Last month, citrus greening disease, huanglongbing (HLB), finally appeared on San Diego County, in backyard citrus in Oceanside. County officials held it off for a long time but, sadly, it was inevitable since HLB has been in all the surrounding counties for several years. This is a serious situation. Citrus greening, which is transmitted by a tiny critter called the Asian citrus psyllid, kills citrus trees. It has destroyed Florida’s citrus industry. It threatens to do the same here, and to destroy all our backyard trees, too. Learn the signs of citrus greening disease at californiacitrusthreat.org. If you think your trees are infected, call (800) 491-1899.
There is a citrus quarantine from Carlsbad to Camp Pendleton to Vista. IF YOU LIVE IN THE QUARANTINE AREA, DO NOT MOVE CITRUS FRUITS, TREES, LEAVES or WOOD FROM YOUR PROPERTY.
Self-protection
• As the summer wanes, the days get shorter, but the sun and heat are still intense. Garden early and late in the day. Slather high SPF sunscreen on all exposed skin, including your toes!
• Liquids are essential, for your plants and for you (but hold off on the alcohol until the sun sits low in the sky).
• Before you head out to the garden, cover your arms with a lightweight, long-sleeve shirt with an SPF rating. Get a good lightweight hat with a wide brim, too.
• Three new species of Aedes mosquitoes are spreading across Southern California. These tiny critters bite aggressively during the day, especially around your 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 the mosquitoes out of your house and be vigilant about wearing insect repellant when you head outside.
Vegetable gardening
• August’s unexpected rain and humidity created the ideal conditions for later-than-expected powdery mildew. Remove severely infected leaves. Early in the day, use a hose to rinse leaves hinting at mildew. Make sure leaves are dry long before nightfall.
• Vegetables you planted in early spring — tomatoes, cucumbers and more — are reaching the end of the road. As each finishes producing, pull it out. The plants have likely accumulated powdery mildew, root knot nematodes, and countless other vegetable plant afflictions. If you don’t do hot composting (where compost reaches at least 140 degrees), send the spent plants off in the greenwaste to be composted.
• Take some time to record how well each variety of vegetable did in your garden. Which cucumbers do you want to grow again, and which didn’t do so well? Which basil produced longest and taste best? Which didn’t meet your expectations? This is the time to think about which go into your “plant again” list and which go into the “don’t bother” list.
• Yellow leaves on tomato plants are usually evidence of viruses or fungi. Simply pull the leaves off and let the plants continue to grow and produce for as long as they can.
• Have you made note of where the nightshade plants — tomatoes, eggplants, peppers, tomatillos and potatoes — grew this year? Next year, replant those beds with melons, pumpkins, basil, sweet potatoes (Ipomea), okra, onions and other veggies that are not susceptible to root knot nematode or any other nightshade pathogens.
• Always keep the top 4 inches of soil damp (not wet). Dig into the soil with your fingers to monitor soil moisture.
• Refresh the garden’s straw mulch if it has thinned out.
• 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.
• Do your tomatoes split as they ripen? That’s a sure sign of overwatering. Water less, and the problem should disappear.
• Feed melons and pumpkin plants. Remove any that have soft spots or insect damage.
• Keep melons, winter squash and pumpkins off the soil by setting them atop a bed of straw or an upside-down yogurt container. If they grow on a trellis, them with a sling made of old stockings.
• 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.
• At midmonth, start seeds for fall veggies like broccoli, cauliflower, kale and kohlrabi. 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.
Fruit trees
• Don’t pick figs until they are fully ripe. Unlike most fruits, figs don’t continue to ripen after they are picked.
• Do green fig beetles get the ripe figs before you do? Cover the figs with nylon mesh drawstring bags. The bags are see-through, making it easy to monitor the figs as they ripen.
• Prune fig trees as soon as you pick the last fruit. Don’t be shy about cutting your fig tree back a little or a lot. It will resprout and fruit again next year.
• 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 https://bit.ly/2CNUGNO to see how.
• Continue to harvest grapes as they ripen.
• Pineapple guavas ripen and “self-harvest” this month. Wait for the oval green fruits 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. Water the fertilizer in, then cover with several inches of wood-based mulch. Don’t let mulch touch trunks and stems.
