Tanque Verde Gardens

The extra challenges of gardening in the desert often discourage people from attempting to cultivate their own vegetables. Extreme summer temperatures and alkaline, often compacted soils with a caliche base frighten off many but the most devoted and insistent potential home gardeners. Here are a few basic tips to remember when working with desert gardens.

Sunken, rather than raised beds increase water catchment and retention. Any raised portion of a garden or bed will correspondingly raise the temperature of the soil and increase the rate at which it loses its moisture. This works when you live in a wet and mucky area but will greatly increase the need for watering here in the arid Southwest.

If you are renting or otherwise cannot dig holes where you live, an alternative method is to erect a modified straw bale type raised bed using 4 to 6 bales, erected on their sides in a rectangle. The straw bale walls may be fortified by staking the outsides with short pieces of rebar dug into the perimeter, which support the bales. The inside of the straw bale rectangle is filled with topsoil and the thickness of the walls of the bed minimizes soil heating and evaporation. Using this method, you can have a well-insulated raised bed without making holes.

When possible, dig deep. The shallow tilth layer of many Arizona soils begs for an initial deep digging, at least several inches deeper than the level worked if using a roto-tiller style cultivator. Optimum digging depth in the first year of a new garden bed is 2 feet. This may be difficult in a hard soil, particularly if you have an underlying caliche base. Extra depth in your garden bed means lots of extra water retention and maximizes conditions for roots and beneficial microbes to thrive.

In hard soil conditions pre-soaking the area for a couple of days and waiting a couple of more days to begin your digging makes things easier.

And remember, there may be underground utilities hiding under your pick and shovel so make sure and call1-800-STAKE-IT or visit www.azbluestake.com the week before you begin so that the utility companies can come mark any utility-conflicted areas free of charge.

Use lots of compost and other organic matter.  Desert soils tend to have an alkaline pH and will benefit from the addition of generous amounts of organic matter. Over the course of a few seasons, regular mixing of the soil with organic amendments will balance and sweeten the soil. A sprinkling of powdered gypsum should also be added in your first few seasons to help unlock macro and micro-nutrients for plants and beneficial microbes. Un-composted organic amendments such as straw require extra nitrogen to decompose properly, so make sure and add some herbivore manure or other nitrogen source to help the process along.

Mulch heavily, particularly in the summer. Mulching decreases evaporation rates from the bed and keeps the soil much cooler than an un-mulched area. This greatly reduces plant stress.  Thick mulches of 3 to 6 inches of organic matter like straw, compost, and well-composted herbivore manure, are common.

Take advantage of afternoon shade. While growing recommendations for many plant varieties such as tomatoes, chilies, and eggplants call for full sun, our solar intensity often is a bit much for all but the hardiest crops. Providing a little afternoon shade (the dappled sunlight around mesquite trees is ideal) can help plants survive extreme conditions.

Drip irrigation is good, hand watering is better. While drip irrigation can save lots of water and time, automated drip systems can hardly provide the generally available moisture that makes a healthy soil thrive. If you are using drip, regular applications of additional water in the areas that surround the emitter zone contribute to a garden beds’ general wellness.

Plant appropriate to season. In the mild Arizona winters it is possible to grow most leaf and root crops. Summer is the time for plants from which we harvest their fruits. Typical winter crops include lettuce and other greens, radishes, carrots, beets, broccoli, and cauliflower. Most of these cool-loving crops die back or bolt to seed when temperatures rise in April or May. Warmer spring temperatures signal the time to plant crops such as corn, early potatoes, okra, melons, squash, tomatoes, and chilies. We are also blessed with what might be considered a third planting season, the monsoons. Planting with the summer rains was the common practice for indigenous people of the southwest. Most summer crops planted in July through August still have enough time to mature before the cold season arrives.

Plant appropriate varieties. Seed varieties bred for northern climates sometimes have a difficult time adapting to our intense desert heat or relatively short day length. One example of day length adaptation is onions. Many bulbing type storage onions do not form well at anything less than 38° latitude. Look for short day or day length neutral varieties if you expect beefy onion bulbs. Likewise, seek out heat and drought tolerant cultivars, many of which have been maintained by indigenous farmers. Native Seeds/SEARCH is an outstanding Tucson institution that carries an extensive line of desert adapted seeds.

Additional resources:

Arbico  www.arbico-organics.com: Catalina based business offering organic soil amendments and biological insect controls. A great source of high quality compost.

Johnny’s Seeds  www.johnnyseeds.com: Source of many interesting seed varieties both conventional and organic. Offers several types of heat resistant lettuce and other greens.

Tucson Organic Gardeners  www.iwhome.com/nonprofits/TOG: Local site for information and alliances of like-minded gardeners.