Pruning should be done to maintain plant health (remove dead, damaged or diseased portions, cross branching, etc.), to highlight the “natural” shape of the plant, to train a young plant, and to eliminate hazards. Excessive or heavy pruning causes significant stress to trees and shrubs.
The best practices are to prune the least amount necessary and prune for legitimate reasons. How much to prune depends on the size, species, age, as well as your intentions.
Two good principles to remember–a tree or shrub can recover from several small pruning wounds faster than from a single large wound and never remove more than 25% of the canopy in a year. For more information register for a Garden class on pruning that will teach you the proper pruning techniques for trees and shrubs or visit http://www.treesaregood.org for information on proper pruning of young and mature trees.
Lightly prune native and desert-adapted trees to avoid breakage during the summer thunderstorms in July and August if needed. Do not prune excessively as this will expose the tree trunk to the blazing sun causing it to sunburn.
Pruning newly planted trees is not recommended and in fact, can be detrimental. However, at planting time prune broken or torn and diseased branches. Save other pruning actions for the second or third year. For more information on developing a healthy tree visit www.treesaregood.org.
Prune your cacti if necessary to maintain size, for propagation or to remove a damaged or diseased stem; prune at joint or segment. Use a sharp, clean pruning tool and spray tool periodically with a 70% alcohol solution to prevent infection.
If the pruned stem is to be used for propagation, allow the cutting to dry out for a week before planting.
Continue to prune old flowering stalks from Hesperaloes (Hesperaloe spp.), Agaves (Agave spp.), Yuccas (Yucca spp), and Aloes (Aloe spp.).
To encourage continued flowering, deadhead herbaceous perennials such as Desert Marigold (Baileya multiradiata), Chocolate Flower (Berlandiera lyrata), Texas Blanket (Gaillardia pulchella), Red Sage (Salvia coccinea), Angelita Daisy (Tetraneuris acaulis), Mealy Cup Sage (Salvia farinacea), and Tickseeds (Coreopsis spp.).
Most native and desert-adapted plants in the landscape do not generally require fertilizer as they are adapted to our soil conditions. In most cases, fertilizers are generally applied to prevent deficiencies. If fertilizers are needed, one application for the year is usually sufficient. The best time to fertilize landscape plants are in March, April or the early part of May.
We do not recommend fertilizing your desert-adapted landscape plants during the summer months. Fertilizing will cause excessive, luxuriant growth that requires more water and new growth is too tender to take the excessive heat and sun exposure. Wait until next spring to fertilize, if needed.
Periodic fertilizing may be needed for plants in containers as nutrients in the soil will have diminished over time. Always follow directions on the label.
Continue to fertilize your warm-season annuals and herbaceous and woody perennials in containers if necessary.
Cacti and warm-season succulents in containers should be fertilized at least once during the month depending on the type of fertilizer used. If using a slow-release granular fertilizer for your cacti and succulents in containers, fertilize in late March and again in July or early August.
Do not fertilize any winter-growing succulents such as Succulent Geraniums (Pelargonium spp.), Iceplants (Malephora spp., Drosanthemum spp.,Cephalophyllum spp.), Living Stones (Lithops spp.) and crassulaceous plants (Kalanchoe, Cotyledon, Echeveria, Dudleya) as they are summer dormant.
Continue to water and fertilize your Karoo Roses (Adenium spp.) to promote bloom through the warm season.
Continue to fertilize your vegetable and herb garden as needed.
Mosquitoes are now commonplace throughout the Valley particularly after rain events. Be sure to empty any containers, buckets, bowls, etc. that might catch rainwater as the larvae require water in which to mature.
Ants and termites are swarming and if you see the mud tunnels of termites crawling up your plant stems, just wash them off. They are not harming the plants.
Defoliation of many landscape plants can occur with the appearance of a high infestation of grasshoppers. Population size varies year to year and they are a difficult insect to control in the garden. When population numbers are low, hand-pick and remove. If infestation is high, use a protective cloth or floating row cover to protect your plants. Allow natural predators such as birds, lizards and spiders to help keep the population under control.
