It's fine to move your grapefruit tree outside once the danger of frost has passed. Your tree will thank you for a summer vacation outdoors. Just remember that taking it outside and leaving it in full sun and wind immediately could shock the plant. Move it outdoors gradually so it can get used to the new conditions. Start by leaving it in a protected spot, such as the north side of your house. Then slowly move it to full sun (or leave it in the protected spot all summer long). Indoors, give this plant as much light as possible, and keep the humidity high near it. Citrus trees can attract insect pests such as spider mites or mealybugs during the winter when there's dry air around them. But it's a good idea to keep an eye out for insect pests on a weekly basis all year long. Wait to fertilize until spring, but once your plant is growing outdoors, you may want to feed it with a timed-release granular fertilizer designed for citrus.