43 tasks in the September garden: Take stock of summer successes, plan for fall planting
Warm, wet soil from a late-season soaking might imperil established plants; careful, consistent monitoring is key
After August’s surprise hurricane, I’m curious to see our plants’ and gardens’ responses to rain in the heat of summer. This time of year, we often lose California native plants — along with drought tolerant trees and shrubs from South Africa and Australia — to deadly root fungi that thrive in warm, wet soils. This is why I always discourage people from watering established plants in summer.
So what happens when Mother Nature provides the rain?
Prepare for fall
As the long days of summer start to wane, it’s time to think about fall planting. The most important thing to do is to plan before you plant. Here are some tips:
- Do a garden walk-through. Look for space to be filled.
- Measure empty spaces — both width and height. Look for plants that grow to those dimensions, no larger. If you choose plants that grow too large for the spot, you’ll be pruning forever.
- Match new plants to each bed’s existing irrigation schedule. Don’t plant thirsty plants into dry beds and vice versa.
- Add interest by adding plants that flower or fruit or are otherwise interesting in a different season than the existing plants.
- Make a list of your goals for planting: extending the bloom season, attracting pollinators, adding texture, screening out views, etc.
For more information on how to prepare for fall planting, check out my webinar “Dig Deep: Plan for Fall Planting Success” at waterwisegardener.com.
- Plants, both ornamental and edible, are best irrigated with inline drip irrigation. Inline drip looks like long hoses with holes. Inside, each hole connects to very sophisticated emitters that release water one drop at a time. This is the most efficient irrigation and the best way to get water to plant roots, which is the goal of all irrigation.
Inline drip releases water very slowly so has to run a long time — 30, 60, 90 minutes or more — depending on your soil and how long it takes for water to penetrate down to plant roots.
- Keep the soil in vegetable beds damp (not wet) at all times. Depending on where you live, vegetable beds may need watering two or three times each week.
- Let the soil in ornamental garden beds dry out between waterings. Water these beds no more than once a week. For mature drought tolerant plants, natives, and succulents, water just once every few weeks or even once a month. Always water deeply and infrequently.
- Figure out how often to water by using the Canary Test. Find it here: tinyurl.com/2p8bf7e6
- Mulch all beds with at least 3 inches of mulch. Match the mulch to the type of plant: straw mulch for vegetables; stone or rock mulch for cactuses and other succulents; wood-based mulch (not bark chunks) for all other plants.
- No matter the irrigation method, always water until the water penetrates all the way down to plant roots. After the irrigation runs, test how deep the water has gone by digging into the soil, using a soil probe, or sticking your finger as deep as it will go. Is it wet all the way down? If not, water again.
- Spring vegetable plants like tomatoes, cucumbers, etc. are nearing the end of their lifespan. Remove each plant as production wanes. Healthy plants go into compost. Diseased plants (with powdery mildew, root knot nematode etc.) go into greenwaste, unless you plan to hot compost them.
- Take notes on how vegetable variety performed. Which varieties were so good that you’ll plant them again? Which disappointed? Keep track.
- Draw your garden. Note where you planted tomato, pepper, tomatillo, eggplant and potato. Move them all to beds that grow cucumbers or melons or basil, okra or other plants this year. Crop rotation is critical for plant health.
- Pick ripe fruits and vegetables to eat, to preserve and to keep scavengers from eating them before you can.
- Dehydrate surplus tomatoes to make tomato “raisins.” Find directions here: bit.ly/2EcmBHR
- Do your tomatoes split after last month’s rain? Toss those fruits and wait for the next crop. Take care not to overwater.
- Feed melons and pumpkin plants. Remove ones that have soft spots or insect damage.
- Set melons, winter squash and pumpkins onto a bed of straw or an upside-down yogurt container to keep them off the soil. If they grow on a trellis, support them with a sling made of old stockings or a COVID mask.
- Harvest pumpkins, melons and winter squash when the stems turn brown and start to pull away from the fruits, the undersides yellow a bit, and they sound hollow when slapped.
- Let peppers turn red, yellow, orange or purple before harvesting. They taste better and are easier to digest once they are fully ripe. They are prettier, too!
- Late in the month, start seeds for fall veggies like cabbage, spinach, lettuce, cauliflower, etc. The seedlings will be ready to plant when the weather cools in October
- Buy seeds for cover crops to plant next month. Choose seeds based on your garden’s needs: Some cover crops add nitrogen; others loosen compacted soil; some add organic matter, etc.
- Pick figs only once they are fully soft and ripe. Unlike other fruits, figs stop ripening the moment they are picked.
- Protect figs and other soft fruits from green fig eater beetles by covering them with nylon mesh drawstring bags. Since the bags are see-through, they are easy to monitor as they ripen.
