The Ornamental Garden in October
The beautiful fall days make garden chores a happy excuse to be outside. It won’t be long before we’re raking and mulching leaves, and putting things to bed. But we still have some time before we turn the last seasonal page on this year’s garden. What should we do now, and which plants need our attention both in and out of the garden?
The nights have already started to get nippy, and it’s conservatively safe to take houseplants inside once the nighttime temperatures start dropping below 55⁰F. Inspect plants for insects and diseases. Wipe the leaves with a damp cloth or spray them with the hose. Soak the pot in a tub of lukewarm water for about 15 minutes to force insects out of the soil. Check to see if roots are pushing through the bottom of the pot; if so, the plant needs to be repotted. If plants have gotten leggy over the summer, remove them from the container, and prune the top and roots in equal proportions. Replant in a cleaned pot with fresh potting soil (not garden soil).
Plants will need to adjust to the lower indoor light level. Be careful not to over water. If plants are dropping leaves, they may not be getting enough light. Place them in a south-facing window, if possible, or at least in an east-facing window. Place pebble trays with water below plants that benefit from humidity. It’s a good time to take some cuttings from plants that have grown large over the summer. You can also take cuttings from larger annual plants, such as coleus or begonia. Either root cuttings in water, or dip them in root hormone and place in soil.
CARING FOR TENDER BULBS
Tender bulbs, including dahlia, canna lily, elephant ear (Colocasia), caladium, begonia (Begonia tuberosa), and gladiolus, are planted in the spring for summer bloom but cannot survive cold winter temperatures and must be dug up each fall.
Using a shovel or garden fork, carefully dig up the bulbs (or underground tubers or rhizomes). To the extent possible, avoid damaging the bulbs; diseases can easily contaminate plants through cuts and bruises. Although the general process is the same, the preparation requirements vary by type of plant. Most are dug up after the first frost but there are a couple of exceptions. The tops are cut back, but the recommended height varies. Some species should be washed, most are air- dried. The curing or drying period differs, as does the recommended curing temperature. Even storage temperatures vary. The Missouri Botanical Garden and the University of Minnesota Extension are good resources for highlighting requirements specific to different plants. Remember to label stored plant material carefully.
FORCING HARDY BULBS
Making a plant flower at a predetermined time or under artificially imposed conditions is called forcing. Hardy bulbs are particularly suited for forcing indoors and offer a succession of color throughout the winter and spring months. Hardy bulbs are planted 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 up 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 to 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 flowers in February, and in mid-November for March and April flowers. Refer to Forcing Bulbs Indoors, Clemson Cooperative Extension, for detailed instruction 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. Another useful source is the Virginia Cooperative Extension publication, Fooling Mother Nature: Forcing Flower Bulbs for Indoor Bloom.
GENERAL GARDEN TASKS AS THE MONTH PROGRESSES
Plant spring-flowering bulbs once the soil temperature has dropped to 60°F at a depth of 6-12 inches, (usually after the first heavy frost). For USDA hardiness zones 5 to 7 in Virginia, try to plant bulbs in October and November; in the small section of hardiness zone 8 in southeastern Virginia, plant in December.
Cut back perennials with disease or insect pest problems to reduce the chance of infection the following season. Bee balm (Monarda) and phlox (Phlox paniculata) with powdery mildew are examples. Remember to destroy, not compost, diseased stems and leaves. Cut back hostas and remove all their leaves from the ground as soon as the frost takes them. Dead hosta leaves harbor slug eggs. Although many plants add structure and interest to the winter garden, as well as seeds for hungry birds, cut back plants with browning or blackened foliage and bare stalks that don’t add anything visually to the winter garden such as peonies (Paeonia), daylilies (Hemerocallis), and speedwell (Veronica).
