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.