Several years ago I was visiting gardens in the eastern United States, where gardens are often lush, and foliage on a particular plant much larger than it is in our western gardens. One of the gardeners commented to me that they had been enduring a drought that particular summer.
Since we were looking at Impatiens that looked fine to me, I could not resist asking when they were last irrigated. The answer: When it rained two weeks previously. Now you have to understand that this was August. Two weeks without irrigation in the Sierra foothills in August and the same plants would be dead or beyond recovery.
This is a perfect example of how the higher humidity in the eastern United States reduces irrigation needs. In our sunny and dry foothill climate, plants lose a lot of moisture on a daily basis. If rainfall or irrigation meets the needs of the plant, it will still perform well. However, if the plant does not get the water it requires, it may wilt, lose leaves, reduce growth, and even die partially or totally.
The answer does not lie only at the end of the hose. The solutions to the challenges of growing plants in the foothills are: 1) choose the right plant, 2) know the plant’s needs, 3) prepare the soil optimally, 4) mulch to protect the soil surface and conserve moisture, 5) irrigate deeply and only as needed, and 6) zone your landscape, grouping plants with similar needs together.
First consider the natives in our region. This past rainfall season they did not receive optimal moisture. For this reason, most natives now have far less moisture in their foliage. June foliage is more like August, increasing the concern of fire risk.
If your landscape includes natives that have not been irrigated since the last rain, a deep soaking now will be beneficial. Another deep irrigation in early August will not injure the natives this year. And while you are addressing fire risks, recheck the defensible space surrounding your home: Is it the required 100 feet?
A recently planted native may need regular irrigation in the heat of the summer for the first year. A good example is an incense cedar (Calocedrus decurrens). Other natives may not. Years ago I planted my first matilyja poppy (Romneya coulteri) in July, watered it deeply, and have never watered it again. I tried the same method with the native bleeding heart and discovered that it needs a little more water the first year. However, if it is watered regularly each subsequent summer, it will die. Know your plant.
Encourage strong roots with ample compost and organic phosphorus. Deep-rooted plants need to grow in deep soils. Plants with strong root systems need less water.
Mulch as soon as you have finished planting. Decomposing straw makes a perfect mulch for many plants, protecting the soil surface from sun and wind, and extending the periods between irrigation’s.
When it is necessary to irrigate, water deeply and only as needed. A tomato plant with a three to four-inch straw mulch may need water twice a week when it is growing actively, and may need water only once a week when it begins to set fruit. While it wilts at the end of a hot day, so do you. Check in the morning. If the foliage is no longer wilted, hold off on watering.
Yellowing leaves are often a sign of overwatering. Yet some plants may respond to frequent irrigation with lush foliage. Unfortunately, while the foliage may be very beautiful, the plant now requires even more water to sustain this beauty. The end result of your overwatering may be a landscape that demands more water than it really needs.
Carolyn Singer has gardened in Nevada County for 28 years. She is the owner of Foothill Cottage Gardens (www.fcgardens.com). Send your garden questions and comments to email@example.com.
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