September is a hopeful month that begins to remind us that winter will be here again someday. It has become harder to predict what kind of September we will have. Historically, we should enjoy cooler temperatures both day and night, mostly due to the ever-shortening days.

Planting:. We can finally begin to plant trees, perennials and shrubs as nighttime temperatures drop into the low sixties and high fifties degrees Fahrenheit. Be prepared to provide additional irrigation all month as any rain we receive will mostly likely be insufficient. Almost all native plants can be planted towards the end of the month, but you may want to wait until October or even November for oak, redbud, buckeye, Ceanothus, manzanita and bush lupin. All of these do better planted in cooler soils with natural rain to get them established.

Even if you don’t plant until later in the fall season, September is a good last month of the year to remove your warm season lawn (Bermuda grass). If you wait until the weather is too cool, the grass will be dormant and you won’t know if it’s gone or dead until next summer when it comes roaring back to life. It’s too late to solarize, but I like the following no-herbicide method in our area:

Use a sod cutter or remove with a shovel as much of the grass and crown as you can. This is a terribly dirty and heavy job with a lot of material to haul away or move somewhere on the property you don’t mind having the grass. A pasture is a good place! Next, water the area thoroughly. Wait a week or more and dig out any sprouts and any non-grass weeds that come up. Repeat this method again and perhaps again, for a month or more. Alternatively, you can cover the area with weed cloth and/or mulch, but it is harder to remove the weeds. Once you plant, be prepared to cover the area with three inches of mulch right away and watch for any sprouts through the warm weather and again next summer.

The edible garden is plenty busy in September. Start the following from seed: Asian greens, beets, carrots, cilantro, lettuce, green onions, radish, rutabaga, spinach and turnips. Transplant broccoli and cauliflower seedlings you started last month into the garden. Set out strawberry plants for next year’s fruit. It’s time to make some hard decisions as we remove summer vegetable plants that are fading or attracting pest insects and diseases. Add disease-free warm season vegetable plants to the compost bins. Or you can keep a few heat-lovers going or even start another planting of short-season beans. But it’s also okay to do a change-over of everything. Feel free to leave some areas for cover crops or fallowing with straw cover to prevent soil erosion. Just try to keep the fallow areas weed-free.

Maintaining: This is a good month to do a semi-annual clean up in the native and no-lawn garden. Prune, trim, hedge, weed, chip or haul out…and get that garden looking fresher and ready for winter. This is also the month to dig out and divide over-crowded perennials and bulbs. Extra bulbs can be cleaned up and stored in a cool dark place for planting in cooler fall.

Deep water trees and shrubs through the month. Hose off cobwebs once or twice this month to discourage mites. September is also a good month to apply pre-emergent herbicide to prevent annual blue grass and other winter weeds from taking over the garden. You must water it in, however, so be prepared to saturate the garden, or wait another month and apply right before a rain event.

Spittlebugs are common this time of year, especially on woody shrubs like sage, lavender and rosemary. Don’t worry about it. They don’t harm your plants. Most native plants can tolerate a lot of aphids and scale too, although I suggest hosing them off to reduce over all populations, especially if you also have roses, crape myrtle trees or an edible garden in which these sucking pests are a modern scourge.

If you still have a cool-season lawn, this is the month to apply fertilizer. Follow the package directions, use a fertilizer meant for lawns, and err on the side of too little instead of too much. You can also give your roses a treatment of ¼ cup each of Epsom salts and Ironite per bush. Apply to the soil around each plant.

September is a good month to begin trimming back woody spring-blooming plants.

Conserving: While you’re trimming and slashing your way through the garden, keep an eye out for wildlife you want to conserve. Lizards, spiders, toads and moths are still active and all of them have a place in the well-managed garden. Continue with ant baits to reduce these enemies of beneficials without using highly toxic broad-spectrum insecticides. Keep the bird baths full. Trim flowers off tropical non-native milkweeds. Those are the ones with yellow/orange flowers. Experts tell us this helps prevent monarchs from staying in our valley too long into winter and then not being able to migrate before the cold kills them. Plant native milkweed if you can find them in local nurseries. Look for names like “narrow-leaf milkweed” and “showy milkweed,” and don’t be afraid to ask if it’s locally native. If you plant this fall, expect it to take a year or two for the Monarchs to find your plants: be patient. Which is a lesson from gardening we can use in all parts of our lives. Good things take a little time. The careful work we do in September will give us satisfaction immediately but will really pay off next year with healthy plants, abundant flowers and a mini nature preserve outside our doorstep.

Purple milkweed, (Asclepias cordifolia) one of our California native species

Adapted from “monthly Garden Tips – September 2020” written by Peyton Ellas, UCCE Master Gardener and owner of Quercus Landscape Design.

By Peyton