are only produced in the fall and are manufactured from the sugars that are trapped in the leaves. They are water soluble and appear in the watery liquid of leaf cells.  Their purpose is to protect leaves from being eaten or from getting sunburned.

Many of us are puzzled by the fact that fall colors are vibrant some years and subdued in other years.   The intensity of color is influenced by temperature, sunlight, and soil moisture levels before and during the time chlorophyll is dwindling in the leaves.  The most brilliant autumn colors are generally produced in years with a warm wet spring, favorable summer weather with adequate rainfall, and warm sunny fall days with crisp, cool nights.  See the US Department of Agriculture Forest Service website for more information on the Science of Fall Colors.

INVASIVE ALERT

Japanese Honeysuckle (Lonicera japonica) is a rapidly spreading nonnative vine that competes for both above- and below-ground resources, inhibiting the growth of desirable trees, shrubs, grasses, and wildflowers.  A woody perennial vine, Japanese honeysuckle retains its leaves well into winter (year-round in mild climates). Hand pulling young vines is effective only if all roots are removed.  Any roots left in the soil will resprout.  A foliar spray may be a more effective way to kill the entire plant. The best time to spray is autumn and early winter after most native plants have lost their leaves or are dormant, but before a hard freeze (25°F). Foliar sprays are less effective in spring because the herbicide does not thoroughly move from the leaves into the roots during spring growth.

For additional information on methods for eradicating Japanese Honeysuckle, refer to the Fact Sheet/Japanese Honeysuckle published by the Blue Ridge Partnership for Regional Invasive Species Management (PRISM). Also see the  Invasive Plant Control Calendar in the May 2022 issue of The Garden Shed.

 

 

 

SOURCES:

Featured Photo of  Aromatic Asters (Symphyotrichum oblongifolium):  Fern Campbell

Monthly Gardening Tips/October/Piedmont Master Gardeners/Gardening Resources