September is an “in-between” month when daytime temperatures still feel summery but cooler nights signal the beginning of autumn. As long as the weather continues to be mild, weeds will continue to grow, plants will need to be watered, and the garden will need to be kept tidy.
Weeding – Summer weeds are coming to the end of their normal growing season now, but cool-season weeds such as henbit deadnettle (Lamium amplexicaule) and common chickweed (Stellaria media) are starting to appear. If not removed this fall, they will overwinter in your landscape and resume growing next spring. A few minutes spent weeding now will significantly reduce the number of weeds facing you next spring.
Watering – If there’s no rain in the near-term forecast, continue providing supplemental water to your perennials, shrubs, and trees, particularly those newly planted this year.
Tidying – In addition to weeding, a general sprucing up can make a big difference in your garden’s appearance this month.
- Cut back diseased and unsightly flower stalks of perennial species once they have finished blooming. But don’t get too aggressive with your tidying. If the flower stalks are healthy, they may be left in place to provide habitat for overwintering insect species.
- Re-edge flower beds to provide a nice sharp line of demarcation between lawn and garden. This simple task can make your garden look well maintained even if the plantings don’t look their best.
- Remove damaged or diseased leaves of hostas, day lilies, and other perennials. Not only will this make the garden look neater but, more importantly, it will remove foliage that might otherwise harbor fungal diseases and other pathogens over the winter.
- Cut back and fertilize leggy annuals early in the month to improve their appearance and to encourage one more round of blossoms. Or, if the plants appear to be beyond hope, replace them with cool season bedding plants, such as mums or ornamental cabbage and kale.
- Unless you have already stopped deadheading perennials, consider leaving the seed heads in place for the birds to enjoy. The seeds from coneflower, black-eyed Susan, aster, and other late season blooming plants are a vital source of food for many bird species in the winter.
- If mounding perennials, such as hardy geraniums, catmint, and spiderwort look messy, overgrown, and out of control at this point, make a note (for future reference) to shear them back after they finish blooming in the summer. This will help improve the overall appearance of the plant and encourage it to sprout fresh new growth which will look attractive through fall. Depending on the species, some perennials may even reward you with another round of blossoms before frost.
AUTUMN-SPECIFIC GARDENING TASKS
With cooler temperatures on the horizon, the timing is perfect for dividing perennials and planting trees and shrubs, among other autumn-specific tasks.
Divide Perennials. September and early October are ideal times to divide plants due to the combination of warm soil, cooler temperatures, and a greater chance of rain. Technically, a plant may be divided any time during the growing season, but you’re likely to have best success if you divide spring- and early summer-blooming plants in the fall and fall-blooming plants in the spring. Pick a cool day for this task. Water the divisions well when you plant them and continue to keep them watered so that they become well established before the ground freezes.
While most perennials benefit from being divided every 3 to 5 years on average, some plants, such as asters, may need to be divided more often. Others, such as peonies, may not need to be divided at all. Look to the plant for clues that it needs to be divided such as:
- Fewer or smaller-sized flowers than in past years.
- A dead area in the center of the plant’s crown.
- Less vigor than in past years.
- Weak inner flower stalks that flop over and can’t hold up flowers.
- Sparse foliage at the bottom of the stems.
- Too large for its allotted space in the landscape.
Not all plants can be easily divided. For example, false indigo (Baptisia), milkweed (Asclepias), monkshood (Aconitum), and balloon flower (Platycodon) have taproots that are difficult to divide without severely injuring or killing the plant.
For more information on this topic, see Guidelines for Dividing Perennials in the March 2021 issue of The Garden Shed.
Make Stem Tip Cuttings. While you can certainly dig up and overwinter wax begonias, geraniums, coleus, and other bedding plants, they don’t always respond well to the transition indoors. It’s usually more effective to root new plants from stem cuttings. The cuttings don’t take up as much room indoors and they’re generally easier to keep alive over winter than a full-size plant. Here’s how to propagate a plant from a stem cutting:
- Fill a clean container with a moistened sterile potting mixture.
- Select a healthy stem or branch and cut a 3” to 6” long piece of it with a sharp knife just below a leaf node.
- Remove any leaves or flower buds from the portion of the stem that will be below the soil line.
- Dip the cut end of the stem in a rooting stimulant. This helps the cutting root better but is not essential.
- Using a pencil or other pointed instrument, make a hole for the cutting in the potting mixture.
- Insert the cut end of the cutting and gently tamp soil around it to hold it upright.
- Cover the entire container with a clear plastic bag.
- Place the container in a warm spot that has bright but not direct sunlight.
- Check the potting soil regularly and mist it with warm water as needed to keep it moist but not soggy.
- Once the cutting resists a gentle tug, that’s a sign that roots have begun to form.
