The Ornamental Garden in September

  • By Pat Chadwick
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  • September 2017-Vol 3. No.9
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September marks the end of summer and the beginning of the autumn equinox. Daytime temperatures may still be hot and humid but night-time temperatures are beginning to cool down. As the seasons change, it’s time to devote more time to the garden for tackling end-of-summer maintenance tasks and preparing for cooler weather ahead. While you’re at it, look for gaps in the border where color is missing and consider options for making next year’s fall garden more exciting.


Some gardeners equate their late summer ornamental garden to a “dead zone” where very little appears to be in bloom. But that needn’t be the case. An easy solution is to plant groupings of cushion mums or pansies throughout the border for instant color. For a longer lasting and more creative solution to the problem, think outside the box. Besides the usual asters and chrysanthemums, lots of other plants offer both color and interesting texture. To amp up the glitz factor in your late summer garden, consider adding some of the following plants:

  • Anise hyssop (Agastache ssp.)
  • Artemisia
  • Beautyberry (Callicarpa)
  • Blue mist flower (Caryopteris)
  • Boltonia
  • Bugbane/black cohosh (Actaea racemosa)
  • Coral bells (Heuchera)
  • Culver’s root (Veronicastrum virginicum)
  • Dahlias
  • Goldenrod (Solidago)
  • Globe amaranth (Gomphrena)
  • Joe Pye weed (Eupatorium)
  • Lamb’s ears (Stachys)
  • Lantana
  • Mexican bush sage (Salvia leucantha)
  • Monkshood (Aconitum)
  • Ornamental peppers
  • Perennial Sunflower (Helianthus)
  • Pineapple sage
  • Pink Muhly grass (Muhlenbergia)
  • Red spider lilies (Lycoris radiata)
  • Russian sage (Perovskia)
  • Sneezeweed (Helenium)
  • Stonecrop (Sedum)
  • Toad lilies (Tricyrtis hirta)
  • Turtlehead (Chelone)
  • Zinnias

Hot Pink Zinnias Liven Up the September border.

For shadier gardens, include plants with interesting or colorful foliage such as coleus, fern species, variegated Solomon’s seal (Polygonatum), variegated hostas (unless you have a deer problem), Japanese forest grass (Hakonechloa) or wild ginger (Asarum).


It’s important to continue all those routine gardening maintenance tasks that you handled over the summer months. As long as the weather continues to be mild, weeds will continue to grow, plants will need to be watered, and spent flowers will need to be deadheaded.

Weeding – Crabgrass was particularly prolific this summer, thanks in part to the very hot, dry weather that it seems to prefer. Now that the weather is cooling down a bit, don’t ease up on your weeding tasks. In addition to keeping the crabgrass under control, stay alert to common ragweed (Ambrosia artemisiifolia) in your landscape and remove it before it produces flowers.  Just as summer weeds come to the end of their normal growing season, cool-season weeds (for example, henbit and chickweed) are beginning to appear among your plantings. 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 to provide supplemental water to your perennials, shrubs and trees. This is particularly vital for new plantings. Until the ground freezes, newly installed plantings need at least 1 to 2 inches of water per week while they are establishing roots.

Deadheading – To keep hanging baskets and container gardens blooming until the first frost, regularly remove spent flowers. Continue to deadhead perennials to coax more blooms from them before the frost finishes them. Also, focus on removing and discarding dead and diseased foliage that might otherwise harbor pathogens or pests over the winter.


With so much to do in the late summer garden, here’s a check list of activities that should be handled now:

Save Seeds.  Collect seeds from your favorite annuals and perennials for use in next year’s garden. Don’t forget to label and date the container so that you can correctly identify the seeds next spring.   Keep in mind that seeds collected from hybrid plants are unlikely to be identical to the “parent” plant.

Cut “Everlasting” Flowers. Collect sprigs of celosia, globe amaranth, statice, strawflower, and other plants that dry well. Bundle them loosely and hang them upside down in a dry, well-ventilated space away from direct sunlight.    

Make Stem Cuttings. While you can certainly dig up and overwinter wax begonias, geraniums, coleus, and other bedding plants, it’s usually more effective to root stem cuttings. They don’t take up as much room and they’re generally easier to keep alive over winter than a full-size plant. If you are new to stem cuttings, here’s how to do it:

  • 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.
  • 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.

Install new trees and shrubs.  Autumn is the optimum time to install new trees, shrubs, and perennials in your landscape. Here’s why:

  • The soil is generally warm enough to allow the new plants to establish roots before the plant goes dormant.
  • The cooler air temperatures exert less stress on the plant, allowing more energy to go into root development than just coping with hot weather.
  • Cooler weather means photosynthesis slows down, requiring less water to keep the plant alive and functioning.

Divide Perennials.  Many perennials can be divided either in spring or in fall. However, as a general rule of thumb, spring-blooming plants should be divided in the fall and fall-blooming plants thrive best when divided in the spring. Most perennials benefit from being divided every 3 to 5 years although some may need to be divided sooner. Some clues that a plant needs to be divided include:

  • Smaller-sized flowers than normal.
  • A dead space in the center of the plant.
  • Less vigor than in past years.
  • Allotted space is too small for the size of the plant.
  • Sparse foliage at the bottom.

Not all plants can be divided. For example, false indigo (Baptisia), milkweed (Asclepias), monkshood (Aconitum), and balloon flower (Platycodon) have taproots, which are difficult to divide without severely injuring or killing the plant.


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. In reality, 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. It spins a cocoon using silk and its own body hairs.  After about 2 weeks, it finishes its metamorphosis and emerges as an adult Isabella Tiger moth.

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. Spiders are both fascinating and fear-provoking. On the one hand, these shy creatures fascinate us because of the fragile, yet strong and elegant, silken webs they spin. On the other hand, spiders are scary looking. They have eight eyes, eight legs, and are related to ticks and mites. Many people fear them in the mistaken belief that they are all poisonous. In reality, most spiders are harmless to humans. However, 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. Very efficient predators, spiders 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.


Start preparing houseplants for the return indoors.

  • If your houseplants are currently in a sunny location, move them into a shadier spot so that they can adjust to lower light levels. You’ll want to move them indoors before night-time temperatures drop below the mid-50s.
  • Before moving houseplants indoors, wipe down the containers to remove cob webs, dirt and debris.
  • Thoroughly inspect each plant for insects, such as scale, white fly, or mealy bug.

Acclimate patio plants such as tropical Hibiscus for overwintering indoors. Before you move a tropical Hibiscus indoors, cut it back to about 6” tall.  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.






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