By Okhoo Hanes, U. C. Master Gardener of Napa County
If you are a home gardener in Napa Valley, you can successfully grow olive trees. Olives are one of the most popular trees in the valley, and with a few pointers extrapolated from University of California research and other sources, you can enjoy their beauty in your own landscape.
Olive trees are evergreen and both ornamental and edible. They are relatively easy to grow and maintain, suitable for the fairly arid Mediterranean-type climate of the Napa Valley. They are not fussy about fertilizer, needing only nitrogen. Nor are they water hogs. Once established, they take to xeriscaping or even no watering at all, cutting down on irrigation chores.
The olive tree's silver foliage, smallish, oblong leaves and graceful branches add interest to any landscape, large or small, including container gardens.
But olive trees are not without drawbacks. For one, growing your own olives for pressing or curing may cost more than you expected. In all likelihood, your olive oil or cured olives will cost you more than store-bought olive oil or olives and take more care and time than you imagined. Nonetheless, you may decide that the experience and satisfaction of growing and producing healthy food of your own is worth the expense and the journey.
David Layland, a U. C. Master Gardener of Napa County and past president of the group, has had an experience with olives that is probably typical. He planted nine olive trees primarily for landscaping purposes. Fruit production was almost incidental. The laborious harvesting required the help of friends.
Layland encountered unexpected costs for cultivation, care and maintenance, including the unavoidable pest problems, most notably the olive fruit fly. Then there's the inevitable reality that friends move or fade away over time. Still, he is happy to be taking the olive tree journey.
The nutritional virtues of extra-virgin olive oil, a heart-healthy monounsaturated oil and antioxidant, have been widely touted. But research hasn't shown whether there is any discernible difference in the health benefits between local and imported oils. What is certain is that extra virgin olive oil contains more antioxidant polyphenols than virgin olive oil and is a healthier choice.
For pressing or curing, available varieties for home gardeners include Mission, true Picholine (not Redding Picholine), Majestic Beauty and Manzanillo. Five-gallon plants provide a good head start, but one-gallon plants, if available, are considerably less expensive. The Kalamata variety is excellent for brining or salt-curing.
Fruitless varieties (Little Ollie, Wilsonii and Swan Hill) are better choices for those who are not interested in food production. Alternatively, you can minimize fruit formation by applying a plant-growth regulator (available at garden centers) or using a high-pressure hose during bloom. But these methods are not reliable, so fruitless varieties are a more sensible choice. Fruitless varieties also produce fewer allergens.
Full-size olive trees reach 25 to 30 feet in height and can be just as wide. They can take heavy pruning but consider the available space before you plant. University of California research suggests that more space between the trees leads to better fruit production. Although 16 to 20 feet is recommended, such generous spacing may not be practical in a home orchard.
If you have limited space, consider a dwarf variety such as Skylark Dwarf, which tops out at about 16 feet. Another method for selecting a suitable variety is by tasting oil samples at farmers' markets or retail stores.
Olive trees need about 200 hours of winter chill. Some require a pollenizer variety, such as Pendolino, for good fruit production.
Fresh olives are too bitter to eat without curing, but they can be pressed for oil. If you don't have enough olives to meet the minimum at a commercial pressing facility, such as Jacuzzi in Sonoma, you can combine your harvest with others to meet the minimum. The olives must show no sign of pest damage. For curing, follow the step-by-step instructions in UCANR Publication 8267 (“Olives: Safe Method for Home Pickling”). You can get a copy of this publication at the Master Gardener office (address below).
Napa Valley olive trees have suffered from infestations of the olive fruit fly, which damages the fruit. Trapping, seasonal spraying, good sanitation (picking up all fallen fruit) and biological controls are among the tactics growers employ. Research is ongoing and, in the meantime, Napa County home gardeners should contact the Master Gardeners office about the current recommended methods for fruit-fly control.
And consult this information from UC Integrated Pest Management:
Free Tree Walk: U. C. Master Gardeners of Napa County will host a guided tree walk of Fuller Park, 560 Jefferson, in Napa, on Monday, July 10, from 10 a.m. to noon.Enjoy a fun, informational stroll through the park, learning about its history and 41 different trees on site. Wear comfortable shoes. Restrooms are available and handicap accessible. The book Trees to Know in Napa Valley will be available for $15 each (cash or check only).
To register, call 707-253-4221. Walk-ins are welcome, but you are guaranteed to receive a complimentary map and additional information if you register at least 48 hours in advance.
Workshop: U. C. Master Gardeners of Napa County will conduct a workshop on “Growing Olives” on Saturday, July 22, from 9:30 a.m. to 11:30 a.m., at Big Dog Ranch, 1020 Congress Valley Road, Napa. Got an olive tree? Want to grow one? Learn the details for each season's necessary activity for a healthy and tasty harvest. Controlling olive pests is also on the agenda. Online registration (credit card only);
Mail-in registration (check only or drop off cash payment).
