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.
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.