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September Garden Checklist

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

By Kelly Young

What to Plant

Low Elevations

COOL-SEASON VEGETABLES–Start seeds of cauliflower, broccoli, Brussels sprouts and cabbage indoors now to transplant outside in mid-October, once daytime temperatures have dipped below 100 degrees. After midmonth, sow beet, carrot, radish, turnip, leek, rutabaga, arugula, leaf lettuce, chard, spinach and snap pea seeds directly into garden soil. The ground should be free of weeds, grass and stones prior to planting.

NATIVE TREES AND SHRUBS–Species indigenous to the Sonoran Desert are adapted to local conditions and will look great with minimal irrigation and care. Arizona rosewood (Vaquelinia californica) is a slow-growing evergreen tree that produces dense shade and blooms creamy white flowers in spring. Elephant tree (Bursera microphylla) matures into a large shrub or small tree. Native to some of the harshest conditions the desert offers, elephant trees store water in their girthy trunks.

ORNAMENTAL GRASSES–Bunch grasses can be quite striking in desert landscapes and come in a variety of colors and sizes. Little bluestem (Andropogon scoparious) is a compact grass that grows up to 2 feet tall and wide. It is bluish in color during the warm season and takes on a reddish hue during the dormant winter months. Deer grass (Muhlenbergia rigens) reaches 5 feet in height and width and sends up striking flowering spikes throughout the summer. To make ornamental grasses stand out in the landscape, plant in clusters.

FLOWERS–Sow seeds of calendula, foxglove, bells of Ireland, blanketflower, poppy, petunia, dianthus and snapdragon. Keep the seedbed damp but not waterlogged until seedlings have two to three true leaves. Then scale back irrigation frequency to every five to seven days.

Middle Elevations

COOL-SEASON VEGETABLES–Sow broccoli, cabbage, carrot, chard, leaf lettuce, onion, radish and turnip seeds no deeper than 0.5 inch to ensure germinating seedlings make it to the soil surface. Plant garlic cloves 6 inches apart to give bulbs ample room to develop.

WILDFLOWERS–Sow seeds of penstemon, flax and California poppy in a weed-free area. If you used a pre-emergence herbicide to manage weeds during the summer, the product may also prevent wildflowers from becoming established.

NATIVE TREES AND SHRUBS–Create a landscape that will last for decades by choosing native species that are proven winners. Canyon hackberry (Celtis reticulataI) is a tough deciduous tree that grows up to 60 feet tall. Manzanitas (Arctostaphylos spp.) are striking shrubs with mahogany-colored stems.

High Elevations

NATIVE TREES AND SHRUBS–Transplant cold-hardy natives before midmonth to give their root systems a chance to colonize the soil before daytime high temperatures start dipping below 60 degrees. Chokecherry (Prunus virginiana) is a small tree with red bark that offers fall color. Rock spire (Holodiscus dumosus) is a hardy shrub and great pollinator plant that produces pink flowers in the spring. When planting, dig the hole twice the width but no deeper than the rootball to encourage lateral root growth.

Garden Maintenance

Middle Elevations

KILL BERMUDA GRASS–If you want to remove your lawn altogether, this is your last chance to kill Bermuda grass before it starts going dormant. Solarize soil using thick, clear plastic for a chemical-free solution. If you choose to use an herbicide, check the label to ensure that it is effective against the grass species you are trying to manage and follow the instructions exactly.

STRATIFY WILDFLOWER SEEDS AND BULBS–Certain wildflowers, such as Mexican hat, lupine, milkweed and primrose, as well as bulb-forming species, such as tulip and narcissus, require a period of cold before emerging in the spring. Mimic a cool, mild winter by storing seeds and bulbs in your refrigerator’s vegetable crisper for six to eight weeks prior to planting outdoors later in the fall.

REVIVE TOMATOES–Prune tomato plants to stimulate a fresh flush of growth and blooms.