Whiteflies are small, sucking insects that are often found on many ornamental and vegetable plants. Plants infested with whiteflies show symptoms of sticky, yellowing leaves and when the plant is disturbed the small insects will fly generating a white “blur”. There are many species of whiteflies and they are abundant at different times of the year. Whiteflies are difficult to manage and insecticides are not recommended as it can disrupt and destroy their natural enemies. If you choose to use an insecticide, use an insecticidal soap or oil to help control populations.
Large, green caterpillars may be appearing on tomatoes, eggplant and even the Sacred Datura (Datura wrightii). They can either be the tobacco or tomato hornworm feeding on the leaves, flowers and stems. After three to four weeks of feeding, the larva will burrow into the soil to pupate. In about two months, the large adult moth will appear and are often mistakenly identified as hummingbirds.
These moths are important pollinators for many nighttime flowering plants including the Sacred Datura (Datura wrightii), Fragrant Evening Primrose (Oenothera caespitosa), and the Queen of the Night (Peniocereus greggii). No method to control is necessary. If infestation is high, hand-pick caterpillars off your plants or allow naturally occurring parasites to help control the population.
A white, cottony mass may appear on ornamental and edible plants and is sometimes confused with cochineal scale because they too produce a waxy, white cottony substance but it is most likely mealy bugs. Both insects feed on plant juices, however, cochineal scale feed exclusively on cacti such as Prickly-pears (Opuntia spp.), Nopalea spp. and Chollas (Cylindropuntia spp.).
Mealy bugs are often difficult to control and systemic insecticides may be used, but are not always effective. However, usually dipping a cotton swab with a 50-50 mixture of rubbing alcohol and water solution and then wiping on these insects can help manage the population. Mealy bugs are also a common problem for many cacti and succulents grown indoors or in greenhouses and are often found either on the stems or roots.
Take the infested plant(s) outdoors during the summertime as this seems to help get rid of these pests. It takes constant vigilance to keep them under control.
The male cicadas’ mating calls are a cacophony of sound that permeates the desert air and often heralds to the gardener that summer has arrived. The Apache cicada is common to low-desert regions and the adult has a mostly black body with a pale band behind its head. The nymphs spend almost their entire life underground feeding on the roots of many desert trees, shrubs and other ornamentals.
As the nymph becomes an adult, it will then surface from the soil and undergoes one last shedding of its exoskeleton. The adult cicada will feed on the plant sap of many trees or shrubs. After mating, females will make small “hatch” marks on the slender tips of trees or shrubs to lay their eggs. This physical damage can cause the tips to “die” back, but is not detrimental to the plant and is often thought of as “natural pruning”.
There is no need to control cicadas as they are part of the desert ecology. Allow natural predators to control the population as many birds and lizards find the cicada nymph and adult to be a tasty treat.
If it has been a dry season, rabbits may be nibbling on plants that they may not have eaten before. Most mature plants can handle rabbit sampling, but newly planted plants should be protected until they have attained a larger size. Protect plants with a wire cage or spray Liquid Fence TM to help deter these animals. Allow mesquite pods to fall and remain on the ground for rabbits to eat as they are a vital food resource for many desert animals. It might even help distract them from eating your most prized plants.
Cochineal scale, the cottony, white substance on your Prickly-pears (Opuntia spp.) and Chollas (Cylindropunita spp.) may be active now. Remove by using a fast stream of water or spray insecticidal soap.
Adult ocotillo borers are now active in search of stressed or recently planted ocotillos in which to lay their eggs. The eggs are laid in the bark and the larvae or grubs excavate into the stems causing a hasty decline of the plant. Look for signs of borers by watering the ocotillo during the warm season. If the stems do not leaf out, examine for grubs and remove any infected stems by pruning back to base of the plant.
The large, black-brown beetle bumbling onto your porch during the sweltering summer nights is the Palo Verde Beetle. It has just emerged from its subterranean home looking for a mate. For the past two to four years it has lived underground as a grub or larva feeding on the roots of many native and non-native plants, not just Palo Verde trees as the common name suggests.
When the grubs become adults they will ascend and can be seen in late June, July, August and September particularly after rainfall. Once the female adults mate, they lay their eggs and die soon after making their life span about one month. Using pesticides is not recommended as the beetle is already gone by the time you notice any damage.
To prevent root borers keep your plants healthy as possible as they will be less vulnerable to an attack. There are many natural predators of the adult beetle including roadrunners, coyotes, owls and even bobcats. Grubs are eaten by skunks.