Droopy Leaves on a Hot Afternoon. Water...Or Not?

Do your plants have droopy leaves on a hot afternoon? 

   

There are two schools of thought.

One school says plants conserve moisture on a hot afternoon by allowing their leaves to sag.


The other school says: "Don't believe that first school."

Drooping leaves are usually indicative of a lack of water from the root zone. "Large, thin leaves, common in many of ornamental, annual and vegetable species, do not conserve water," writes Washington State University Horticulture Professor Linda Chalker-Scott. "Tomatoes, zucchini and black-eyed Susans...are not water conservers. Chronic wilting of these and others can eventually cause leaf tip and margin necrosis (or tissue death). It also reduces growth, so that your yield of tomatoes, zucchini and black-eyed Susans will be decreased."
She advises applying a layer of mulch around those plants to help conserve water.

Also, check the moisture at the root level before watering.
To determine the amount of water at the root level:

• A day or two after watering, dig down 8 to 10 inches with a trowel or small shovel, near the drip line (outer canopy) of the plant. Doing this in two or three spots would be more helpful.

• At that depth, grab a handful of the soil. Squeeze that handful. If it is muddy and watery, reduce your watering for plants that require regular (but not frequent) irrigation. If it is so dry you cannot form a clod in your hand (it turns to dust instead), increase your watering (for those plants that require moderate amounts of water).

• If you can form a dirt clod in your hand, yet break it apart with a little effort, that is probably the correct soil moisture for your plant.

• Steve Zien, owner of the Citrus Heights-based organic landscaping consulting service, Living Resources, recommends the use of a soil sampling tube to determine the moisture at root level. "Just press the tube down six to eight inches into the soil after you are done watering," says Zien. "When you bring it back up, the open slot along the side of the tube will let you see if the soil at that depth is wet, moist or dry. Adjust your watering time so that the soil sample is moist, not too wet or dry."

• An easier, but more unreliable way to measure the water content of the soil: purchase an inexpensive (under $10) moisture meter, available at most nurseries. Test its accuracy by putting its probe into a glass of water. If the probe does not read "wet", choose another. Expect it to function for only a year or so.

• Battery operated moisture meter probes may set you back a few more dollars, but in my experience - with proper care (clean them after each use, don't leave them outdoors) - they will last many years.

• Extended, infrequent, slowly applied irrigation is the most efficient watering method. Soaker dripline or drip irrigation systems work best. Here in the Central Valley, foothills and Bay Area, run them for 3 to 6 hours at a time, twice a week, in the summer. This is only a guideline to get you started. Adjust that timing to your particular soil type and plants.

• And, don't forget: add more drip emitters and drip lines as the plant grows, especially for trees and shrubs. Make sure to get water to the outer canopy of the plant (and beyond) where the roots travel.

Improper watering is the number one cause of plant failure. Knowing how wet the soil is at the root level can help you keep your plants healthy.

Keep in mind: different plants have different watering needs. Learn those needs, then group plants together with similar watering requirements when designing your landscape. The Sunset Western Garden Book is a good source for that information.

Signs of not enough water at the root level of plants:
Wilted leaves in the morning. Wilted leaves in the afternoon.
Wilted leaves in the evening.
Red-brown margins of leaves.
Premature fall color of leaves.
Growth reduction.
Leaf drop.
Branch dieback.

Signs of too much water (also called aeration deficit) at the root level of plants:
The soil has a foul smell, like rotten eggs.
Soil is a blue-gray color.
Yellowing, wilting and/or dropping of leaves.
Limited new growth.
Small, corky outgrowths on the undersides of leaves.

Be warned, though: sometimes, symptoms of overwatering and underwatering can be the same (such as leaf wilting). And, symptoms of soil water problems may actually be another problem...that was caused by your watering regimen! Root rots, for example, thrive in saturated soils.

Frequent, light watering leads to shallow rooting, increasing the chances of plant problems.

How much water does your lawn need?

