From the bud to harvest: the phases of the blueberries development
Blueberry plants are perennial, woody shrubs that take about 10 years to reach their full size, but with proper care, they can live over 50 years. In spring they begin to grow new shoots from the crown buds. During and after flowering, new shoots delevop, and flower and leaf buds form in late summer. The development of flower buds occurs from the tip of the shoots downward and is dependent on weather conditions. Effective pollinators are native bee species such as solitary bees and bumblebees.
The fruits ripen on stems that are two to eight years old, with five-year-old stems being the most productive. After pollination, the fruit color changes from green to reddish-violet to dark violet. A waxy coating protects the fruits from moisture loss and decay, while their flavor depends on the sugar-acid ratio. Blueberries have rhizomes and a shallow root system with two main types: thick, long-lasting roots for water and nutrient transport and finer, short-lived roots for nutrient absorption, often supported by mycorrhizal fungi. Root growth begins in spring and reaches two peaks: one in late spring to early summer for fruit production and one in late summer for nutrient storage. The roots spread mainly in the upper foot of the soil and can be influenced by irrigation methods and soil conditions. Drip irrigation is most commonly used, as it delivers water directly to the root zone, minimizing water loss to the atmosphere and preventing wetting of the fruit. However, locations requiring frost protection also need overhead irrigation capabilities. Optimal soil conditions are measured by pH values, which for blueberry growth should be between 4.5 and 5.0, although they can be as high as 5.2 in clay soils. In soils with higher pH, blueberries often struggle because they require specific nutrients that are more available in acidic soils. A common deficiency in blueberries is nitrogen, which they absorb in the ammonium form, while many other plants prefer the nitrate form. At a low pH, more nitrogen is available in the ammonium form. Therefore, it is important to keep the soil pH low. Suitable fertilizers are ammonium sulfate (21-0-0) or urea (46-0-0), which provide nitrogen in the ammonium form.
Blueberries can also suffer from magnesium and potassium deficiencies, especially in soils with high calcium content. These nutrients compete for exchange sites in the soil, leading to deficiency. To remedy magnesium deficiency, foliar sprays or soil applications with Epsom salt (magnesium sulfate) are helpful, though in larger amounts. For potassium deficiency, potassium sulfate or sulfo-magnesium can be used, especially when magnesium is also low.
The growth and development of blueberry plants are divided into several phases. Photosynthesis, in which the plant uses sunlight, water, and carbon dioxide to produce carbohydrates, is crucial for growth. Transpiration, the loss of water through the leaves, helps the plant cool itself and affects the water balance. Carbohydrates are transported from the “sources” such as leaves and roots to the “sinks” such as fruits and shoot tips, with a balanced supply being important for healthy growth and good fruit production.
The cold hardiness of blueberry plants varies depending on the variety. Northern varieties are more cold-resistant than southern ones. Excessive nitrogen fertilization can reduce cold hardiness and make the plant more susceptible to cold damage. Overall, these phases and factors are crucial for the growth, fruiting, and overall health of blueberry plants.
Blueberries form local species diversity depending on the location, adapting to the conditions. For example, several native blueberry species grow naturally in Maryland, USA. These wild plants should not be dug up, nor should cuttings be taken from them. For cultivation in gardens and commercial agriculture, there are three basic types:
Northern Highbush (Vaccinium corymbosum): This species is the most widespread and cold-resistant, reaching a height of three to six feet.
Southern Highbush hybrids (Vaccinium corymbosum X southern species): These hybrids can tolerate a variety of soil conditions and are both heat- and drought-tolerant. They break dormancy earlier than Northern Highbush varieties and should thrive in all regions except western Maryland. The plants reach a height of six to seven feet.
Rabbiteye (Vaccinium ashei): This southern species can be grown in southern Maryland and on the East Coast, reaching a height of six to twelve feet.
The most common blueberry species are the wild Lowbush blueberry (Vaccinium angustifolium), the cultivated Highbush blueberry (Vaccinium corymbosum), and the Rabbiteye blueberry (Vaccinium virgatum, syn. V. ashei). These species differ in their soil and climate requirements. The Lowbush blueberry is tolerant of a wide temperature range and is often found on abandoned pastures. Northern Highbush blueberries, on the other hand, are limited to colder climate regions, while Southern Highbush blueberries, which are interspecific hybrids of V. corymbosum, V. angustifolium, V. darrowii, V. ashei, V. tenellum, and other species, are better suited to warmer regions. The Rabbiteye blueberry, native to the southeastern United States, is more heat- and drought-tolerant than Lowbush and Highbush blueberries.
