A reader recently asked why their blackberry bush has wilting leaves. While I had an idea, I wanted to do more research and provide the best answer. Here’s what I found.
Blackberry plants get wilting leaves from improper watering, hot weather, transplant shock, and diseases such as Fusarium wilt and Verticillium wilt. To prevent droopy leaves, only water when the top 2-4 inches of soil is dry and apply compost and mulch. Also, provide partial shade when temperatures exceed 90ºF.
Let’s take a look at how we can identify the issue causing drooping and wilting leaves on blackberry plants, and how we can fix it.
1. Improper Watering
The best way to water blackberry plants is to only water when the top 2-4 inches of soil is dry. I check this by pushing a finger into the soil.
By watering in this way, we’re preventing both under and over-watering.
Under-Watered
When blackberry plants are under-watered, their roots don’t have enough moisture to pass to the leaves. As a result, their leaves dry, droop/wilt, curl, brown, and drop from the plant.
Under-watering is made worse when the climate is hot and dry (more on this later). This further speeds up the evaporation of water from the soil, drying the blackberry plant’s leaves in a matter of days or hours.
So, while following the rule of only watering when the top 2-4 inches of soil is dry is best, you can also slow the evaporation of water from the soil and keep it protected from the elements.
Apply 2 inches of compost every 1-2 months. Compost increases the soil’s richness, provides valuable plant nutrients, and promotes healthy soil life. For example, every 1% increase in the soil’s organic matter leads to an additional 20,000 gallons of water held per acre.
Apply 4 inches of mulch every 3-6 months. Mulch dramatically reduces evaporation, regulates soil temperature, and prevents erosion. Like compost, mulch feeds beneficial soil life such as earthworms and mycorrhizal fungi.
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
Over-Watered
Blackberry plants that are over-watered show symptoms such as leaves drooping/wilting, yellowing, and dropping. If the issue isn’t corrected, it can lead to a dying blackberry plant.
You can tell if a blackberry plant’s soil is over-watered if it’s staying sopping wet for more than 24 hours. Ideally, soil should have moisture similar to a wrung-out sponge.
As with under-watering, aim to only water when the top 2-4 inches of soil is dry.
While over-watering can be caused by watering too frequently, it’s more commonly caused by poorly draining soil. This is typical with soil that is high in clay.
Let’s take a look at how to identify, test, and amend poorly draining soil.
Poor Drainage
- Check – Initially check the soil’s drainage by feeling if the top 2-4 inches of soil is dry or wet. If it’s sopping wet for more than 24 hours, it’s getting over-watered. In this case, move to step 2.
- Test – The best way I’ve found to test soil is by doing a percolation test (pictured above). To do this, dig a 1-foot by 1-foot hole, place a yardstick in, and fill the hole with water. Wait an hour and measure how many inches the water has drained. The goal should be around 2 inches per hour.
- Amend – If the soil is draining well under or over 2 inches an hour, amend it by placing 2 inches of compost on top of the soil. Compost fixes both poor and fast drainage as it retains water while breaking up the larger chunks of soil.
2. Hot Weather
Blackberry plants that are too hot and dry get wilting leaves as the moisture is leaving the leaf faster than the roots can supply it. And if the roots don’t have sufficient moisture, the leaves can curl, curl, brown, and drop in a matter of days or hours.
Ideally, grow blackberry plants in USDA zones 4-10, depending on the variety.
This is generally between -30ºF to 90ºF. Anything below or above this range can lead to issues such as leaf drop and the plant dying.
As most gardeners don’t experience temperatures below -30ºF, we’re going to focus on what to do in hot weather.
But first, it’s helpful to know how blackberry plants cool themselves so we can expand on it.
Blackberry plants keep themselves cool by sending moisture from their roots to their leaves and through a process called transpiration.
Transpiration is when plants exhale moisture (much like how we do). This is the reason why walking into a dense forest can feel extremely humid.
Professional German forester Peter Wohlleben mentions in his book, The Hidden Life of Trees, the top side of a leaf is like a solar panel (photosynthesis) while the bottom side is for breathing (transpiration).
Now, let’s take a look at how we can boost these two methods to help keep blackberry plants cool.
Hot Weather Tips
- Apply compost and mulch – as mentioned in the watering steps, provide 2 inches of compost and 4 inches of mulch to drastically reduce the effects of the hot and dry weather.
- Provide partial shade – blackberry plants evolved as understory species, so they prefer to have a few hours of afternoon shade. You can do this by planting trees, using shade sails, or planting on the north or east side of your property.
- Plant on the northern or eastern side of your property – In the northern hemisphere, the north and east sides of properties are usually the coolest and have the least amount of sun. Just make sure your blackberry plant gets at least 4 hours of daily sunlight (ideally 6+ hours).
3. Transplant Shock
If your blackberry plant was recently planted or repotted, and its leaves are wilting or drooping, 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 blackberry plants 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
4. Diseases
Verticillium Wilt
Verticillium wilt is a fungus that is similar to root rot in that it usually occurs in soils with excess water. Additionally, over-fertilizing can also cause it.
The most susceptible fruit crops that contract verticillium wilt are nightshade (tomatoes, peppers, and eggplants), but other fruiting plants such as blackberry plants can also be infected. Symptoms of this disease include leaves wilting, yellowing, and dropping, and potentially branch dieback.
Prevent and treat verticillium wilt by pruning infected branches, avoiding excess water and fertilizers, and following best gardening practices.
Fusarium Wilt
Fusarium Wilt is a plant disease caused by the soil-borne fungus Fusarium oxysporum. This pathogen can infect a wide variety of plants, including blackberry plants, leading to wilting, yellowing, and ultimately plant death.
The fungus enters the plant’s vascular system, obstructing the flow of water and nutrients, which results in the wilting symptoms.
Symptoms:
- Yellowing and wilting of leaves, starting from the lower parts of the plant and progressing upwards.
- Stunting of plant growth.
- Browning of the vascular tissue, visible when the stem is cut.
- Plant death in severe cases.
Prevention:
- Cultivate disease-resistant varieties: Choose blackberry cultivars that are resistant to Fusarium Wilt to minimize the risk of infection.
- Maintain good soil health: Ensure proper drainage and avoid over-watering, as the fungus thrives in poorly drained, waterlogged soils. Incorporate organic matter.
- Remove infected plants: If you detect Fusarium Wilt in your blackberry plants, remove and destroy the infected plants to prevent the spread of the disease to nearby healthy plants.
- Sanitize tools and equipment: Clean and disinfect gardening tools and equipment to avoid spreading the pathogen.
