It's fine to move your lemon tree (Citrus limon) outside for the summer and keep it inside in the place where it's happy for the winter. Stop feeding it during the winter, and water less frequently. The soil should be allowed to dry slightly between waterings during the winter. Overfeeding will reduce flower and fruit production and cause weak roots. Feed in spring and summer only once a month. Use an acid fertilizer specifically formulated for citrus. Remove the tree from the pot every few years and repot the plant with new soil.