The Ornamental Garden in September

QUESTION: Who doesn’t like to be told, “Do less, and things will be better.”

ANSWER: A lot of gardeners

Gardeners, on average, are an energetic lot. I also consider myself somewhat of a neatnik, and this characteristic is probably typical of many gardeners, at least in their outdoor space. In my old-style, nonnative garden, I looked forward to the autumn ritual of “putting the garden to bed.” I had learned to amend the soil with mulched leaves, but I also enjoyed cutting down the perennials and disposing of the spent foliage and brown flower heads. It gave me such pleasure to see the garden tidied up and tucked “safely” away as it waited for spring. I didn’t visualize all the activity that should have been going on.

Although we’ll address the details of preparing for the cold weather in our October/November issues, this is an early reminder of thinking about the ongoing relationship our gardens have with living things in every season. This often means “staying the hand” that wants to get a jump on things!

“Messy is definitely good to provide food and shelter for birds during the cold winter months,” says Tod Winston, Audubon’s Plants for Birds program manager. Birds are not the only wildlife who benefit. Cavity-nesting bees overwinter in waterproof cocoons inside spongy stems of plants such as elderberry and Joe Pye weed. Queen bumblebees often overwinter in small spots obscured by leaf litter. Butterflies need shelter and overwintering areas. Removing dead flower heads and dead plant foliage may accidentally remove eggs or pupating butterflies. As the September days and nights get cooler, don’t be too eager to “tidy up” the beds.

WHAT TASKS SHOULD WE DO?

• Keep watering shrubs, trees, and perennial plants that need regular moisture.
• Heading into the winter with dry roots can mean major trouble for trees in the spring. If we don’t receive adequate rain, keep watering trees on a regular schedule through the fall and until the ground begins to freeze (usually late October or November).  When there is little to no snow cover and little precipitation, plan on watering your trees 1-2 times per month until they begin leafing out in the spring. Water early in the day when the temperature is above 40°F and there is no snow or ice on the ground near your trees. See this article on when and how to water trees from fall through winter.
• Keep weeding! See this list of weeds with photos from the University of Maryland Extension for help with weed identification.
• Remove anything that looks diseased and do NOT compost. As an example, I’ve already cleaned out the lower, diseased-looking foliage of some purple coneflower (Echinacea), along with some seed heads that showed a fungus. I left the healthy-looking seed heads for the birds. Goldfinches seem to especially love purple coneflower seeds.
• Leaving the seed heads will also allow self-seeding. If your garden has space, this is a big bonus. If not, be on the lookout for seedlings next spring. Transplant to other areas or pot up for sharing.
• Remove the foliage of plants that have been infected by powdery mildew. This mildew often appears later in the growing season. Many fungal diseases can overwinter in plant debris and cause infections the following year when growing conditions promote disease. For example, powdery mildew is often prevalent when conditions are cool and wet. Powdery mildew thrives in 60-70°F, especially when humidity levels rise above 50%.

  

