A reader reached out and asked why their blueberry plant leaves are curling. After doing a quick search, I realized there’s not a lot of information out there. So, I did some research and put together this guide. Here’s what I found.
Blueberry leaves curl from improper watering, climate, and nutrients, as well as transplant shock, aphids, and leafrollers. Ideally, only water when the soil is dry and apply compost and mulch. Depending on the issue, leaves can curl up or down. They can also turn yellow or brown, indicating a deficiency or dryness.
While blueberry leaves curl for multiple reasons, how can we tell which issue is causing it, and how can we fix it? Let’s take a look.
The most common reason why blueberry plants curl is a lack of water. This issue is fairly easy to identify as the soil will be bone dry. If the soil is dry for too long, the plant’s leaves begin to dry, curl, brown, and drop.
The best way to water blueberry plants is to only water when the top 2-4 inches of soil is dry. I like to check this by pushing a finger into the soil, under the plant’s canopy.
When watering, make sure to soak the soil down to at least 1 foot as the majority of the roots are located at this depth.
In general, blueberry roots do not extend very far from the plant. In most soils, 50% to 60% of the roots are located in the top foot of soil and are within 8 to 12 inches from the crown.Professor Bernadine Strik, NWREC Berry Crops Research Leader
Additionally, apply 2 inches of compost and 4 inches of mulch under the canopy.
Compost provides valuable nutrients and retains moisture in the soil. Every 1% increase in the soil’s richness or organic matter leads to an additional 20,000 gallons of water held per acre (source).
Mulch reduces evaporation, regulates soil temperature, and prevents soil erosion. Since blueberry plants evolved as understory plants in forests, they’re used to plenty of mulch in the form of fallen branches and leaves. As permaculture guru Geoff Lawton says, “A forest grows on a fallen forest.”
When applying compost and mulch, keep the materials at least 3 inches from the blueberry plant’s stem to avoid mold buildup. Reapply compost every 1-2 months and mulch every 3-6 months.
2. Extreme Heat and Dryness
|Blueberry Variety||Hardiness Zones|
|Rabbiteye or Southern Highbush||7-9|
Even if you’re watering your blueberry plant correctly, it can dry out extremely quickly in weather that’s too hot or dry. Add to that if the blueberry plant is already under-watered, and is now under heat stress, it can often decline and start dying within days or even hours.
Most often, you can tell if a blueberry bush is suffering from excess heat and dryness if its leaves are starting to curl. If the plant continues to dry out, other symptoms include leaves drying, browning, and dropping.
For this reason, it’s best to grow the majority of blueberry bush varieties in USDA hardiness zones 4-7. These climates are generally going to be cooler and less dry.
However, we can’t control the weather and there will be times that blueberry bushes will become drought-stressed, no matter the climate.
So, what do we do?
First, it’s helpful to know how blueberry bushes cool themselves.
Plants keep themselves cool by sending moisture from their roots to their leaves, and through a process called transpiration.
Just like how humans exhale moisture when we breathe, plants do the same. Releasing moisture from the underside of leaves is called transpiration, and it’s a major reason why forests are cooler and more humid than their surrounding areas.
So, how can we use this to our advantage?
Tips for Hot and Dry Weather
- Compost and Mulch – as mentioned above, these two materials are essential for preventing evaporation and sponging rainfall in the soil. As long as the sun’s rays don’t get too strong, blueberry bushes will be able to effectively cool themselves.
- Partial Shade – blueberry bushes evolved as understory species in forests, so they prefer lots of mulch and partial shade (especially from the hot, afternoon sun). Some ideas to create shade are umbrellas, shade sails, or larger plants. Generally, provide partial shade from the western sun.
- Create Density – to improve transpiration moisture and help cool blueberries, plant as many different species and as densely as possible. Doing this also has other companion plant benefits such as increased disease resistance and pollination.
3. Lack of Nutrients
|Nutrient Deficiency||Leaf Symptom|
|Nitrogen||Entire leaf is pale or yellow|
|Iron||Dark green veins, rest of the leaf is yellowing|
|Manganese||Broadly pale leaves, foliage color looks mottled or smeared|
Other than causing blueberry leaves to curl, a lack of nutrients also causes yellow, brown, and dropping leaves. While you can sometimes determine the exact deficiency blueberry plants might have, it’s generally difficult.
For this reason, it’s best to practice proper fertilizing.
The Best Way to Fertilize Blueberry Bushes
The two main ways to fertilize blueberry bushes are with chemical fertilizers or with compost.
While chemical fertilizers can work in the short term, they often come with long-term consequences such as dry and poor soil. Because of this, many gardeners are finding that compost is replacing their fertilizers.
