September Gardening To-Do List

Watch for pansies at your favorite plant shopping spot and pick up enough to fill pots and planting beds. Fall-planted pansies stage a flower show all autumn long in most regions. In warmer zones, pansies deliver fresh-faced color through winter. Ideal temperatures for flower development are nights in the 40s F and days in the 60s F. In the landscape, avoid planting pansies where they’ll be exposed to road salt or standing water. A well-drained location is the secret to overwintering pansies, especially in regions where snow cover melts in spring. Pansies with medium-size flowers generally survive winter better than large-flowered varieties, a fact that’s most important in Zones 4 and 5.

Cut back tropical plants you plan to bring indoors for the winter. Prune hibiscus by removing up to one-third of the plant. Do this by cutting back specific branches to soil level or pruning the entire plant to reduce height and spread. For tropical vines including mandevilla, jasmine and bougainvillea, cut plants back by 25%. Shift plants to a spot on a porch to help them adjust to less light. They’ll drop leaves and fewer flowers will open as days shorten. Soil dries out more slowly as temperatures fall; reduce watering accordingly.

Sow seeds or plant seedlings for fall salad crops, including lettuce, spinach, arugula, peas and greens — mustard or collard. The best lettuces for cold weather are romaine or butterhead types. The French heirloom lettuce sold as 'Four Seasons' or 'Merveille de Quatre Saisons' (shown) is a go-to choice for frosty temperatures, as are ‘Arctic King’ and ‘North Pole.’ Consider ‘Winter Marvel’ or ‘Brune d’Hiver' for regions with cold winters. In mild winter areas, sow seeds of ‘Four Seasons’ or any oakleaf type. Use floating row covers to protect plants from frost or nibbling critters. In the future, if you know you want to grow lettuce in the fall, get seed earlier in the growing season so it’s on hand and ready to sow.

Give your landscape a refresh by replenishing mulch that has broken down. If you’re planting pansies, ornamental cabbage or other autumn color, definitely mulch around plants. Also mulch around newly planted perennials, trees or shrubs. Fall mulching helps soil retain moisture and reduces weeds. Applied in a 2- to 3-inch-thick layer, mulch also helps slow soil freezing as colder weather arrives. This allows plant roots to keep growing longer, which is important for helping new plantings get established before winter.

Early fall is the right time to transplant existing hydrangeas in your yard. It’s also a good time to snag a deal on hydrangeas at the garden center. These beauties are usually sold when they're flowering in spring, which means by autumn they’re frequently discounted because blossoms are long gone. Clip any faded hydrangea flowers you’d like to bring indoors for winter. If you want to remove spent blooms to neaten the garden, clip them off with just an inch or two of stem attached. Don’t prune hydrangeas in the fall, especially in Zones 5 and colder. Pruning makes plants more susceptible to winter damage.

Improve your odds of success with storing butternut squash, pumpkins and other winter squash by doing two things. First, harvest squash leaving a 1- to 2-inch-long stem section. Don’t carry the squash or pumpkin by this stem; it’s not a handle. Winter squashes without a stem won’t store well. Plan to eat those first. Second, cure fruits after picking by placing squash outdoors in the sun for 10 to 14 days. This hardens the skins, which helps squash to store longer. If frost is in the forecast, shift squash to a protected location overnight.

As greenery disappears, deer start munching plants they don’t normally touch. This includes things like heuchera, Lenten rose, hollies and other evergreens, as well as cool season edibles. Take plants off the menu by using a combination of deer-proofing techniques. Drape bird netting over perennials; build hardware cloth cages around small shrubs or trees. Apply deer repellents, rotating the products. Many gardeners report success with Plantskyyd, Deer Defeat and Bobbex.

Forget raking leaves — mow over them! By attaching a grass catcher bag to the mower, you can collect a ready supply of chopped leaves that make a fantastic addition to a compost pile. Smaller leaf pieces decompose more readily than whole leaves, which can mat together and actually repel rain. Chopped leaves also make a great mulch for planting beds. Or add a layer of chopped leaves to the vegetable garden to cover soil through winter.

Stay on top of weeds in lawn and garden areas, taking advantage of fall rains to pull small plants. Avoid letting any weeds set seed, or you’ll be dealing with the progeny come spring. For tough perennial weeds, such as dandelion, thistle or dock species, clip all but a few leaves and spray what’s left with herbicide. In fall, plants transport nutrients from leaves to roots for winter storage, which means herbicide is more likely to kill these weeds at the root.

