How to Adjust Your Soil pH For Blueberries
If you grow blueberries on your homestead or plan to add some to your garden line-up, you’ll need to adjust your soil pH. Getting pH levels right will allow your plants to uptake the nutrients they need to thrive. Join organic farmer Jenna Rich as she discusses ways to adjust your pH, why it’s important, and when to start.
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They say the best time to plant a tree is ten years ago. Well, the best time to adjust your soil’s pH for blueberries is 3 to 12 months ago. Blueberries need the goldilocks of soil pH to perform at their best. They prefer acidity levels to sit between 4.5 and 5.5 in well-draining, loamy soil with organic matter between 4-7%. Creating the perfect environment is crucial so their fibrous, shallow roots can properly uptake nutrients.
Understanding soil pH can be confusing and overwhelming. If you take anything from this article, we highly recommend soil testing, especially when growing something with specific soil needs, like blueberries. Experts will help you interpret your results so you can have a great growing season.
When adding blueberries to a new plot, test the soil six months to a year in advance to prepare the plot. Let’s talk about what soil pH is and why it’s important. Then, we’ll jump into a few ways you can adjust your soil to appease your blueberry bushes.
What Is Soil pH?
Soil pH ranges from 0 to 14 and indicates acidity or alkalinity. Higher numbers indicate more alkalinity, and lower numbers indicate more acidity, with 7.0 being neutral. Soil pH level is often a second thought to the NPK and micronutrient levels when it should be top of mind. Appropriate pH for what you’re growing can make all the difference between a thriving garden and one that has you guessing all season.
When the pH levels are just right, your plants can take full advantage of all you do to provide the right amount of minerals, as well as macro and micronutrients. Why does pH matter? Growth will be healthy, yields will increase, fruits will be abundant, and disease risk will be reduced.
How To Test pH
We recommend an annual soil test performed by a university or your local extension office. The results will offer you a baseline of knowledge so you know how to treat your soil pre-season and throughout the year to ensure your crops have exactly what they need to thrive.
When growing crops like blueberries that prefer acidic soil, it’s best to have a good-quality pH meter to measure pH levels in real time. This is an inexpensive and easy way to get a pH read to adjust the soil as needed. Simply insert the probe into the soil and read the meter. In general, readings below 5.0 or above 7.2 will require swift action.
How Does pH Level Affect Blueberries?
Blueberry bushes growing in soil with a high pH (low acidity) may begin to show symptoms of chlorosis and stunted growth. This indicates the plant is struggling to uptake proper nutrients from the soil.
When blueberries are planted in neutral soils that most other crops will thrive in, they may fail to grow. It’s more difficult to adjust pH levels once plants are present.
How To Lower pH Levels
Before selecting a method of adjusting the pH, be familiar with your plot’s soil texture and type. Recommendations on application amount will differ based on its ability to convert and absorb. Lowering pH levels in clay soils is more difficult than in sandy soils. According to Michigan State University’s Extension, the CEC (Cation Exchange Capacity) given in your soil test results can be used to estimate the soil texture if it’s not outwardly stated.
High pH levels can lead to boron, phosphorus, zinc, and iron deficiencies. This can occur when plants are over-fertilized, experience poor drainage, or are fed calcium nitrate. Below are a few ways to lower soil pH levels.
Elemental (Soil) Sulfur
This is an inexpensive and easily accessible amendment that should be used if soil tests indicate that calcium deposits caused the increased pH level.
Elemental sulfur is converted to sulfate more quickly when the soil is warm (above 55°F or 13°C) and moist. This is when the soil bacteria that help speed along the process are most active. These helpful bacteria are inactive in late fall or winter, so many growers apply it in the spring. However, since this form of sulfur won’t leach away, feel free to apply it in the fall.
Ideally, apply your amendments a year before planting. This gives the sulfur time to incorporate and take effect, and you time to test several times before transplanting.
You can also apply a surface application around established plants. You can buy a soil acidifier online or from a local garden supply. It’s more difficult to incorporate into the soil, and its effects take longer. Irrigate regularly and consistently to help along the process. As organic matter in the soil is broken down by bacteria, sulfur may convert to hydrogen sulfide if oxygen levels are low. This is certainly the case if you smell a rotten egg stench. When this happens, the sulfur will not act as intended.
Follow the recommendations on your soil test and product packaging. Sulfur products break down, so you’ll need to add more over time to keep the soil from becoming too alkaline. Mix in organic matter like a well-aged compost to help slow this process down.
Iron (Ferrous) Sulfate
This is a much more expensive option because about eight times more than sulfur is needed to get the same effect. However, you’ll see the results sooner.
Interveinal chlorosis and yellowing of young leaves may indicate a lack of a healthy root system and high pH levels. An iron sulfate application will provide the plant with much-needed iron and acidify the soil, killing two birds with one stone. The general application recommended is one teaspoon for each foot of the blueberry bush’s height. Iron chelate may be applied to foliage to jumpstart vegetative growth while amendments added to the soil take effect.
