Question: I bought a potted lemon tree this summer and it produced three lemons. However, they’re still green. The plant is now indoors for the winter, but the fruits don’t appear to be ripening. Should I harvest them now even if they’re not mature or should I leave them on the plant?
Answer: Leave them on the plant. Citrus fruits are very slow to ripen. It can easily take 4 to 6 months even when the plant grows under optimal conditions, but up to 11 or 12 months under lower quality conditions … such as on a temperate-climate terrace or indoors. And unlike tomatoes that will ripen after harvesting, citrus fruits won’t ripen once you’ve removed them from the tree. So you have to leave them on the tree until they reach full maturity.
Once the fruits are mature, though, you can often leave them on the plant for a month or a bit more if you want to enjoy their ornamental effect for a longer time.
To learn more about growing citrus fruits in a temperate climate, read A lemon or orange tree from seed?