By Okhoo Hanes, U. C. Master Gardener of Napa County
The olive tree (Olea europaea) is well suited to Napa Valley. The tree's Mediterranean origin makes it a natural fit for our sunny, arid and temperate climate. Our warm summers encourage fruit growth, and winter provides the necessary 200 to 300 chill hours (hours under 45°F). The olive tree is frost-resistant, withstanding temperatures down to 15°F.
Rich soil and fertilization improve fruit yield, but the olive tree tolerates poor soil. Deer do not like olive leaves, fortunately, as many a plant in the Napa Valley succumbs to their voracious appetite.
Once established, olive trees require little or no water. Still, deep watering every other week in a hot summer results in better fruit production and helps sustain the tree during drought years. Generally, a rainy winter will almost fulfill the tree's annual watering needs, unless your objective is a good fruit crop.
Extreme weather does not appear to affect olive trees drastically. Even so, growing olive trees in the Napa Valley is not entirely trouble-free.
The olive tree can be grown for both culinary and ornamental purposes. Raw olives are not edible but you can cure them or press them for oil. Branches make beautiful wreathes. In landscaping, the silvery-green olive tree contrasts nicely with dark green redwood trees and the brighter greens of oaks.
The olive tree is evergreen, low care and drought tolerant. Due to this generally unfussy habit, it makes a suitable accent patio container tree, a privacy screen or even a hedge. Dwarf varieties tend to reach six to eight feet in height, adequate for a hedge. But standard varieties can reach 30 feet in height and width. With close spacing and systematic pruning, they can create a tall, dense barrier. Olive trees in containers will need regularly watering to maintain moisture levels due to their limited root zones.
If you are growing olive trees purely for ornamental or hedging purposes, consider a fruitless variety. Then you can avoid the hassle of harvesting or cleaning up fallen fruit, the patio staining caused by dropped fruit and the necessity to spray for olive fruit fly. Fruitless varieties include Swan Hill, Majestic Beauty, Wilsonii, Bonita and Little Ollie, a dwarf type topping out at about eight feet. Although Swan Hill produces neither pollen nor fruit, other fruitless varieties may produce tiny flowers and fruit occasionally.
If you would like to cure olives, you can find a detailed recipe online from the University of California Cooperative Extension (http://anrcatalog.ucanr.edu/Details.aspx?itemNo=8267 ). Or plan to attend the U. C. Master Gardeners of Napa County food-preservation workshop on July 27 (details below).
If you would like to press your olives for oil, some commercial facilities such as Jacuzzi Winery in Sonoma accommodate home growers with small production by aggregating the fruit for pressing. For current information about local olive-mill options, contact the Master Gardener office.
Popular olive varieties for oil include Arbequina, Mission, Manzanillo, Sevillano and Frantoio.
Depending on the variety and when the olives are picked, the oil can range in flavor from peppery to buttery. Before planting olive trees for oil, educate yourself about the flavor differences. Many wineries that grow olives offer olive oil tastings and many specialty-food markets carry varietal olive oils.
Olive fruit fly is the most common pest of olive trees in the Napa Valley. It lays its eggs in the fruit, rendering the olives unusable. Do not add damaged fruit to your compost pile; discard the olives in a brown yard-waste bin. The fly was first found in Napa in 2001 and is now ubiquitous throughout the county. Preventing or minimizing the infestation is critical to slowing its spread.
If you have fruiting olive trees but don't care about harvesting the fruit, spray trees with a plant growth regulator containing ethephon (available in many nurseries) in May or June to prevent fruit set. Alternatively, water the trees with a high-pressure hose during flowering. If your trees do produce damaged fruit, harvest it and discard it. Be sure to pick up any fruit on the ground as well.
If you do want the fruit, spray trees with Spinosad, an organic control, following manufacturer's directions. Harvest early in November and pick up all fallen fruit.
The University of California website has excellent information on growing olives in the home garden. (http://homeorchard.ucanr.edu/Fruits_&_Nuts/Olive/). Paul Vossen, an olive authority and former UC farm advisor for Marin and Sonoma Counties, produced a detailed slide presentation on olive cultivation, titled “Olive as a New Crop” (http://cesonoma.ucanr.edu/files/27719.pdf). Although intended for commercial producers, the presentation's content should be of great interest and usefulness to home gardeners as well.
Workshops: U. C. Master Gardeners of Napa County will hold a workshop on “Growing Olives” on Saturday, July 14, from 9:30 a.m. to 11:30 a.m. Location will be provided after registration. Would you like an olive tree or two in your garden? Olive trees are an attractive evergreen and can provide fruit when properly cared for. Learn what to do in every season to have a healthy tree and tasty harvest. Online registration (credit card only); Mail-in/Walk-in registration (check only or drop off cash payment).