This quick fix can reduce pH in as little as three to four weeks by adding 500 grams per 10 square feet. You should notice plants greening up within this timeframe.
Cottonseed Meal
This byproduct of the cotton industry is a triple-duty amendment. Cottonseed meal is a great slow-release fertilizer for acid-loving plants like blueberries, it’s full of valuable nutrients, high in organic matter, and can be used as mulch to help decrease weed pressure. Adding this to your soil will help plants uptake nutrients, reduce competition, encourage healthy soil microbial activity, and enhance soil health.
Cottonseed meal is generally a 5-2-1 NPK composition. Application rates are 10 pounds per 10 square feet.
Sphagnum Peat Moss
Incorporate this into your growing medium to quickly alter the pH level and help aerate the soil. Use this if you want to plant out blueberries, but the pH is between 5.5 and 7.0. Depending on the starting pH level, remove four to six inches of soil from your plot (not just the planting hole) and replace it with the same amount of sphagnum peat moss. Mix it into the soil and re-test it in six to eight months to determine how much it adjusted. Amend as needed. Soil decomposes with time and erosion, so plan on amending the soil regularly.
Note that there are environmental concerns about mining this product. Carbon has been sequestered over thousands of years and is stored globally in bogs. Collectively, bogs contain more carbon than all of our combined forests. The harvest of peat moss causes carbon to be released back into the atmosphere and destroys native habitats.
While some consider peat moss a renewable resource because bogs can be replanted, it’s believed that carbon continues to be released for up to 40 years after the harvest, causing serious concerns for environmentalists.
Ammonium Sulfate
For pH levels above 5, use ammonium sulfate. This is especially effective if phosphorus levels are low. Ammonium sulfate used continually may decrease pH levels below the desired blueberry range, so take caution when using it.
How to Increase pH Levels
Take caution when attempting to increase pH levels. Remember, you can add more if needed, but you can’t take it away. When soil pH is too high, nutrients take longer to dissolve. Plants can only uptake dissolved nutrients so when it takes longer to become available, plants experience deficiencies that can lead to stunted growth or chlorosis.
Aluminum toxicity can sometimes occur when pH levels drop too low, so make adjustments to avoid this.
Urea
Urea will allow you to make small adjustments when pH levels are under 5. It’s less acid-forming than other amendments. Have a pH meter on hand for quick testing.
Wood Ash
If you use a wood stove to heat your home, wood ash is easily accessible. Be aware that it contains high levels of potassium and calcium so refer to your soil tests before choosing this amendment. It works quickly and is readily available to plants upon application.
Standard application for home gardeners with 1,000 square feet of space is about a five-gallon bucket once annually. Incorporate it in before planting.
Maintaining pH and Overall Blueberry Plant Health
Blueberry plants are light feeders, so over-fertilization will have negative effects. If you’re familiar with the acidity needs of azaleas and rhododendrons, feed your blueberries the same. In late spring, apply water-soluble fertilizer. Blueberries are sensitive to nitrates, so avoid using any fertilizer that contains nitrogen in that form.
Focus on amending the soil of the entire blueberry patch, not just at the base of each plant. When applying fertilizer, create a six to eight-inch ring around each plant, being careful not to put any directly on the crown, as this can be damaging. Creating this ring will allow the roots to find food wherever they reach.
After your initial pH adjustment, soil test annually and stay consistent so your berry production doesn’t suffer.
Ineffective or Harmful Blueberry Amendments
These items are not reliable or harmful amendments and should not be used:
- Mulched leaves: They’re too neutral as they break down too quickly to have much of an effect.
- Coffee grounds: Varying acidity levels from different sources make this an unreliable amendment. In addition, if your soil is high in nitrogen, adding coffee may stunt flower and fruit production.
- Aluminum sulfate: This may be toxic to blueberries and should not be used to adjust pH.
- Limestone: Lime is great at neutralizing soil pH to between 6.0 and 7.0, which is ideal for most plants, but not blueberries. Neutralizing their soil can be very damaging for them. Lime is slow-moving, so adjusting levels can take years.
- Pine needles: It’s a myth that pine needles acidify the soil. However, they do make a lovely and free, mulch!
- White vinegar: While vinegar can lower the pH quickly and temporarily, a lot is required to alter the levels. In addition, vinegar only affects the water solution pH and not the mineral solution. This means that when regular irrigation begins, the pH will revert to what it was before the application.
Final Thoughts
Blueberries are one of a few crops that prefer their soil on the acidic side. Annual soil testing by a reputable lab is highly recommended.
If you want to add blueberry bushes in the future, start adjusting your soil today so they start on the right foot. Amend slowly to avoid any plant damage, and test often.
