Our neighbors asked me the other day why their strawberry plants are turning red. While I had an idea, I did some research and put together this guide for them. Here’s what I found.
Strawberry stems are naturally red, but their leaves turn red due to old age, improper watering, nutrient deficiencies, or pests and diseases like verticillium wilt or red stele. To fix this, only water when the soil is dry, provide compost or fertilizer, and check for signs of pests or diseases to treat accordingly.
So, while strawberry plants get red leaves from several causes, how do we know which one is causing it, and how do we fix it? Let’s take a closer look.
1. Age or Seasonal
It’s normal for strawberry stems to be red, but red leaves are a different story.
Strawberry plants naturally get red leaves when the leaves are nearing the end of their life, or dropping off before winter. In these cases, you’ll notice the leaves are a solid red instead of red spots (more on strawberry diseases later).
In USDA hardiness zones 4-9 (best for most strawberry varieties), the strawberry plant should go dormant during the winter, getting red and dropping leaves. By spring, its leaves should start growing again.
Sometimes it’s because the strawberry plant isn’t getting enough chlorophyll. In this case, make sure your strawberry plant is getting at least 6 hours of daily sunlight.
Overall, if you’re going into late fall and you notice your strawberry plant’s leaves are turning red, then there’s nothing to worry about.
But, what if it’s spring or summer and your strawberry plant has red leaves? What do we do then?
2. Improper Watering
The best way to water strawberry plants is to only water when the top 2-4 inches of soil is dry. I check this with the “finger test”, which is simply pushing a finger into the soil, near the plant’s stem or trunk.
By only watering when the soil is dry, you’re preventing both under and over-watering.
Under-Watering
You can tell if your strawberry plant is under-watered if the soil is constantly dry.
Common symptoms of under-watered strawberry plants are leaves drying, curling, browning, and dropping. While rare, they can also turn red.
If you do the finger test and find your strawberry plant’s soil is drying too fast, here are a couple of things you can do to help.
- Compost – Apply 1 inch of compost around your strawberry plants every 1-2 months. Compost not only provides valuable nutrients, but it increases water retention and feeds beneficial soil life.
- Mulch – Apply 2 inches of mulch on top of the compost every 3-6 months. Mulch dramatically reduces evaporation, regulates soil temperature, and prevents erosion.
For example, every 1% increase in the soil’s organic matter leads to an additional 20,000 gallons of water held per acre. Compost also feeds the soil life such as earthworms and mycorrhizal fungi, leading to benefits such as increased nutrients and pest and disease resistance.
Mulch dramatically reduces evaporation, regulates soil temperature, and prevents soil erosion. Since strawberry plants evolved as a groundcover species in forests, they prefer plenty of mulch in the form of fallen leaves and branches.
Mycorrhizal fungi promote many aspects of plant life, in particular improved nutrition, better growth, stress tolerance, and disease resistance.
Department of Biology, University of Fribourg, Switzerland
As permaculture guru Geoff Lawton says, a forest grows on a fallen forest.
While compost and mulch help soil that drains too quickly, what happens if the soil has poor drainage and is over-watered?
Over-Watering (Poor Drainage)
Over-watered strawberry plants are usually caused by poorly draining soils. If water isn’t allowed to drain through the soil, mold builds up and can attack the plant’s roots, leaves, fruit, and more. Over time, the strawberry plant dies.
Common symptoms of over-watered strawberry plants are leaves turning yellow, brown, red, and dropping.
If you do the finger test and find your strawberry plant’s soil is constantly staying wet (usually for over 24 hours), then it likely needs to be amended for better drainage.
Amending Soil
Interestingly, the solution for both poor drainage and fast drainage is the same—compost.
Compost not only breaks up the clumps of ground in poorly-draining soil, but its organic matter retains water in fast-draining soils.
As mentioned above, I recommend providing your strawberry plants with 1 inch of compost every 1-2 months. Over time, the compost will work its way into the soil.
If you can’t wait for the compost to do its job on the soil, you can also move your strawberry plant to an area with better drainage such as a raised bed or mound of soil.
If you have potted strawberry plants, you can skip the wait and instead repot them with fresh potting soil.
Keep in mind, avoid mulching until your strawberry plant has well-draining soil. This is because mulch can make drainage worse by preventing evaporation.
If you checked your strawberry plant, and watering is not the issue, the next thing to look at is nutrients.
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 |
| Zinc | Yellow blotches |
| Manganese | Broadly pale leaves, foliage color looks mottled or smeared |
If you haven’t fed your strawberry plant in the past few months, there’s a good chance it may be getting red leaves from a lack of nutrients. Specifically phosphorus.
Phosphorus plays a vital role in the plant’s root development, flowering, and fruiting, and a lack of it can lead to red or purple-tinted leaves. To correct phosphorus deficiency, provide a balanced fertilizer or add a phosphorus-rich amendment like bone meal to the soil.
Strawberry plants also commonly get a nitrogen deficiency and get lightly colored or yellow leaves.
Let’s take a look at the ideal way to prevent a lack of nutrients for your strawberry plants.
The Best Way To Fertilize Strawberry Plants
There are three main ways to fertilize strawberry plants.
