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Red maple leaves sun-scorched in recent heat wave and drought.
It was a pleasure seeing and hearing the rain last Sunday. Then on Monday morning, I stepped outside to check my rain gauge. The air was cool, fresh, and fragrant. What a relief. The rain gauge showed .74 inches, quite a surprise for September in Napa. It was enough to refresh the air and rinse away the dust, but did it make a dent in the drought?
Using my soil probe I checked the front lawn, which has been on a water-conserving schedule of one brief irrigation per week. The turf has been looking very stressed and my red maple in the lawn, now about 11-inches in trunk diameter and over 20 years old, shows mild symptoms of stress: a few sun-injured outer leaves from the recent heat wave, and some premature fall color, from chronic water stress this summer. The probe showed powdery dry soil to a depth of about 4-inches and could go no deeper, surprisingly dry after a nice rainy day.
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Going about my business around town and in my neighborhood in southeast Napa, I have been seeing dry, golden brown front lawns, sadly, with trees to match. Typical examples are Japanese maples, longtime favorites in Napa landscapes. Is that water conservation or neglect?
A dead lawn is readily replaceable but a 20, or 30-year-old tree? That is a different matter. I am talking about water-needy trees that have been surviving on lawn irrigation that has, probably, not been penetrating more than a few inches all summer long.
I checked a couple online references on water penetration in various soil types. One reference (Sunset Watering Guide) states one inch of rain penetrates 12-inches in sand, 7-inches in loam, and 4 to 5 inches in clay. That .74-inch rainy day might have done some good.
Napa Valley has a remarkable range of soil types, generally not sandy, but commonly clay or clay-loam in urban subdivision yards. So the amount of rainfall needed for a soaking to a depth 6 -inches, where a large proportion of a lawn-tree’s fine absorbing roots are located, is difficult to calculate. In my front lawn, I am sure the thick thatch of Bermuda grass acts like a sponge, preventing normal penetration of water.
The equivalent of one inch of rainfall is 620 gallons on 1,000 square feet (or 62 gallons per 100 square feet, or .62 gallon per square foot). Based on the Sunset Watering Guide, it will take more than one inch of rainfall to penetrate to a depth of 6 inches in clay loam soil. That is, probably, well over 620 gallons on a 1,000 square foot lawn or tree root zone.
My well-established October Glory red maple is getting by in the water-stressed front lawn, but I am contemplating conversion to a more drought tolerant front garden. If I can muster the gumption to do it, I will consider saving the tree with the Tree Ring Irrigation Contraption (TRIC) designed by the UC Davis California Center for Urban Horticulture.
See it at this link: ccuh.ucdavis.edu/tric/tric-parts-and-assembly.
Briefly, it consists of a spiral of drip irrigation tubing laid out in courses spaced one foot apart under the canopy of the tree and attached to a simple timer on the hose bibb. The parts add up to about $100.
Assisted by their website, the user can calculate the run time required for a good watering cycle, putting precious water right where it is needed.
Experiencing the current climate changes and anticipating longer, hotter dry seasons, heat waves and drought, we can at least strategize to save valuable trees and keep our home grounds livable. Trees are a big part of this.
Many people try to save water just to do the right thing (and save money too). But when serious drought hits, and state and local governments enforce restrictions, water conservation becomes non-negotiable.
So far this summer, nearly 65% of the United States and Puerto Rico is experiencing “abnormally dry” weather, according to the U.S. Drought Monitor. Almost 43% of those locations are contending with “moderate” drought, and nearly 47% with “severe,” “extreme” or “exceptional” drought. That means more than 109 million people are living under drought conditions.
And a lot of them have plants or yards to worry about.
Unfortunately, it's a little late in the season to begin trying two of the best ways to conserve water in the garden. First, rain barrels and other rain harvesting methods are of little use when there’s no rain to fill them. Second, xeriscaping, the practice of planting drought-tolerant plants, many of them native to a region, works only if those plants are already in place. Consider both for next year.
Native plants are well-adapted to their climate and more tolerant of adverse conditions like drought. In California, for instance, where roughly 98% of the state is experiencing drought, plants like California poppy, California fuchsia, California lilac and manzanita are among the best native xeriscape plants to use.
Check the EPA’s compilation of drought-tolerant plant resources, listed by state, at epa.gov/watersense/what-plant to find your best options.
If you're gardening under water restrictions, prioritize which plants need water most and which can be sacrificed if need be. Newly planted trees and shrubs are high on the priority list. They require regular watering until their roots become established, which can take a full year.
Older trees, especially fruit, nut and ornamental trees, but also evergreens, can suffer from drought, so don’t forget about them.
Perennial flowers, which return year after year and are more expensive than annuals, should be next on the list, along with vegetables in their flowering and fruiting stages. Melons and squash, which have deep roots, can typically get by with less water than crops like corn, which have shallow roots.
Low on the list of priorities should be annuals, which are not long-term investments anyway; crops with high water needs, like beans, cabbage, cauliflower, celery, corn, lettuce and radishes; and plants growing in pots, as they require more water than their in-ground counterparts. None will likely thrive with the little water that can be offered under mandated restrictions.
Most plants require an average of 1 to 1 ½ inches of water per week under normal conditions, which amounts to a little more than a half-gallon of water per square foot of garden space. That need could increase, however, during periods of extreme heat, when the soil dries out more quickly.
Regardless, don’t apply your plants’ weekly water needs all at once. Divide it over two or three sessions per week, opting for deeper, less-frequent waterings over daily sprinkles, which are wasteful and ineffective at saturating roots. Watering deeply also establishes stronger, deeper roots that are better able to sustain plants when surface water becomes less available.
Avoid using overhead sprinklers, which wet foliage, pavement and other areas instead of directing water to plant roots. Instead, place soaker hoses or drip-irrigation tubing on the soil directly over roots. Watering cans and hand-held hoses aimed at the soil work, too.
Water only in the morning (or in the evening, if absolutely necessary), but avoid midday, when moisture is likely to evaporate before reaching roots.
Consider using so-called gray water, recycled household water, to water plants. Unsalted water left over from boiling eggs or vegetables provides a nutrient-rich bonus. Dish and bath water that’s not too soapy won’t harm ornamental plants. Just don’t apply it to edibles. And water captured while rinsing fruits and vegetables can be used around the garden.
Keep beds and borders free of weeds, which compete with your plants for water and nutrients. A 3-inch layer of bark mulch, wood chips or gravel around plants will help prevent weed seeds from taking hold, retain soil moisture and keep the soil cooler.
Set mower blades high to promote deeper roots. Taller grass needs less water because it grows slowly and shades the soil. Repair or replace leaky hoses and bib connections.
Some don’ts: Avoid fertilizing plants during drought; This might seem counterintuitive, but fertilizers promote fast growth, which increases the need for water. Avoid using weed killers, which tend to drift to other areas in hot weather; they’re less effective in high temperatures anyway.
Don’t plant anything new, and avoid pruning plants, which stresses them and increases their water needs.
Going forward, consider replacing the lawn with native groundcovers. Incorporate generous helpings of compost into beds and planting holes to improve water retention. Observe the sun-exposure requirements on plant tags (shade lovers need more water when exposed to too much sun). And use more native plants.
Next summer, this could be easier.
Severe drought, heat waves and deadly floods occurred all while 2022 had the third warmest summer on record.
Bill Pramuk is an ASCA registered consulting arborist and an ISA certified arborist. Visit his website, www.billpramuk.com. Email questions to info@billpramik.com, or call him at 707-363-0114.
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Red maple leaves sun-scorched in recent heat wave and drought.
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