Blueberry bushes offer delicious fruit and attractive foliage but have unique nutritional requirements. Successful fertilization requires precise timing and specific product selection. Due to the blueberry’s shallow, fibrous root system and strong preference for acidic soil, a thoughtful fertilization strategy is necessary for a bountiful harvest.
Preparing the Soil for Successful Fertilization
The foundation for a healthy blueberry bush is a highly acidic soil environment. Blueberries thrive when the soil pH is maintained within a narrow range, typically between 4.5 and 5.5. This low pH is necessary for the plant to effectively absorb nutrients, such as iron and nitrogen, from the soil.
If the soil pH is too high, the blueberry bush will develop chlorosis, a yellowing of the leaves with green veins, indicating an iron deficiency. Before establishing an annual feeding schedule, test the soil to confirm the current pH level. For soils that are not naturally acidic, elemental sulfur can be incorporated to lower the pH, but this process is slow and should be done several months before planting. Incorporating organic matter like peat moss can also help lower the pH and improve soil structure.
Annual Fertilization Schedule for Established Bushes
The best time to fertilize established blueberry bushes is based on the plant’s active growth cycle. The first application should occur in early spring, just as the buds begin to swell and before the first leaves fully expand. This timing ensures nutrients are available at the start of the active growth phase.
A second, smaller application is recommended four to six weeks after the first to sustain the plant through fruit set and early development. Growers in areas with a long growing season may benefit from a third application immediately following the harvest. This post-harvest feeding helps the bush restore depleted energy reserves, promoting strong bud development for the following year.
Fertilization must stop by late summer or early fall, typically no later than mid-July to early August, depending on the climate. Applying fertilizer too late encourages tender, new growth that will not harden off before the first frost. This unhardened tissue is susceptible to winter injury. The goal in late summer is to allow the plant to naturally transition into dormancy.
Choosing the Right Fertilizer Type
Selecting the correct fertilizer type is as important as the timing, particularly regarding the form of nitrogen supplied. Blueberries prefer and efficiently utilize nitrogen in the ammonium form, rather than the nitrate form. Nitrogen sources like ammonium sulfate, urea, or sulfur-coated urea are excellent choices because they help maintain the low soil pH.
Gardeners must avoid fertilizers that contain nitrogen in the nitrate form, such as calcium nitrate, as this form can be toxic to blueberry plants and hinder their growth. Many specialized fertilizers formulated for acid-loving plants, like azaleas and rhododendrons, are suitable for blueberries because they contain the preferred nitrogen sources.
When examining the NPK ratio (Nitrogen, Phosphate, and Potash), a high nitrogen content is preferred. Blueberries require little additional phosphorus or potassium if the soil has been properly prepared and maintained. Ratios such as 12-4-8 or similar high-nitrogen, low-phosphorus blends are appropriate for established bushes.
Fertilizing Newly Planted Blueberry Bushes
Newly planted blueberry bushes require a different approach to fertilization than established plants. The primary consideration is preventing fertilizer burn, which can damage the delicate, shallow roots of a young plant. Experts advise delaying the first application until the plant has become established.
The first feeding should occur four to six weeks after planting, once the bush shows signs of new growth. This initial application must be very light, using only half the amount recommended for a mature plant. Spread the fertilizer in a small circle around the base, ensuring the granules do not contact the main stem or foliage.
The reduced quantity and delayed application help the young root system acclimate without being overwhelmed by concentrated salts. Subsequent light applications can be made every four to six weeks during the first growing season, but only through early summer. The goal in the first year is to encourage robust root development, with the dosage gradually increasing in subsequent years as the bush matures.