lemon tree (Citrus limon)

We have a lemon tree in our backyard that bloomed very late this year. The lemons on the tree are still green and we do not know what to do. Should we take them off or leave them on the tree? Are green lemons good for anything? Any information about lemon trees will be appreciated.
— Andy and Gerileah Toth, Simi Valley
`Eureka’ is the most widely grown lemon variety and is probably the one growing in your backyard. Since you said it bloomed late, its shoots were probably killed back by January’s severe freeze and may only have started leafing out again in March and not flowered until April or May.
`Eureka’ is more frost-sensitive than the other two popular varieties, `Lisbon’ and `Improved Meyer.’
`Lisbon’ is a more robust, if thornier, tree that grows to a height of 30 feet, as opposed to the 20-foot height reached by `Eureka.’ The fruit of these two varieties is quite similar. By contrast, the virus resistant `Improved Meyer’ is a spreading tree, often grown in patio containers on a dwarfing rootstock, with thinner skin and sweeter fruit. `Improved Meyer’ also has a more compact growth habit and is sometimes grown as a hedge.
In Southern California, lemons are a winter crop and should start turning yellow any day now. Green lemons always turn yellow so just be patient. You may have to wait until the end of December to see some fully ripened fruit. In truth, you may have lemons ripening throughout the year but most should ripen in the next few months as long as we do not experience another freeze.
Incidentally, the fruit of many citrus varieties can be stored on the tree, since after ripening it will not drop on its own and retains its freshness for several weeks or more.
This citrus characteristic of staying on the tree is not a natural tendency. If you go to the part of the world where all citrus species originate — tropical China and Southeast Asia — you will find that citrus fruits immediately fall from the tree after ripening.
Once they have grown to maturity, lemon trees can be pruned annually without sacrificing fruit production. This pruning will be necessary to keep the trees in bounds, since they tend to grow haphazardly and do not conform to any standard geometric form.
The best time to prune would be in the spring, after most of the fruit has been harvested and the danger of frost is past.

Photo credit: Mouse / Foter.com / CC BY-NC-ND