By Russell T. Nagata
By Russell T. Nagata
University of Hawaii at Manoa College of Tropical Agriculture and Human Resources Komohana Research and Extension Center, Hilo
Fall and winter months are a great time for citrus in Hawaii, as that is the time of year when the most types are available right from your garden. Citrus varieties originate in Southern Asia and the surrounding Indo-Pacific islands, with most of the domestication occurring in India and China over many thousands of years.
Explorers and adventurers transported the citrus to the Middle East and Europe where it became important industries. It was also transplanted to the America’s early in its exploration. The first citrus to arrive in Hawaii was a Valencia type of orange brought to Hawaii in 1792 by Captain George Vancouver to the Kona coast. The orange flourished in the dry Kona climate, somewhat similar to that of the Valencia region of Spain, from which this particular variety of orange originated.
Many acres of what came to be known as “Kona” oranges were grown, and for many decades during the 19th century, these oranges were a major export item from the region. Many of these oranges were bound for the West Coast of North America, with some making their way into the gold fields of California. A few trees still exist of these Kona oranges, bearing fruit to this day.
Currently, Hawaii grows only a very small fraction of the estimated 68 million tons grown worldwide, and only for local consumption, mainly due to fruit flies.
However, we can grow very tasty citrus with a little effort.
Planting a citrus tree is a long- term investment, for a well-cared-for tree will provide generations of high-quality fruit. First decision is to select the type of citrus that you will want to grow. Easy-peeling tangerines and mandarins are a good choice, along with oranges, lemons or limes. Most sweet- fruit citrus is best grown below 500 feet in 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 good quality fruit and, in general, the leeward side of the island is slightly better than the windward side in this regard. Many citrus do not generally breed true from seeds, and trees from seeds will vary in fruit quality. (Great if it is better, but most likely it will be inferior, and seedlings take five or more years to begin flowering.)
The best choice is to plant clonally propagated plants, those produced by grafting, rooted cutting or airlaying. These trees will be of known quality and can flower and begin to produce fruit within a year of planting. Site location and ground preparation are essential for good citrus growth and fruit quality. Depending on how you will manage the mature tree and type of citrus, site location 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 are smaller and require 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, and any location where water puddles after a heavy rain will probably not be suitable for citrus.
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 due to its low mobility in soil, even for soluble forms. 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 citrus 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 gotten from the CTAHR publication “Citrus for Hawaii’s Yards and Gardens,” via the website, below.
Citrus can be plagued by a number of insects, from aphids, scales, white flies, fruit flies, leafminers, 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 biocontrol predators. If necessary, a range of pesticides is registered for use on citrus. Always read and follow label direction on any pesticide that you use, no matter how safe you think it may be. Lures and traps are also an option to the control of certain insects.
There are a few disease problems with growing citrus in Hawaii. The most important is citrus tristeza virus, which 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; however, severity can be diminished by variety selection and use of disease-free propagation material.
Another common disease is citrus melanose, caused by a fungus. While rarely affecting the fruit pulp, it can cause extensive blemishes on the rind and on the foliage. Tangelo and limes are very susceptible to citrus scab, a fungal disease which causes rough patches on the fruit and foliage.
For more information on these and other gardening topics, please visit the CTAHR electronic publication website at http://www.ctahr.hawaii.edu/Site/Info.aspx, or visit any of the local Cooperative Extension Service offices around the Island. I can be reached at russelln@hawaii.edu.