WHAT TO PLANT
ARIZONA’S LOW DESERT
Hold off planting anything until midmonth or whenever daytime temperatures consistently fall below 110 degrees. Most plants struggle to become established in extreme heat.
Cool-season vegetables—Sow seeds of leafy green and root vegetables, such as chard, kale, lettuce, spinach, mustard, cabbage, endive, leek, green onion, beet, carrot, radish, turnip, parsnip and rutabaga. Be patient with transplants for broccoli, cauliflower and Brussels sprouts, as they take longer to mature.
Herbs—Plant parsley, cilantro, dill, fennel, chives, chamomile, anise and chervil from seed. Put out oregano, mint and thyme transplants in a location near the kitchen for quick and easy access.
Landscape plants—Plant Sonoran Desert natives and other desert-adapted plants after mid-month. Cover the soil with a thick (3- to 4-inch-deep) layer of mulch to help insulate and prevent soil compaction.
ARIZONA’S MIDDLE ELEVATIONS
Wildflowers—Sow seeds of native wildflower mixes for spring color.
Landscape plants—Transplant trees, shrubs, vines and perennial grasses so they can become established before first frost. An excellent choice for landscapes is blue grama ‘Blonde Ambition’ (Bouteloua gracilis ‘Blonde Ambition’) (pictured right). The ornamental grass grows to 3 feet tall and wide and produces a striking mass of greenish-purple flowers in the spring and summer.
ARIZONA’S HIGH COUNTRY
Microgreens—Plant sunflower, radish, broccoli, beets, arugula and dill indoors in shallow (3-inch-deep) flats. Harvest the seedlings when they start to produce their first “true” leaves, usually two to three weeks after planting. Use microgreens to add spice and color to sandwiches and salads.
Adjust irrigation—As temperatures cool, extend the time interval between watering. Plants don’t need to be watered as often in the fall as they do in the heat of summer.
Scout for pests—While pleasant September temperatures may usher in a wave of plant-feeding pests, the use of insecticides is rarely—if ever—warranted in the garden or landscape. Most pests can be managed by hand: Simply pluck off the hungry caterpillar or wipe away the aphids. At higher elevations, a fall frost will eliminate most insect problems.
Remove tree stakes—Once strong winds of the monsoon season end, check to see if staked trees can stand on their own. Untie the supports, and free the trunk. If after an hour or two the tree is still upright, pull up the stakes or cut them off at the soil line. If the tree is still unable to stand, replace the supports, making sure that the wire doesn’t directly contact and damage the trunk.
Cull failing plants—Dispose of any plants that are infested with insects or plagued by disease, and clean up the garden to remove hiding places for any remaining pests.
ARIZONA’S LOW DESERT
Incorporate cover crops—If you planted cover crops in May or June, chop them up and mix them into your garden soil now. By October, the plant residues will have been broken down by soil microbes, providing a rich environment for your fall vegetable garden.
Remove plastic from solarized soil—If you solarized your soil in order to kill Bermuda grass or other weeds and pests, remove the plastic now. For vegetable gardens, incorporate compost into the soil and let it “rest” for two to four weeks before planting.
Resist the urge to prune flowering shrubs—such as Texas ranger (Leucophyllum frutescens) (pictured below) and yellow bells (Tecoma stans), that have grown large and lush from monsoon rains. Enjoy their blooms throughout the fall, and prune them early next spring to manage their size and remove frost damage.
Cover new plantings—Use floating row covers, which are made of white fabric that shields new plantings from insects while allowing sunlight to filter through. Once plants have produced six to eight true leaves, remove the covers and store them until winter, when they can be used to protect against frost.
Fertilize lemons and limes—If you did not already do so in August, give lemons and limes their last feeding in September. To learn more about citrus fertilization, read University of Arizona Citrus Specialist Glenn Wright’s complimentary publication, Citrus Fertilization Chart for Arizona, available for download at https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1671-2015.pdf.
ARIZONA’S MIDDLE ELEVATIONS AND HIGH COUNTRY
Harvest fruit and summer vegetables—Keep your eye on fruit trees and vines and harvest when ripe. Bear in mind that birds are also monitoring your plants, so check often. Yearly variation in mature fruit size and color due to environmental conditions, such as temperature, means that the only way to tell if the fruit is ready to pick is to taste it. Keep written records of your harvests to remind yourself next year when to start checking for ripeness. Continue picking eggplants, peppers and tomatoes to keep them producing right up to the first frost.
Protect against frost—Watch for freeze warnings, and cover sensitive and recently planted landscape plants at night.
Kelly Young is an agroecology researcher and educator with a master’s degree in botany from ASU.