Houseplants
• Thrips on your houseplants? Whiteflies? 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. The gnats will disappear in a week or so.
• Scale and mealy bugs are some of the most challenging houseplant critters. Scrape scale away with your fingernail. Carefully dab mealy bugs with a cotton swab saturated in rubbing alcohol. Check the plant’s crevices for juvenile scale and mealy bugs. Alcohol kills them too.
Ornamental plants
• There’s still time to solarize grass and weeds to eliminate them IF you start at the beginning of the month. 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 six to eight 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, go to https://bit.ly/3giAdy1.
• Established waterwise plants need very little attention now. They may look dry, but that’s OK. These plants are adapted to dry conditions. Deep-water once, maybe twice this month with drip irrigation, run at night when the soil and air are coolest.
• Run overhead spray early in the morning so leaves dry out before night. Better yet, replace the overhead spray with in-line drip irrigation, which is far more efficient and effective.
• Clean up dried-out foliage, dead branches and other spent plant materials — in part for aesthetics but, more importantly, for fire safety. Dead, dry plant material is more flammable than living plants.
• Resist the urge to water native and drought-tolerant woody trees and shrubs. Warm, wet soil develops soil fungi that kill the plants. Instead, irrigate only occasionally if at all, using in-line drip (for natives too!). Run drip at night when soil is at its coolest.
• 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 Ixia, Watsonia, Gladiolus and Ferraria.
• Take a hard look at your trees, shrubs and perennials. After the spring and summertime growth, they could be in need of a good haircut. Hire a certified arborist to do the work. Insist that the arborist remain on-site while the work is being done. Find certified arborists at isa-arbor.com.
• NEVER TOP A TREE. Topping trees disfigures trees. It leaves trees exposed to decay and pests. Topping reduces the tree’s structural strength and shortens the life of the tree. Topping trees also stimulates rapid growth of new, weak wood. If a tree is too tall for its spot, it is the wrong tree. Replace it.
• Plan for fall planting when the weather cools late next month. Photograph your garden beds, then examine each one to determine what needs to come out, what needs to be added, and so on.
Mulch
• Leave a 5-by-5-foot area of bare, well-draining soil for ground-dwelling native bees. Cover the rest of the soil with mulch
• Use straw mulch for vegetables; rock, gravel or decomposed granite for succulent gardens; and wood-based mulch for everything else, including plantings of mixed succulents and nonsucculents. Layer on mulch at least 3 inches thick.
• Never let mulch touch plant stems or trunks. Leave 6 or 8 inches of soil bare around trunks and stems — more for larger plants.
Deal with pests
• Floppy fronds on Canary Island palm trees 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.
• Check for masses of tiny, disorganized webs on leaves and stems of trees and shrubs — the sure sign of spider mites. Use a sharp spray of water to wash them off.
• Citrus scale happens when ants “farm” the scale, placing them on citrus stems and branches. They require a two-pronged approach.
Compost
• Set up a worm bin to compost kitchen vegetable scraps. Worm composting (“vermicompost”) is quick, easy and odorless. Keep worm bins in shade; they’ll cook in the sun.
• Pile grass clippings, leaves and other small bits of plant material in a back corner where they can break down over time to make mulch. Or leave them under plants as natural mulch
• Never rake under or around avocado and bamboo. These plants, in particular, recycle nutrients back into the plants from fallen leaves.
, learn, participate
• the party! The Garden Party, that is, benefiting the San Diego Botanic Garden, from 4 to 8 p.m. on Sept. 11. This year, the garden is hosting an intimate evening of botanical beauty, fabulous food and bubbly beverages, as you stroll through the garden in Encinitas, enjoying the beauty of the flora that surrounds you. For tickets and information, visit sdbgarden.org/GardenParty.htm.
• Do you love to garden? Are you new to gardening? Are you an experienced gardener who’s just moved to the area? Please the San Diego Gardener Facebook Group at facebook.com/groups/sdgardener to become part of the community.
• 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. Order a signed copy at waterwisegardener.com.
Sterman is a waterwise garden designer and writer and the host of “A Growing ion” on KPBS television. More information is at agrowingion.com and waterwisegardener.com.
