Winter is a great time for citrus in Hawaii, as many types might now be available right from your garden.
Citrus originated in Southern Asia and the surrounding islands, with most of the domestication occurring in India and China. Explorers transported citrus to Europe and the Middle East, and later, the Americas, where industries developed around the fruit.
The first citrus to arrive in Hawaii was a Valencia type of orange brought to the Kona Coast by Capt. George Vancouver in 1792. The orange flourished in the dry climate, similar to that found in the Valencia region of Spain from which the variety originated. Many acres of what came to be known as “Kona oranges” were grown and, for many decades during the nineteenth century, these oranges were a major export from the region. Many of these oranges were bound for the West Coast, with some making their way into the goldfields of California. A few Kona orange trees still exist, bearing fruit to this day. Currently, Hawaii grows a very small fraction of the estimated 68 million tons grown worldwide, and only fruit for local consumption.
Planting a citrus tree is a long-term investment. A well cared for tree will provide generations of high-quality fruit.
First, select the type of citrus you want to grow. Easy peeling tangerines and mandarins are good choices, along with oranges, lemons or limes. Most sweet fruit citrus are best grown below 500 feet elevation, but this is not a hard and fast rule. Climate, environment, and care all play equally important roles in the quality of citrus fruit. Sunshine is essential for quality fruit. The leeward side of the island is generally better than the windward side, in this regard.
Many citrus do not breed true from seeds and trees from seeds will vary in fruit quality. The best choice is to plant clonally propagated plants, those produced by grafting, rooted cutting or air layering. These trees will be of known quality and can flower and begin to fruit within a year of planting.
Site location and ground preparation are essential for good citrus growth and fruit quality. Most citrus requires full sun and sufficient room for the canopy to develop. Most oranges, pummelo and tangerines will have a spread of 10 to 20 feet when mature. Lemons and limes require only about 8 to 12 feet. Proper pruning can significantly reduce the size of mature trees and shorter trees are easier to harvest. Citrus prefer well-drained soils. Soil pH should be between 6 and 7. Phosphorus is an important component of fertilizer that should be incorporated into the soil of the planting hole. Prepare a planting hole about two to three times the diameter of the plant root ball you will be transplanting. Be careful to set the tree at the same soil level as in the container in which it was growing to prevent killing the young tree.
Use a commercially available citrus fertilizer for your trees at the label rate. Citrus fertilizers normally have lower phosphorus levels and typical analyses are in the ratio of about 13-6-13 or 10-4-10 for nitrogen, phosphorus and potassium. More information on fertilizing your citrus can be found at the University of Hawaii College of Tropical Agriculture and Human Resources publication website below, by searching “Citrus for Hawaii’s Yards and Gardens.”
Citrus can be plagued by a number of insects from aphids, scales, white flies, fruit flies, leaf miners, beetles, caterpillars and others that will suck, chew and burrow your plant into lower yields and even death. Many of these are controlled by introduced predators. If necessary, a range of pesticides are registered for use on citrus. Always read and follow label direction on any pesticide you use. Lures and traps are also options to control certain insects.
There are a few disease problems with growing citrus in Hawaii. Citrus tristeza virus causes internal stem pitting on trunks and branches which may lead to premature plant death by reducing the flow of nutrients and water. No control is known for this disease, but its severity can be diminished by variety selection and use of disease-free propagation material. Another common disease is citrus melanose. While rarely affecting the fruit pulp, it can cause extensive blemishes on the rind and on the foliage. Tangelo and limes are susceptible to citrus scab, a fungal disease which causes rough patches on fruit and foliage.
For more information on this and other gardening topics, visit ctahr.hawaii.edu/Site/Info.aspx or visit any of the Cooperative Extension Service islandwide.
Russell Nagata is the Hawaii County administrator of the University of Hawaii at Manoa College of Tropical Agriculture and Human Resources. He can be reached at russelln@hawaii.edu.