Citrus Trees for Indoors

Q. I'd love to give a friend in Illinois a citrus tree for Christmas. Which kind would grow best indoors and how much light will he need to provide?

A. Citrus fruit trees are usually tough plants to overwinter indoors, but if your friend can offer the plant plenty of light — for example, near several large south-facing windows — and cool nights, it has a good chance of doing well until spring when he can set it outside.

Master gardener Paul James, host of Gardening by the Yard, says that achieving the correct moisture level is critical: Keep the tree evenly moist and don't let the soil completely dry out between waterings, but also don't over-water. Root rot is a common wintertime malady. "When the soil is dry an inch below the surface, add water," he says.

Some citrus grows better than others indoors. The sour types — like lemons and limes — don't need as much sun to sweeten their fruit as oranges do. Choose Meyer lemon, lime, sour orange, grapefruit, kumquat, mandarin and limequat. Dwarf varieties that have been bred to do well in small spaces and containers are best.

Also, citrus trees are heavy feeders. Your friend will want to nourish his tree four to six times a year with a chelated mix of manganese, iron and zinc (most multipurpose fertilizers contain these minerals).

Citrus greening disease. One of the most serious problems affecting all types of citrus today, greening disease results from the action of a bacterium that's spread by a tiny insect, the Asian citrus psyllid. The bacteria can live for a couple of years on a citrus plant before symptoms being appearing. Signs of the disease include mottling, leaf chlorosis and misshapen, bitter or salty fruit. Some of the symptoms can also be mistaken for nutritional deficiencies; it's important to get a diagnosis.

There is no cure for citrus greening disease. The most important thing gardeners can do to help prevent its spread: Don't move citrus plants, even if you think a specimen is perfectly healthy.