Growing macadamias a great option for Florida farmers

Are you searching for a nut that you can grow in Central Florida? Macadamias are a tropical nut from Australia that will also grow here, although we are borderline for cold hardiness. That means older trees can survive cold winters with a little die back, but small trees will need to be protected from cold temperatures below 25 to 26 degrees Fahrenheit. Temperatures below 28 degrees will damage flowers and young fruit and reduce production. On the other hand, macadamias don’t like too much heat either, and trunks may be painted with white latex and the leaves dusted with kaolin clay in the summer to keep them cool.

There are two main species of macadamias, smooth shell and rough shell, and many cultivars of each. The smooth shell ones are the main commercial cultivars because of the white kernel and mild flavor. The rough shell types are more cold-hardy with more sugar that will turn brown during the drying process and so are not as desirable for commercial use. Hybrids combine the best characteristics of both species. Plant two cultivars to increase fruit set.

Both species will form trees 60 feet or more in height with brittle, hard wood. When pruning, aim for a single trunk with horizontal branches that is open enough to allow air movement to reduce fungal diseases associated with moisture. Be sure to keep branches that have a wide crotch angle to increase branch strength, and remove branches with narrow, upright angles. It will usually take five to eight years before plants produce many nuts. A mature tree may produce as much as 150 pounds of in-shell nuts. Nuts may be weighed in the shell or out of the shell, but common yield measurements are in-shell weights right off the tree.

Plants flower in February, and it takes several months for the nuts to ripen. Mature nuts should fall to the ground, but some growers have had issues with cultivars like “Beaumont” retaining nuts on the tree until they are too old. Nuts should be picked up at least weekly to avoid molding. The husk must be removed, and the nuts are usually dried before cracking and roasting. Macadamia nuts are especially difficult to crack, requiring 300 pounds of pressure. Regular nut crackers are difficult to use with macadamias, and when they do crack, they tend to shatter the nut. Specialized nut husker and cracker machines are used in commercial production.

Macadamias are relatively drought-resistant and like well-drained acid soils. However, during establishment, flowering and fruit set, supplemental irrigation will probably be needed to reduce plant stress and fruit drop. Macadamias like fertilizer higher in phosphorous than other fruit crops, a 10-22.5-10 ratio is good, with inclusion of micronutrients zinc, manganese and iron especially.

The main pest of macadamias in Florida are squirrels, which will eat the nuts before they harden. If you can keep the squirrels away, the other main pest is green stinkbugs which injure the fruit while very young, causing fruit drop and deformation. Also watch out for several other pests including mites, thrips, root weevils and nut borers.

Although this nut has been grown in Florida for many years, there is little research on cultivars and more information is needed before making recommendations for this area. The plants do not come true to seed and are commonly grafted on seedling rootstocks to accommodate the tap root. However, a grower in Plant City has had success air-layering four-foot branches and growing the plants on their own roots.

Juanita Popenoe is a multi-county commercial fruit production agent IV at the UF/IFAS Lake County Extension Center. Email