Citrus do not ripen off the tree; they may color up, but if they are not ripe when you pick them, they will never get better (juice/sugar). If the lemons are ripe but not colored when you pick them, the best way to color them (aside from liquid or gas ethylene) is to put them in the dark, not the sun.

Will lemons continue to ripen after picked?

Lemons will have glossy skin and can be green, greenish yellow, or fully yellow when ripe. Lemons are citrus plants that continue to ripen after being picked. This means that ripe lemons can turn yellow after you bring them home. Lemon trees will bear fruit sometime between 4 and 12 months after the flowers blossom.

When should I pick my lemons off the tree?

Lemons are ready to pick as soon as they are yellow or yellow-green in appearance and firm. The fruit will be 2 to 3 inches (5-7.5 cm.) in size. It's better to wait until they are the right size and not worry so much about the color than to wait for them to be completely yellow.