Propagating Hyssop stem tip cuttings. Photo: Pat Chadwick
Save seeds. One of the great pleasures of gardening is growing plants from seeds collected in your own garden. If you are new to saving seeds, annuals and biennials are grown from seed. Some perennial species may be grown from seed (such as coneflower, rudbeckia, and cardinal flowers) but most are grown from cuttings or divisions. Be sure to save seeds from open-pollinated or “heirloom” species rather than hybrids. This ensures the offspring will resemble the parent plant from which the seeds were collected. Plants grown from hybrid varieties often revert to characteristics of earlier generations and are not likely to resemble the parent plant.
- Gather seeds when they are fully ripe but leave some for the birds to eat over winter.
- If seeds aren’t already fully dry, spread them out on newspapers or leave them in an open paper bag to dry.
- Place the dried seeds in envelopes or glass jars labeled with the seed’s name and the date.
- Store the packaged seeds in a cool place. Some gardeners like to store their seeds in the refrigerator.
To learn more about saving seeds, see the article on Growing Plants From Seeds You Collect in the September 2017 issue of The Garden Shed.
Cut and preserve flowers, such as globe amaranth, statice, strawflower, and other plants that dry well, for use in dried flower arrangements. A simple method for drying them is to bundle them loosely and hang them upside down in a dry, well-ventilated space away from direct sunlight. Purdue University Cooperative Extension service has good information on how to preserve plant materials.
Direct sow seeds this fall of cool-season annuals, such as calendula, California poppy, larkspur, love-in-a-mist, snapdragon, and sweet alyssum. These species require a period of cold, moist weather (a process called stratification) to break down the seed coating so that the seed can germinate. While technically these seeds may be planted very early in spring, greater germination success may be achieved by planting them in the fall.
Got deer? Install plastic fencing, chicken wire, or other barriers around shrubs and trees, particularly young or newly planted ones, to prevent damage this fall from deer browsing and antler rubbing. Another approach is to install 4 or 5 sturdy metal fencing stakes around vulnerable plants.
Buy bulbs for fall planting while supplies are still plentiful. As you plan ahead for next year’s spring garden, expand your horizons and experiment with bulbs other than daffodils and tulips. Invest in some of the early-blooming minor bulbs such as snowdrops (Galanthus nivalis), starflower (Iphieon), scilla (Siberian squill), crested iris (Iris cristata), glory-of-the-snow (Chionodoxa), and other easy-to-naturalize hardy bulbs for planting this fall. As extra incentive to you, the deer, rabbits, voles, and other wildlife generally do not bother these early bloomers.
TREES AND SHRUBS
Fall is traditionally the best time of year to plant woody ornamental species in the landscape. Newly planted trees and shrubs are happiest when soil temperatures range between 55°F and 75°F. Without the stress of hot summer weather, they can focus on developing good root systems before the onset of winter. Root development stops once soil temperatures drop below 40°F. To give those plantings the best possible chance for success, keep them well watered. Don’t rely on rainfall alone to maintain adequate moisture levels. Also, be sure to maintain a three-inch layer of mulch over the root ball area, but not up against the trunk of the plant, to help hold in moisture and to moderate the soil temperature. For suggestions of shrubs and trees to plant, check out the Virginia Cooperative Extension’s publication 450-236, Problem-Free Shrubs for Virginia Landscapes, and The Virginia Department of Forestry’s publication on Common Native Trees of Virginia.
Don’t become alarmed if the needles on white pines (Pinus strobus) start to show some yellowing around mid to late September. It’s perfectly normal for the older, interior needles to shed.
HOUSEPLANT CARE
Remember – you gradually acclimated your plants for their transition to the sunny outdoors this spring. Now that it’s time to bring the plants indoors for the winter, you need to reverse the process.
- If your houseplants are currently in a sunny location, move them into a shadier spot about 2 weeks in advance of bringing them indoors so that they can adjust to lower light levels.
- Before moving the plants indoors, wipe down the containers to remove dirt and debris.
- Thoroughly inspect each plant for insects, such as scale, white fly, mealy bugs, and fungus gnats, or insect eggs and larvae. Don’t forget to check under pot rims for spiders. Inspect the bottoms of containers as well as the bottoms of saucers for insects or their egg cases.
- While daytime temperatures may be hot, night-time temperatures become noticeably cooler in September, particularly toward the end of the month. Plan to move houseplants indoors before night-time temperatures drop below the mid-50s.
Acclimate patio plants such as tropical Hibiscus for overwintering indoors. Before you move a tropical Hibiscus indoors, cut it back to about 6” tall and inspect it for insects. This plant is particularly prone to white flies. Once the plant is indoors, position it near a bright window where it will get plenty of light. Lightly water it over the winter months.