PREPARE GARDEN SOIL–Before planting vegetable, flower and herb beds, enrich the soil with compost and a fertilizer that

contains both nitrogen and phosphorus, such as ammonium phosphate. Spread 3 inches of finished compost on the surface and sprinkle with fertilizer (5-10 pounds per 1,000 square feet if using ammonium phosphate) and work into the top 8-12 inches. Rake the area smooth, and gently irrigate to settle the soil and dissolve the fertilizer. If cover crops were planted during summer, mow or chop them to ground level but do not disturb the surface. Allow the roots to decompose in place to conserve moisture and protect soil structure.

High Elevations

MANAGE WEEDS–Mow or hoe annual weeds before they bloom and set seed. Post-emergence herbicides are generally most effective when applied when weeds are small, with fewer than four or five leaves.

ADJUST IRRIGATION–After midmonth, begin reducing the frequency of irrigation to deciduous trees, shrubs and vines to encourage dormancy.

Pro Tip: Growing Strawberries

By Gregory Ware, local grower, Gregory’s Garden

September, October and November are the best months for establishing a bed of strawberries. Fall-planted strawberries will build a large root system through the cool autumn and winter seasons, allowing them to bear a plentiful harvest.

  • Plant in well-prepared garden soil. For containers, choose a high- quality potting soil, preferably one that contains coir or peat moss.
  • Whether in ground or potted, plant at the proper level, with the root ball level with the soil’s surface. If the root ball is emerging from the soil, roots will be exposed and the plant will dry out. Extra soil on top of the root ball or against the stem will cause the stems to rot.
  • Water plants thoroughly so that the root ball is wet and the soil around it is saturated. For the first week or two, check plants daily by sticking your finger in the root ball, watering when it is between damp and dry.
  • Keeping the ground constantly wet can lure populations of soil-dwelling insects that later will feast on ripening berries. When the top 1 inch of soil has dried to the point of being between damp and dry, and the surface of the soil is visibly dry, water again deeply and thoroughly.
  • Fertilize every six to eight weeks with a dry granular organic fertilizer formulated for flowers and vegetables. If you prefer to use a liquid fertilizer, supplement with fish emulsion every four to six weeks. When berries are beginning to turn color, cover the plants with netting to prevent birds from ruining your harvest.

Garden Solutions

We just moved to Gilbert from Seattle and were surprised to find snails all over our patio after a heavy rain. Are they common here? Do they damage landscape plants?

There are a few species of snails and slugs that are common to the Arizona desert. The brown garden snail has a smooth, round shell, while the gray garden slug lacks an exoskeleton. Both will devour garden seedlings and damage leafy greens. Decollate snails, which have pointed, helical shells prey on brown garden snails. If there are no garden snails for the decollate snail to feed on, they will turn to plants and can cause damage similar to the other desert mollusks. Reduce snail and slug populations by removing their hiding places and letting the soil surface dry out between watering.

Our agave bloomed three years ago. Although the big leaves on the main plant died, a bunch of small ones sprouted along the flowering stalk. Aren’t agaves supposed to die after they bloom?

The original agave that was planted in your landscape did technically die. Those green leaves along the stalk are young plants, called bulbils.  Some species of agaves, such as octopus agave (Agave vilmoriniana) and smooth agave (Agave desmetiana), are known to produce bulbils along the flowering stalk. Bulbils may form at the base of flowers that were not pollinated and are clones of the mother plant, similar to a cutting. You can cut the bulbils from the stalk with a sharp knife and transplant them into your landscape or give them away to everyone you know, as there are probably hundreds.

Is homemade compost safe to use in vegetable gardens?

The safety of homemade compost depends on a few factors. The primary consideration is whether or not animal manure is an ingredient. Dog, cat and human waste should never be added to the compost heap because of the potential for disease-causing germs. Poultry and livestock manure can be composted and used in the garden if strict protocols are followed, which include ensuring the compost exceeds 130 degrees for no fewer than four consecutive days and that at least 120 days have elapsed since the animal produced the waste and the compost was added to garden soil. Most sources recommend aging poultry and livestock manures at least one year before applying to edible crops, just to be on the safe side. If you are not using animal waste in your compost, the hazard potential is greatly reduced. Plant-based ingredients are safe to use once the compost is “finished.” When ready to use, it will exhibit a dark brown color; have a sweet, earthy smell; and no longer resemble the original ingredients.


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