Hot enough yet? While we might choose the air conditioning, swimming pool, the river or a nice shady tree to spend our time in, it’s good to remember that our best landscape plants have learned to adapt to our hot summers. Some plants even prefer the heat. A few even require the heat to perform at their best. I try to spend time each summer admiring and appreciating my summer-loving garden plants, both in the edible and ornamental gardens. Many plants from California and Mediterranean climates slow or stop growing in the summer. Some plants display partial dormancy, which can mean brown, shriveled, even dropping leaves. This is all normal. We don’t worry when our oaks and stone fruit trees lose their leaves in winter because we are used to it. Most of us are used to wilting squash leaves on summer afternoons and know the plants will recover in the cool evenings. Summer partial or full dormancy is another survival strategy and it is worth the effort to learn which of your plants are in summer dormancy and which are in true drought stress.
Planting: If you can, wait until cooler weather to add new ornamental plants. If you must, choose heat loving plants that can also tolerate watering in warm soils. Examples are California Fuscia (Epilobium/Zauschneria) and California Goldenrod (Solidago velutina). You can also plant fall-flowering crocus, Lycoris and Sternbergia right through summer.
Edibles to plant in July include tomato, basil, and artichoke from well-developed seedlings. From seed, plant corn, winter and summer squash, radish, peas, bulb and green onion. Late in the month, you can start seeds for fall-harvested vegetables like broccoli, cauliflower, chard, kale, and cabbage. Plant in the ground or start seeds in containers for transplanting in September.
Maintaining: Monitoring watering is the biggest maintenance job in July. Monitor and test your irrigation system at least once during summer, especially if you will be gone more than a few days. Don’t overwater your garden plants in summer—it’s a waste of water and can encourage disease and insect pest problems. Established ornamental trees and shrubs should be deep watered, but on a less-frequent schedule than smaller perennials and new transplants. The edible garden, including fruit trees, should receive a consistent supply of water sufficient to replace water lost through transpiration and needed for fruiting. For almost all plants, that doesn’t mean the ground should be wet all the time. Let the first inch or more dry out between watering. If a heatwave is predicted, water a day or two in advance, and then not again until the soil dries out a little.
Avoid over-watering lawns. If your lawn is water soaked, disease and pest insects are almost guaranteed in valley-floor soils. Water does not cool turf grass, it only replaces what the plant transpires during the day. Plants don’t sweat the way mammals do. Use a moisture monitor or poke your fingers down into the crown of your lawn to see if it’s lacking moisture. Fescue lawns can suffer heat stress, sunburn, and warm-season diseases, and all of them may look like you need to water more. Our University of California system has a website devoted to lawn care: ipm.ucanr.edu/TOOLS/TURF. Check it out for research-based ways to care for your lawn.
On the other hand, if lawn removal is your goal, July is an excellent month for solarization or mechanically removing the sod and allowing the summer heat and lack of moisture to kill any remaining bits. Remember to cover your bare soil with mulch, cardboard or weed cloth, or spray with herbicide until fall planting time to avoid opportunistic weeds becoming the lawn replacement “garden.”
Continue dead-heading roses and daylilies. Remove spent flower heads and the entire flowering stem from hydrangea, leaving only a few buds per stem for next year. You can begin to divide bearded iris in July or wait another month if they still look lush and green. If you decide to divide, lift the entire clump. Trim leaves to about six inches. Set exposed sections in the sun to dry for a few days to callus over any cut sections. Plant the rhizomes (that big gnarly root-like mass) just below the soil surface, water well and mulch.
Prune spent berry canes to the ground after harvesting. Trellis new canes as they emerge. Pinch new growth on chrysanthemums. Lightly prune bougainvillea to promote more flowers.
Major pruning should wait until the weather cools, unless it’s for safety. You can lightly prune in the cool morning or evening hours, but not if a heat wave is predicted in the next few days.
Do not fertilize anything during July with high-nitrogen products, including lawns. Fertilizing itself is stressful to plants. July is a good month to let the garden rest.
Weeds are a year-round challenge, so keep up with those heat-loving weeds. Monitor and control rodents and insect pests. For insects, hose off plants as a first treatment. Insecticidal soap sprayed in the evening is the second treatment. We are all busy and would rather do a one-time-and-done style of pest management, but gardening is like caring for other living beings: steady observation and small corrections are the key to a garden full of beneficial wildlife, happy plants and happy humans.
Conserving: Healthy plants can tolerate quite a bit of damage. Chewed leaves may be from grasshoppers, but if you find caterpillars, try to identify them before removing or reaching for the chemicals. Try to tolerate damage from native species to support native moths and butterflies. Tobacco or tomato horned worms and other exotic pest larvae are easy to handpick. You can use Bacillus thuringiensis (BT—sometimes labeled as Caterpillar Killer) if pest caterpillar populations are out of control, and then return to monitoring and handpicking as needed. Don’t use pesticides as a preventative, especially broad-spectrum poisons. Pesticides are a remedy to a specific problem you have identified. Native bees and wasps are active in the summer months. Most of these tiny insects are hardly noticed because European honeybees are also active. Leave flowering (“bolting”) plants like radish, onion, and carrots for beneficial insects, and if you can, leave a little bare dirt here and there for ground-nesting solitary bees.
Whether you are still spending more time at home or have begun to pick up the active life again, I hope you will continue with the vegetable garden you started in spring. There are few things more rewarding than harvesting from your own backyard garden and few things that are better therapy than spending time at the end of the day working in the garden. A little weeding, insect management, observation and daily harvesting is part of a great life. At least I think so. Happy gardening!
Due to the shelter-at-home guidelines, the Master Gardeners have canceled all public events for the time being, but their phone lines are still open: 559-684-3325, Tuesdays and Thursdays between 9:30 and 11:30 a.m.