Pick herbs for drying to keep garden-fresh flavor on the menu all winter long. Clip long stems and bundle them together to hang them upside down. For the best flavor, dry them in a warm, dark place. Or hang them where it’s convenient for use, like from a pot rack in the kitchen. Once herbs are dry, store stems in tightly sealed containers in a cupboard, away from light. For best flavor, place entire stems in jars, removing leaves as you need them. Good candidates for drying include oregano, sage, basil, thyme, rosemary and bay. Mints also dry easily and make for a fantastic cup of tea when chilly days arrive.

If you want to force bulbs into bloom for upcoming holidays or winter flowers, get bulbs now so you’ll have time to provide the necessary chilling hours. Tulips, hyacinth and scilla need 12 to 14 weeks of chilling before they’ll sprout and eventually flower. Research the chilling times for bulbs you want to force, decide when you want flowers on hand, and count backwards on a calendar to figure out when you need to plant bulbs.

Keep hummingbird feeders clean and filled this month, as these tiny birds are migrating and need nourishment along their journey. It’s a good idea to fill feeders every three days to ensure food is consumable. Tiny but feisty, hummingbirds are territorial, and their in-air battles increase in autumn. If possible, hang a second feeder in a separate spot in your yard. Better still, plant flowers that bloom later in the season. For fall flowers that hummers can’t resist, look to the sages, both annual and perennial, such as pineapple sage (Salvia elegans), Mexican bush sage (Salvia leucantha), scarlet sage (Salvia coccinea) and autumn sage (Salvia greggii).

When late blight hits tomatoes, diseased leaves fall away, creating leafless plants that can be loaded with ripening tomatoes. As temperatures drop below 50°F, tomatoes stop turning red. So before temperatures are consistently in the 40s, gather all tomatoes and bring them indoors for ripening. Place them in a single layer on a platter or tray. Check fruits every few days for ripening and/or spoilage. In a 70-degree environment, green tomatoes typically ripen in two weeks. Cooler air causes slower ripening — for instance, 28 days at 55° F.

Unsure if green tomatoes on the vine will continue to ripen indoors? Here’s how to tell. Slice through a tomato. If seeds are encased in gel, tomatoes will fully ripen indoors. If no gel sac is present, use those green tomatoes for frying, salsa, pie, pickles or relish. The right time to make your assessment is when temperatures are forecast to stay below 50º F. If fall weather delivers multiple nights in the 40s but rebounds during the day, understand that cold temperature effects on tomatoes are cumulative. The more often a tomato experiences temperatures below 50° F, the less likely it is to ripen properly.

This time of year, even the coldest, shadiest compost pile has some finished product to offer. Empty your compost bin, filling a wheelbarrow or garden cart as you go. Add that finished compost to the garden, focusing on perennial, edible crops, like raspberries, rhubarb, asparagus or fruit trees. In the veggie garden, layer on compost from 3" to 6" thick — however much you have. Don’t spread all of your compost around in the fall, though. Keep some back to add to clematis, roses and new plantings in spring.

Dig and divide spring and summer flowering perennials up until six weeks before frost. A few perennials that fit this category include bearded iris (shown), lily-of-the-valley, heart-leaf brunnera, Oriental poppy, campanula, veronica and peonies. Divide large clumps into smaller pieces and tuck back into the garden. Toss the woody, bare center of overgrown perennials and offer extra divisions to friends or neighbors. A community or school garden often accepts donations of weed-free perennials, although you may need to help with planting. Water newly planted perennials weekly until autumn rains arrive.

Take advantage of nice fall afternoons to start cleaning the vegetable garden. Start by gathering all ripe and unripened produce that you intend to either ripen indoors or use at an immature stage. Cut down crops that are finished, leaving root systems in place to nourish microorganisms in the soil. Pick up all plant debris: stem, leaf and fruit bits. Don’t compost diseased plants — discard them. Refresh mulch over empty beds, maybe even adding fresh compost topped with a layer of chopped leaves.

In fallow (empty) parts of the vegetable garden, it’s best to cover the soil for winter. Use straw mulch, chopped leaves or compost — or any combination of these materials. Or plant cover crops to help nourish and enrich soil. Good choices include crimson clover (shown), peas, oats, annual rye grass and hairy vetch. Till crops under in spring before they flower and set seed. Otherwise, you risk having permanent patches of cover crops in the garden.

As you tackle garden clean-up, keep your eyes peeled for insects — both friend and foe. In autumn, beneficial insects like assassin or wheel bugs (shown) or green lacewings are mature and can deliver nasty bites. At the same time, you might stir up pests, such as squash bugs, stink bugs or harlequin bugs. Kill any pests you see. Maybe even walk through garden areas you intend to clean with a jar of soapy water to kill problem insects before you start cleaning up plants.

