WHAT TO PLANT

ARIZONA’S LOW DESERT

August signals the beginning of the fall gardening season in the low desert. Hold off on planting cool-season crops until soil temperatures fall below 85 degrees, usually around midmonth. You can buy a reliable yet inexpensive soil thermometer at most garden stores. Or research weather data online. Choose the weather station nearest your home and monitor the daily averages for the soil temperature at four inches, labeled “ST04” in the table.

Cool-season vegetables—Once soil temperatures have cooled down a bit, plant seeds of carrots, radishes, turnips, lettuce, kale, chard, spinach, mustard, kohlrabi and bok choy directly into soft earth that has been raked smooth. Start seeds of broccoli, Brussels sprouts, cabbage  and cauliflower indoors for transplanting into your garden in October.

Warm-season vegetables—Sow corn, squash and bean seeds for a fall harvest. Be sure to plant corn in blocks rather than rows for better pollination and full ears of kernels.

Landscape plants—For better transplanting success, wait until next month to plant most ornamental trees and shrubs.

Palms—Plant palms during the heat of summer. Be sure to keep the soil evenly moist but not soaking wet while roots colonize their new territory.

ARIZONA’S MIDDLE ELEVATIONS

Cool-season vegetables—Sow seeds of cabbage, carrot, chard, kale, lettuce, Irish potato, radish and turnip. Set out pepper transplants now for harvest until the cold begins.

ARIZONA’S HIGH ELEVATIONS

Cool-season vegetables—Select fast-growing, early-maturing and frost-tolerant varieties of lettuce, spinach, chard, radish, green onions and mustards. You can start harvesting outside leaves from these crops once they have grown six to eight mature leaves. Don’t pick the center leaves as they protect the growing point of the plant where new leaves are produced and allow continual harvest throughout the fall.

Landscape plants—Plant ornamental trees, shrubs, vines and perennial grasses now. Arizona fescue (Festuca arizonica) and mountain muhly (Muhlenbergia montana) are native bunch grasses that do well at high elevations and are relatively salt-tolerant.

GARDEN MAINTENANCE

ALL ELEVATIONS

Weather summer storms—Monsoons can bring strong winds, hail, lightning and flash flooding to all elevations, wreaking havoc on gardens and landscapes. Make sure newly planted trees are properly staked and can sway in the wind without falling over. If staked too rigidly, they will not develop “reaction wood” that makes the trunks stronger and better able to resist breaking in a storm.

Adjust irrigation—Monsoon rains tend to run off before they percolate into the earth. Check the soil moisture with a probe fashioned from a narrow 3-foot long metal rod. The probe will easily penetrate moist ground and stop abruptly when it reaches dry dirt. Supplement summer rain with irrigation so that plants are watered to the correct depth: 1 foot for grasses and annual plants, 2 feet for shrubs and vines, and 3 feet for trees.

Cover vegetables—Five minutes of hail can destroy your vegetable garden. If possible, have heavy plastic tarps ready to protect your tender plants from an icy barrage. Promptly remove the tarp after the storm.

Scout for pests—Turn over leaves on vegetables, fruit trees and vines to find plant-feeding insects or their eggs. Inspect stem tips for aphids and simply wipe them off with a wet, soft cloth. Remember that not all insects and spiders in the garden are pests. In fact, many insects and all spiders prey on plant-feeding pests.

Manage weeds—Don’t let weeds compete with desirable plants for water and nutrients. Keep basins around fruit trees weed-free by pulling them, roots intact, immediately after watering while the soil is soft.

Harvest crops and cull failing plants—Pick melons, cucumbers, squash, tree fruits and other edibles as they ripen. Remove and destroy plants plagued by disease or overrun by insect pests, as they may infect nearby healthy plants.

ARIZONA’S LOW DESERT

Incorporate cover crops—If you planted cover crops earlier in the year, now is the time to chop them down, mulch and dig them into garden soil. Irrigate well, and let soil microorganisms break the residue down in preparation for a lush fall garden.

ARIZONA’S MIDDLE ELEVATIONS

Divide spring-blooming perennial bulbs and store them in your refrigerator’s vegetable crisper until fall planting.

Deadhead roses and other summer-blooming shrubs. Removing spent flowers is a good way to stimulate new blooms for color all season long.

ARIZONA’S HIGH ELEVATIONS

Nighttime temperatures can dip into the danger zone in late August. Watch local weather forecasts, and protect frost-sensitive plants as needed.

Keep compost active by turning every few days and not letting it dry out. Compost is finished when it has turned dark brown in color, smells of sweet
forest soil and the original organic material is no longer recognizable.

Kelly Young is an agroecology researcher and educator with a master’s degree in botany from ASU.