Right time to use Blueberry Fertilizer: Blueberries are one of the simplest fruits for home gardeners to cultivate. They are low-maintenance, have minimal pest issues, don’t require much space, and can provide berries for years. Blueberry plants are also very cold-hardy and have an uncomplicated care routine. In a previous article, I discussed blueberry pruning and received numerous questions about fertilizing. This guide will cover the best fertilizers for blueberries, the ideal timing for application, and the correct amounts to use.
Optimal Conditions for Growing Blueberries
Before diving into the specifics of blueberry fertilization, it’s crucial to highlight the importance of placing your blueberry bushes in the right conditions for optimal growth and yield. When your plants are positioned correctly and receive adequate sunlight and water, the reliance on fertilization becomes less critical. More importantly, even the best fertilization practices won’t compensate for poor growing conditions; without the right environment, your blueberry plants won’t reach their full potential.
Here’s a brief overview of the ideal conditions for growing blueberries:
- Position your blueberry plants in full sun, ensuring they receive at least 8 hours of sunlight each day.
- To achieve the best fruit production, grow at least two different blueberry varieties. Most blueberries are not self-pollinating, so their flowers need pollen from a different variety to produce high-quality fruit. If you only have one variety, your fruit yield will likely be minimal.
- Blueberries are native to areas with nutrient-poor, acidic soils, so achieving the right soil pH is crucial for their health and productivity. If the soil pH isn’t optimal, blueberries cannot properly absorb essential nutrients, even if you fertilize them correctly. Aim for a soil pH level between 4.5 and 5.1 for optimal growth. For guidance on testing and adjusting soil pH, refer to this article.
- Blueberry roots are sensitive to poorly-drained soils, so avoid planting them in low-lying, boggy areas.
- They thrive in soils rich in organic matter. Before planting, enrich the soil with composted leaves, compost, well-rotted manure, or other organic materials to provide the ideal growing conditions.
Best Times to Apply Fertilizer for Blueberries
Blueberries have modest nutrient requirements and are quite sensitive to over-fertilization. Excessive nutrients in the soil can lead to issues, so it’s important not to over-fertilize. Most nutrition-related issues can be avoided by ensuring your soil pH is correct. Blueberries thrive in acidic soils, similar to azaleas and rhododendrons. Therefore, testing your soil pH before applying any fertilizer is essential. This process is both inexpensive and straightforward. You can use a simple home test or purchase a soil test kit from your local agricultural extension service or government agricultural agency.
You should plan to retest the soil pH around your blueberry plants every 4 to 5 years. This testing will not only reveal your current soil pH but also recommend suitable fertilizer types and quantities for the upcoming growing season. The guidance provided in this article will assist you in managing blueberry fertilizer needs during the intervals between soil tests.
As highlighted, maintaining the correct soil pH is crucial for effective blueberry fertilization. Soil pH is fundamental because it influences the availability of nearly all the nutrients in the soil. Depending on the pH level, some nutrients may become locked up and inaccessible to the plant, while others remain readily available for uptake.
Symptoms of Nutrient Deficiency
The most noticeable indicator that the soil under your blueberry plants may not have the optimal pH level is the appearance of nutrient deficiency symptoms. For blueberries, a common sign is chlorosis in the leaves. This condition, known as “interveinal chlorosis,” causes the area between the leaf veins to turn yellow or pale green while the veins themselves remain a vibrant green. In addition to leaf discoloration, you might also observe poor plant growth and reduced yields, which can signal issues with soil pH and nutrient availability. Healthy new growth should appear lush and green, rather than showing red or yellow hues.
Effective Fertilizers for Blueberry Cultivation
There are three main types of fertilizers for blueberries. The first type is designed specifically to lower the soil pH to the optimal level. The second type focuses solely on providing essential nutrients without affecting the soil’s acidity. The third type is a dual-purpose fertilizer that both acidifies the soil and supplies necessary nutrients. Let’s explore each of these options in detail.
1. Fertilizers for Acidifying Soil
When your soil pH is too high and needs to be lowered, but the nutrient levels are already sufficient, you should use products designed specifically for acidification.
Ammonium sulfate is a popular choice for maintaining an acidic soil pH. The amount to apply initially depends on your soil’s current acidity, but generally, 2 to 4 ounces per bush per year is enough to keep the pH within the ideal range of 4.5 to 5.1. However, I prefer to avoid ammonium sulfate. It’s easy to apply too much, and since it’s a synthetic fertilizer, it’s not suitable for organic farming practices.
Elemental sulfur
Elemental sulfur is my preferred choice for acidifying soil for blueberries. This fertilizer works slowly, allowing time for soil microbes to break it down and adjust the pH effectively. Compared to ammonium sulfate, elemental sulfur poses a lower risk of root damage or over-application. Additionally, it is approved for use in organic farming by the USDA’s National Organic Standards Program.
In Pennsylvania, where the soil is naturally acidic (pH 5.8 to 5.2), I apply about 1 cup of elemental sulfur to each of my blueberry bushes every one to two years to maintain the ideal pH. The amount of sulfur you need may vary depending on your initial soil pH, so it’s best to refer to your soil test results for precise guidance. Re-testing your soil every 4-5 years will provide an accurate assessment. I prefer using Jobe’s Organics Soil Acidifier and Espoma Organic Soil Acidifier, both of which have recommended application rates on their labels.
