I have a variegated pink lemon plant which is kept outdoors in the warm months and brought indoors for the winter. I live in Toronto. It flowers prolifically, but never fruits. Any suggestions? Thanks in advance.
I expect your problem is that the flowers on your tree are not pollinated. If your tree flowers when inside, it will not set fruit because there are no insects to do the pollination. Even if it flowers when outside, although bees and other insects could carry out the pollination, you can increase the likelihood of fruit by pollinating the flowers by hand, which it is not difficult.
Here is an image of a lemon tree flower:
To pollinate you should carefully rub the antlers (the yellow tips of the small stamens around the centre of each flower), with a paint brush or cotton swab to collect the pollen. You then rub the pollen on your tool on the stigma (the taller centre stalk of the flower) until it sticks. After that nature should take over. It is best to do this in the morning.
Here are links to a couple of Youtube videos taking you through the steps: