Blueberry
Vaccinium asher
Florida's winter season is short and mild with intermittent periods of warm temperatures. Most deciduous fruit cultivars have too great a chilling requirement to grow well in Florida. That is, they require more exposure to cool temperatures during the winter than they are likely to experience in Florida. With insufficient chilling, plants do not flower and leaf out satisfactorily during the spring. Growth can be weak and erratic. However, low-chill cultivars of some deciduous fruits, including blueberry, have been developed by plant breeders at the University of Florida and elsewhere. These cultivars were developed specifically for regions with mild winter temperatures such as in north and central Florida.
Two types of blueberries grow well in Florida, rabbiteye (Vaccinium ashei) and southern highbush (interspecific hybrids of V. darrowi, V. ashei and V. corymbosum). However, only the low-chill cultivars of each are adapted to Florida. Generally, rabbiteye blueberries grow well in areas of Florida that have winters as cold, or colder, than Ocala. The southern highbush cultivars that are commonly grown in Florida are well adapted to areas south of Ocala and north of Sebring, although they will grow reasonably well in Alachua County. The southern limits of southern highbush adaptation in Florida have not been fully determined.
Site Requirements
Both rabbiteye and southern highbush thrive on acid soils which contain more organic matter than is usually found in Florida's soils. If mulched, rabbiteye blueberries will usually grow satisfactorily on soils with 1% organic matter, but they do better with 2-3% organic-matter soils. Southern highbush blueberries are not recommended for soils with less than 3% organic matter and usually require mulching for optimum growth. Organic matter can be added to soils by incorporating peat moss prior to planting. Also, pine bark mulch will eventually decompose and add to the soil organic matter. Where blueberry plants have been heavily mulched for several years, it is not uncommon to observe most of the fibrous roots growing in the decomposed litter above the natural soil.
Blueberries require a soil pH of 4.0 to 5.5. At higher soil pH values, tissue levels of micro-elements such as iron and zinc become deficient. Deficiency symptoms develop on new growth and plants lose vigor. Soil can be acidified by thoroughly mixing a small amount of granulated sulfur into the soil several months before planting. Many fertilizers are acid-forming and will gradually lower the soil pH. A soil test is needed to determine the soil pH and whether or not acidification of the soil is necessary.
Blueberries require a well-drained soil profile of at least 18 inches in depth. Where water stands within 18 inches of the soil surface for prolonged periods during the rainy season, blueberries should be planted on raised beds. If blueberry roots are exposed to water-saturated soil for more than a few days damage from Phytophthora root rot may become severe. Generally, blueberries will grow well where azaleas, camellias and other "acid loving" plants are proven performers.
Planting and Establishment
The best time to plant blueberries is from mid-December to mid-February. Either bare-root or container-grown plants can be used. Plants about 2 feet tall with well developed root systems that are not pot-bound are best. Keep the roots of bare-rooted plants moist but not wet prior to and during planting. The root balls of potted plants should be broken up slightly and the roots of bare-rooted plants should be spread out evenly in the planting hole. In most situations, dooryard blueberry plants benefit from the incorporation of 1/4 to 1/2 cubic foot of acid sphagnum peat moss into the planting hole. Dig the hole large enough to accommodate the roots and peat moss. The plants should be set at the same height as they grew in the nursery. If blueberries are planted on raised beds, flatten the bed in the vicinity of the plants and set the plant in a slight depression so that irrigation and rain water will not flow away from the plant.
Pine bark mulch aids in the establishment of young blueberry plants. A layer of pine bark 3 inches deep extending about 2 feet out from the plants in all directions, or a pine bark strip about 4 feet wide extending down the row will provide a good substrate for surface feeder roots. Mulch also moderates soil temperatures, aids in weed control, provides protection from mechanical injury and adds organic matter to the soil. Weed control is extremely important for young plant establishment because blueberries are shallow-rooted plants that compete poorly with weeds for water and nutrients.
Blueberries should be pruned at the time of planting. If plants have a well-developed root system and irrigation is used, pruning should not be severe. Select the tallest, strongest cane and leave it unpruned. Remove the weak, "twiggy" growth at the base of the plant. If the plant has a large top compared with the root system, remove all the stems and canes except for the strong, dominant, cane and prune it back to half of its original height. During the first growing season, remove all flowers before fruit set occurs. This will prevent fruiting during the first year and promote strong vegetative growth and good plant establishment. This is especially important with some southern highbush cultivars that flower heavily as young plants.
Plant in a sunny area away from the roots of trees except pines, and at least 20 feet away from any building foundation.
A mature rabbiteye blueberry plant can reach 12-15 ft in height with canes sprouting over an area 8-10 feet in diameter. Southern highbush plants tend to be less vigorous and smaller than rabbiteyes. Plant size can be controlled to some degree by pruning. However, severe pruning will reduce yields the following spring. Allow at least a 7' x 7' area for rabbiteyes and a 4' x 4' area for southern highbush. Plants may be set 3 feet apart (southern highbush) or 5 feet apart (rabbiteye) for a hedgerow effect.
