SEPTEMBER IS OPPORTUNITY MONTH: the opportunity (especially up north) to divide or add perennials; to plant shrubs and trees; to repair or renovate lawns; to fight some of the worst weeds; to put up harvests; to save seed. It’s also perhaps the best month of all to take stock, to really look at the garden critically (before it’s mere memory) for it strengths, weaknesses…and opportunities.

Here in Zone 5B, where frost can come as early as late September, you’d think I’d be feeling more as if the season’s “end” was in sight. But I have worked hard (and keep on doing so) to load the landscape with elements of a 365-day garden, remember?—one that colors up extra-early, keeps showing off till hard frosts say “slow down,” and even has strong structure to carry me visually through winter.

Take inventory now—walk around, make notes—and plan in detail to extend and enrich your garden’s season. Reviewing some of my recent tip-filled interviews with landscape designers like these may help.

weed and pest control and prevention

WEED WAR! Now is the time limit next year’s weeds. Some species are actually easier to thwart in late summer and fall, like these (including knotweed, ragweed, Ailanthus, bindweed, curly dock and more).

SPECIFIC WEED WISDOM:

• Clearweed, or Pilea pumila 
• A weed I planted (oops!), Houttuynia or chameleon plant
• Garlic mustard, Alliaria petiolata
• Commelina and Galinsoga
• Mugwort and prunella
• Hedge bindweed and spotted spurge
• How to ID your weeds—links to online guides
• Smothering weeds with cardboard and newspaper
• Piling on the mulch for weed suppression and control

PEST PROBLEMS? When you start your fall cleanup, do so with pest control in mind, too. Deer, voles, cabbage worms, squash bugs and other garden pests can be limited with tactics like this.

lawns (and crabgrass)

THE WAY WE MOW—in fall, and throughout the active growing season—and when we do our raking up affects how many lawn weeds grow, particularly opportunists like crabgrass. Repair compaction, minimize weeds and overseed now.

vegetable garden

SAVE SEED: The time is now for saving tomato seed (and other “wet” seeds such as peppers, squash, cucumber, melon). How to save tomato seed.

SEND IN SOIL SAMPLES for testing if you’re seeing poor results in some beds. Contact your local cooperative extension on how to sample.

AS AREAS COME EMPTY from harvest, build vegetable-garden soil by sowing cover crops. These “green manures” will be turned under to improve soil tilth and fertility. Don’t sow in areas reserved for fall-planted garlic, or very early spring crops.

MY FALL VEGETABLE GARDEN PLANS were covered in this archive story and podcast. Still ahead to plant here: more salad, garlic (next month) and spinach. How you can plan for an extended harvest in every region.

KEEP ASPARAGUS well weeded and watered, too. Let asparagus ferns grow till hard frost, when they are fully browned—or even leave them up till spring cleanup.

GARLIC should be curing in an airy, sheltered place. Read all about growing garlic, and storing your harvest. Order organic bulbs now for October-ish planting.

TOMATO, CUKE OR SQUASH TROUBLES? Tomatoes have a range of possible problems, but who could go without this garden favorite? If your issue is cucumbers or summer squash, start here. Peppers can be tricky in some seasons; pepper tips and recipes and storage tips.

PROCESS TOMATOES the easy way: roasted then frozen; as easiest, skins-on freezer tomato sauce; even just whole in freezer bags for use later in soups and stews.  

I FREEZE MANY HERBS, too, including parsley, rosemary and chives, or make them into pestos to freeze as well. Here’s how. If it’s vegetables you are storing, start here. Lots more harvest-stashing recipe ideas, from pickles to frozen peaches.

flower garden

ORDER BULBS promptly, and plant as they arrive (lilies most urgently). Have color from bulbs from earliest spring onward, if you plan like this. Top 7 tips on shopping smart for flower bulbs.  Many bulb-growing questions are answered in my Bulb FAQ.

DON’T DEADHEAD FADED perennials, biennials and annuals if you want to collect seed (non-hybrids only) or let some self-sow. Nicotiana, annual poppies, larkspur, clary sage and many others fall into this leave-alone group. So do plants with showy or bird-friendly seedheads, like coneflowers, some sedums, clematis and grasses.

DAYLILIES can be dug and divided as they complete bloom, right into fall, if needed.

PEONIES are best divided and transplanted in late August through September, if they need it. Remember with these fussy guys that “eyes” must not be buried more than an inch or two beneath the soil surface.

SOME FAMILIAR ANNUALS are better overwintered as rooted cuttings rather than by nursing along leggy older specimens. Geraniums, coleus, wax begonias, even impatiens (to name just a few common ones), if grown in good light indoors and kept pinched and bushy, will yield a new generation of cuttings for spring’s transplants—but expend this serious effort and space on an unusual form of something, not the garden variety.

DID YOU HAVE IMPATIENS problems? Learn about downy mildew and plan to avoid it next year.

IF TUBEROUS BEGONIAS or other bulb-like things start to go slack, let them dry off and rest early, or they will rot. Take your cue from the plants! I move my pots under cover so rain doesn’t contribute to sogginess.

PREPARE NEW beds for fall planting by smothering grass or weeds with layers of recycled corrugated cardboard or thick layers of newspaper, then put mulch on top.

RE-EDGE BEDS to make a clean line and define them. Don’t let them get overrun just because summer’s wound down. A clean edge makes a big difference.

trees and shrubs

ON THE DRY SIDE? Water trees and shrubs deeply through hard frost, so that they enter dormancy well-hydrated. Evergreens (needled ones and broadleaf types like rhododendron) are particularly vulnerable to desiccation and winterburn otherwise.

DON’T PANIC IF EVERGREENS start to show some browning or yellowing of needles this month and next. The oldest, innermost needles typically shed after a few years. The details.

ALWAYS BE on the lookout for dead, damaged, diseased wood in trees and shrubs and prune them out as discovered. Ditto with suckers and water sprouts. No hard pruning now, though; too late to risk encouraging regrowth. No fertilizer this late, either.

houseplants

REST AMARYLLIS BULBS by putting them in a dry, dark place where they will have no water at all for a couple of months. I put mine in a little-used closet.

IF HOUSEPLANTS NEED repotting, do it before they come inside later this month (less messy than in the house!). Don’t step up more than an inch (on small pots) or a couple (on large ones). Most plants don’t like to swim in their containers. Springtime’s fine for this, too, but I am often too busy then.

compost heap and mulch

I USE BULK MULCH, which is cheaper than the packaged kind and also eliminates the waste of all those heavyweight plastic bags. Many local nurseries deliver. Top up mulch in all garden beds as they get cleaned up gradually. What good mulch is made of.

DON’T LET THE HEAP dry out completely, or it will not “cook.” Turning it to aerate will also hasten decomposition, but things will rot eventually even if not turned. I extract more finished material and screen it each fall, to work into the gardens (and make more room for incoming fresh debris). How my expert friend Lee Reich makes amazing compost.

(On using this list in your garden: The monthly A Way to Garden chores are based on my Zone 5B Berkshire MA/Hudson Valley NY location; adjust accordingly.)