Watering in the heat of the day. (Getty Images)
One of the most persistent gardening myths concerns wetting the leaves of plants during the heat of the day: “Water droplets act like tiny magnifying glasses, concentrating the sun's rays and causing the plants to burn” is common knowledge among most gardening enthusiasts.
But that's far from the truth.
In Australia, an overhead misting system was installed on a 40-acre Granny Smith apple orchard to prevent fruit scorching. Apple yield losses due to sunburn were reduced from 10 percent to 2 percent. Misting systems are particularly effective at cooling planters on hot patios and balconies, and are readily available from online vendors.
You don't have to go to Australia to understand that overhead watering doesn't harm plants by wetting their leaves. Of the 55 million acres of irrigated farmland in the United States, 28 million acres are watered with overhead sprinklers in center pivot systems that slowly circle the fields for 24 hours at a time. Crops that are watered overhead during the heat of the day include alfalfa, wheat, corn, soybeans, cotton, sugarcane, sugar beets, and watermelon.
The fact that overhead irrigation can keep plants from burning in extreme heat is one reason to keep traditional spray sprinkler systems. A steady spray of rain-like water droplets from above can help cool the leaves on hot days. Or you can use pulsed sprinklers (also called impulse or impact sprinklers) to distribute water over a large area. There are pulsed sprinklers that can cover up to 5,000 square feet and cost about $20 each. Some of these sprinklers have a stable base to which the hose connects, and the unit is fully mobile and can be moved easily. For overhead irrigation of orchards, pulsed sprinklers can be mounted on a tripod to ensure that the pulses of water produced rise far enough to reach the tree canopy.
Regardless of the weather forecast this summer, early morning irrigation is recommended, and a layer of mulch up to 6 inches thick is effective in minimizing moisture loss from the soil. However, make sure the mulch does not cover the bark of shrubs or trees, which could allow pathogens to enter. If the leaves of a plant are burned, do not cut them off, as they will shade the leaves below. Cutting dead leaves can also burn new leaves that emerge.
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Victoria Morse Chafee emailed me this plea for help: “The ants have built a huge base at the base of my 60 year old grapefruit tree and have worked their way up into the crown. And they are stinging!! I don't know what to do but I am worried about my dogs and I can't go near the base for fear the ants will fall on me and bite me. They attacked me again this morning and bit me. What can I do and will they damage my beautiful tree?” she asked.
Ants are especially attracted to citrus trees because of the variety of sap-sucking insects that make their home there, especially aphids (sometimes called “ant cows”) and scale insects, but also whiteflies and leafhoppers, which excrete a sticky substance called honeydew that serves as a food source for ants. Even more terrifying, ants also repel insects that are natural enemies of the pests they displace, and then carry the pests from branch to branch on the same tree, or even from tree to tree.
To prevent ants from climbing a tree, wrap plastic tape around the trunk a few inches above the ground and liberally apply a sticky substance such as Vaseline to the tape. There is also a product called Tanglefoot that is used for this purpose. Ants will get caught in the sticky barrier and die. The ant carcasses act as a bridge for other ants to climb the tree, so you should check regularly and scrape off any dead ants. The stickiness of the traps will decrease over time, so it is recommended that you replace them once a year.
Either way, the health of an established tree like yours shouldn't be affected by ants, much less by what you think are fire ants, since your house is being bitten by them. Fortunately, fire ants are omnivorous and can even prey on pests that harm trees. I'm not a veterinarian, so I can't recommend what to do if your dog is bitten by fire ants. But you can research ways to get rid of them. There are at least two products that are advertised as safe for pets (but it's worth researching and convincing yourself about their effectiveness): Terro Liquid Ant Bait Stations and Advion Ant Gel.
California Native of the Week: Gardening enthusiasts are probably familiar with the common sea lavender (Limonium perezii), native to the Canary Islands. This plant produces purple-tinted flowers, most often on 2-3 foot stalks. The flowers last a long time and are perfect for dried flower bouquets. California sea lavender (Limonium californicum) also exists and is also called Western Marsh Rosemary. Think of this species as a miniature version of its more commonly known relative. The flower stalks are only 14 inches tall, but the leathery, oval leaves closer to the ground measure 12 inches. It has a woody rhizome, making it a hardy perennial. California sea lavender grows along the coast from Oregon to Baja California, but its habitat, the salt marsh saline playas, is shrinking and is now endangered. That's reason enough to cultivate this plant. Unfortunately this plant is rarely seen in the nursery trade so if anyone knows where to get this species or its seeds please let me know.
Please send your questions, comments, and gardening successes and struggles to joshua@perfectplants.com.
