Designing a successful grove

05/01/2008 02:00:00 AM
Elizabeth Ashby, editor

Before you start ordering citrus trees and digging holes, do your due diligence. Grab your pencil, eraser, graph paper and calculator. Call a local extension agent or citrus expert for help. Careful planning is necessary to ensure that a new citrus grove or new plantings within an established grove lead to success rather than failure.

There are several questions citrus growers need to answer before they can start designing a grove. None should be considered separately from the whole. Bob Rouse, citrus specialist with the UF/IFAS Southwest Florida Research and Education Center in Immokalee, says growers need to enter into grove design with their eyes wide open.

"These are long-term decisions that require money and capital," he says. "You need to know what your challenges are now and what they could be."

Decide your purpose

When it comes to planting a citrus grove, the first thing to consider is the end result, says Steve Futch, extension agent multi-county for UF/IFAS.

What do you want to do with your citrus once it is grown and off the tree? Do you want to sell to the juice and processing market? Do you want to produce citrus for the fresh market? The answers to these questions will decide the type of rootstock you need to seek out. For example, Futch says growers intending to reach the juice market will find that hamlins, valencias, and early, mid- and late-season oranges are essential. If it is fresh fruit growers seek, Futch says they will have to decide whether they want a tangerine type, a mandarin, etc.

Rouse says the space you have available also plays a role in this decision. Juice and processing plants need a large volume, so you need to be able to plant thousands of acres to enter the juice market, he says. On the other hand, there are plenty specialty markets out there for fruit preferred by ethnic groups that might work well for growers with smaller acreage around 20 to 40 acres. Take pummelos, for instance, which are preferred by Asians, Rouse says.

"Growers could plant a thousand acres [of pummelos], overwhelm the market and go broke. Or they could plant a few acres, hit the market and do very well," he says.

Once you know what market you want to hit, that provides the foundation for selecting specific varieties, each of which need to be considered thoroughly based on the aspects of the trees. Futch says orange trees aren't as vigorous as grapefruit trees, and flying dragon rootstock tends to produce a smaller tree.

Available space is key

After you have selected your market and your varieties, next comes what most scientists say is the most important decision: analyzing your acreage and deciding your tree density.

"For the future, we are not going to be able to plant our citrus groves the way we have in the past. We are going to, and growers are already moving in this direction, design the grove so that it will produce high yields in earlier years in order to get a cash flow coming in sooner than later. We can't plant a tree any more and expect it to break even in six or seven years and become the most productive on a per-acre basis at nine or 10 years. We need that within four or five years," Rouse says.

The standard for current plantings is using a north-south orientation, 24 to 25 feet between rows and 10 to 15 feet within the rows. While the orientation isn't changing, the distances are being tested and altered by many growers and scientists trying to achieve maximum light interception.

Futch says to think of a leaf as a solar collector. The more leaves a grower has collecting the sun, the better off he is going to be because there will be less bear ground collecting the sun, thus producing weeds, grass or other vegetation. If growers achieve the maximum light interception in a grove, they will have greater yields.

Growers are testing spacing between rows anywhere from 8 feet to 10 feet to 15 feet. While planting in such a manner is possible, part of the test is making sure trees remain manageable in these rows that are closer together. "You can be successful with smaller row spacing if you use a less vigorous rootstock, but you also can set yourself up for failure if you use the wrong rootstock," Futch says.

Rouse says planting trees closer together also helps when growers discover citrus greening in their groves. "When you tighten up your trees, if you do get infected, and you will, you could remove those diseased trees and other ones will fill in that empty space because they are already close together," he says. "You can afford to lose those trees and not lose bearing space or volume because the other trees will move in."

Another way to become more profitable is to use rootstocks that produce small- to medium-sized trees (also known as dwarfing trees).

"We can no longer, I believe, function with a 16 to 20 foot tree in height. There are a lot of labor issues and safety issues there to pick a tree," Rouse says. The industry standard, the swingle, makes a moderately sized tree already, and growers can maintain it around 12 feet tall. Other rootstocks on the market are topping out between 8 feet and 9 feet.

Finally, with regard to spacing, growers also need to keep in mind the possibility of mechanical harvesting when designing their grove. Rouse says he thinks every grower should request and buy high-headed trees from the nursery. High-headed trees are grown higher than normal before they are allowed to start branching. This allows space to use mechanical harvesting equipment.

"It is much easier to plant a tree designed for that than to take a tree that is already planted, prune it and make it possible for mechanical harvesting," Rouse says. "It doesn't cost anymore and it gives you an option you may want to exercise in the future."

Analyze soil type, make water management plans

Soil and topography, also known as site selection, is a topic that has much information and data available to the grower. Articles on the UF/IFAS EDIS Web site detail the various types of soil conducive to citrus groves and how to prepare the land. This also effects your planned water management.

According to "Water and Environmental Considerations for the Design and Development of Citrus Groves in Florida," an article by Brian Boman, Nigel Morris and Mark Wade, "the rolling sand hills in Central Florida (the Ridge) are largely well drained. These light sandy soils are usually underlain by a sandy clay layer. Clay or organic matter in the soil helps to retain moisture and nutrients for use by the trees."

The Indian River and Southwest Florida are noted as poorly drained flatwoods soils, according to the article, which will need a different type of preparation before planting. "If you are in a very wet area called the Flatwoods in south Florida or on the east coast where the water is much closer to the surface, then you will need more canals, drainage, etc.," Futch says.

Growers also need to consider the type of irrigation they will use in their grove. Rouse says the standard spray jet emitters under each tree are turned on and off every two or three days by employees. These water a large area of soil. But some growers are considering or testing the use of open hydroponic systems. These restrict the wet zone to a small area where all the tree roots grow, Rouse says. Growers turn the system on two or three times a day and water a much smaller area only putting on enough water at any given application to wet the soil to a certain depth.

While this does require a financial investment of computers in the pump station that turn the system on and off throughout the day, as well as censors in the field measuring the wetness of the soil, now the growers only apply enough water that the tree needs. These systems have only been tested for the past year or two, so results are not conclusive. But the goal is to use water more efficiently and maybe even reduce the amount of water used, Rouse says.

Time to get started

While all of these topics must be carefully considered, you don't have to do it alone. Rouse and Futch recommend growers seek help and guidance from UF/IFAS extension officers, researchers and scientists. If you are comfortable on a computer, spend time searching the Internet and read articles to become familiar with terminology, the latest technology and issues that might come into play in the future, Rouse says. Futch says the National Resource Conservation Service from the U.S. Department of Agriculture can help with irrigation design.

"Seek out as much information as you can to make the best decision because you are going to live with it for a number of years," Rouse says.



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