An important factor in determining the suitability of a plant to your home and envisioning the care it will need, is to know the origin of the plant. Plants that are native to desert regions will require substantial amount of sunlight and loose, fast-draining soil. Plants from the floor of a rainforest will need some protection from strong sunlight and generous humidity.
Citruses comprise about 15 species (and many more hybrids and cultivars) of small trees and shrubs, including fruit bearing lemons, limes, oranges, tangerines, and grapefruit. These plants originate in tropical forest and scrub regions of Asia and can be a challenge as indoor plants because of their need for humidity, air circulation and strong light. If successfully grown, citrus plants can produce many fragrant flowers and brightly colored fruit in your home.
Growing a citrus plant indoors successfully requires providing it with at least eight hours of strong sunlight daily. Place your plant in the brightest spot in your home, with best results in a south or southwest facing window. In summer, you can place your plant outdoors in bright light for vigorous growth. Acclimate it to this change in venue slowly.
Your plant will not produce flower and fruit if it does not have a minimum of 6 hours of strong sunlight each day.
Citrus needs humidity indoors. Provide increased humidity by standing potted citrus plants on trays of damp pebbles or moist peat moss. Mist-spray occasionally. The humidity necessary to keep a citrus plant in good health is above 50% and pebble trays are a good way to localize that humidity.
Water actively growing plants moderately, allowing the top inch of the potting mix to dry out between regular, thorough waterings. There is no set schedule for watering that works well in every home. Temperature, light, type of heat, soil mix, type of container and humidity all influence the rate at which water is reduced in the soil so use a test of dryness with your finger or a moisture meter as a guide. Do not let the roots dry out or they will be burned by the fertilizer salts in the soil. Water citrus plant less in the slow growth period during the winter.
Normal room temperatures, between 55 and 85°F. are fine; growth will stop at temperatures below 50 degrees. In summer heat, the plant must have good air circulation but be kept out of draughts.
Stable warmth is important. Do not subject the plant to temperature shocks. Like many houseplants, a variation of ten degrees between day and night temperatures is best for the plant and will enhance flowering.
In winter, a rest period takes place and gradually adjusting to cooler temperatures of 50 to 60°F. is healthy for the plant.
This plant needs to be firmly tucked into quick-draining, lightly acidic soil and kept fairly pot-bound. Repot in the spring, as necessary, every two years or so in a deep pot that will help balance the weight of the tree. A mixture of equal parts peat, compost and sharp sand are excellent or use a citrus-specific potting mix.
Feed citrus a fertilizer with a 2-1-1 ratio (or a specialized citrus fertilizer), given every two weeks for actively growing plants, especially during flower and fruit development. Feeding is not necessary at other times.
Flowers and fruit, may simultaneously grow in various stages of development, though the flowering period for most citrus plants is late spring through summer with fruit developing for ripeness in fall or winter. Citrus do not require cross-pollination and a single indoor plant may develop fruit. Pollinate your plant by hand, brushing the flowers with cotton balls.
The process of fruit ripening on the plant may take many months. The length of time varies with the type of citrus; lemons and limes generally progress from flower to mature fruit in six to nine months and oranges take longer. The ripe fruit may remain on the branches for several months.
A citrus plant may not produce fruit until it is mature.
Yellow leaves may indicated a nutritional deficit (such as magnesium) and require more feeding.
Flowers, small fruit and leaves will all drop off if the plant does not get enough sun, adequate water and humidity, or if the plant experiences a temperature extreme.
Inspect your plant for pests regularly. Spider mites are particularly common in low humidity situations. Quick removal and increased humidity will prevent an infestation.
You can prune unbalanced branches in the spring, using sterilized pruning shears.
Purchase a dwarf plant that is well suited to indoor growing. Lemons and limes need less heat to ripen and are thus more successfully grown indoors. Some plants to try include -
Citrus limon ‘Meyer’ (Meyer’s lemon) grows leaves up to 4 inches long and rounded. The fruit is thin skinned and pale yellow.
C.l. ‘Ponderosa’ (American wonder lemon) has similar leaves, but a larger, thick- skinned, orange-yellow fruit.
C. x latifolia (Tahitian lime) produces large fruit and is thornless.
Citrus sinensis (sweet orange) is fast ripening and produces a sweet tasting fruit. Nip out growing stem tips at any time to encourage bushier growth.
C. medica (citron) has yellow, bumpy fruit with a thick rind and limited juice.
C. japonica (kumquat) is a great, small, tart fruit for making preserves.
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The Houseplant Survival Guide by 