- Chemical fertilizer
- Organic Fertilizer
- Compost
I prefer feeding my strawberry plants with organic fertilizer or compost. While chemical fertilizers have plenty of nutrients in quantity, they often lack quality and can harm the soil (and therefore the plant).
This happens because the chemical fertilizer disrupts the nutrient exchange between the plant and the soil life. If the plant is getting all of the nutrients from the fertilizer, then it stops feeding the soil life.
And when the soil life dies off, deeper nutrients are no longer brought up to the surface and the soil loses its water-retaining properties.
If you choose a fertilizer for your strawberry plants, aim for one with a balanced NPK (nitrogen, phosphorus, and potassium), such as a 10-10-10.
If you’d like to see which fertilizers I recommend, check out my recommended fertilizer page.
Remember to supplement with phosphorus amendments such as bone meal to help treat the red leaves.
Alternatively, you can use compost.
I recommend applying 1 inch of compost every 1-2 months under the plant’s drip line followed by 2 inches of mulch.
Keep in mind that while nutrients are essential, they aren’t everything.
Imbalanced Soil pH
Strawberry plants prefer a soil pH of 5.3 to 6.5.
The reason strawberries (and most plants) prefer a slightly acidic soil pH is that it dissolves the nutrient solids in the soil, making them more accessible to the plant’s finer roots.
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, Instructional Support Specialist, Department of Forest and Natural Resources Management
When strawberry plants have an imbalanced soil pH, they develop issues such as discolored and dropping leaves. Additionally, their flowers and fruit drop early and the plant is more likely to develop other issues.
Two good ways to test your soil’s pH are with pH strips or a meter. I prefer using a pH meter since they’re affordable and easy to use. To see which pH I recommend, check out my recommended tools page.
If you find your strawberry plant’s soil is too alkaline (above 6.5), provide acidic amendments such as peat moss, sand, and coffee grounds.
On the other hand, if your soil is too acidic (under 5.3), provide alkaline amendments such as charcoal, wood ash, and lime.
4. Extreme Climate
Weather that’s too hot or cold can cause strawberry plant leaves to turn red.
For example, temperature fluctuations, particularly during the colder months or early spring, can cause leaves to develop a reddish hue. This is a natural response to colder temperatures, as the plant produces anthocyanins, pigments that help protect the plant from damage caused by cold temperatures.
Another climate-related cause of red leaves is excessive sun exposure, especially during hot weather. The strawberry plant’s leaves might turn red as a stress response, trying to protect themselves from sunburn and damage.
During the day, aim for temperatures between 60-80°F (15-27°C), while nighttime temperatures should ideally be in the range of 50-60°F (10-15°C). These temperature ranges promote healthy growth, flowering, and fruiting in strawberry plants.
However, strawberries are fairly adaptable and can tolerate temperatures outside these ranges. This range is just the ideal figure for growth and fruiting.
Tips to Protect Strawberries
If you believe your strawberry plant is getting red leaves from a change in temperature, here are some tips that should help:
Cold Weather
- Use frost protection: Use row covers, cold frames, or cloches to shield plants from low temperatures and frost, especially during early spring or late fall.
- Mulch for insulation: Apply a thick layer of mulch (straw or leaves) around the plants to help insulate the roots and conserve soil moisture.
- Choose cold-hardy varieties: Plant cold-tolerant strawberry varieties like ‘Mara des Bois’ or ‘Earliglow’ to ensure better survival in colder climates.
Hot Weather
- Provide shade: Use shade cloth or a temporary shading structure during extreme heat or intense sun exposure to protect plants from heat stress and sunburn.
- Water consistently: Increase watering frequency to ensure the soil stays consistently moist, but avoid over-watering. Consider using drip irrigation to provide water directly to the plant roots.
- Mulch for cooling: Apply a layer of mulch around the plants to help regulate soil temperature, conserve moisture, and reduce evaporation during hot weather.
5. Pests
Spider Mites
Spider mites are tiny, reddish-brown or pale-colored arachnids that feed on plant sap, causing leaves to turn red or bronze. They are often difficult to see with the naked eye, but their presence can be detected by the fine, silken webbing they produce on the undersides of leaves.
Symptoms
Infested strawberry plants may display red, curled, or dried leaves, and the overall plant vigor may be reduced. Severe infestations can lead to leaf drop and even plant death.
Common Regions
While spider mites are widespread pests and can be found in various regions, they tend to be more problematic in areas with hot, dry climates. Greenhouses and indoor growing environments are also common for infestations.
Prevention and Treatment
- Regularly inspect plants for signs of spider mite infestation, paying particular attention to the undersides of leaves.
- Encourage natural predators, such as ladybugs and lacewings, by planting beneficial insect-attracting flowers like marigolds or yarrow.
- Keep the growing area clean, and remove any debris, weeds, or dead plant material that could harbor pests.
- Maintain adequate moisture levels and avoid over-fertilization, as dry and dusty conditions or excessive nitrogen can promote spider mite population growth.
- Spray the plants with water to dislodge the mites or use insecticidal soap or neem oil as a targeted treatment. Follow the product label instructions for proper application rates and methods.