U. C. Master Gardeners of Napa County will hold a workshop on “Freezing and Dehydrating” on Saturday, July 21, from 9:30 a.m. to 11:30 a.m., at Napa Farmers Market, 195 Gasser Drive, Napa. Freezing and dehydrating are ways to preserve your summer bounty in its prime, whether you have too much ripe at once or simply want to get a head start on stocking up for winter. Join UC Master Gardeners as they discuss the benefits of each method and some different ideas for snacks and pantry staples. The workshop is free but registration is required. Online registration.
U. C. Master Gardeners of Napa County will hold a workshop on “Basic Food Preserving” on Saturday, July 27, from 10 a.m. to noon, at University of California Cooperative Extension, 1710 Soscol Avenue, Napa. Canning, freezing and drying are among the most basic food preserving methods. It is important to practice safe methods and to stay up-to-date with the most reliable d information about food safety. Master Food Preservers will discuss each process, the equipment required and hazards to avoid, and give demonstrations and recipes. Online registration (credit card only); Mail-in/Walk-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, 707-253-4221, 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.
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:
http://ipm.ucanr.edu/PMG/PESTNOTES/pn74112.html
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.
About 16 years ago, well before I was a Master Gardener, I planted my first olive trees. My goal was simple. I wanted to block the view of a neighbor's collection of old non-working cars, trucks, boats and various other treasures.
My decision-making process was also simple. I was walking through Home Depot one day, saw nine Manzanilla olive trees in 15-gallon pots, thought olive trees were cool, so I bought them, took them home and planted them.
What have I learned from this experience? First, I'm a lucky person. All of my olive trees are alive and well despite being cared for by a former Midwestern with zero knowledge of olive trees. However, in the intervening years, I've learned a bit about them.
Did you know that some types require a pollinizer to produce olives? My Manzanilla trees did not produce much fruit until I planted two Picholine olive trees nearby.
Again, luck played a major role. I was strolling through the Napa Farmers' Market one day when McEvoy Ranch was selling olive trees. I bought two because I had room, and by chance they were Picholines, a pollinizer for Manzanilla.
Pruning slipped by me for the first 10 years or so. The trees grew tall and filled out, which I thought was the goal until I realized I had a jungle with fruit higher that I could reach with a ladder.
Folk wisdom says that olive trees should be thinned enough so that a bird can fly through them. A bird could do this in my little olive orchard only if it were carrying a chain saw.
For the last six years or so, I've been on a pruning rampage. I have reduced tree height to about eight feet, and it is now possible to walk between the trees.
Fortunately, olive trees are forgiving and can handle heavy pruning. Some fruit trees have a narrow window for pruning but not olive trees. I now do a heavy pruning in the winter and prune to shape and to remove suckers and water sprouts all year long. Someday I hope to witness a bird fly through my trees rather than over or around them.
It seems that all trees have an enemy or two, and olive trees are no different. I discovered early on that yellowed leaves with dark spotting and a halo around each spot were suffering from a fungal disease called peacock spot. This fungal disease causes partial defoliation, which weakens the tree and reduces fruit set. The fungus thrives when we get significant fall, winter and spring rain such as we had this past year.
The only preventive measure is to spray your trees with copper fungicide as early as possible after harvest. If you, like me, were lulled into a false sense of security by four years of drought and did not spray last year, there is nothing you can do now about peacock spot other than to hope it doesn't get worse. Note to self: spray this fall.
The major enemy of olive trees in our area is the olive fruit fly. An adult is only about a quarter-inch long, but these critters run in a gang and can ruin an entire crop. Three years ago, none of my olives was acceptable for curing or pressing. They all ended up in the garbage as they were not fit for compost either.
If you have any olive trees, you must take measures to combat the fruit fly even if you don't intend to harvest your olives. Doing nothing is akin to allowing an olive fruit fly hotel and spa to flourish before going on to your neighbors' trees where they will wreak havoc. If you want more information about control, you can find a wealth of information online.
I now have 22 olive trees. I have to say I enjoy them even when they present a problem or two. I find pruning to be therapeutic and the time spent harvesting in the fall most rewarding when I see those buckets of olives awaiting milling or curing.
Workshop: U. C. Master Gardeners of Napa County will hold a workshop on “Growing Olives” on Saturday, July 9, from 9:30 a.m. to 11:30 a.m., at Big Dog Ranch, 1020 Congress Valley Road, Napa. Learn what varieties to plant, where to plant them and how to maximize fruit size and yield. Presenters will also discuss drought tolerance, irrigation, harvesting methods and managing olive pests. On-line registration (credit card only) Mail-in/Walk-in registration (cash or check only).
Guided Tree Walk: Join U. C. Master Gardeners of Napa County for a free guided tree walk through Napa's Fuller Park on Monday, July 11, from 10 a.m. to 11:30 a.m. There is no charge for the walk but registration is recommended as space is limited. Meet at the corner of Jefferson and Oak Streets. Online registration or call 707-253-4221. Trees to Know in Napa Valleywill be available to purchase for $15 each. Cash or check payable to UC Regents. Sorry, we are unable to process credit cards.
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.