Certain plants do not like to be cut to the ground before winter because the foliage protects their crowns. Plants that like some winter foliage protection include: butterfly weed (Asclepias tuberosa), chrysanthemums, coral bells (Heuchera sanguinea), Siberian bugloss (Brunnera macrophylla), Salvia x sylvestris, lungwort (Pulmonaria), bearded penstemon (Penstemon barbatus), catmint (Nepeta), and Shasta daisy (Leucanthemum x superbum). If a perennial is growing new basal leaves, cut off the spent stalks but don’t disturb the base.
Don’t be in a rush to cut back healthy perennials, advises PennState Extension. Cut back after several hard frosts have killed the tops. In the spring, the plant sends up energy from its roots to produce beautiful foliage and blooms. Allow the roots time to reclaim that energy from the dying plant, keeping it strong for re-emergence in the spring.
Evergreen perennials such as certain ornamental sedges are not cut back in fall; remove dead foliage in spring and summer.
Rake leaves out of flower beds. If left in place, they may harbor pests and possibly certain diseases. If leaves mat down, they can prevent moisture from getting to the soil. After raking them up, mulch them with a lawn mower or mulcher and spread on flower beds.
Make leaf mold compost by collecting raked leaves in a pile. A simple bin made of chicken wire works well to keep them from blowing away. The video, How to Make Leaf Mold, Turn Fallen Leaves into Gardener’s Gold, has some good tips (and the presenter has a very convincing British accent). Viewers took exception to his saying that pine needles create acidic mulch. See the Q/A from Oregon State University Extension. People were also surprised that it took two years to make the finest textured leaf mold. Of course, you can use leaf mold compost that is not totally broken down as a 1-2” layer of mulch laid on top of the soil. For the science behind the process of making leaf mold as well as instruction, see the University of Wisconsin Extension Pepin County publication, Leaf Mold Compost.
Start cleaning and storing any breakable lawn ornaments or structures that a hard frost might harm. Clean pots in the fall to make to make things easier next spring. For concrete containers, try the following: leave the plant in the pot, dig a hole, bury the pot up to the top of the soil, cover the pot with leaves but leave the foliage exposed. I’ve had success the past two years doing this with an autumn fern (Dryopteris erythrosora. ‘Brilliance’). The fern came back nicely each spring.
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. The vast majority of woody plants should be pruned in winter when the plant is dormant. There are some exceptions. Check the Virginia Cooperative Extension’s Publication 430-462 Shrub Pruning Calendar, Publication 430-460 Deciduous Tree Pruning Calendar, and Publication 430-461 Evergreen Tree Pruning Calendar for a listing of common woody plants and the best time to prune them.
“Transition House Plants to the Indoors,” University of Vermont, https://pss.uvm.edu/ppp/articles/bringin.html
“Storing Bulbs, Rhizomes and Tubers, University of Minnesota Extension, https://extension.umn.edu/how/planting-bulbs-tubers-and-rhizomes#storing-tender-bulbs-1403111
“Gardening Help FAQs, Missouri Botanical Garden,” http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/gardening-help-faqs/questionid/12/afmid/4462.aspx
“Forcing Bulbs Indoors,” Clemson Cooperative Extension, https://hgic.clemson.edu/factsheet/forcing-bulbs-indoors/
“Fooling Mother Nature: Forcing Flower Bulbs for Indoor Bloom,” Virginia Cooperative Extension, https://pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/HORT/HORT-76/HORT-76-PDF.pdf
“Making Leaf Mold,” University of Wisconsin Extension Pepin County, Mike Travis, https://pepin.extension.wisc.edu/?s=Making+leaf+mold
“How to Make Leaf Mold – Turn Fallen Leaves into Gardener’s Gold,” GrowVeg, YouTube.
Plant Finder, Missouri Botanical Garden, https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=265190&isprofile=0&
“Cutting Down Perennials in the Fall,” PennState Extension, https://extension.psu.edu/cutting-down-perennials-in-the-fall
“Myth Versus Reality – What’s the Truth Behind Some Common Garden Practices?” Oregon State University Extension, https://extension.oregonstate.edu/news/myth-vs-reality-whats-truth-behind-some-common-gardening-practices
Feature Photo: Autumn Colours, Siddharth Mallya, Wikimedia Commons