SEPTEMBER CREEPY CRAWLIES
Banded Woolly Bear Caterpillar – According to a common urban myth, the color bands on the harmless woolly bear caterpillar are a predictor of just how mild or severe the winter will be. If the black bands on either end of this bristly-looking caterpillar are longer than the center reddish band, the winter will be harsh. Conversely, a wider center band supposedly indicates that the winter will be mild. Neither is true. In fact, the wideness of the center band has more to do with the age of the caterpillar than its ability to predict the weather. Woolly bears, also called “woolly worms,” become very active in autumn as they search for protected places to spend the winter. They may be handled but the bristles covering their bodies are prickly to the touch and may cause a rash on sensitive skin. This amazing little creature produces a cryoprotectant in its tissues, which allows it to survive harsh winter weather even when frozen solid. In spring, it becomes active again and briefly resumes feeding before pupating. After about 2 weeks, it finishes its metamorphosis and emerges as an adult Isabella Tiger moth (Pyrrharctia isabella), which is indigenous to the United States and parts of southern Canada.
Spiders – Friend or Foe? The sight of sunlight sparkling on early morning dew is uncommonly beautiful at this time of year, particularly when it reveals a surprising number of spider webs glistening in the landscape. On the one hand, spiders fascinate us because of the fragile looking yet strong and elegant webs they spin. On the other hand, spiders are scary looking. They have eight eyes, eight legs, and are related to ticks and mites. Although most spiders are harmless to humans, two spiders in this area of Virginia are poisonous — the black widow spider and the brown recluse spider. A bite from either one of these dangerous species can cause serious symptoms requiring prompt medical attention. To learn more, see the Virginia Cooperative Extension’s publication on Spiders of Medical Concern in Virginia. Spiders are very efficient predators and feed entirely on other insects or animals that are small enough for them to catch. In fact, they play a significant role in helping to control many pest insects. For that reason, give them a wide berth if you are afraid of them, but give them credit for the beneficial role they play in our gardens.
INVASIVE ALERT
Porcelain-Berry (Ampelopsis brevipedunculata) is easy to spot in September and October when clusters of different-colored berries ripen to bright turquoise blue. This invasive vine is a rapidly growing woody perennial vine with a vast hard-to-kill root system. Herbicidal foliar treatment is most effective for eradicating the vine when applied between midsummer and early fall. It is the only feasible option for treating large infestations. Cutting back the vines and spraying the regrowth is a good way to reduce the amount of herbicide needed. Another method is to cut the largest stems down near the ground (cut stump method) and apply a concentrated, recommended herbicide immediately to the cut. A third method is to use a basal bark application if you can reach the largest stems in the tangle. This requires applying a concentrated, recommended herbicide mixed with horticultural oil to the lowest 12” of the stems; no cutting is needed. For additional information on Porcelain-Berry, see the Blue Ridge Partnership for Regional Invasive Species Management (PRISM) Factsheet.
Autumn olive can be controlled in autumn, or at any time of year (except during spring growth), by cut-stumping or hack & squirting. For detailed guidance, including a very helpful video, take a look at Autumn Olive/Sept. 2023/The Garden Shed.
Many invasive plant species are easier to identify in fall because of their brightly colored berries, fall foliage, or both, and Porcelain-Berry is just one example. To learn more about other invasive species in this area of Virginia and methods for controlling them at this time of year, see the Blue Ridge PRISM website. See also the Invasive Plant Control Calendar in the May 2022 issue of The Garden Shed.
PESTICIDE WARNING
Pesticides (which include herbicides, insecticides, rotenticides, etc.) are poisonous. Always read and carefully follow all precautions and safety recommendations given on the container label. Store all chemicals in the original labeled containers in a locked cabinet or shed, away from food or feeds, and out of the reach of children, unauthorized persons, pets, and livestock. Consult the pesticide label to determine active ingredients, signal words, and proper protective equipment. Pesticides applied in your home and landscape can move and contaminate creeks, lakes, and rivers. Confine chemicals to the property being treated and never allow them to get into drains or creeks. Avoid drift onto neighboring properties and untargeted areas.
FEATURED PHOTO: New England aster ‘Violetta’ with rough-stemmed goldenrod ‘Fireworks’. Photo: Pat Chadwick
SOURCES
The Perennial Care Manual (Ondra, Nancy J., 2009)
The Well-Tended Perennial Garden, Third Edition (DiSabato-Aust, Tracy, 2017)
“Indoor Plant Culture,” Virginia Cooperative Extension (VCE) Publication 426-100
“Planting Trees,” VCE Publication HORT 426-702
“Porcelain-Berry,” Blue Ridge PRISM Factsheet.
“Spiders: An Undeserved Bad Reputation,” VCE Publication ENTO-393NP.
“Wooly Bear Caterpillar: Winter Predictor or Not?” National Weather Service Article, www.weather.gov/arx/woollybear
Virginia Tech Weed Identification Website VA Tech Weed Identification list.