• Leave healthy foliage to help protect the crowns of some plants from cold temperatures. The energy from healthy foliage will remain in the plant to feed the roots. What types of perennials should retain foliage? Do not remove fern fronds because they protect the crown. Do not remove the evergreen foliage of hellebores. Perennials with basal crowns (a rosette of leaves that connects the stem to the roots) often die back to the crown. If a perennial is growing new basal leaves at the crown, cut off the spent stalks but don’t disturb the new leaves at the base. Examples of these perennials are coral bells (Heuchera sanguinea), Siberian bugloss (Brunnera macrophylla), Salvia x sylvestris, lungwort (Pulmonaria), black-eyed Susan (Rudbeckia), purple coneflower (Echinacea), rose campion (Lychnis coronaria) and wild blue indigo (Baptisia).
• Cut back grasses and sedges in early spring rather than in fall; this helps protect the crown during the winter, and provides habitat for insects, birds, and small mammals. The beautiful colors and textures of grasses and sedges also add winter interest to the landscape.
• Do not prune shrubs and trees in autumn unless you are removing damaged, dead, or diseased limbs. Pruning now may trigger new growth that cannot harden off before winter. Most woody plants should be pruned in winter when plants are dormant. According to the Shrub Pruning Calendar published by Virginia Cooperative Extension, only sumac is recommended for pruning in September, but this shrub can be pruned in any month with the exclusion of April-July. This pruning calendar is a very handy reference.
• Remove annuals that are spent, diseased, or if you know they’ll turn “slimy” with the first frost. Impatiens are a good example of annuals turning black with the first frost.
• Rejuvenate your planters by adding autumn flowers to your healthiest summer annuals. Although I enjoy getting a “second life” out of annuals, this year my containers are looking very ragged. I’ll need to start anew with fall flowers.
• Bring houseplants indoors before nighttime temperatures drop into the 50s. Inspect the plants carefully for insects such as scale, white fly, mealy bugs, spider mites, or fungus gnats. Wipe down the containers and the saucers, including the bottoms of each, to remove cobwebs, dirt, and debris. Pay particular attention to the undersides of leaves where pests are most often found. See this article from the Clemson Cooperative Extension for more information on identifying and treating houseplant pests.
• Fall is the time to rejuvenate the lawn. Get a soil test every three years; only fertilize according to test results. Fall is the time to add lime if you need to raise the pH. Aeration is also done in the fall. See “Responsible Lawn Management in the Era of Climate Change,” for more information.
• The cooler temperatures make this an ideal time to plant trees and shrubs. Newly installed woody plants do best when soil temperatures range from 55-75° F. Root development typically stops once soil temperatures drop below 40° F. Water newly planted trees and shrubs until the roots become established. Typically, this is a 2-year period.
• Consult the Native Plant List by Zip Code for a list of shrubs that you would like to try. Check the recommendations against the Audubon Native Plant list by Zip Code for trees and shrubs that attract certain birds.

 

DIVIDE PERENNIALS

September is an excellent time to divide perennials. Most recommendations cite 4-6 weeks before the first freeze date so that plants can set roots. The first freeze in our area (Zone 7a) typically occurs between October 15 — October 25.  This means that perennials should be divided starting in September and finishing by about mid-October (this is a low-risk recommendation, i.e., a low probability of getting caught by an early freeze.) This timing recommendation can also differ by hardiness of plants. More tender plants need a longer adjustment period.  For a chart showing the likelihood of a freeze (and how hard a freeze it might be) on particular dates in October, see the 10/20 issue of The Garden Shed.

Although many perennials may be divided in either spring or fall, a general guideline is to divide spring-blooming perennials in the fall and divide summer-to-fall blooming perennials in the spring. For detailed information on dividing perennials, see this article from The Garden Shed, “Guidelines for Dividing Perennials.”  This article also refers to a listing from the Minnesota Cooperative Extension on determining spring or fall division for specific perennials.

Fall is also a good time to plant perennials that you might find on sale at the end of season. Just be aware of the same first-frost date and 6-week guideline as described above.

PLANT BULBS

Plant spring-flowering bulbs when average nighttime temperatures are in the 40-50°F range, or when the soil temperature has dropped to 60°F (usually after the first heavy frost). For USDA hardiness zones 5 to 7 in Virginia, try to plant bulbs in October and in November. For good bulb selection, shop early and store the bulbs in a cool, dry dark place at a temperature of 60-65°F. If you are filling in spots among your established bulbs, hopefully you took a picture or left a marker last spring to show where additional bulbs are needed. If not, make a note for next spring!

FORCING HARDY BULBS

Making a plant flower at a predetermined time or under artificially imposed conditions is called forcing. Hardy bulbs are planted in pots in the fall for spring bloom and include crocuses (Crocus species), daffodils (Narcissus species), hyacinths (Hyacinthus species), and tulips (Tulipa species). Bulbs should be potted anytime from mid-September to December, depending on the desired date of flowering and the length of storage. If you cannot plant your bulbs immediately, store them in a cool place (35-55 °F). Bare bulbs can be stored for several weeks in the refrigerator prior to potting. Store them in a mesh bag or a paper bag with holes to permit ventilation. In general, plant in mid-September for flowering in late December, around mid-October for flowering in February, and in mid-November for March and April flowering. Refer to Forcing Bulbs Indoors, Clemson Cooperative Extension, for detailed instructions on planting and forcing bloom. This source also discusses how to force paperwhite narcissus (Narcissus tazetta; synonym N. papyraceuss) and amaryllis (Hippeastrum cultivars) without cooling.