- Shorten the new growth on peach, plum, apples and other deciduous fruit trees now (you’ll prune again for fruiting and shaping in winter). Shortening branches keeps future fruits within reach. Visit bit.ly/2CNUGNO to see how.
- Pineapple guavas ripen and “self-harvest” this month. Wait for the oval green fruits to drop onto the ground. Gather them, cut them open and enjoy their sweet, cream-colored flesh.
- Fertilize citrus and avocado. Use organic fertilizers and follow label directions. Pull back mulch, apply the fertilizer and water it in. Replace the mulch.
- If you live in north coastal and north inland San Diego County, please mind the citrus quarantine area so you don’t spread citrus greening disease, Huanglongbing (HLB). This is a serious situation. Citrus greening is transmitted by a tiny critter called the Asian citrus psyllid. HLB kills citrus trees. If you live in the quarantine area, do NOT move citrus fruits, trees, leaves or wood from your property. Learn the signs of citrus greening disease at californiacitrusthreat.org.
- Thrips on your houseplants? Scale? Mealy bugs? Put the plants outside in a shaded spot for fresh air and rejuvenation. The pests’ natural predators will eat them. Leave the plants outside until October.
- If your houseplants are infested with tiny, flying gnats, reduce watering. Cover potting soil in an inch-thick layer of small round pebbles or marbles or other inert material. The pebbles block gnats so they can’t lay their eggs in wet potting mix. They will soon disappear.
- Collapsing agaves is usually caused by the agave snout weevil. The female weevil chews her way into the base of the plant to lay her eggs in spring. When the eggs hatch, the larvae — which are grubs — feed on the core of the plant, leaving it vulnerable to rot from the inside out. Once you notice the damage, it’s too late. Dig up and seal infected plants, stems, leaves, etc. in a plastic bag and place in the trash, not the greenwaste.
- There’s a little time left to solarize grass and weeds. The sun must be high in the sky to superheat the soil to “cook” plants, weeds and seeds in the upper layer. This simple process involves clear (NOT BLACK) plastic and takes 6 to 8 weeks in the hottest months of the year. Beneficial soil microbes die in the process, so mulch afterward to re-establish their populations. For directions: bit.ly/3giAdy1.
- Clean up dried out foliage, dead branches and other dead plant parts — in part for aesthetics but more importantly, for fire safety. Dead, dry leaves, grasses and branches are more flammable than living plants.
- Wash dusty leaves using a Bug Blaster hose end nozzle. These nozzles put out a sharp spray of water to clean leaves and blast away pests. Spray leaves top and bottom, stems, branches, etc.
- If your plants look a little droopy at the end of the day, don’t water. In the intense heat, some plants lose water to the air faster than their roots can take it up from the soil. Overnight, the roots catch up and the leaves get perky again. However, if leaves are still droopy in the morning, it’s time to water.
- Plant spring flowering South African bulbs such as species Ixia, Watsonia, species Gladiolus and Ferraria.
Deal with pests
- Aedes mosquitoes are aggressive little daytime biters that relish mammal legs and ankles. They lay their eggs in standing water (as little as a quarter-inch deep) both indoors and out, so be vigilant about emptying water dishes, screening rain barrels, and running fountains to prevent standing water. Add mosquito fish to ponds. Fix torn window screens to keep mosquitoes out of your house and be vigilant about wearing insect repellent when you head outside.
- Floppy fronds on Canary Island palms are a sure sign of the deadly, invasive South American palm weevil. Once the damage shows, the palm is doomed. Have it removed by a professional arborist who knows how to dispose of infected palms without spreading weevils to other palms. Report infested palms to the UC Riverside Center for Invasive Species Research here: cisr.ucr.edu/invasive-species/palmarum-survey.
- Check for masses of tiny, disorganized webs on leaves and stems of trees and shrubs. Those webs are made by spider mites. Wash them away with a sharp spray of water.
- Citrus scale and aphids appear when ants “farm” the critters, placing them on citrus stems and branches. They require a two-pronged approach to control the ants and wash away the scale and aphids. Use a boric acid-based bait for the ants. Wash away aphids. Smother scale with a spray of light horticultural oil (NOT Neem).
Support, learn, participate
- Support the San Diego Botanic Garden by attending this year’s Garden Party from 4 to 8 p.m. on Sept. 9. Find tickets at sdbg.org.
- Would you like to be a better gardener? Sign up for my fall webinars, all aimed at making you a better gardener. Find more information at waterwisegardener.com.
Sterman is a garden designer, journalist and the host of “A Growing Passion” on public television. She runs Nan Sterman’s Garden School at waterwisegardener.com.