Blueberries

History

Blueberries are a member of the Ericaceae family, also known as the heath family, which also includes cranberries and huckleberries along with thousands of other flowering plants like rhododendron, azalea, and heather (see Figure 1). Characteristics of this plant family often include tolerance to acidic soils, and flowers that produce a berry.

Blueberry is a deciduous shrub and one of the few fruit crops native to North America, existing in the wild for thousands of years. Blueberries were commonly harvested, dried, and stored by Native Americans, and the entire plant was said to be used for medicinal purposes. European colonists learned how to grow and care for blueberry plants from the Native Americans, but domesticated blueberries have only been grown since the early 1900s. Frank Coville, a botanist for the U.S. Department of Agriculture, researched and experimented with native blueberry species and developed gardening recommendations and modern varieties.

Blueberries gained national attention in the late 1990s, leading to greatly increased production, after being identified as a “superfood” due the presence of vitamins, anthocyanins (which give the blue color) and other phytochemicals, and their many health benefits. If the right planting site and variety are selected, blueberries grow very well in the South and are a popular summer berry.

Varieties

There are primarily three types of blueberries grown in the U.S.: (1) Rabbiteye, (2) Southern Highbush, and (3) Northern Highbush. Blueberry varieties are grouped by the timing of fruit production: (1) early season, (2) mid-season, or (3) late season. Blueberries require at least two different varieties of the same type (Rabbiteye, Southern Highbush, or Northern Highbush) for adequate pollination to occur and fruit to set. Bloom times of two or more varieties should occur during the same season (early, mid, or late) or must overlap for proper pollination. Early and mid-season varieties will overlap, as will mid- and late-season varieties. Cross-pollination also improves fruit-set, size, and earliness of ripening. For a longer harvest season, it is recommended to plant varieties that bloom in each season (early, mid, and late).

Rabbiteye blueberries, named as such because berries ripen from pink to blue (resembling a rabbit’s eye), are grown throughout the southeastern U.S. and southern California. Rabbiteyes are recommended for Louisiana as they are well suited to the climate of Gulf Coast states, have little to no insect pest pressure, and have the lowest chilling requirement for flowering and fruit production (300-700 hours).

Southern Highbush blueberries are increasing in production in Louisiana. This type of blueberry requires more exact growing conditions than Rabbiteyes and is considered higher maintenance, less vigorous, and more susceptible to pests. The advantage to Southern Highbush blueberries is that the earliest varieties ripen at least 2 weeks earlier than early season Rabbiteye varieties, but have the same average chilling requirements. With extra care and following recommended growing practices, Southern Highbush blueberries are also recommended for Gulf Coast production.

Northern Highbush blueberries are grown in Michigan, eastward to Maine, and as far south as North Carolina, as well as in Washington and Oregon. Northern Highbush varieties require a longer winter chilling period and cannot tolerate hot summer temperatures; therefore, this type is not recommended for Louisiana.

Chilling requirement, as measured in chill hours, is the number of hours below 45 degrees F that the blueberry plant must receive each winter in order to bloom and produce fruit. This is an essential period of dormancy or rest for the plant before resuming fruit production. Be sure to select varieties with annual chill hours that match what the growing area typically receives. Varieties with similar chill hour requirements will have the most bloom overlap for adequate pollination.

See the recommended Rabbiteye and Southern Highbush blueberry varieties for Louisiana in Table 1.

Table 1. Blueberry Varieties for Louisiana

When and How to Plant

Blueberry plants are perennial shrubs that produce fruit during the warm season. It is recommended to start with a containerized blueberry plant that is 12-36 inches tall or about 2 years old in 1-gallon or larger containers. Obtain healthy plants from a reputable nursery. Water the plants when you get them and keep them moist until planting; do not let them dry out. When transplanting containerized plants, make sure the plants are not root bound. If the roots have reached the edge of the pot and are starting to circle around the edge, they may continue to grow in a circular pattern around the root ball in this pattern after planting. To encourage root growth into the surrounding soil, slightly break up the root ball with your fingers or use a knife to make a few vertical slashes when planting. This will reorient the roots and encourage growth out into the soil from the planting hole.

Bare root plants may also be used with good success in the dormant season. It is recommended to plant bare root plants immediately. Water the plants when you get them and keep them moist until planting; do not let them dry out. Bare root plants should be handled with care as the roots are more vulnerable and have less volume than containerized plants.

Refer to the Blueberry Planting Guide (Table 2) for the recommended dates to transplant these young blueberry plants outside. Planting blueberry plants during the dormant fall and winter seasons gives the plant more time to establish roots before spring arrives and new growth resumes.