Over time, soils that have been acidified will gradually return to their original pH levels, regardless of the product used. Therefore, you will need to reapply sulfur or another soil acidifier every one to two years to maintain the desired acidity.
2. Blueberry Fertilizer for Nutrient Addition
If your soil pH is already within the ideal range but your soil test indicates nutrient deficiencies, you’ll need to focus solely on providing the necessary nutrients without affecting the pH. Young blueberry plants are sensitive to fertilizers high in nitrogen and can be damaged by synthetic fertilizers with high salt content. Avoid products containing nitrates or chlorides. Blueberries benefit from nitrogen in a slow-release form. Organic granular fertilizers that include nitrogen (N), phosphorus (P), potassium (K), and essential micronutrients are excellent choices. While urea is often suggested as a nitrogen source, it is not suitable for organic farming due to its synthetic nature.
Phosphorus is less accessible to plants in acidic soils, but blueberries need a significant amount for optimal fruit production. Additionally, blueberries have shallow, fibrous root systems that make it challenging for them to absorb all necessary nutrients. To address this, blueberries form a symbiotic relationship with specific mycorrhizal fungi in the soil that aids in nutrient absorption. Synthetic chemical fertilizers can damage these beneficial fungi, so it’s best to avoid them. If your blueberry bushes are lacking phosphorus, you may notice that their leaves take on a darker, purplish-green hue.
To provide sufficient nitrogen, phosphorus, potassium, and essential micronutrients (including zinc, calcium, manganese, magnesium, and copper) to your blueberries, use a balanced organic granular fertilizer. These fertilizers are typically made from natural ingredients such as blood meal, seaweed, bone meal, and potash. For 2- and 3-year-old blueberry plants, apply ¼ to ½ cup of fertilizer per plant annually. For mature blueberry bushes, use 2 to 3 cups per bush per year to ensure they receive the necessary nutrients.
3. Fertilizers for Blueberries That Both Acidify Soil and Provide Nutrients
From my experience, the best blueberry fertilizers are those that both acidify the soil and provide essential nutrients. Fertilizers designed for acid-loving plants, such as rhododendrons, azaleas, and hollies, are particularly effective. One of my preferred brands is Holly-tone. It stands out because it releases nutrients slowly over time, supports beneficial soil microbes, and includes a balanced mix of nitrogen, potassium, phosphorus, calcium, and magnesium. Additionally, it contains elemental sulfur, which helps maintain the acidic soil pH. Holly-tone is made from natural ingredients like feather meal, poultry manure, and alfalfa meal. If you choose this fertilizer, there’s usually no need to apply separate sulfur unless your soil pH is extremely alkaline.
Best Times to Fertilize Blueberries
Whether you’re fertilizing to adjust the soil pH, add nutrients, or both, you can apply blueberry fertilizer either in the spring or fall. Alternatively, you can divide the application, using half in the spring and the other half in the fall.
When fertilizing blueberries in the spring, apply the fertilizer before the buds start to swell. If you miss this window, it’s not a major issue, as organic fertilizers and elemental sulfur need time to be processed by soil microbes. Remember, it’s a gradual process rather than a quick fix. If you prefer to fertilize in the fall, do so about four weeks before the first expected frost. With a slow-release, organic fertilizer that is gentle on roots, timing is less critical. Consistency is key: fertilize annually or biennially and check your soil pH every 4 to 5 years.
Best Practices for Fertilizing Blueberries
No matter which product you choose for your blueberry bushes, apply it around the base of the plants, reaching out to the edge of the bush’s leaf canopy. Keep in mind that blueberry roots are shallow and fibrous, not deep. Avoid piling the fertilizer in one spot at the base. Instead, spread it evenly by hand or with a container. While the granules don’t need to be perfectly uniform, aim to distribute them as evenly as possible.
When applying blueberry fertilizer, I either pour it directly from the measuring cup or hold a handful in my partially closed hand, shaking my hand side to side to let the granules fall evenly onto the soil. The process is quick and should only take a few seconds—it’s a straightforward task that doesn’t require much time.
Should You Incorporate Blueberry Fertilizer into the Soil?
Due to the shallow nature of blueberry roots, avoid turning, tilling, or deeply cultivating the soil after applying fertilizer. These actions can damage the roots and disrupt the delicate mycorrhizal fungal network associated with them. If necessary, you can lightly scratch the fertilizer into the top inch of soil using a pronged cultivator or your fingers, but this step is not crucial. Over time, with the help of microbes and water, the fertilizer will naturally permeate the soil and reach the root zone without additional assistance. Attempting to help it along could end up causing more harm than good.
How to Use Mulch After Fertilizing Blueberry Plants
Mulching helps protect blueberry plant roots, maintain consistent soil temperatures, and suppress weeds. However, due to their shallow root systems, it’s important not to overdo the mulch, as too much can suffocate the roots. A layer of one to two inches of pine straw, wood chips, or shredded leaves is sufficient. You can either apply the mulch on top of the fertilizer or place the fertilizer directly on the mulch. Both methods work effectively.