Answer: Sudden leaf drop can be a result of your tree being over-watered, in too cool a spot, or not getting enough sunshine. Citrus trees can be successfully grown indoors as long as you provide the following conditions:
Temperature: Citrus plants grow best indoors with 65? days dropping five to ten degrees at night.
Light: Some direct sun is desirable for at least part of the day. During the summer, citrus plants may be placed outside to take advantage of better growing conditions and extra light. Let the plants acclimate to sunny conditions by placing them in the shade of a tree or north side of the house for the first several days. Make sure they have plenty direct light eventually. Re-acclimate them to lower light at the end of the summer by keeping them in a shady place for a week or so before bringing them back indoors.
Soil: A soil containing a fair amount of organic matter (leafmold, peatmoss or compost) is best. Since citrus plants prefer acid conditions, use peat in the potting mix to help keep the pH down. Use about one-third sterile potting soil, one-third perlite or vermiculite, and one-third peat or other organic matter in the potting mix.
Fertilizer: Use a fertilizer formulated specially for acid-loving plants, mixed so it's half the recommended strength. Fertilize the plant only when it is actively growing, usually April through August or September.
Pests: Scale, whitefly, and spider mites are some of the more common pests of citrus. Many insects can be prevented from gaining much ground by making sure the foliage is kept clean by periodically washing the leaves. Pay special attention to the undersides as well as the tops of leaves. To treat insects chemically, check garden centers for products currently approved for use on houseplants.
Following the above recommendations should help your orange tree regain its health. Hope so!
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