By Susanne von Rosenberg, U. C. Master Gardener of Napa County
One of the questions that home gardeners ask Napa County Master Gardeners most frequently is: How much should I water? As with many gardening questions, the answer is: It depends.
Watering adequately is important to avoid stress on permanent plantings such as trees and to keep your vegetables and flowers producing well. When plants don't get enough water, they have to choose between photosynthesis and survival, so they will tend to stop growing. Plants also use water to cool themselves.
You need to adjust your watering to the time of year and the weather. In Napa Valley, plants typically need the most water in early July, when the days are the longest and hottest. By the end of August, plants need about one-third less water than they did at the height of summer because the days are cooler and shorter. By mid-October, they are using only about one-third of the water that they needed in midsummer.
If you water at the same rate all season, you are likely overwatering early and late in the season and underwatering in the middle of summer. Of course, if we get a hot spell, such as the one we just had, your plants will need extra water. While we can normally stop watering when the rainy season starts in October, we've had several years recently when rain came late or not at all. If that happens, you'll need to keep watering.
Here are some additional watering guidelines:
Non-native annual plants, including flowers and vegetables, need to be watered when the soil is dry to a depth of about 1 inch. How do you know that the soil is dry that far down? Simply test the soil with your finger. You'll be able to tell if it's dry or moist. If you prefer not to get dirt under your nails, buy a soil-moisture gauge that uses electrical conductivity to determine if the soil is moist enough. Simply follow the instructions that come with the probe.
You'll want to couple the soil test with your observations. Plants will tell you when they are water stressed. If you are not watering enough, leaves will tend to get dull, and many plants will change the orientation of their leaves from fairly flat (to capture the most sunlight) to more vertical. Some plants will start to fold up their leaves.
Of course, wilted leaves are a pretty good sign that your plants need water. However, squash, pumpkin and cucumber plants are a special case as they will often wilt in the afternoon. If they recover by evening, then they do not need more water.
It's also possible to overwater your plants, which can lead to root rot and fungal diseases. Both problems can cause plants to wilt, which may make you think that you need to water even more. As long as you check your soil, you'll know whether you're watering the right amount.
What about deciduous trees? Young trees need to be watered roughly every two weeks during the dry season. One-year-old trees need one to two gallons of water per day (15 to 25 gallons at a time if you are watering every two weeks). Two-year-old trees need about double that. Three-year-old trees need five to ten gallons per day, and four-year-old trees may need as much as 15 gallons per day.
A mature deciduous tree that is 25 feet tall with a canopy 20 to 25 feet wide may need as much as 50 gallons of water per day (1,500 gallons per month). Mature deciduous trees should typically be watered monthly, although given the large volume of water they need, it may be easier to water them twice a month. Water needs for other perennial plants vary widely. Please contact the Napa County Master Gardeners for more specific information.
Most California native plants are adapted to our dry summers and need little or no water. However, newly planted natives benefit from being watered a couple of times during the summer. By the time they are three years old, they should be able to survive without additional water if we had normal winter rainfall.
During drought years, even most native plants will need some supplemental water in summer. Make sure you know specifically what your native plants need. Some may die if they receive any water during the summer, while others are adapted to moist, shady areas such as creek beds and need a consistent supply of water.
Next workshop: “Home Vineyard: Part 2” on Saturday, September 14, from 9:30 to 2:00 p.m., in Calistoga. Learn techniques to maintain your new or existing home vineyard. Workshop location will be provided after registration. For more details & online Registration go to http://napamg.ucanr.edu or call 707-253-4221.
The UC Master Gardeners are volunteers who provide UC research-based information on home gardening and answer your questions. To find out more about upcoming programs or to ask a garden question, visit the Master Gardener website (http://napamg.ucanr.edu) or call (707) 253-4221 between 9 a.m. and noon on Mondays, Wednesdays or Fridays.
The challenges of caring for houseplants are often underestimated, and the successes rarely celebrated. A flower garden is easily visible to passersby, who may stop to discuss it and compliment you on your green thumb. Indoors, however, our efforts (sometimes, thankfully) go unseen.
Houseplant care can be likened to gardening in an exotic climate, one that can be deceptively inhospitable to plant life. Indoor growing conditions, such as light, humidity and temperature, are often significantly different from those outside. While this environment protects us and our plants from harsh outdoor weather, houseplants usually find it less than comfortable.
A large majority of the houseplants at nurseries are species that originated in tropical climates. As such, they prefer warm, slightly humid environments with medium to high levels of light.
Light is the most common challenge for houseplant growers. On average, indoor light is only two percent as bright as outdoor sunlight, and often less. Our eyes are astoundingly adept at adjusting to changes in light levels; plant leaves much less so. With some exceptions, houseplants want to be as close to a sunny window as possible.
Most people keep their homes within a healthy temperature range for many houseplants. Home heating and air conditioning often dries out the air, however, causing plants to lose moisture more quickly than they would in their native climates. If your plant is near a heater or drafty area, check the soil frequently for dryness.
Misting plants with a spray bottle is a common tactic to fight dehydration, yet it is not very effective. If a houseplant seems to be struggling, place it on a shallow tray of gravel filled with water. As the water evaporates, it will provide a nice aura of moisture that your plant will love. Alternately, you can run a humidifier in your home, helping all of your green friends at the same time.
Container gardening poses unique challenges, and houseplant care is no different. Houseplant soil often develops a whitish crust, the residue of salts from fertilizers and tap water. This buildup will eventually adversely affect your plant, but you can prevent it by thorough watering. Let the water flow from the bottom of the pot, then discard the excess. This procedure will help flush the unwanted salts and keep your soil clean and healthy.
If you are anxious about keeping a houseplant alive, I recommend Zamioculcas, also called Zanzibar gem or ZZ plant. This houseplant is one of the easiest to care for that I have ever encountered. It has a unique appearance, resembling a tall, green feather. It grows in low light and with little water, which makes it ideal for people who have challenging home environments. The roots of these amazing plants are actually succulent rhizomes that divide within their pots, eventually creating more plants.
Another easily managed houseplant is Beaucarnea recurvata, the ponytail palm. It starts with incredibly dainty sprouts but can grow into an enormous, bulbous tree. Don't worry; the palm is very slow growing. It requires moderate to bright light but is drought tolerant. The ponytail palm grows so well that it received the Royal Horticultural Society's Award of Garden Merit.
If you are an accomplished houseplant grower, you may be interested in a challenge. Trachyandra is not easy to find and a bit fussy to care for, but it is an excellent conversation piece. Native to Africa, this odd specimen grows from a bulb and appears as several green corkscrews sprouting from the soil. Every time I see one of these fascinating plants I am reminded of the incredible diversity and unexpected beauty of the plant world.
Indoor gardening presents some hurdles, but the rewards are many: cleaner air in your home, the feeling of nature around you, and the knowledge that you helped something grow. Napa County Master Gardeners can help you with any questions you have and help make your home verdant inside and out.
We usually source our accompanying pictures from the anonymous web. Lately, however, we have noticed the disclaimer on every photo that it may be subject to copyright. Thus, we have begun to tag our photos with the (source of the photo.)
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. U. C. Master Gardeners of Napa County ( http://ucanr.edu/ucmgnapa/) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.