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Elinor Teague on Gardening: Smart techniques stretch limited water supply

The drought may force the state to mandate more widespread water rationing this year. We can only hope that the current restrictions, rather than rationing, will encourage residents to step up their efforts to conserve enough water.

Landscape irrigation accounts for an average of 60% to 70% of a household’s water use; most irrigation is used to maintain lawns. That water would be better used during this fourth drought year to save mature shade trees and valuable fruit and nut trees and to irrigate summer vegetables grown to help reduce food costs and to add nutritious, fresh foods to our diets.

Precious water will be most efficiently delivered to plants’ roots and plants’ roots will be able to grow deeper and faster if the soil in vegetable planting beds is light and friable (meaning a damp handful crumbles apart easily after being compressed). Much of the soil in our area is clay-based, creating a heavy soil that clumps or packs tightly when compacted. Clay-based soils hold water well but become impermeable when dried out, which often happens when irrigation is inconsistent or limited. Sandy soils, which are prevalent is some areas, do not retain water or nutrients well.

Because we have few locations with sandy loam soil, the ideal texture and weight for planting, we must regularly amend our soil to lighten it or to add water-retaining materials. The usual recommendation for amending soil is to lay down a 2-inch layer of compost or humus and turn it into the natural soil in planting beds before starting seeds or setting out transplants. Unless you’ve been amending your soil for years, the native soil may still be too heavy or too light to retain water well enough so that vegetable plants can survive on two waterings per week, or fewer, this year.

This year, the recommendation is to forgo amending all the soil in planting beds. Instead, dig a planting hole for each vegetable transplant and fill the individual holes with a good quality planting mix after transplanting tomatoes, peppers and eggplants. A trench a foot deep and wide can be dug and filled with a planting mix before planting bean and cucumber seeds. Summer squash and melon seeds are often planted in hills or mounds. This year, use a planting mix to make the hills (maybe digging in a little of the native soil to weigh down the mix and keep the hill or mound from falling apart).

Planting mixes are not quite the same formulations as potting soils or soil amendments. Most planting mixes contain a combination of composted materials such as fir bark, redwood and/or mushroom compost as well as several types of animal-based sources of nutrients including bat guano, earthworm castings and chicken manure. Pumice, a non-compostable material that retains water and that resists compaction, is often added to planting mixes.

Potting soil mixes and soil amendments can also be used for filling planting holes, trenches and for making mounds if mixed with composted materials. The planting mixes placed into individual holes and trenches this year can easily be turned into beds next year, if the rains come.