August Gardening Tips for the Desert Southwest

August blends excessive heat with high humidity and monsoon rains. Learn tricks to keep your landscape looking its best.


    Beat the Heat

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    When August temperatures send the mercury soaring, heat protection and irrigation become crucial to plant survival.

    With the combination of warm nighttime temperatures (above 90 degrees F) and high humidity, succulents suffer. Water succulents carefully during hot, humid periods like this as it's when succulents are most susceptible to overwatering.

    Late in the month, the sun's shift in the sky may cause side burning on some plants, especially cacti and succulents. If you notice burning, install small sections of shade cloth to protect plants until cooler weather arrives.

    Water-use restrictions dictate irrigation timing. Don't water just because it's your time to do so. Check soil moisture and make sure watering is necessary.

    Install or check the backup battery in your irrigation timer. Flush filters and header lines. Clean or replace drip emitters that aren't working properly.

    Renew mulch to cool soil and slow water evaporation.

    Test Garden Tip: Reset irrigation timers as soaking monsoon rains arrive. Otherwise, you risk overwatering cacti, aloes, and California chaparral plants, such as white sage and Cleveland sage.

    August Planting

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    Fall is the best time to plant, but this month's typical higher humidity makes August tree and shrub planting successful, as well. Summer rains loosen soil, and that makes digging easier. Choose native, drought-tolerant, or low water-use plants.

    Now's an ideal time to sow crops of cowpeas, red amaranth, small gourds, devil's claw, and tepary beans. You can also plant tomato seedlings if you're able to shade them. At higher elevations, tuck seedlings of society garlic, chives, rosemary, and oregano into soil. At lower elevations, plant basil, pineapple sage, lemon verbena, and nasturtium.

    Indoors, start seeds for fall crops such as broccoli, cabbage, and cauliflower.

    Test Garden Tip: Late month brings shorter days and rains, both of which cool soil. Take advantage to direct-sow hardy annuals, biennials, perennials, and wildflower seeds. Plants will sprout this fall, overwinter, and grow vigorously next spring. Choices include larkspur, bachelor's button, rudbeckia, poppies, and hollyhock.

    August Pruning in the Southwest

    In lower-elevation areas, cut back tomatoes: Shear plants to 12 inches tall, fertilize, and water deeply to rejuvenate them. New growth will emerge, and you'll be harvesting in September.

    Trim honeysuckle after flowering. Shape plants and keep growth in check. You can prune oleander this month. If plants are woody or leggy, remove one-third the stems at the base. If plants are too tall, cut all stems back to 12 inches. Fertilize and water after pruning.

    High humidity spurs fresh growth on trees and shrubs. Don't tackle heavy pruning this month. It's okay to remove dead or storm-damaged limbs.

    August Garden Chores in the Southwest

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    Fertilize Citrus. Late in the month, give citrus trees their final fertilization of the year. Use a citrus-specific fertilizer, applying it according to label instructions. Remember to water deeply before and after feeding.

    Amend Soil. Add iron to soil to green up leaves of flowering plants that are looking faded and pale. Frequent summer watering leaches nutrients from soil. To replace lost minerals, apply chelated iron or ironite according to package instructions.

    Maintain Container Gardens. Continue to fertilize container plants with a water-soluble fertilizer to keep them growing and lush. Remove any plants that have succumbed to the heat and replace them with fresh varieties for extended color.

    Clean Up. Deadhead flowering trees and shrubs, such as crape myrtle, bird of paradise, oleander, roses, and chaste tree. Removing spent blooms will ensure flowers continue to open until frost.

    Pest Control. Wash cochineal scale off prickly pear cactus with a blast of water. Use the same technique to dislodge aphids from plant stems. Aphid excrement often fosters sooty mold development on penstemons and desert milkweed. Removing aphids is the best control.

    Composting. Give your compost pile a bit of water now and again to keep it moist. If it stays too dry, the natural decomposition process happens much more slowly.

    Enjoy. Many xeric plants are in bloom now -- red devil verbena, gaura, butterfly bush, Liatris, Gaillardia, and Caryopteris. Make plans to add some of these colorful, low water-use perennials to your landscape.

    Learn more about growing citrus trees.

    • Continue to mow regularly, your best defense against weeds!
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