ately, some gardeners in the Tucson area will have to deal with caliche (calcium carbonate that often forms a cement-like impenetrable layer that must be broken up or removed before planting).
Plants compete with each other for light, water and soil nutrients. Use recommended spacings when planting, both within and between rows. Don’t hesitate to thin plants that have been over-seeded or are too close to each other. Plants often compensate for less space by growing smaller, producing fewer fruits or even smaller seeds. More plants in an area doesn’t necessarily translate into more yield. Don’t skimp on the space required to produce healthy, abundant seeds. Additionally, good air circulation between plants can help reduce insect and disease problems.
Recommended plant spacings for desert crops (within a row):
4-6 inches: Bean, Garbanzo, Garlic, Lentils, Onions (shallot-like), Peas, Wheat
6-12 inches: Amaranth, Basil, Black-eyed Peas, Chiles, Corn, Herbs, Mustard Greens, Tobacco, Tomatillo, Tomato
12-18 or more inches: Cotton, Devil’s Claw, Gourd, Melon, Okra, Squash/Pumpkin, Sunflower, Watermelon
New gardeners often worry about how deep to sow seeds. For very small-seeded crops, such as carrot, seeds are only covered by 1/4 inch or so of soil. Larger seeds can be planted up to a few inches (2-4 inches). The main trick is to ensure that soil in which seeds are planted remains moist, but not waterlogged, until the seeds germinate.
Perhaps the most difficult task for those new to desert gardening is watering. Forget what you learned in more humid climates, it won’t help much in the desert. Desert soils around Tucson tend to dry out somewhat quickly and can become hard as rock on the surface, making it difficult for young emerging seedlings to break through. Mulching helps keep soil surfaces moist for germination. A light spray of water on the surface is all that’s needed, as no more than the top 2-4 inches of soil needs to be moist for germinating seeds. Once seedlings emerge, however, deep watering will be necessary.
A common mistake among gardeners new to the desert is to water often and shallowly. Deep watering encourages vigorous deep root growth early in the season, which helps discourage water stress later in the season. Deep watering is accomplished by slowly flooding an area and allowing it to soak deeply into the soil profile. This also helps to flush out salts and prevent salt buildup. There is no standard guide to how often watering should be done in desert gardening. The best method is to simply watch the plant. Water stress is typically detected by leaf wilting. Some wilting is common during the day, even in well-watered plants. If plants do not recover overnight from day-time wilting, then they are likely in need of water.
A common misunderstanding is that ‘drought-adapted’ or ‘aridlands’ crops don’t need much water, as evidenced by the fact that they grow in drought-prone or arid areas. Even within these areas, most crops are grown during the rainy season, however scarce it may prove to be in any given year. ‘Drought-adapted’ or ‘drought-tolerant’ doesn’t mean a crop prefers to grow under drought conditions. Rather, it means a crop might survive some drought conditions where other, more conventional crops might not. Don’t be fooled, plants require sufficient water, nutrients and light to produce healthy seeds, regardless of whether they are considered ‘drought-tolerant’ or not. Some plants, such as tepary bean and black-eyed peas, are not tolerant of soggy soils. When their roots are submerged in standing water for days on end, their leaves often turn yellow and drop, a symptom that also occurs under conditions of insufficient water!
Plants need nutrients. Addition of compost and well-aged manures, as well as green manures and cover crops, are good ways of maintaining soil nutrient levels and adding organic matter, which continues to break down slowly over time. These are best added before planting. Mid-season fertilizers are easily accomplished with fish emulsions or manure or compost teas. Not all plants hav