Clean and sharpen digging and cutting tools before putting them up for winter. Use a wire brush and/or medium grit sandpaper to remove rust on shovel blades and scrub the surface with a bucket of dishwashing detergent. Wrap up the chore by rubbing light machine or synthetic oil into the blade. For pruners and loppers, clean blades with rubbing alcohol, sharpen and oil moving parts.

In desert regions, fall explodes with floral fireworks. Traditional autumn bloomers add to the scene, including xeriscape-worthy New England aster (shown), New Mexican sunflower (Helianthus maximiliana), giant hyssop and rabbitbrush chamisa (Chrysothamnus nauseosus). Annuals sown by seed in June also sparkle in the fall flower show: cosmos, celosia, ageratum, petunia and marigold. If your desert garden lacks fall color, look to some of these tried-and-true favorites to add living hues.

Fall’s cooler air and rains awaken cool-season lawns from dormancy caused by summer heat. As lawns experience a spurt of growth, it’s a good time to fertilize. An easy trick to remember to fertilize in the fall is to time it with Labor Day. Look for lawn food labeled for fall use. If you plan to aerate your lawn, do so prior to fertilizing. For warm-season grass in the warmest parts of the South, feed with a complete product, such as 16-4-8. Follow label instructions regarding application timing and watering in. There’s one deal-breaker on applying fall lawn fertilizer: prolonged summer drought. If your region is plagued with drought, don’t feed the lawn until autumn rains have kick-started grass growth.

Refresh container gardens with dazzling fall color. Good plant choices include garden mums, ornamental grasses and flowering kale or cabbage. Consider adding a winter squash or pumpkin to the mix, or try pansies and violas. Fall plantings in Zone 5 and colder typically don’t grow quickly due to cold air and soil. That means you’ll have the most glorious containers if you buy the biggest plants you can find to create a full, lush pot.

It’s safe to plant shrubs and trees right up until the ground freezes, but you’ll have better overwintering in the coldest zones if you get plants in before hard frosts arrive. Plant tops may die back after frost, but roots will continue to grow through early winter. By spring, fall-planted trees and shrubs should have healthy, extensive root systems that can support a season of growth. Remember to water fall-planted additions to your landscape until the ground freezes. In regions with mild winters where the ground doesn’t freeze, plan to water new plants through winter during dry spells.

Wait to harvest potatoes until plant tops have turned brown. You can wait as long as two weeks after tops die back to dig up potatoes, but do so before autumn rains arrive. It’s easier to lift tubers from dry soil. Wet soil clings to tubers and cold, wet soil can jump-start rotting. When digging potatoes, handle tubers gently and don’t rub off the soil. Cure potatoes first, which helps to toughen skins so they store well. To cure, place potatoes in a dark, cool place (55° F is ideal) for two weeks. After curing, rub soil off tubers before storing. Wearing gloves makes quick work of removing soil from cured potatoes.

Try not to let leaves pile up on the lawn. If left to sit in a thick layer, they have the potential to damage or even kill the grass. Leaves rake easiest when they’re dry. If possible, consider mulching leaves using a lawnmower. You can let small pieces lie and work their way down to the soil to help nourish the turf. Or you can mow with a grass catcher and transfer the chopped leaves to planting beds as mulch.

For cool-season turf types, including Kentucky bluegrass, perennial ryegrass, fine fescue and tall fescue, fall is the ideal time for aerating. You might need to aerate if your lawn is heavily compacted, has a thatch layer more than three-quarter inches thick or has roots that extend only 2 inches into soil. Using a core aerator is best because it extracts small soil cores from the lawn, allowing air, water and fertilizer to reach grass roots. Autumn is also the right time to overseed existing lawns to thicken grass, which makes it more resistant to weeds and insects. If you plan to do both of these activities, aerate first and then overseed.

Gather seeds for next year’s garden from plants like cleome, moonflower or four o’clocks. With flowers including cosmos, zinnia, echibeckia, Verbena bonariensis or tithonia, snip off whole flower heads and place them on screens to dry. Once the heads are dry, remove the seeds, working gently to separate seeds from chaff. When saving seeds, focus on heirloom varieties. The seeds of hybrid plants won’t produce the same plant as the parent.

Keep leaves from falling into a water garden with a pond shelter kit that supports netting on a frame. With this type of pond protection, leaves never touch the water. Or you can stretch a net across the pond surface, which may need daily emptying during periods of heavy leaf fall. Scoop out any leaves that land in the water and keep the skimmer basket emptied of leaves. Decomposing leaves in a pond will release materials that can harm fish and muddy the water.

