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August Garden Checklist

Learn what to plant this month, get maintenance advice and troubleshoot gardening challenges with an expert.

By Kelly Young

What to Plant


Low Elevations

Warm-season vegetables–Sow seeds of black-eyed peas, bush beans, pumpkins and squash into moist soil and don’t let the seeds dry out before they sprout. For pie pumpkins, try “Cinnamon Girl”; “Jack-o-lantern” is a good carving variety, and “kakai” produces hulless seeds, which are excellent for roasting. These varieties are available from Johnny’s Selected Seeds (johnnyseeds.com) and other seed companies.

Cool-season vegetables–Start Brussels sprouts, broccoli, cauliflower, cabbage and head lettuce seeds indoors to transplant into the garden in early October.

Palms–Plant landscape palms in a hole at least twice the width of the container to encourage rapid root growth. Don’t make the hole any deeper than the root mass. Planting too deep can cause the stem to rot and the palm to fail. Always research the mature size of the plants and install them far enough apart so that

Biodegradable fiber pots minimize transplant shock.

fronds from neighboring plants do not interfere with one another. To learn more about growing palms and types that perform well in Arizona, download “Arizona Landscape Palms” at extension.arizona.edu.

Middle and High Elevations

Landscape trees and shrubs–Plant woody, perennial trees and shrubs while the soil is warm and the roots are actively growing to get them established before cool fall temperatures settle in. When selecting nursery stock, look for specimens that are pushing out new leaves and don’t have broken or crossed limbs, which would require corrective pruning.

Middle Elevations

Cool-season vegetables–Sow seeds of radish, turnips, peas, leaf and head lettuce, kale, collard greens, chard, mustard greens and spinach. Cover newly planted beds with floating row covers to keep hungry birds from eating the seeds and sprouts.

High Elevations

Sow seeds of radish, beets, leaf lettuce, kale and spinach. Select varieties that will be ready to harvest in fewer than 50 days to ensure they mature before frost kills them. “Babybeat” is a beet variety that can be harvested 40 days after planting and can be eaten with the leaves intact.

Garden Maintenance


All Elevations

Adjust Irrigation–Because August often brings higher humidity and rainfall to Arizona, less supplemental irrigation is typically required to meet plant water needs. Use a soil moisture sensor to measure the ground’s water content at 3 or 4 inches beneath the surface to determine whether or not to irrigate. Every time you irrigate, apply the water to the soil at the at the edge of the canopy where most of the plant’s absorptive roots are located. Water deeply to flush salts out of the root zone and support healthy root systems.

Tackle summer weeds–Use a hoe to chop amaranth, tumbleweed, spurge and other annual weeds at ground level before they get a chance to set seeds and spread. Bear in mind that herbicide applications to annual weeds that have already begun to set seeds are likely to be ineffective and may even hasten seed ripening. If you choose to use an herbicide, be sure to follow directions on the product label.

Tend compost–Turn compost with a garden fork every week, and add water so the compost material is damp but not dripping wet. Chop up larger pieces to speed decomposition.

Low Elevations

Give garden beds—and yourself—a break–Vegetable, herb and flower beds that have been in continuous production for several years may benefit from a fallow, or temporary, period when no plants are being cultivated. A month of fallow can break pest cycles and save water. If pests have been a problem in the past, covering the bed with thick, clear plastic will raise the temperature of the underlying soil and kill most organisms in the top few inches. Alternatively, cover the soil with 4 inches to 5 inches of straw to keep the soil cool and suppress weed seed germination while the soil fallows. Once the daytime temperatures stop breaking 100 degrees next month, the plastic or straw can be removed to prepare for fall planting.

Prune overgrown mesquites–Mesquite trees respond to hot temperatures and plentiful irrigation with rapid growth, causing the limbs to sag. Reduce the weight by cutting the stems back to buds 5 inches or 6 inches from the tip. Add supplemental irrigation for the first three or four years, particularly during the hot, dry months. After that time, they should be able to get by on rainfall and water scavenged from irrigated plants nearby.

Middle and High Elevations

Deadhead flowering shrubs and roses–Snip off spent flowers to encourage a fresh flush of blooms. Make sure your tools are clean and sharp to reduce the chance of invasion by diseases, such as fireblight or bacterial canker.

Harvest vegetables–Harvest the outer leaves of chard, kale, spinach, arugula and leaf lettuce, leaving the actively growing crown and inner leaves to keep the plants producing.

Pro Tip: Summer Bug Watch

By Justin Lugo, vice president of outside sales and design, The Green Goddess, Phoenix


  • Monsoon dust and winds bring insects, such as mealybugs, spider mites, caterpillars and weevils, out of hiding. Check plants periodically for damage. If you find bugs or evidence of pests you cannot identify, snip off a sample, seal it in a plastic bag, and bring it to your local garden center for help in determining the best course of treatment.
  • Protect Texas mountain laurel, Tecoma stans (yellow bells) and bougainvillea from caterpillars, which can destroy plants if left untreated. To eliminate caterpillars, wash plants using a hard-nose hose water spray followed by an application of Thuricide worm killer.
  • The agave snout weevil (Scyphophorus acupunctatus) pierces the agave’s core and lays eggs inside. Grubs hatch and feed on the roots and core of the agave plant, eventually killing it. To help prevent infestation, apply a grub control product to the soil once in early spring once at the beginning of summer.
  • Be on the lookout for the shiny webs left by spider mites on yuccas, agave, cypress, junipers and many other plant varieties. These pests love our warm dry summer. Keep your plants in good health and hose them down periodically to help reduce the chances of infestation.

Garden Solutions


Do cicadas harm plants?

The incessant mating call of male cicadas is nature’s summer theme song. Once mated, the female cicada makes small slits toward the tip of pencil-sized branches (usually mesquite trees) into which she lays her eggs. After approximately six weeks, the eggs hatch and the young cicadas, or nymphs, drop from the branches and burrow underground, where they feed on plant roots until they surface a few years later. The emergent nymphs crawl up a tree or other stationary structure, shed their skin for the last time and continue the cycle. Contrary to suburban legend, adult cicadas do feed on plant juices. Although this may sound like a lot of feeding damage, cicadas are not serious threats to plant health and are even considered beneficial because they help limit the growth of mesquite trees. No treatment is recommended; just sit back and enjoy the music.

Can I plant the living basil I bought at the grocery store in my garden?

Believed to have originated in Central Africa and Southeast Asia, basil thrives in hot, dry and sunny conditions, so the plant you purchased at the grocery store should be fine outdoors. It will have a better chance of success, though, if given an opportunity to ease into its new environment first. Before moving the plant from the relatively dark and climate-controlled kitchen to the hot, bright landscape, place it in a sunny window for a day or two. Then transition it to a shady location outdoors for another day or two before planting into full sun in the garden. Because soil dries more quickly outdoors, be sure to check the ground’s moisture every day and water when it is almost dry. But remember, too much water is as deadly as too little water. Overwatering basil creates an environment favorable to root rot that can kill the plant.

A branch broke off of our eucalyptus tree during a wind storm. Luckily no one was hurt, but I’m worried that other limbs may fall in future storms. The tree provides wonderful shade, and I don’t want to remove it if we don’t have to. What do you suggest?

The tree should be evaluated by an arborist certified by the International Society for Arboriculture to assess the potential hazard it poses to human safety and property. Together, you and the arborist can discuss your options, which may include corrective pruning or removal. Since you value the shade the tree offers, factor into your decision the increased energy costs to cool your home for several summers, until a replacement tree is large enough to provide adequate shade, if it is removed. Visit treesaregood.org/findanarborist to search for a certified arborist in your are

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