Experts tackle readers’ garden questions.
Q: I have a Robertson navel orange that is about 6 years old. This winter, there are ripe oranges as well as developing green oranges at the same time. We have been eating the ripe ones and they are juicy and sweet. All branches are growing clearly above the graft. Is this common?
Robert Munoz, Elk Grove
Bee garden writer Debbie Arrington: Yes, although more so on Valencia orange trees than navels. Valencias, which need 12 to 15 months to ripen, often have two crops on the tree at the same time.
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Navel oranges take 10 to 12 months to develop and ripen, although they may ripen as quickly as seven months depending on growing conditions. (Hot summers prompt faster ripening.) The ripe fruit may hang on the tree for weeks or even months after reaching maturity.
In addition, a mild summer increases the number of weeks needed for the oranges to fully ripen. It’s not unusual for the tree to start blooming and setting more fruit while bright-colored oranges still hang on the branches.
More likely in your case – judging by the size of those green oranges – is that your tree produced some extra blooms during late spring after its usual bloom time in late winter. Called “off-bloom fruit,” this second wave of oranges often develops a thicker skin than normal navels and may not be as sweet. Off-bloom fruit may grow on the tree at any time of year including when the tree is in full flower.
Commercial growers remove off-bloom fruit to force the tree to concentrate its energy on its main crop and to kick it back onto its regular schedule of late winter bloom and December-to-February harvest.
At age 6, your tree is very young to be bearing a heavy crop (or two crops at the same time) and may benefit from removing those “off-bloom” oranges. Also, those late oranges could interfere with your tree’s regular bloom time and affect next winter’s crop. You may have fewer flowers or more fruit drop as the new oranges are developing.
By the end of February, all your ripe navels should be harvested and it will be time to make a decision on that “extra” crop.
According to University of California research, Robertson navel oranges tend to ripen faster than the more common Washington navel. The fruit also is maintained much longer on the tree. (That also helps explain your tree’s overlapping crops.) Because its fruit develops more rapidly than other oranges, the Robertson tends to drop fewer baby oranges during June when the tree naturally thins its crop. Robertson navels often grow in clusters and bear heavily at an early age, like your tree.
A natural “sport” or mutation found on an old Washington navel tree, this variety was originally discovered in an orange orchard near Redlands by Roy Robertson in 1925. It was patented by Armstrong Nurseries and released to the public in 1936, but never caught on as a commercial tree. But because of its small size and ability to bear a lot of fruit early, the Robertson navel is still popular as a backyard orange or container-grown patio tree.
The Bee’s Debbie Arrington is a consulting rosarian and lifelong gardener. Reach her at email@example.com, 916-321-1075, @debarrington.
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