Tarnished Plant Bug
These bugs are brownish, oval-shaped insects with a distinctive “Y”-shaped marking on their backs. They feed on strawberry plants, causing the leaves to turn red and curl upwards.
Symptoms
When tarnished plant bugs attack your strawberry plants, you’ll notice red, distorted leaves, and stunted growth. They can also cause your strawberry fruit to become misshapen.
Common Regions
These insects are found throughout North America, especially in areas with lots of weeds, grasses, and wildflowers. They’re not picky about the weather and can thrive in various climate conditions.
Prevention and Treatment
- Keep an eye on your plants and check for any signs of tarnished plant bugs. The sooner you spot them, the easier it’ll be to control them.
- Remove weeds, grasses, and dead plant material from your garden, as these can serve as hiding spots for the bugs.
- Attract natural predators like ladybugs, lacewings, and minute pirate bugs by planting flowers they love, such as dill, fennel, and coriander. These helpful insects will feast on tarnished plant bugs, keeping their population in check.
- If you do find tarnished plant bugs on your strawberries, try spraying your plants with insecticidal soap or neem oil to knock out the pests. Just be sure to follow the label instructions for the best results.
Recommended: 50 Companion Plants for Strawberries: Benefits, Tips, & Plants to Avoid
6. Diseases
Verticillium Wilt
Verticillium wilt is a soil-borne fungal disease caused by the pathogens Verticillium dahliae and Verticillium albo-atrum. This disease affects a wide range of plants, including strawberries, and can cause their leaves to turn red, wilt, and eventually die.
Symptoms
Infected strawberry plants will exhibit red or yellow leaves that wilt and curl, typically starting from the plant’s base and progressing upward. As the disease progresses, the leaves may die and fall off, and the plant’s overall vigor can be severely reduced.
Common Regions
Verticillium wilt is a widespread disease that affects strawberry plants in various regions, particularly those with moderate temperatures and moist soil conditions. The pathogens can survive in the soil for several years, making it a persistent issue for many gardeners.
Prevention and Treatment
- Start with resistant varieties: Plant strawberry varieties that are resistant to Verticillium wilt, such as ‘Allstar’ or ‘Honeoye,’ to minimize the risk of infection.
- Practice crop rotation: Rotate your strawberry plants with non-host crops (e.g., grasses or grains) for at least three years to reduce the pathogen population in the soil.
- Maintain soil health: Ensure good drainage, avoid over-watering, and maintain a soil pH between 5.3 and 6.5 to create an environment less conducive to the growth and spread of the pathogens.
- Solarize the soil: Before planting, consider solarizing the soil by covering it with a clear plastic tarp for 4-6 weeks during the hottest part of the summer. This method can help reduce the pathogen population in the soil.
- Remove infected plants: If you spot plants showing signs of Verticillium wilt, promptly remove and dispose of them to prevent the disease from spreading. Avoid composting infected plant material, as the pathogens can persist in the compost.
Red Stele Root Rot
Red stele root rot, caused by the fungus Phytophthora fragariae, is a soil-borne disease that primarily affects strawberry plants. It attacks the roots, leading to red discoloration in the stele (central core) of the root system, which can cause the leaves to turn red and the plant to wilt.
Symptoms
When infected with red stele root rot, strawberry plants may display red or purple leaves, reduced growth, and wilting. As the disease progresses, the plants may die, and fruit production will be severely impacted. Upon inspecting the roots, you’ll notice a reddish core, which is a telltale sign of this disease.
Common Regions
Red stele root rot can be found in various regions, but it is more prevalent in areas with cool, wet climates, as the fungus thrives in saturated soils and poorly drained conditions.
Prevention and Treatment
- Choose resistant varieties: Plant red stele root rot-resistant strawberry varieties like ‘Surecrop’ or ‘Redchief’ to minimize the risk of infection.
- Improve soil drainage: Plant your strawberries in well-draining soil or raised beds to prevent waterlogging, which can encourage fungal growth.
- Avoid over-watering: Water your plants consistently, but don’t overdo it. Excessive moisture creates an ideal environment for the fungus to thrive.
- Practice crop rotation: Rotate strawberries with non-host crops for at least 3 years to reduce the pathogen population in the soil.
- Solarize the soil: Before planting, consider solarizing the soil by covering it with a clear plastic tarp for 4-6 weeks during the hottest part of the summer. This method can help reduce the pathogen population in the soil.
- Remove infected plants: If you find plants showing signs of red stele root rot, remove and dispose of them promptly to prevent the disease from spreading. Avoid composting infected plant material, as the fungus can persist in the compost.
Sources
- https://extension.umn.edu/strawberry-farming/strawberry-nutrient-management#:~:text=Strawberries%20prefer%20slightly%20acid%20soil,one%20year%20prior%20to%20planting.
- https://ipm.ucanr.edu/agriculture/strawberry/lygus-bug/#:~:text=Lygus%20bugs%20are%20one%20of,area%20surrounding%20the%20feeding%20site.
- https://ipm.ucanr.edu/agriculture/strawberry/red-stele/
