Despite our current, most welcome rains, we remain below the normal precipitation level for this time of the year and water conservation in the landscape continues to be important.
For long-term conservation, plant California native plants or other drought-tolerant plants from the world’s Mediterranean climates. Succulent plants are increasingly popular for this reason, and for their varied forms, textures and colors, and low maintenance needs. (Desert conditions are not ideal for succulents: all need some water and quick drainage, and many enjoy partial shade.)
Shorter-term water conservation strategies include composting and mulching to retain water, using drip irrigation for efficiency, selecting vegetable varieties for low water requirements, eliminating seasonal weeds to reduce competition for scarce water, and irrigating only when plants need water. See “More” (below) for water conservation tips from Master Gardeners.
Garden priorities for March include fertilizing trees, shrubs and perennials when they begin to show new growth.
For roses, give each plant two cups of a balanced fertilizer, i.e., 10-10-10 or 12-12-12, plus a quarter-cup of Epsom salts, two cups of alfalfa, and a half-cup of rock phosphate or bone meal.
There are differing views for fertilizing some plants. With bearded irises, for example, some growers recommend just a generous handful of a balanced fertilizer for each plant; others advocate low-nitrogen fertilizer, e.g., 6-10-10, plus bone meal and superphosphate. (The thinking is that adding more nitrogen could encourage root problems.)
March is a good time for pruning still-dormant trees and shrubs, following recommendations for each plant. Here are examples from my garden:
Thin a large Wild Mock-orange (Philadelphus lewisii) by cutting about one-third of the larger branches to the base of the plant.
Shape a large Milkflower Cotoneaster (C. lacteus) by removing old, unproductive limbs and spindly branches, and generally lifting the canopy to provide more sunlight to the understory.
Renew Salvias by cutting old growth to the ground when the plants begin to show early spring growth. Another shrub that responds well to this treatment is the Tree Daisy (Montanoa grandiflora), from Mexico, which can grow up to ten feet high in one season. This annual treatment might seem drastic but the plants otherwise will become scraggly.
A good book on pruning is The American Horticultural Society’s huge “A-Z Encyclopedia of Garden Plants” (Revised edition, 2004), which briefly describes thirteen pruning categories and indicates which to use for each of 15,000 plants.
The following paragraphs, also from the Sonoma County Master Gardeners, provide brief recommendations for water conservation in the garden.
1. Compost, compost, compost! Add organic matter to the soil. If soil is sandy, the addition of organic matter allows the soil to hold more water. Organic matter also helps open up soil allowing roots to go deeper and find more water at lower depths if there is any. Higher soil nutrition helps plants produce better yields with the same amount of water. Avoid adding excessive amounts of nitrogen as this encourages lush leafy growth that requires more water to sustain.
2. Mulch, mulch, mulch! Mulch keeps soil cool, conserves moisture and reduces weeds. Use three to four inches on top of the soil. The larger the material size, the deeper layer you need to provide. Choose from straw, fallen leaves, hulls, shredded bark, grass clippings and newspaper. It is not advisable to use plastic sheeting as mulch because it deprives the soil of much-needed oxygen. Keep mulch two inches away from the base of the plant to avoid the possibility of rot. When hand watering, pull back mulch so that water goes directly into the soil.
3. Use a drip system. Learn about individual plant moisture needs and group plants that have the same need together on the same valve. If using in-line emitters in one-fourth inch tubing that use one-half gallon per hour per emitter and there is a length of ten feet with emitters spaced every foot, five gallons of water an hour is used on that section of tubing. Add up all drip lines to determine total water used. Install a timer. Install shut-off valves at the beginning of drip lines in order to turn them off when an area is fallow. Irrigate only as long as it takes to moisten the active root zone. Water, preferably, in the morning or in the cool hours of the evening so that soil stays evenly moist. Don’t forget the drip system once it is set up. Monitor and adjust it, as needed.
4. Be selective. Consider the water available to support crops through harvest, and grow only the amount and types of vegetables the family will consume. For example, plant two beds of vegetables instead of six; plant four tomatoes instead of ten. To get the most out of the water you apply, grow high yielding vegetables like beans, chard, mustard, eggplants, peppers, tomatoes, squash, quinoa and amaranth.
Do not grow crops that need consistent moisture. Examples include most brassicas (broccoli, cabbage, Brussels sprouts, kohlrabi, cauliflower and radishes), lettuce and other greens, beets, carrots and other root crops, celeriac, celery, leeks and onions. Avoid these unless a particular variety has been bred to need less water. Generally, cool season crops are not drought resistant and growing them during the heat of the summer requires lots of extra water to keep them cool.
Consider the following observations on which crops need the most water and when:
- Some beans and sweet corn need considerable water to produce a good crop. Beans need water most when they are blooming and setting fruit.
- Corn needs water most during tasseling, silking and ear development. Yield is directly related to quantities of water, nitrogen and spacing.
- Peas need water most during pod filling.
- Other vegetables, such as cucumbers and squash, and fruits, such as melons, need water most during flowering and fruiting.
- Tomatoes, peppers and eggplant need water most during flowering and fruiting. (Note that after tomatoes set, they can do very well with reduced water).
After deciding what to grow, choose varieties that tolerate dry conditions. Look for the terms “drought-resistant” or “drought-tolerant” in seed catalogs or on plant labels (note that “heat-tolerant” refers to above ground air temperature and is not the same as drought-resistant or drought-tolerant). Even these varieties require water. Some water is needed to start seeds or establish a seedling, and to periodically irrigate the plant through the growing season. Selecting varieties that are described as “widely-adapted” in addition to drought-resistant and drought-tolerant also may be helpful.
5. Consider days to maturity. A crop needing fewer days to mature requires fewer irrigations before harvest (e.g., 62-day ‘Stupice’ vs. 85-day ‘Cherokee Purple’ tomato). Look for early-maturing or short-season varieties. Days to maturity will vary from one part of the country to another as well as from one microclimate to another.
6. Increase plant spacing. Spaced plants are not competing as much for water in the soil. Very deep, open soil or French intensive double dug beds allow vegetables to be planted closer together because the roots have more room to grow deeper and find water if it is present. Try increasing the spacing recommended in the SCMG “Vegetable Planting Summary,”iv by 50 percent or even doubling the spacing if you have room.
7. Eliminate weeds. Weeds compete for water. Be aggressive in removing them from growing areas.
8. Use light-weight row covers. Cover plants as a means to collect dew. Dew drops onto soil and keeps it moist. While using row covers can help prevent insect damage, look under the cover from time to time to monitor plant growth and check for unwanted insects trapped inside.
9. Use shade. Heat-sensitive vegetables can benefit from being planted where they receive some afternoon shade. Plant them underneath or behind taller plants or consider using shade cloth.
10. Use windbreaks. The moisture on leaf surfaces is dried by moving air, causing the plant to need more water. In coastal and other windy areas, windbreaks will help roots keep up with leaf demands.
11. Determine when it is time to water again. Use a soil moisture meter. Or squeeze the soil in your hand: if it sticks together, it is still moist; if it is crumbly and falls apart, it is time to water.