Basic Requirements of Indoor-Outdoor Lemon, Lime, and Orange Trees
Lemons require 8-12 hours of sunlight daily to prosper, 5-6 hours to just survive. Grown indoors, a South or west facing window is best.
Citrus plants unlike other fruits do not normally go through a period of dormancy or hibernation in the winter, but will tolerate slightly lower light conditions during this phase of slower growth.
Supplemental light, such as grow lights or fluorescent plant lights will help them produce better, especially if your location is not optimally sunned.
Citrus plants will not be happy with night time temperatures lower than 55 degrees F. During the summer Daytime temperatures around 70 - 80 degrees F are ideal. They will usually tolerate temperatures hovering above 32 degrees for a few hours or heat over 100 degrees so long as they are well watered. Temperatures should not be a major problem in an indoor environment. Temperatures below 55 will invoke a dormancy, extended periods below 55 could result in their extinction.
You should be using a light [low clay], well-draining soil mixture with an abundance of peat, and perlite or vermiculite. Adding additional perlite or vermiculite to any soil you purchase is advisable.
You can also add wood chips, redwood shavings or even hamster bedding and semi-sterile compost in moderation . Using dirt from your yard is a bad idea.
A common problem with indoor citrus trees is chlorosis. Symptoms of chlorosis are yellowing leaves or yellow spots on the leaves. The leaves frequently turn yellow while the vein remains green. Using a balanced fertilizer such as 18-18-18 or a fertilizer specifically designed for citrus is recommended.
If plants get too dry, salts accumulate in the soil. Under natural conditions these salts would be moist and soluble and harmless to the plants.
Water regularly to keep the soil moist, not saturated, just moist. A layer of decorative sterile mulch such as bark or any other organic mulch is advisable to retain soil moisture.
Allow the potting soil to slightly dry between watering, not "DRY-OUT" just slightly dry. Allow the surface of the soil to get dry, but water the plant so there is ample moisture around the roots.
Water modestly 2 - 3 times weekly , test the soil by hand - stick your finger in about a half inch to be certain it is semi dry before adding more water. Over watering is just as deadly as under watering