The Humboldt Master Gardener/Del Norte Help Desk is staffed by volunteers trained by the University of California to answer gardeners' questions using information based on scientific research. Thank you to Annie Sicotte, Humboldt Master Gardener, for researching this question.
Q. I have a Meyer lemon tree that has been covered with fruit for months, but not all of them are turning yellow. The fruit looks to be mature size, but some are still dark green. Recently, my tree has started to bloom again. Is this normal? Can I harvest the lemons even if they have not turned yellow?
A. One great thing about Meyer Lemon is that it can bear fruit all year round. Lemons will flower and fruit more than once per year if conditions are favorable. On the coast, Meyer Lemons often have blooms and fruit in varying stages throughout the year.
Meyer lemons are typically ready to harvest when they have turned a deep yellow or orange color and feel firm to the touch with just a slight “give.” They should also be fragrant. It's best to harvest them when they are fully ripe for the best flavor. The heaviest harvest is usually late Winter/Spring.
The reason your fruit has not turned yellow may be that we have not had enough cold weather to encourage the color change. It occurs naturally as the fruit ripens, but cold weather speeds up the process.Citrus turns color in Fall, but the color does not affect the sweetness of the fruit.
The Meyer lemon is a cross between an orange and a lemon and is known for its milder taste, so if you pick it green, it will be more acidic in taste than your typical Meyer lemon, and you may be disappointed. The fruit is usable at any stage past dark green but will have a stronger acid flavor if you pick it before it is fully ripe. Meyer lemons don't ripen any further once picked, so if it's the milder taste you want, then it's best to leave the fruit on the tree as long as possible. That said, when citrus fruit freezes, it can become pithy and lose its juiciness. Protect your tree and the ripening fruit by covering it with a blanket, heavy tarp, or row cover on those nights when it's predicted to dip below freezing.
The best place to store the fruit is on the tree. Once you pick the fruit, it does not increase in sweetness or ripen more fully. However, if you do pick the fruit, it will keep for about 4 to 6 weeks under refrigeration. Juice from lemons can be frozen for up to 4 months.
For more information on growing citrus and frost protection, check out
The University of California book, The California Backyard Orchard, or on the web https://homeorchard.ucanr.edu/Fruits_&_Nuts/Citrus/
https://sonomamg.ucanr.edu/Food_Gardening/FRUITS/Meyer_Lemon/