A NEW GARDEN BED WITHOUT DIGGING!

Try sheet composting, also called “lasagna gardening,” to add new perennial beds and avoid the work of removing sod. This process requires about 6 months for the organic materials to break down, so fall is the perfect time to prepare the bed. Decide on the bed shape, mow the grass short, outline the bed with an edge. Cover the desired area with over-lapping cardboard (or newspaper), water, cover with a 2-3” nitrogen layer (compost, well-rotted manure, grass clippings), add a 2-3” carbon layer (wood chips, dry leaves, sawdust). Repeat with alternating nitrogen and carbon layers until you have reached a height of 18″-36″. Add another layer of cardboard and mulch. Decomposition will occur over the winter and the new garden bed will be ready for planting the following spring! See this article from The Garden Shed and an article from PennState Extension which includes a video.

FEED THE MANY

Before choosing which trees and shrubs to plant this fall, spend some time thinking about the overall needs of your landscape design. What kinds of birds, pollinators, or other wildlife do you hope to attract? Providing food and cover year round requires a variety of trees, shrubs, and other plants. Have you planted native bushes, such as viburnums, that provide berries? (See this article on viburnums from The Garden Shed.) Did you check to see how many of your shrubs act as larval hosts for certain butterfly or moth species? You can check this out through referring to the Native Plant Finder by Zip Code. One goal for fall could be to provide more food for birds through plantings, and reduce the reliance upon bird feeders. Feeders can fill a need when food is less plentiful between November-March.

INVASIVE WATCH FOR SEPTEMBER

We usually focus on one or two invasive plants based on seasonal alerts from Blue Ridge PRISM (Partnership for Regional Invasive Species Management). Many invasive plants described by PRISM are easily identifiable in fall because of either brightly colored berries, fall foliage, or both. In addition, the proposed eradication methods for these invasives are effective at this time of year. To see PRISM Fact Sheets on each plant and photos for identification, click on the link highlighted in the plant’s name.  For control methods, see Blue Ridge PRISM/Fact Sheets/Control Methods.  It is easy to feel discouraged at the length of this invasives list. You may consider devoting some of your fall energy to eradicating one or two invasive plants from your property. That would be a great start!

AUTUMN OLIVE (Elaeagnus umbellata)

Identify in fall when its silvery olive-green foliage stands out against the fall color or leafless branches of other vegetation.  Autumn olive is difficult to control, but it can be done with the cut-stump method.  Cut or saw all stems to several inches from the ground and immediately spray cuts with a ready-to-use stump killer or a concentrated herbicide.  For types and amounts of the herbicide recommended for autumn olive or any other invasive, Blue Ridge PRISM refers to Va. Dept. Forestry/Non-Native Invasive Plant Species Control Treatments.

BRADFORD PEAR (Pyrus calleryana ‘BRADFORD’) AND OTHER ORNAMENTAL PEARS

The fall fruits are round and vary from pea- to cherry-sized and ripen from green to brown with russet dots. Their leaves remain green later than most plants, turning bright colors very late in autumn. Best timing for all three methods of eradication described by Blue Ridge PRISM is fall through early winter.

JAPANESE HONEYSUCKLE (Lonicera japonica)

This vine retains its leaves well into winter (year round in mild climates). The tubular flowers are sweetly fragrant and bloom in pairs on opposite sides of the stems from early summer into fall. They open white or pinkish and mature to yellow. Small green berries, which ripen to black, may form after the flowers fade. 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 (24°F).

JAPANESE STILTGRASS (Microstegium vimenium)

Mowing is best done just before flowering in August and September and need be done only once if you wait until then. Cut stiltgrass as low as possible, scalping the ground, to remove all flowers.