The University of Minnesota's fruit breeding program has developed several blueberry varieties that are particularly well-suited to the local climate in USDA Zones 3 and 4. These varieties have been extensively tested to ensure they can withstand the climatic conditions. It is recommended to plant at least two different varieties, as cross-pollination with pollen from another variety produces larger and more berries. Bumblebees and other native insects are efficient pollinators that can increase yield.
Here are some blueberry varieties suitable for Minnesota:
Blaukrop: This variety has good to fair winter hardiness and yields 3 to 12 pounds per bush. The berries are large and mild in flavor and ripen in mid-season.
Chippewa: With excellent to good winter hardiness, this variety yields 3 to 8 pounds per bush. The medium-sized, sky-blue berries are sweet and ripen in mid-season.
Northcountry: It has very good to fair winter hardiness and yields 3 to 5 pounds per bush. The small, sweet berries ripen early in the season.
Northblue: This variety offers excellent to good winter hardiness and produces 3 to 9 pounds per bush. The berries are large, dark blue, and firm, ripening in mid-season.
Patriot: This variety produces very large, tart berries with a yield of 3 to 12 pounds per bush and ripens early in the season.
Pink Popcorn: With very good to good winter hardiness, this variety yields 3 to 5 pounds per bush. The berries are medium-sized, cream-colored to pink, and ripen from early to mid-season. It is self-pollinating.
These varieties have been specially developed for the climatic conditions in Minnesota and offer a good combination of winter hardiness, high yield, and excellent taste. They are ideal for gardeners who want to grow blueberries successfully in colder regions.
For berry cultivation, polytunnels with plastic covers or bird and shading nets have become increasingly popular, helping protect against excessive radiation. Blueberries have specific requirements for soil, temperature, pH, and water quality. As a result, cultivation is increasingly shifting from open fields to hydroponic systems under covers. This method offers advantages such as better control over water and nutrients, improved root growth, and higher plant density. However, covers can also have disadvantages by reducing the transmissibility of photosynthetically active radiation (PAR) by 30-40%. This can decrease the photosynthesis rate and negatively impact yields and fruit quality. Additionally, covers with UV stabilizers or absorbers block UV radiation, which is important for enhancing the bioactive composition of the fruits. Blueberries grown under covers often show reduced flavonol content and lower antioxidant capacity compared to outdoor fruits. Even under colored photoselective nets, the berries grow larger but with lower anthocyanin values than in sunlight. A 90% shade from black nets has particularly strong negative effects on growth, ripening, and anthocyanin accumulation.
Light influences the growth, color, ripening, and quality, including its nutritional value through light quantity, quality, duration, and direction. Plants perceive light through various photoreceptors that regulate different aspects of their development. For photosynthesis, plants only use the range of 400 to 700 nm (PAR). UV radiation, especially UV-B, can promote flavonoid production and antioxidant properties in plants by triggering stress responses. Different light wavelengths affect the development and quality of fruits differently, depending on the plant. Optimal light intensity is also important, as too much or too little light can impair photosynthesis and plant productivity.
Plants adapt to environmental stresses such as temperature, water scarcity, salinity, and light intensity by utilizing antioxidant systems that include flavonoids and vitamins. Salt and water stress increase the concentration of secondary metabolites in fruits and improve their nutritional quality. Temperature stress, especially cold, often increases antioxidants.
Blueberry breeding focuses on fruit size, flavor, and stress resistance. Modern techniques such as marker-assisted selection and CRISPR/Cas9 accelerate breeding and allow improvements in fruit quality and antioxidant production.
Sources:
Krishna, P., Pandey, G., Thomas, R., & Parks, S. (2023). Improving Blueberry Fruit Nutritional Quality through Physiological and Genetic Interventions: A Review of Current Research and Future Directions. Source
Oregon State University. (2024). How blueberry develop and grow. Source
PennState Extension. (2023). Keys to Establishing a Successful Blueberry Planting. Source
University of Maryland Extension. (2024). Growing Blueberries in a Home Garden. Source
University of Minnesota Extension. (2024). Growning blueberries in the home garden. Source