Plant garlic cloves at least two weeks before your region’s first average fall frost date. If you miss that window, don’t worry. You can still tuck garlic into soil up until a few weeks before the ground freezes. Plant cloves 2 inches deep and 4 inches apart, using the largest cloves from each bulb. Larger cloves produce larger garlic bulbs. Water well after planting and cover the soil with mulch. If the ground freezes where you garden, mulch with 6 inches of straw or 4 inches of chopped leaves. For areas where the ground doesn’t freeze over winter, use a 2-inch-thick mulch layer.

Fall flowering perennials weave gorgeous hues into an already glorious scene. Wildflowers like blue bottle gentian (Gentiana andrewsii), turtlehead (Chelone glabra), cardinal flower (Lobelia cardinalis), coneflower (Echinacea) and ironweed (Vernonia gigantea) all adapt well to the garden. Goldenrod (shown) is another stunning native plant that’s often wrongly maligned as the cause of fall allergies (that honor belongs to ragweed). Goldenrod not only adds color to the fall garden but also offers seeds that small songbirds love to eat.

Before nights in the 40s arrive, harvest what’s left of your basil to make pesto. It freezes well and provides summer-fresh flavor in the heart of winter. Experiment with other pestos to preserve the greens of autumn: spinach, arugula, carrot or radish tops, sage, parsley — and many more. Freeze pesto in an ice cube tray, and pop the cubes into a zipper bag for easy access. Many other vegetables also freeze well, including green beans, corn, peppers and onions.

New additions to your landscape — perennials, shrubs or trees — need water their first year in the ground to help them survive their first winter. This is especially true if summer has been dry. Provide consistent watering to plants before winter arrives. If winter brings frozen soil without snow, give your plants a drink when temperatures are above freezing. Plan ahead and get what you need to ferry water to plants.

Tulips aren’t famous for a truly prize-winning perennial performance year after year. Most often, they tend to falter and eventually fizzle out. Tricks to improve tulip performance include planting bulbs extra deep: 8" to 10". It’s also important to choose the right varieties. Darwin Hybrid tulips are known for their strong return, year after year, as are species tulips, many of which are diminutive beauties that multiply over time, like these ‘Red Riding Hood’ tulips.

In Southern regions where winter chill is scarce, the secret to beautiful tulips is pre-chilling the bulbs, essentially tricking them into thinking winter has come. Tuck them into the fridge in the crisper for eight to 10 weeks. Plan for planting in January to give bulbs time to grow adequate roots to support a spring flower show. Treat tulips in Zones 7 and higher like annuals — you get just one show.

Fall is prime canning time, with many crops still growing strong. The list includes roma tomatoes, carrots, cauliflower, peppers, cucumbers, raspberries and grapes, among others. Continue canning and prepping batches of salsa (red and green), grape juice, berry jam and tomato sauce. Can smarter by preparing batches of products that are more recipe-ready, such as tomatoes with onions and peppers, or carrots and onions in chicken broth. Pickle things you’ve never tried before, like carrots, peppers or green tomatoes.

Get cool-season crops off to a solid start by refreshing soil in raised beds. Add organic matter such as homegrown compost, composted manure, bark fines or whatever local material is available to you. You can add bagged soil products, along with slow-release fertilizer you mix into soil. Top the bed with mulch — chopped leaves, straw, pine straw or whatever you typically use. Fall greens savor rich, well-drained soil, and this type of soil prep delivers healthy crops.

Early fall is the ideal time to tuck peony tubers into soil. These spring bloomers thrive in full sun to part shade and well-drained soil rich in organic matter. Prepare the planting area by working plenty of organic matter into the soil. Plant peony tubers so the eyes or growing points are no more than 2 inches below the soil surface. Don’t plant them too deeply or they won’t produce flowers. Time planting for four to six weeks before the ground freezes. After planting, water well and add a 2- to 3-inch-thick mulch of chopped leaves or straw.

Keep savoring fresh-from-the-garden fare by potting up clumps of your favorite herbs. Chives, oregano and sage grow well indoors. Thyme thrives in a clay pot in the coolest spot you can provide. Don’t transplant basil. Instead, take tip cuttings and root them in water before planting. Place herbs where they’ll receive bright light. Pick often to prevent long, floppy stems.

Thanksgiving and Christmas cacti start setting buds this month in response to day length. Plants that sit outdoors for summer on a porch or shady deck will set buds naturally as days start to shorten. For plants kept indoors year-round, cover plants at night or slip them into a dark closet to provide 14 to 16 hours of darkness daily for one week. Do this approximately six to eight weeks before you want plants to bloom.