Alternatively, compost provides more than sufficient nutrients, promotes soil health, and retains water in the soil.
If you choose a chemical fertilizer, aim for one with a fairly balanced NPK (nitrogen, phosphorus, and potassium). Generally, nitrogen is the primary nutrient used for canopy growth, while phosphorus and potassium are used for the plant’s health, flowering, and fruiting.
If you choose compost, remember: the fresher the better. This is because the beneficial microbes will still be alive and will begin assisting the soil by transporting nutrients and water.
Either one you choose, you can check out my recommended fertilizer page for more.
Improper Soil pH
While nutrients are essential to plants, they’re unattainable without a balanced soil pH.
Blueberry plants prefer a soil pH of 4.5 to 5.5 (source).
The reason why blueberry plants prefer an acidic pH is because it’s helpful to dissolve the nutrient solids in the soil. Without an acidic pH, the nutrients won’t be as available for the plant’s finer roots which leads to nutrient deficiencies.
Fourteen of the seventeen essential plant nutrients are obtained from the soil. Before a nutrient can be used by plants it must be dissolved in the soil solution. Most minerals and nutrients are more soluble or available in acid soils than in neutral or slightly alkaline soils.Donald Bickelhaupt, SUNY College of Environmental Science and Forestry
While I recommend applying as much compost and mulch as possible for your blueberry plants, these materials typically have a neutral pH.
As a result, consider testing your blueberry plant’s soil to make sure it’s leaning more acidic.
Two quick and easy ways to do this are with pH strips or a pH meter. I prefer using a pH meter since they’re simple and affordable. To see which pH meter I use and recommend, check out my recommended tools page.
If you find that your blueberry plant’s soil is too alkaline (above 5.5), use acidic amendments such as peat moss, sand, or coffee grounds. For soil that’s too acidic (below 4.5), use alkaline amendments such as wood ash, biochar, or lime.
4. Transplant Shock
If your blueberry bush was recently planted or repotted, and its leaves are starting to curl, it’s likely due to transplant shock. Transplant shock occurs when a plant is exposed to a new environment and has to establish a new root system.
Avoid transplanting blueberry bushes unless necessary as it can take up to 1 year for recovery.
To help avoid transplant shock, I like to plant with the following steps in mind:
- Have the new ground (or pot) prepared
- Remove as much of the plant’s current topsoil as possible, without damaging the shallow roots
- Grab the base of the plant’s stem and wiggle lightly
- Using your other hand, scoop up and support the rootball
- Lightly place the plant in the new ground (or pot) and fill it in
- Make sure the soil is at the same level on the plant as before
- Apply 2 inches of compost and 4-12 inches of mulch to the top of the soil
- Water generously and add more soil as needed
Aphids are small bugs that suck the sap from underneath the blueberry plant’s leaves. This loss of sugar and moisture causes the leaves to curl, discolor, and drop. Aphids also deposit honeydew, which attracts ants. If left unchecked, aphids can damage the plant’s health and potentially stunt or kill it.
These bugs come in multiple colors including white, yellow, or black, and usually are found hiding underneath the leaves. Typically, aphids won’t cause damage to the fruit, but because they suck sap from the plant, they can compromise its health and therefore reduce fruit size and yield.
The best ways to get rid of aphids (and mites) on blueberry plants is by spraying the infected leaves with water or neem oil, or releasing ladybugs (a natural predator of aphids and mites). Most often, a jet of water is enough to knock them off and kill them, but neem oil is a good second option.
For example, when my potted Kaffir lime tree had aphids, I found that a jet of water was sufficient to blast them off and prevent them from coming back. All I did was remove the hose nozzle and used my thumb to increase the pressure. Just keep in mind that too strong of a blast can damage the leaves.
Leafrollers are caterpillars that feed on blueberry leaves, flowers, and green fruit. They normally appear in the spring, when blueberry plants begin to bloom. The most common leafroller to infest blueberry plants is Obliquebanded leafrollers.
The leafroller moths lay their eggs directly on blueberry leaves, on which the caterpillars hatch and begin eating. They hatch after about 10-12 days. Similar to other caterpillars, leafrollers use webbing to curl the leaf and hide in it.
You can manage leafrollers by using pheromone traps and encouraging natural predators such as spiders. Sprays are not recommended.
Unless leafroller numbers are very high, spraying is not necessary. Repeated or unnecessary sprays will harm natural enemies that are present, such as native parasitic and predatory insects and spiders that will reduce their populations.Blueberry IPM Manual, Washington State University
To learn more about leafrollers, check out these resources:
- Blueberry IPM Manual, Washington State University
- Pacific Northwest Pest Management Handbooks
- Michigan State University IPM 1 and 2