September gardening: 22 things to do this month

Women hand irrigation Organic Green Bean plant in garden

Vegetable garden soil should be damp but not wet at all times.
(Getty Images)

With temperatures soaring, it’s important to monitor irrigation

We lose an hour of daylight this month as the sun begins to sink a bit lower in the sky. Still, late summer is often hot, hot, hot in San Diego, and sometimes we get a tropical thundershower coming up from the south. For plants, we are in the heat of summer.

Schedule your outside gardening time early in the morning and in the late afternoon. Stay out of the midday sun and heat. Even though it’s hot, keep your arms and legs covered. Look for lightweight sun protectors that cover the outside of your hands yet don’t interfere with gardening.

Always wear sunscreen and reapply every few hours. Get a comfortable hat with a wide brim to shade your face, neck and shoulders. Now, you are ready to garden!

1. With irrigation at peak demand this month, we have to manage water carefully. Water ornamental plants deeply; run the water for a long time, then let the soil dry a bit before you water again. Every time you irrigate, make sure water penetrates at least 6 to 8 inches down into the soil.

To water ornamental plants, run overhead sprinklers in the early morning hours so leaves dry out before sunset. Drip irrigation doesn’t wet leaves, so run it in the cooler hours; late afternoon, evening or early morning.

Irrigating vegetable gardens is completely different. Vegetable garden soil should stay damp at least 4 inches deep, at all times. Damp, not wet. Stick your fingers down into the soil to feel the soil; it can be dry right at the surface but no deeper.

2. Cover almost every soil surface with a 3-inch-thick layer of mulch — use straw mulch for vegetables; rock, gravel or decomposed granite (DG) for succulent gardens, wood-based mulch for everything else. If you mix succulents and non-succulents, use a wood-based mulch.

Wood and stone mulch should never touch plant stems or trunks. Keep 6 or 8 inches of soil bare around trunks and stems — more for larger plants. It’s fine to mulch right up against vegetable plants with straw.

Leave patches of bare soil for ground-dwelling native bees. They need just a few square feet of open space, best in well draining soils. These bees seldom sting and are very important garden pollinators.

3. If your plants look a little droopy at the end of the day, don’t water. Instead, wait and check them in the morning. 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, they are telling you it is past time to water.

4. Be especially water frugal with native and drought-tolerant woody trees and shrubs. Too wet, warm soil encourages deadly soil fungi that kill the plants. Instead, irrigate only occasionally if at all, using in-line drip (for natives, too!). Run the drip at night when soil is coolest.

5. In the hot weather, tiny spider mites take up residence on dusty leaves. They are too small to see; instead, you’ll see small, dense webs that often catch leaves and debris. Wash off the webs and spider mites with a sharp blast of water.

6. If you have a palm tree with flopped fronds, chances are, it is infected by the deadly, invasive South American palm weevil. This big beetle is killing palms, especially Canary Island date palms across the southland. 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 the weevil to palms on other properties. Report infested palms at cisr.ucr.edu/palmarum_survey.html.

7. If you plan to kill your lawn by solarizing it, do it early this month while the sun and heat are strong enough to superheat the soil and kill plants, weeds and seeds in the upper layer. This simple process involves clear (not black) plastic and takes six to eight weeks in the hottest months of the year. Beneficial soil microbes will die in the process, but their populations rebound quickly after the soil cools. For directions, visit waterwisegardener.com/killer-rays-from-sun.

8. Pick ripe fruits and vegetables to eat, to preserve, to freeze and to keep scavenging rats, possums and other critters from treating your garden as their favorite fast-food joint.

9. Prune fruit trees right after the harvest to keep them short for easy access. You’ll prune to shape once the trees go dormant in winter. For now, simply cut back the tall growth to keep the branches (and fruits) within reach. Visit www.davewilson.com/home-gardens/backyard-orchard-culture for more information.

10. Fertilize summer vegetables, citrus and avocado. Use organic fertilizers and follow label directions. Water the fertilizer in, then cover with a few inches of mulch. Keep mulch pulled back from trunks and stems so they stay dry.

11. Start fall vegetables now from seed: broccoli, spinach, lettuce, arugula and so on. They’ll be ready to plant out in about six weeks, just as the weather cools.

12. Buy seeds for cover crops to plant in your vegetable garden next month. Cover crops add nitrogen and organic matter to the soil. They also loosen overly compacted soils and act as natural mulch.

13. Feed pumpkin plants and remove any pumpkins that have soft spots or insect damage. Put a bed of straw under the good pumpkins to keep them off the dirt. Elevating them on an upside-down yogurt or cottage cheese container is another option. Do the same for melons.

14. Continue to harvest late season figs and grapes as soon as they ripen.

15. Pineapple guavas ripen and “self harvest” this month. As fruits drop to the ground, gather them, cut them open and enjoy their sweet flesh.

16. Continue planting spring flowering South African bulbs such as species SparaxisHomeria and Ferraria.

17. Survey the garden for plants that died over the summer. Cut them down, dig out their roots and send them off to the green waste facility, where they’ll be hot composted to kill any pathogens or insects that caused their demise.

18. This is a good time to appreciate succulents. Their forms and textures add so much to the garden, especially in gardens planted with lots of fine- or narrow-leaved plants. Add some broad-bladed succulents and the garden will come into balance.

19. When you rake leaves, don’t send them off in the green waste container. Instead, pile them in a back corner of the yard and let them break down naturally over time to make mulch. Or leave them under plants to create natural mulch, especially for plants like avocado and bamboo, which count on recycling nutrients back into the plants from their fallen leaves.

Earthworms

Worm composting is quick, easy and odorless when done correctly.
(Getty Images)

20. If you haven’t already, set up a worm bin to compost kitchen scraps and small bits that come out of the garden. Worm composting (“vermicompost”) is quick, easy and odorless when done correctly. Set up bins in a shaded spot so the worms don’t cook in the heat and sunlight.

21. Do you love to garden? Are you new to gardening? Are you an experienced gardener who’s just moved to the area? You are invited to join the conversation about gardening in San Diego on Facebook. Please join the San Diego Gardener Facebook Group, www.Facebook.com/groups/SDGardener

22. Looking for late-season garden color? This time of year, rather than relying on plants, paint a wall or use accessories to add color to your garden. Read how in my latest book, “Hot Color, Dry Garden,” available in bookstores.

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