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.
Given Napa Valley's mediterranean climate, it's no surprise that olive trees have long been grown here. But in recent years, the trees have grown increasingly popular as landscape trees and as a source of olives for curing and pressing.
I planted nine olive trees sixteen years ago with no objective other than to block the view of our neighbors' collection of old cars, trucks, boats and whatever else they could not part with. However, once our trees started bearing fruit, the prospect of our own olive oil was too hard to resist.
At first it was fun recruiting friends to help with harvest and then taking our olives to a local mill to be pressed for oil. But then the friends we recruited, all long-time Napans, all moved away. Apparently picking olives in return for a quart or two of olive oil was not how they wanted to spend a weekend.
Also, we realized that the olives were not really free. We incurred growing costs: spraying for the olive fruit fly; buying compost and fertilizer; paying for water and for milling. After considering all of the costs, we knew it would be cheaper to drive to Corning and buy a few gallons of olive oil from a local producer.
But the most serious negative we encountered was the olive fruit fly. Despite spraying, we couldn't eliminate them. At first we simply had to cull some damaged olives before milling. But in 2013, the fruit fly devastated our entire crop. The situation was not quite as dire in 2014, but the problem persists.
Previously we had harvested in late November when most of the fruit had started turning black. This is also when the fruit fly is most evident and the most damage has been done. The female fly lays its eggs in the summer when the olive is about the size of a pea. The most serious damage occurs as the fruit matures and begins to soften and turn color.
If we harvest in early September, when the fruit is still green, we can avoid much of the damage. Green olives yield slightly less oil, and the oil is more bitter and often higher in antioxidants. Many people like the peppery, bitter quality of early-harvest oil, so harvesting green olives is not a bad thing to do and probably the path we will follow this year. It still doesn't make economic sense, but why does everything we do have to make economic sense?
If you decide that harvesting olives is more work than you want, you can spray your trees during bloom (May-June) to reduce fruit set. A hose with a high-pressure nozzle can effectively blow the blooms off the tree, or you can spray with a product containing ethephon, a growth regulator that eliminates unwanted fruit.
Doing nothing is not an alternative. If you are going to allow your trees to produce fruit, then you must combat the fruit fly. Otherwise, your trees become a breeding ground. Olive fruit flies can travel 100 miles in one year, so they can easily migrate to your neighbors' trees or to a commercial orchard in your area.
Sanitation is extremely important. Olives left on trees can support fruit fly reproduction over the winter. Olives left on the ground may contain larvae that can still complete their development. Collect unwanted olives in plastic bags, seal the bags and place them in your garbage container. Do not put them in your compost bin.
If you are considering planting an olive tree and don't want the work and expense that I've described, then consider a fruitless variety. Local nurseries offer them, and they are no more expensive than a fruiting olive tree.
If I had it to do over again, I would probably still plant fruit-bearing olive trees. Our vineyard doesn't make economic sense either, but we prefer looking at olive trees and grapevines rather than a lawn and landscaping.
Workshops:Napa County Master Gardeners will lead a workshop on “Irrigation Updating and Drought Modifications” on Saturday, June 13, from 9:30 a.m. to 11:30 a.m.., at the University of California Cooperative Extension office, 1710 Soscol Avenue, Napa. Learn how to modify your current irrigation system to make it more efficient and effective. There will be demonstrations and hands-on practice with irrigation controllers, sprinklers, drip systems, rain-water capture and grey-water systems. Bring garden gloves to protect your fingers and a pair of scissors or garden shears.Online registration (credit card only)Mail-in registration (cash or check only).
Workshop: Napa County Master Gardeners will lead a workshop on “Dealing with Drought and Drought-Tolerant Plants” on Saturday, June 13, from 2 p.m. to 4 p.m., in the Napa Library Community Room, 580 Coombs Street, Napa. Learn what to do now to help your garden survive on very little water. Also learn about what kinds of plants do best with minimal water.This is a free workshop but pre-registration is required.
Online registration; Mail in registration
Workshop: Napa County Master Gardeners will host a workshop on the drought on Sunday, June 14, from 2 p.m. to 4 p.m. at the Yountville Community Center, 6516 Washington Street, Yountville.Learn more about the implications of drought in California and get irrigation tips and strategies for low water use in a sustainable yard. We will also cover low water use landscaping plant resources. Register for this workshop by calling the Parks and Recreation Department at 707-944-8712 or visit its website.
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. Napa County Master Gardeners ( http://ucanr.org/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.