Citronella is an oil extracted from the tropical grass Cymbopogon nardus. Plants sold in the United States as "citronella" are geraniums that have had DNA from the Cymbopogon nardus inserted in them. Crushing or rubbing the leaves of this "mosquito geranium" releases the citronella scent.
Mosquito geraniums grow best in full sun or under direct light. However, they will still grow in partial shade. Plants grown inside and in places that don't have good available window light may need artificial light. Any good grow light over the plant will ensure that the plants flourish.
Citronella or mosquito geraniums are not particular about the soil in which they grow. Citronella grows well in clay-based, sand-based, or loam-based soils, as long as the soil is slightly acidic and drains well.
Citronellas need to be kept moist. Dried out roots can harm the plant. No more than the top 1/4 inch of the soil should be dry.
Setting the plant too deep can result in root rot. The top 1/4 to 1/2 inch of the root ball needs to be above the level of the surrounding soil. This will allow water to run off the root ball and saturate the soil around the roots, rather than gathering in the root ball itself.
Citronellas growing in a bed with other citronellas need to have between 18 and 24 inches between the plants. Planting them closer could cause the plants to have to compete too much for soil nutrients and resources. Overcrowding can also result in bacterial leaf spots and bacterial problems on the blossoms.
Mosquito geraniums grow in most parts of the United States. They may not grow well in the northern ½ of Wisconsin, the northern ½ of Minnesota, the northern 2/3 of North Dakota, and the northeastern ½ of Montana. There are also some parts of the Rocky Mountains in Colorado, Wyoming and Idaho where they may not grow well.