At the recommended spacing, dig a hole that is deep enough so blueberry plants can be set into the soil at the same depth they were growing in the container (avoid planting too deep), with the roots positioned straight down into the soil (not bent) and wide enough that the roots are not crowded (see Figure 2). Fill in around the plant with the native soil from the hole, firm the soil around the plant, and thoroughly water. Prune some of the low, small stem growth and remove any flower buds so the plant will focus on root growth rather than fruit production. Here is a helpful video showing how to plant containerized blueberry plants.

After transplanting, it is recommended to cover the bed with a thick layer (3-6 inches) of organic mulch extending 3-5 feet around each bush. Avoid piling mulch around plant stems. Blueberry plants generally flower from February to March with the berries ripening from green, to red, to blue in April through August (depending on variety). Blueberry plants will live for at least 10-15 years with good management.

Table 2. BLUEBERRY PLANTING GUIDE

Where to Plant

Blueberries prefer moist, well-drained, sandy soils and full sun (minimum 6 hours/day). They don’t tolerate excessive moisture but some varieties will tolerate partial shade. Site selection is critical to the success of blueberry planting. Blueberry plants prefer an acidic soil with a pH between 4.2 and 5.5. Soils with a pH above 5.5 should be avoided for blueberry plants as they will not adapt well.

It is recommended to plant blueberries in 3-4 feet wide, traditional raised garden rows that are 8-12 inches tall to ensure good drainage for the shallow root system and prevent disease. An alternative is to plant in a large container (20 gallons or greater). For initial soil preparation, it is recommended to add a 3-4-inch layer of compost, peat moss, rotted hay, or other organic matter and mix into the soil to optimize plant health.

Southern Highbush types require soils with high organic matter or soils with high volumes of pine bark added and replenished annually to avoid root exposure. Peat moss is also commonly used to increase organic matter in blueberry plantings. Southern Highbush blueberries are heavier nutrient feeders and may also require a balanced slow-release fertilizer with minor elements.

Bird netting is recommended to protect blueberries, if they are a pest.

Plant Care

Watering

Blueberries have a shallow, fibrous root system that develops near the soil surface, so frequent watering is required to develop a healthy plant. The critical periods for watering are when plants are young, and during flower bud formation in the fall. Drip irrigation is very helpful to ensure consistent, adequate water for the long production season. On average, plants that are 1 year old require about 3.5 gallons of water per week. Each year of growth doubles the weekly water demand (e.g., plants 2 years old require about 7 gallons of water per week), up to a maximum of 35 gallons of water per week. Deep weekly watering is recommended over daily watering.

Fertilization

Blueberries require only light fertilization and are highly sensitive to over-fertilization. Begin fertilizing the year after planting.

Organic fertilizers such as compost, fish emulsion, composted poultry litter or manure, worm castings, and blood or bone meal originate from living organisms. They are far more environmentally sustainable and safe than traditional synthetic fertilizers. They naturally release nutrients more slowly and over a longer period of time. When applying organic fertilizer, it is important to use in unison with compost, cover crops, and crop rotation, which all work together to build soil health. Learn how to convert inorganic fertilizer recommendations to organic fertilizers here.

Cottonseed meal (6-2-2) is an excellent source of organic nitrogen for blueberries. Rake away mulch and sprinkle a single handful over young plant root systems the first year.  Add a little more every year until you reach one cup for mature blueberry bushes (6-7 years old). Reapply mulch.

Alternatively, use a specialty fertilizer designed for acid-loving plants, like azalea/camellia fertilizer (10-8-6). Broadcast the fertilizer over the bed on top of the mulch in early spring before plants begin actively growing. Apply 2 ounces (1/4 cup) the year after planting. Every year add another ounce per bush (i.e., 3 ounces at 3 years, 4 ounces at 4 years). When plants reach 6 years of age and 6 feet tall, they should top out at 7 ounces per plant and receive 7 ounces every year thereafter. Always water well after fertilizer application.

Weeds

Organic mulch will control most of the weeds; hand-pull weeds close to the plant and reapply mulch as need. It is important to keep a 3-foot weed-free area around each bush to prevent competition for nutrients and moisture, as blueberry roots only extend 8-10 inches from the base of the bush.

Pruning

The general purpose of pruning is to maintain and control plant size and to encourage wood renewal. After the initial pruning during the transplanting process, Rabbiteye blueberry plants don’t need another round of pruning until they reach about 6 feet tall — although low, spreading branches near the ground should be removed as the plant grows. As Rabbiteye blueberry plants reach the 5th or 6th year, older wood in the center should be pruned out to encourage new growth and redirect energy to more vigorous canes (or main branches). As a general recommendation, remove 10-20% of the canes, cutting back to just above the soil level, leaving a maximum of 8-10 strong canes per plant (see Figure 3). This allows for regeneration of the plant in 5 to 7 years. The removal of old canes will improve productivity and fruit size and decrease disease risk. Any canes that are much longer than the others can also be trimmed back a little. Here is a helpful video showing the annual pruning process. Rabbiteye blueberry plants should be pruned immediately after harvest and no later than early August. This allows the plant time after pruning to produce mature wood and develop flower buds for berries next spring.