KUDZU (Pueria montana var. lobata)

It is easiest to spot Kudzu when its reddish-purple flowers appear in late summer to early fall. Treatment with cut stumping is best done in late summer or early fall. Foliar herbicide sprays must be applied twice a year. The first spray is applied in late spring or early summer after leaves mature. The second treatment is applied in late summer or early fall.

MULTIFLORA ROSE (Rosa multiflora)

In addition to its long, thorny canes, this invasive is easy to spot in fall when the rosehips ripen to red. Cut stems about a foot from the ground and paint or spray a recommended concentrated herbicide immediately on the cut stump.

ORIENTAL BITTERSWEET (Celastrus orbiculatus)

Gold-colored foliage and brightly colored berries make this invasive easy to spot from fall into winter. Hand-pulling, cut stump, and foliar sprays are all possible treatments.

PORCELAIN-BERRY (Ampelopsis brevipedunculata)

This invasive is easy to spot in fall when colorful clusters of different colored berries (creamy-white, green, yellow, and lilac) ripen to bright turquoise blue in September and October. Herbicidal foliar treatment is most effective when applied between midsummer and early fall. The cut stump method is successful any time the temperature is above 40°F and is expected to remain at least that warm for 24 hours.

TREE OF HEAVEN, PARADISE TREE, AILANTHUS (Ailanthus altissima)

Male and female flowers occur on separate trees and form large, showy, yellowish-green clusters at the branch tips. Seed clusters on female trees begin creamy-yellow and ripen to yellow-green or red brown, retaining color until winter. Larger trees are best treated from early summer to early winter using either the hack & squirt or cut stump methods.

SOURCES:

“Monthly Garden Tips,” Piedmont Master Gardeners, https://piedmontmastergardeners.org/gardening-questions/monthly-gardening-tips/#September

September Tasks and Tips, The Garden Shed: 2020, 2019, 2018, 2017, 2016

“To Help Birds this Winter, Go Easy on Fall Yardwork,” Audubon, https://www.audubon.org/news/to-help-birds-winter-go-easy-fall-yard-work

“Should Perennials Be Cut Back in the Fall?” University of New Hampshire, https://extension.unh.edu/blog/2019/11/should-perennials-be-cut-back-fall

“Backyard Wildlife Habitats,” Virginia Cooperative Extension, https://www.oldragmasternaturalists.org/uploads/6/7/7/5/67752507/backyard_wildlife_habitat.pdf

“Building a Butterfly Garden,” NC Cooperative Extension, https://onslow.ces.ncsu.edu/2016/08/building-a-butterfly-garden/

“Prepare Your Garden for Winter Now,” Michigan State University Extension, https://www.canr.msu.edu/news/prepare_your_garden_for_winter_now

“Winter Tree Watering Tips,” Arbor Day Foundation, https://arbordayblog.org/treecare/winter-tree-watering-tips/

“Responsible Lawn Management in the Era of Climate Change,” The Garden Shed, https://piedmontmastergardeners.org/article/responsible-lawn-management-in-the-era-of-climate-change/

“A Guide to Successful Pruning: Shrub Pruning Calendar,” Virginia Cooperative Extension, https://resources.ext.vt.edu/contentdetail?contentid=3183&contentname=A%20Guide%20to%20Successful%20Pruning:%20Shrub%20Pruning%20Calendar

“Lasagna Mulching,” The Garden Shed, https://piedmontmastergardeners.org/article/lasagna-mulching/

“Create New Garden Beds with Sheet Composting and Sheet Mulching,” PennState Extension, https://extension.psu.edu/create-new-garden-beds-with-sheet-composting-and-sheet-mulching

“Forcing Bulbs Indoors,” Clemson Cooperative Extension, https://hgic.clemson.edu/factsheet/forcing-bulbs-indoors/

“Invasive Fact Sheets,” Blue Ridge PRISM (Partnership for Invasive Species Management), https://blueridgeprism.org/factsheets/

Feature Photo: Fall Garden, Susan Martin