Advice from the Help Desk of the
Master Gardeners of Contra Costa County
MGCC Help Desk: Thank you for contacting Master Gardeners help desk with your question about growing sweeter oranges.
The fruits from sweet orange trees in your garden may not taste as sweet as supermarket oranges. Many factors affect the flavor of ripe oranges: the climate, when they are harvested, the variety, pruning, cultural care (e.g., mulching), fertilizing, and irrigation. Without knowing what specific type of orange tree it is, it is difficult to know if you actually have a tree that does produce sweet fruit, but we will assume that it is a sweet orange tree in your yard.
Here are some reasons that the fruit may not be as sweet as you would like it to be along with some possible remedies:
Lack of Heat - The amount of heat the garden receives in summer determines whether or not oranges taste sweet at harvest time. Many orange tree varieties need heat to sweeten their fruits, and if they are grown in an area with a mild climate, you may get oranges that are more sour than sweet. Summer heat builds sugar in the fruits. Navel oranges need a lot of heat to develop their signature sweet flavor.
Harvest Too Early - Letting the oranges stay on the trees longer in winter helps to lower their acid content during the cooler winter temperatures. If oranges are picked without taste testing them first, they may taste too acidic or sour for your liking. Solve that problem by sampling a single orange from the trees for flavor before harvesting the rest because oranges do not sweeten any more once they are picked.
Sour Orange Variety - Your orange tree may not produce sweet oranges. Your tree could be a sour orange tree instead of sweet orange tree. Sour orange tree fruits are grown for their bitter peels, which are used to add orange flavor to recipes. Their flesh is exceptionally sour and acidic. Sour orange peels have a dimpled appearance and a slightly reddish cast. If you don't want to remove a sour orange trees, you could use their fruits to make marmalade or jellies.
Rootstock Takeover - Failing to remove suckers from below the graft on an orange tree encourages growth of the rootstock to the point it takes over the scion and produces flowers and fruits of its own. The fruits from the rootstock are not usually the same flavor as fruits from the scion, depending on the rootstock. Some rootstocks compatible with sweet orange trees include sour orange trees and various lemon trees. If those rootstocks produce fruits, they will have the bitter, sour flavor of a sour orange or lemon instead of the sweetness of a sweet orange. You may be able to tell if the rootstock has taken over by considering the following:
|If this tree is grafted (and most orange trees are), and if it was grafted on dwarfing or semi-dwarfing rootstock, they are frequently grafted to trifoliate rootstock, so that can make the diagnosis much easier. If you see any leaves in groupings of 3, it is likely that it is rootstock, as orange leaves are singly produced on a branch. Also, the leave size and shape will be different and the stems may have large thorns. If the rootstock has taken over, you can attempt to prune the rootstock off if there is anything left of the original grafted tree.|
Fertilizing: Citrus do require adequate and regular fertilization to maintain their growth and satisfactory fruit production. Here is a UC link to additional information on citrus fertilization for the home garden: http://www.ipm.ucdavis.edu/PMG/GARDEN/FRUIT/CULTURAL/citfertilization.html
Citrus Culture in Contra Costa County: Finally, in summary of the above, here is a link to an excellent overall MG article about care of citrus in our area. This article will help you to make sure that you are using the right fertilizer and giving the tree the right amount of moisture for optimum quality fruit production in additional to other helpful suggestions for citrus success: http://ucanr.edu/blogs/slomggarden/blogfiles/4260.pdf
Please let us know if we can be of further assistance.
Help Desk of the Master Gardeners of Contra Costa County
Note: The Master Gardeners of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: email@example.com, or on the web at http://ccmg.ucanr.edu/Ask_Us/