Southern Highbush blueberries are pruned differently than Rabbiteyes. They are similar in that the plants require little pruning the first few years, but after 3 years, Southern Highland bushes need to be heavily pruned after fruiting in the spring. Removing canes 12-18 inches above the soil is recommended. The remaining plant will produce multiple short branches, which will regenerate new shoots that will be the fruiting wood for next season. This also reduces potential damage from high winds. In following years, trim back the canes less severely to force additional new growth. Like the Rabbiteyes, Southern Highbush blueberries also require renewal pruning — the removal of old canes — beginning around the 5th or 6th year.

Insect Pests and Diseases

Blueberry plants are generally low maintenance and are not vulnerable to many pests and diseases. The key blueberry pests are birds. Insect pests include blueberry gall midges, fruitworms, beetles, stink bugs, stem borers, and flower thrips. Blueberry plants are susceptible to some foliar (leaf) and fungal diseases (e.g., anthracnose, fruit and leaf spot, and mummy berry). Prevention and regular monitoring can help identify symptoms of these problems to allow for early diagnosis and management. Generally, recommended tools for disease prevention are using mulch; avoiding overhead irrigation; adequate plant spacing; and weed control. See Table 3 to aid in diagnosis and management of some common blueberry insect pests and diseases.

Table 3. Organic and Natural Management for Common Blueberry Insect Pests and Diseases

Harvest and Storage

In general, Rabbiteye blueberries are ready for harvest between mid-May and July, and Southern Highbush blueberries begin ripening in April and continue into June. Harvest when the fruit has turned a uniform blue color; maximum flavor and size are achieved 5 to 7 days after the fruits begin to turn blue. To harvest blueberries without damaging the plant, gently pull the fruit off the stems by hand or roll the ripe fruit into your hand. During fruit production, blueberries may be harvested every 5-7 days for 3-6 weeks per variety. Take extra care when harvesting and storing as the fruits are very tender and bruise easily. Handling removes the bloom or surface wax that gives blueberries their characteristic frosty blue color. Do not wash fruit until ready to eat as this will initiate molding.

Blueberries are highly perishable and fruit should be cooled as soon as possible. Fruit should be placed in pint-sized plastic mesh baskets or clamshell containers and stored at 32-34 degrees F (95% humidity). They should be consumed within 10-14 days.

Preserve blueberries by freezing whole or canning into jellies and jams.

Blueberries are Nutritious and Good for You

Rich in Vitamin C

Important for bones, skin, blood vessels

Good source of dietary fiber

Important for bowel health, lowering cholesterol, controlling blood sugar, and maintaining a healthy weight

Excellent source of Vitamin K

Helps your body heal and is important for bone health

Recipes

Louisiana Harvest of the Month: Blueberry Sauce

Common methods of preparing blueberries

Guide to freezing and canning blueberries

Taste-testing ideas: blueberry muffins, blueberry coffee cake, blueberry smoothie, oatmeal with blueberries, blueberry yogurt popsicles, blueberry pancakes, blueberry parfait, blueberry crepes

Other websites with many blueberry recipes:

USDA MyPlate Kitchen

Produce for Better Health Foundation

SNAP-Ed San Francisco

SNAP-Ed Oregon

Sources

• LSU AgCenter, Home Blueberry Production in Louisiana
• LSU AgCenter, Commercial Crop Production, Small Fruits: Blueberry
• LSU AgCenter, The Louisiana Home Orchard
• LSU AgCenter, Horticulture Hints for Northeast Louisiana
• LSU AgCenter, Louisiana Home Fruit and Nut Production: Rabbiteye Blueberries
• LSU AgCenter, Louisiana Super Plants: Rabbiteye Blueberries
• Mississippi State University Extension, Fruit and Nut Review: Blueberries
• Mississippi State University Extension, Establishment and Maintenance of Blueberries
• Texas A&M University, Rabbiteye Blueberries
• University of Georgia Extension, Home Garden Blueberries
• UMass Extension Vegetable Program: Disease, Insect, and Mites Fact Sheets
• Alabama A&M & Auburn Universities Extension, Crop Production
• University of Connecticut, Integrated Pest Management System, Blueberry Disease Management
• Southern Region Small Fruit Consortium, Southeast Regional Organic Blueberry Pest Management Guide
• Purdue Extension FoodLink: Blueberry
• Illinois Extension, History of the Blueberry
• University of Georgia Extension, How to Convert an Inorganic Fertilizer Recommendation to an Organic One, Circular 853