What To Do in the Garden in September & October
Hairy bittercress
SEPTEMBER
The best time to renovate or install a lawn is late August through September. Cooler, longer evenings and moist weather encourage root growth. It’s easier to keep the seedbed moist for germination, and annual weeds such as crabgrass will be unable to set seed before frost.
Plant colchicum and the true fall crocus bulbs as soon as they are received. Otherwise, Colchicum may bloom in the bag! Go ahead and plant them anyway, and they will be ok.
Replace tree guards around vulnerable tree trunks to prevent “buck rub” deer damage.
Start planning to bring houseplants inside, especially tropicals. This allows for an adjustment period (maybe even quarantine in case they have pests). Holiday cacti and cymbidiums need cool temperatures to set flower buds, but not cold or frost. A cool room inside should suffice.
It’s your last chance to plant veggies outside—only radishes and maybe spinach are fast-growing and hardy enough to get a crop. Consult ccetompkins.org/gardening/food-gardening/last-planting-dates.
Plant a hardy cover crop such as winter rye in vacant garden spaces. Otherwise, I sheet-compost there instead (flattened cardboard covered by leaves).
Consider planting hardy veggies in a cold frame or low (or high) tunnel for winter crops. Think about overwintering potted herbs on a sunny windowsill. I have had good luck with basil, parsley, and sage. Rosemary needs careful watching and watering, as it doesn’t wilt when dry, it just dies.
Keep up with the weeding, but ease off on the deadheading. Roses, for instance, will be better prepared for winter if allowed to set hips.
Visit your local nurseries for great sale plants. Also, tour display gardens and note what is blooming now. There are many fall-blooming perennials besides mums! Hybrid anemones that have not become invasive at my house, even after 20 years, are ‘Honorine Jobert’ and ‘September Charm.’ Cimicifuga ‘White Pearl’ is a fragrant late bloomer susceptible to early fall frosts, so plant it in a sheltered part shade location. Ditto for Korean wax bells (Kirengeshoma spp.) and hardy begonia (a zone six plant that has overwintered for me several years in a sheltered spot). Mark the hardy begonia well since it doesn’t come up until almost June. Fall monkshood is very frost-hardy and brings that deep marine blue to the garden (remember it’s poisonous, though). There is even a late-blooming hosta called ‘Red October’, but only the petioles and flower scapes are red.
Divide and replant hardy spring-blooming perennials as soon as possible. You can also move or divide the hardier perennials such as tall perennial phlox, hosta, or daylilies. Avoid disturbing shallow-rooted perennials like heuchera that are prone to heaving.
Make maps or take pictures of your plantings before the first frost hits and the leaves fall. Replace labels if needed. Pencil lasts a long time on plastic labels and doesn’t fade in the sun. Take notes about what needed to be moved/divided/replaced next year. Finish planting container perennials and woodies. Keep them well watered. I mulch right after planting to allow more root growth before the soil cools off too much, despite the usual recommendation to wait until the ground freezes.
OCTOBER
October is the best month to move peonies (both herbaceous and tree peonies, if necessary, but this is a big job!). We dig, divide, and pot up herbaceous peonies in October for the May plant sale, and most of them will bloom in the pots around sale time. It’s also the best month to dig up and divide hardy lilies. Its time to finish planting your spring-flowering bulbs outside! I mulch crocus and tulips with pea gravel to deter the critters that might be inclined to start digging. Start potting up the hardy bulbs you want to force (you can finish this task in November). Protect potted crocus and tulips from mice.
Mid-October is the best time to plant garlic. Be sure to rotate the garlic to a well-drained area, and mulch after planting. It’s recommended to plant the biggest cloves and save the smaller ones to eat.
Late October is a good time to start cleaning up around your perennials. Consider cutting down dead stalks (except for mums, Japanese painted ferns, kniphofia, and semi-woody plants like lavender, sage, Russian sage, and butterfly bush, which overwinter better with the protection of the old stalks). You may choose to leave stalks in place for winter interest (sedum, e.g.), birdseed (echinacea, black-eyed Susan, e.g.), or overwintering beneficial insects, including pollinators. Pull those winter annual weeds that have sprouted! Hairy bittercress (Cardamine hirsuta) is a particular pest because it blooms at such a tiny size. If you see little clumps of circular white objects resembling tapioca, those are snail or slug eggs. Get rid of them (not in the compost).
This is my best opportunity to apply mulch because my flowerbeds are full of bulb foliage by early spring.
Use your mulching mower on the leaves on the lawn, if possible. Consider collecting leaf bags from your neighbors! I have a special compost bin for leaves. I leave them in the bags (plastic preferred) until the leaves turn into “leaf mold”, which is my main organic soil amendment. Most leaves are wet and ‘dirty’ enough to compost right inside the bag. Any really light bags contain dry leaves—these are set aside for use as mulch in the veggie garden the next season.
Clean up all the old veggie plants, debris from the veggie garden, and fallen fruit. Although most recommendations are to dispose of this in the trash, I have too much to do that. Instead, I put it in a long-term inactive compost pile, so I’m isolating diseases and pests that the debris may hold. Applying fresh mulch will help isolate disease organisms. Be sure to protect fruit tree trunks up to four to five feet above the ground from nibbling wildlife.
Continue preparing to protect vulnerable plants from deer, rabbit, and rodent damage – with fencing, hardware cloth (which is actually wire), plastic tree protectors, and/or repellents.
Move a bucket of good garden soil and/or woodchips into a freeze-proof location. This can be used during winter thaws, to cover the roots of frost-heaved, shallow-rooted perennials such as heuchera. Otherwise, heaving causes the roots to dry out, and generally the ground is still frozen enough a few inches down to prevent replanting. This tip is from the late Elisabeth Sheldon, author of several excellent gardening books, who used to have a nursery near Ithaca.
It’s too early to wrap evergreens in burlap, but not too early to get prepared. The goal used to be to prevent winter wind and sun from desiccating and killing the foliage, especially of broadleaf evergreens such as rhododendrons and hollies. This is still important, and despite the controversy about them, I have been applying antidessicant sprays the last few years, but generally not until Thanksgiving or even later. But now with global warming, early spring damage has become just as important. Warm weather in March is no blessing when it is followed by drastic cold snaps that kill twigs, buds, and leaves that have become de-acclimated. Be sure not to let woody plants go into winter in a drought-stressed condition.
—Pat Curran and the Tompkins County Master Gardeners
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