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Fall Harvest: When to Start Planting Cool-Season Vegetables in Arizona

With thermostats dipping into the 70-degree range in the mornings and settling at just below 100 degrees during the day, October is the time to start planning and planting cool-season vegetables for a delicious winter harvest. Gardeners in Arizona’s low elevations are particularly lucky, as they can grow something almost year-round. When homeowners in other parts of the country are winterizing their veggie beds, growers in the Valley are preparing to start their winter crops.

Cool-season vegetables are those that respond to short days and cool nights. They are grown from September through April in the Valley. October is the perfect planting month for low elevations, as temperatures become mild and the soil is still warm. Whether planting in the ground or in raised beds, site the garden in a location that is level, that will receive at least six hours of sunlight a day and that is near a water source. Most importantly, it should be in an area that is convenient for you to reach and work in. Soil should be worked down to a depth of 8 to 12 inches and should be rich and well-drained with plenty of organic matter. Raised beds are a popular choice because they allow the soil content to be controlled by the gardener—and no tilling is involved.

When planning what to sow, choose varieties that mature quickly. Although everything can be cultivated from seed, those that are somewhat slower to mature can also be planted as starts or transplants. Quick growers, such as leaf lettuce, spinach, chard and radishes, can be planted from seed, while those that are slower, such as broccoli, head lettuce and Brussels sprouts, can be planted as starts. Plant a succession of small plantings every two or three weeks to prolong your harvest and reduce waste.

Some vegetables require more sustenance than others. These include corn, lettuce and greens, such as spinach, collard and kale. A new garden may need an application of fertilizer partway through the growing season or until enough organic matter is built up in the soil.

There are as many types of fertilizers, both organic and inorganic, as there are gardeners, as well as several different methods of application. Most home growers will prefer organic fertilizers. Whatever type of fertilizer you use, follow label directions, and do not overfertilize or you will burn the plants. Vegetables grown for their fruit, such as tomatoes and peppers, require more phosphorous than nitrogen in order to flower and set fruit. Consider grouping plants with specific nutrient requirements together.

Watering is best done with a soaker hose, drip irrigation or laser tubing. The use of sprinklers and hand watering are more apt to damage plants, due to excess water pressure and because more salt can be deposited on leaves. Water deeply. How often you water will depend on the garden’s location and the type of soil in it. A top layer of mulch will help retain moisture.

It is also important to monitor your garden for insect pests. Some presence is to be expected. Learn to tolerate them if their numbers are not too great. Healthy plants will be more resistant to any damage. If an infestation seems excessive, try spraying the plants with a soapy water mixture to drive the invaders away. Remove caterpillars by hand. Never treat food crops with synthetic pesticides, which can contain chemicals that are known to be harmful to humans, animals and the environment. If pesticides are necessary, be sure to use a product that is certified organic.

The diversity of vegetables that can be planted and harvested between now and the beginning of the warm season is astounding. An excellent resource guide is the “Vegetable Planting Calendar for Maricopa County,” published by the Maricopa County Master Gardeners. You can download a copy of the publication by visiting


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