Climate requirements

Citrus trees are subtropical to tropical in nature they suffer severe damage or even death because of freezing temperatures. However, several types of citrus have sufficient cold-hardiness to sustain some freezing conditions, particularly as mature trees.

 

Soil requirements

Citrus trees require deep soil having good surface and internal drainage. Surface drainage refers to runoff to prevent water standing around the tree. Internal drainage is the ability for water to percolate downward through the soil to avoid saturation of the root zone.

 

The presence of vigorous, healthy landscape trees is a good indication that the soil is sufficiently deep and well-drained for citrus trees. Should uncertainty about internal drainage exist, dig a posthole 1 to 2 meters  deep and fill it with water. All water should drain from the hole within 24 to 36 hours. Soils requiring more than 48 hours to drain completely should be avoided unless raised planting beds are used.

 

Most citrus grows well in a soil pH range from 6 to 8. Avoid soils that have a high or are excessively salty, as citrus trees will not grow well in such soils.

 

Selection and planting

Planting depth is of importance to the growth of citrus trees. The rootstock is somewhat resistant to foot rot disease, but the top is quite susceptible. If the bud union is too low with respect to surrounding ground, the tree could contract foot rot and die. The practice of scooping out grass and soil to form a large depression for ease of watering almost guarantees the death of a citrus tree. Mixing topsoil, compost, peat or other materials with the backfill soil is unnecessary in good citrus soils. Set the tree in the hole, backfill about halfway, then water sufficiently to wet the backfill and settle it around the roots. Finish filling the hole and tamp the soil lightly into place. Cover the root ball with 3-5 centimeters of soil to seal the growing medium from direct contact with the air and prevent rapid drying of the root ball. Build a watering ring atop the ground around the tree, about 12 to 20 centimeters high and 15-20 centimeters thick. The ring should be slightly wider than the planting hole.

 

Young tree care

Watering should be done two to three times the first week and one to two times per week for the next few weeks, depending upon soil type, rainfall and time of year. Then, apply water when the soil begins to get dry from 5 cm or so down. Simply fill the water ring each time. The watering ring should erode away over time (4 to 6 months), at which time the tree can be considered established and watered as needed by soaker hose or sprinkler system.

 

Nutrition

Do not apply fertilizer until the tree begins new growth after planting. Fertilize monthly through October. Scatter fertilizer on the ground at least a foot from the tree trunk and promptly water it in thoroughly. Nitrogen is usually the only fertilizer element required in most South African soils, but additional elements should not do any harm.

 

The soil must provide 13 nutrient elements essential to all plant growth. Clay soils usually contain plenty of iron, but citrus trees may exhibit iron deficiency in the early spring. Usually, the deficiency clears up as the soil warms up. If it does not, soil application of iron chelates is necessary. Where iron deficiency does occur, do not use fertilizers which contain phosphorous because high phosphorous aggravates iron and zinc deficiency in high pH (alkaline) soils. Red, sandy soils may need supplemental potassium and sandy soils in general may need additional zinc.

 

Mature, bearing citrus trees should receive enough nitrogen to provide for good but not excessive growth. If the percentage of nitrogen in the fertilizer is less than 15 percent The fertilizer may be applied at one time for the year, usually in February, or it may be split into two or three applications. Two applications are recommended, with two-thirds of the fertilizer applied in February and the balance in September. However, equal applications in February, May and September are just as effective.

 

The most expedient application is to spread the fertilizer uniformly on the soil surface under the tree canopy and slightly beyond and water it in thoroughly. It is not necessary to drill holes in the soil for fertilizer as a thorough watering will carry surface-applied fertilizer throughout the soil profile.
 

Weed control

Good weed control is essential for rapid establishment and vigorous growth of young citrus trees. Eliminate weeds for several meters around the tree. As the spread of the tree increases, widen the grass-free area beyond the drip-line.  Control weeds and grass beneath citrus trees to reduce competition for fertilizer and water. Also, weeds and grass may harbor pests which can affect the fruit or trees. It is easier to control weeds or grass than to mow under citrus trees and perhaps cause bark or fruit damage from lawnmowers.

 

Weed control can be accomplished by mechanical means such as hoeing. Organic mulches are not recommended for citrus trees because of the potential for inducing foot rot disease. If mulches are used, keep at least 30 centimeters of bare ground between the tree trunk and the mulch. Herbicides such as Roundup(TM) and Kleenup(TM) are excellent for control of existing weeds and pre-emergent herbicides may be used to prevent weed seeds from germinating.

 

Mulches are commonly used to conserve moisture and control weeds and grass. Because of the incidence of foot rot disease in citrus, organic mulches are not recommended. If used, keep mulches at least a foot away from the tree trunk. Citrus trees are pruned primarily to control tree size and to remove dead, diseased or damaged wood. Citrus trees should be allowed to grow naturally without pruning.

 

Cold protection

Wraps are used on the trunk of young citrus in the belief that they will provide significant cold protection. With one exception, none provide more than a few degrees of protection to a young tree trunk. The wraps do prevent rodent damage and sprouts on the trunk, but they also may harbor insects, particularly ants, which can cause problems. The best cold protection possible for young citrus is a soil bank, which can be used for the first two to four winters.

 

A soil bank is a mound of soil piled as high as feasible around the trunk and lower scaffold limbs. Thus, the trunk and lower scaffolds will be protected from even the worst freeze, although the unprotected top may be killed completely. The tree will regrow from the trunk and scaffolds without going back to the rootstock.  Before banking, treat the bark to be covered with a suitable insecticide and a copper-based fungicide to preclude problems while the bank is up. Exercise extreme care in removing the banks to prevent damaging the bark, as it will be quite tender from spending the winter underground.

 

Pests  and diseases control

Citrus pests in South Africa include insects, mites and diseases which may affect the health and vigor of the trees or the appearance of the fruit. Few pests actually kill citrus trees, but those that do are noteworthy because prevention is the only control.

 

Tristeza is a virus disease that kills citrus trees quickly, particularly those growing on sour orange rootstock.

 

Foot rot is a fungal disease present in many South African soils. Both sour orange and trifoliate orange rootstocks have some resistance to the disease, so it is not a problem unless the tree is planted too low and the bud union is exposed to soil or standing water.

 

Monitor and control outbreaks of pests or diseases which affect tree vigor, as reduced vigor results in reduced production. Aphids, mites, scales and whiteflies are good examples. Mites, particularly the citrus rust mite, can badly blemish the rind. However, rind appearance does not adversely affect eating quality of the fruit.

 

Productivity and maturity

Most budded citrus trees can produce a few fruit in the second year after planting, but usually do not produce until the third year. Thereafter, production increases annually as tree size increases. Seedling trees may not bear for several years.

 

There usually are four or five flushes of new growth on a citrus tree each year. Each flush is capable of producing flowers and setting fruit, but most citrus rarely produces any flowers or fruit after the spring growth flush. The exceptions are lemons and limes which can flower and set almost year-round, as do kumquats and calamondin. Offbloom (i.e., non-spring flush) fruit of oranges, tangelos, grapefruit and others are puffy, having a very thick peel, and sheepnosed in shape. Rarely is juice quality comparable to normal.

 

Typical citrus trees go through three distinct periods of fruit drop. First is the drop of about 70 to 80 percent of the flowers during and immediately following bloom. The second drop occurs a couple of weeks later, involving small fruit of pea-size to marble-size.