Some tips from the UC Integrated Pest Management Website:


• Avoid planting turf species that require frequent watering, such as bluegrass or ryegrass.
• Design your landscape to minimize water runoff onto hard surfaces and into storm drains.
• To reduce runoff, install non-irrigated buffer areas, which include water-efficient plants or permeable features, next to sidewalks or on slopes.
• Aerate heavy or compacted soils, so water can easily move down to reach grass roots.
• Install an irrigation system that you can adjust to properly water areas of your landscape that have different requirements.
• Water only when your lawn needs it.
• Water requirements vary according to turf species, location, and month of the year.
• Most lawns need water when the top 2 inches of soil have dried out.
• Shady and sunny areas and different soil types will have different water requirements.
• Deeper, less frequent watering is best for most lawns. Water only 2 to 3 times a week.
• Make sure your sprinkler system isn’t producing runoff, especially on slopes. If you see runoff, use shorter watering times and repeat the cycle to allow time for the water to move into the soil.
• Water early in the morning when evaporation and wind are minimal.
• Adjust your watering schedule seasonally, and shut off your irrigation system during rainy weather.

Battling Tomato Hornworms

Doug from Mather writes in:
"As a first time tomato grower, I have two plants in pots (Patio & Bush Better Boy), and four in the ground (Roma, Sun Gold, Lemon Boy, & Black Krim). Something was eating the young tomatoes in the pots. Upon closer inspection I found three juicy, green caterpillars around the plants. I did some research and they seem to be tomato hornworm (Manduca quinquemaculata) - a common pest and best controlled by hand picking and dumping in soapy water, or allowing the beneficial wasps to do the job.
Any other suggestions controlling these tomato eaters?"

Doug, one option might be to stick that critter in the envelope that he’s resting on, and mail it to someone you don’t like. However, the envelope may require extra postage. 

This time of year, many backyard gardeners, in addition to Doug, are glaring at their partially eaten tomato plants, and muttering under their breath, "Just where do these blankety-blank tomato worms come from?"

Contrary to a popular urban legend, the larvae of the tomato hornworm do not lurk inside tomato seeds, a diabolical plot between seed growers and chemical manufacturers to increase profits. Nor are the worms drawn by the scent of your tomato plants from deep within your garden soil, emerging forth to wreak havoc.
 The tomato and tobacco hornworm begin their life cycle as a small, singular, light green egg, about the size of a thick pinhead, laid in late spring and early summer on the underside of a tomato leaf.

That egg got there courtesy of a flying culprit, the sphinx moth. Both the tomato hornworm sphinx moth and the tobacco hornworm sphinx moth have similar features: about a four-inch-wide wingspan, gray body, brown wing streaks as well as yellow and white body markings.
 





The egg laid by the sphinx moth hatches within a week, and the emerging hornworm (technically, a caterpillar) begins eating. And eating. And growing. A full-grown hornworm, satiated by its tomato plant diet (supplemented with whatever else is handy, including potatoes, eggplants and peppers) can get up to four inches long.

If you miss catching the tomato hornworms, these critters will descend into the soil at the end of the season, wrapping themselves into a cocoon:

Disking or rototilling after harvest destroys their pupae in the soil and prevents the adult moths from developing and emerging from the soil the following spring. Again.

 
Hand snipping the tomato worms with scissors or pruners can be a satisfying evening chore. The trick, as seasoned gardeners know, is trying to find the hornworms in the first place. Tracing their black, pellet-shaped excrement from the ground back up the plant usually yields successful results. The best time to find them is in the cool of the morning or evening. Another popular tomato worm hangout: the tender, new growth at the top and sides of tomato plants.

If you prefer to douse tomato hornworms in chemicals, use one registered for use on this pest. Soaps and oils might slow them down but won’t kill them. What does work are stomach poisons that contain a bacterial insecticide, such Bacillus thuringiensis (Bt) or spinosad. They can be applied directly to the offending hornworms. However, this works best while the worms are still small. The bigger ones are more problematic, but there may be help already at work in your yard.

Encouraging birds to hang around your property is a good strategy. they enjoy these green treats. Dense, broadleaf evergreen shrubs are a favorite hangout of many birds. (More info to attract birds)

Besides birds, the tomato experts at UC Davis point out that there are a lot of garden good guys that can help you battle the hornworms. The UCD Integrated Pest Management website says: “Natural enemies normally keep tomato hornworm populations under control. Hornworm eggs are attacked by Trichogramma parasites (a small wasp); another small wasp, Hyposoter exiguae, attacks the larvae."

Hornworm parasitized by Trichogramma wasps. Let it be.

There are also several general predators to keep populations under control, including green lacewings, damsel bugs, assassin bugs, big-eyed bugs, minute pirate bugs, soldier beetles, ground beetles, and spiders.