The Ornamental Garden in October

  • By Pat Chadwick
  • /
  • October 2015 - Vol. 1 No. 10
  • /
  • 1 Comment

by Pat Chadwick

It’s October and the autumn landscape is glorious!   As you enjoy the show, keep in mind that the autumn “to do” list is very long, making this one of the busiest times of the year for the ornamental gardener.   Here are just some of the tasks that need to be completed before the onset of cold weather:

  • Plant spring flowering bulbs such as tulips, daffodils, hyacinths, crocuses, Dutch irises, and alliums after the ground temperature drops to or below 60°F. For more information on using bulbs in the landscape, see this month’s feature article.
  • Plant cool-season annuals such as pansy, viola, snapdragon, calendula, Iceland poppy, sweet alyssum, stock, and larkspur. Transplants of some of these annuals, particularly 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.  Seeds of cool-season annuals sown this fall will give you a head start on next year’s blooms.
  • Dig up the bulbs or roots of tender perennials such as canna, dahlia, caladium, elephant’s ear, tuberose, and gladiolus and prepare them for winter storage. These bulbs are either not hardy to this area or are only marginally hardy. This task is easier if you wait until after a light frost blackens the foliage. At that time, 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 them so that you can easily identify them next spring.
  • Divide and re-plant overcrowded perennials such as daylilies, yarrow, coreopsis, Shasta daisy, and lambs’ ears.   Water them 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 or transplant trees and shrubs before the ground freezes. Keep them well watered until they become dormant. For tips on how to prepare the planting site and how to care for trees and shrubs while they are becoming established, see Virginia Cooperative Extension Publication 430-295, “Tree and Shrub Planting Guidelines” (http://www.pubs.ext.vt.edu/430/430-295/430-295.html).
  • Clean up all flower beds. Remove all weeds, spent annuals, and other debris from flower beds. However, if you’re a bird lover, you may wish to 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 others in place until late winter or early spring before the new foliage emerges. Here’s a brief selected listing of perennials that may be left standing and why:
      • Agastache  If cut back in fall, the hollow stems can allow water to migrate down into the crown of the plant, which could cause it to rot over winter.
      • 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.
      • ChrysanthemumThe foliage and stems help protect the crown over winter.
      • Gaillardia (blanket flower) – This plant may be cut back in either spring or fall. The seed heads 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.
      • Lobelia (cardinal flower) – The leaves and stems help protect the crown in winter. Tip: The crown stays evergreen over winter but does not like to be covered with mulch.
      • Sedum (stonecrop)The thick, fleshy foliage of tall varieties such as ‘Autumn Joy’ falls off when temperatures drop. At that point, the plant may be cut back to within a couple of inches of the crown. However, many gardeners prefer to leave Sedum standing in place over the winter. The brown flower heads are very attractive in the winter garden, especially when they are covered in frost.
      • Perovskia (Russian Sage) — The stems help protect the crown in winter.
      • Tiarella (foamflower) – The leaves on some cultivars change color in the fall and last through the winter, which adds interest to the winter garden.
  • Mark where late emerging perennials are planted so that you don’t damage them next spring when you begin working in your flower beds. Wooden stakes, popsicle sticks, golf tees, and even plastic straws are useful for this purpose. 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.
  • Collect fallen tree leaves and compost them rather than send them to the local landfill. Chop the leaves into smaller pieces to help them decompose faster.
  • 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.
  • Cover your fall-blooming perennials with a frost blanket, old bed sheet, or even layers of newspaper if the threat of frost is imminent. If that’s not practical, consider cutting some of those late blooming flowers and bringing them indoors. To keep flower arrangements fresh for as long as possible, remove all foliage below the water line in the container. Add some floral preservative to the water and mix well before you arrange the flowers. You can easily make your own floral preservative by mixing two tablespoons lemon juice, one tablespoon sugar, and one-quarter teaspoon bleach in a quart of water. Don’t forget to change the water daily (preferably) or at least every other day.
  • Hold off on pruning tasks until after your plants go dormant. Pruning now can spur a plant to put out tender new growth, which cannot tolerate our winter weather.
  • 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.
  • One final item to add to your October “to do” list: Treat yourself to all the glorious autumn displays in and around the area. As you drive around town and beyond, look for interesting trees and shrubs that provide outstanding fall color. Note particularly colorful displays of foliage that appeal to you and consider the possibility of incorporating those plants into your own landscape.

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