A reader emailed me, asking why their blackberry bush is getting yellow leaves. I had an idea, but I wanted to do more research to give them the best answer. Here’s what I found.
It’s normal for a blackberry bush’s leaves to yellow and drop in the fall and winter. However, if its leaves are yellowing in the spring and summer, it’s likely due to improper watering, nutrients, pests, or diseases. These include aphids, spider mites, verticillium wilt, and root rot.
Let’s take a look at how to identify the causes of yellow leaves on blackberry bushes and how to treat them.
1. Seasonal
It’s normal for blackberry bushes to get yellow leaves in the fall and winter as they’re deciduous plants. Deciduous plants are plants that drop their leaves during the colder months as a survival response. This helps them go dormant and reserve nutrients for springtime.
During this time, blackberries and other deciduous plants get a few different shades of leaves including yellow, red, and brown.
However, if your blackberry bush is getting yellow leaves in spring and summer, what could be causing it?
2. Over-Watering
Over-watering is the most common preventable reason blackberry plants get yellow leaves. It’s easy to accidentally over-water, but there’s a rule of thumb that helps prevent it.
Only water when the top 2-4 inches of soil is dry. This prevents both over-watering as well as under-watering.
I check this by pushing a finger into the soil. You can also use a moisture meter, but I found them to be unnecessary and sometimes inaccurate.
If you water only when the soil is dry, you’ll have no issues with over-watering. However, this is difficult when working with poorly draining soils, such as those high in clay.
Poor Drainage
If your blackberry bush’s soil is staying sopping wet for more than 1 day, it likely has poor drainage. In this case, the soil’s particles are packed too tightly to allow any water to flow deeper into the soil.
As a result, the blackberry plant’s roots drown and grow fungus, leading to issues such as yellow and dropping leaves.
While the finger test is a good way to check your soil’s moisture, there’s another way to test its drainage.
Drainage Test
The best drainage test that I’ve found is a percolation test. I first learned about this method in my permaculture design course and it has served me well when diagnosing soil drainage.
Here’s how to do it:
- Dig a 1-foot by 1-foot hole
- Place a yardstick in it and fill the hole with water
- After 1 hour, mark the level that the water drained
Ideally, the soil should have a drainage of 2 inches per hour. However, soil rarely drains exactly at this rate, so don’t worry if yours is way off. This just serves as a good way to identify if you have quick or slow soil drainage.
For example, we have areas in our backyard that drain up to 5 inches an hour.
How to Amend Drainage
The best way to amend soil is with compost. Adding organic matter not only improves the water retention of the soil, but it breaks up the larger clumps of soil (such as clay). As a result, compost is used to amend both poor and fast soil drainage.
Every 1% increase in the soil’s organic matter leads to an additional 20,000 gallons of water held per acre (source).
Apply 2 inches of compost every 1-2 months on top of your blackberry plant’s soil (under the drip line of the plant). Avoid touching the compost to the stems as it can introduce mold.
When your blackberry’s soil has proper drainage, apply 4 inches of mulch to further improve the soil’s water retention and nutrients.
3. Improper Nutrients
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 |
A lack of nutrients commonly causes blackberry leaves to yellow and drop. I put together the above table to help diagnose which nutrient your blackberry plant might be lacking.
While a lack of nutrients is often from poor soils, it can also be from over-watering. This is because water naturally leaches nutrients, diluting them and pushing them deeper into the soil. As the majority of blackberry roots only grow within the first 2 feet of soil, leaching quickly moves nutrients away from the roots.
Excess Nutrients
Too many nutrients also cause blackberry bushes to get yellow leaves as it chemically burns the plant’s roots. This stress leads to leaves yellowing, browning, and dropping.
In this case, leaching by over-watering is likely a good idea, as you can dilute the excess nutrients and disperse them further into the soil.
So, if you believe your blackberry’s yellow leaves are from applying too much fertilizer, water the plant for a good 1-2 hours on a low setting.
Of course, if your plant’s soil has poor drainage, you’ll want to address this first (see the above section).
How to Fertilize Blackberry Bushes
The best way to fertilize blackberry bushes is with organic fertilizers or compost.
While chemical fertilizers are good in the short-term, they often have long-term effects such as killing beneficial soil life. Once the soil dies, it becomes dry and its benefits such as improved water retention, nutrients, and pest and disease resistance vanish.
To see which organic fertilizer I recommended, check out my recommended fertilizer page. I suggest following the instructions on the box for the best results.
However, compost is quickly becoming the go-to replacement for fertilizer. For our backyard fruit trees, I apply 2 inches of compost every 1-2 months and 4 inches of mulch every 3-6 months. I suggest doing the same for blackberry bushes.
Imbalanced Soil pH
Blackberry bushes prefer a soil pH of 5.5-6.5.
Most plants prefer a slightly acidic pH as it dissolves the nutrient solids in the soil and makes them 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, SUNY College of Environmental Science and Forestry
If the pH is outside of this range, blackberry plants aren’t able to absorb nutrients properly, leading to issues such as yellow, brown, and dropping leaves.
The best ways to check your soil’s pH are with pH strips or a meter. I prefer using a pH meter since they’re easy to use and affordable. To see which pH meter I use and recommend, check out my recommended tools page.
If you find your blackberry plant’s soil pH is too acidic (below 5.5), apply alkaline amendments such as wood ash, biochar, or lime.
For soil that’s too alkaline (above 6.5), apply acidic amendments such as sand, peat moss, and coffee grounds.
4. Pests
Aphids
Aphids are small bugs that suck the sap from underneath the blackberry plant’s leaves. This loss of sugar and moisture causes the leaves to curl, yellow, and drop. They also cause some blackberry diseases.
When aphids suck the plant’s sap, they 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.
Spider Mites
Spider mites are similar to aphids, except they’re part of the spider family. They also feed on blackberry plants and cause leaves to yellow, red, and drop.
The main differences in appearance between aphids and spider mites are the spider mite’s ability to spin webs. These webs can cause damage to other parts of blackberry bushes such as the twigs and fruit.
So, if you see small dots on your blackberry leaves, see if they’re depositing honeydew or webs and you’ll identify the pest.
Treatment
The best ways to get rid of aphids (and mites) on blackberry 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 another good option.
For example, when my 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.
5. Diseases
Verticillium Wilt
Verticillium wilt is a fungal disease in soil that causes blackberry leaves to yellow, brown, and drop. Over time, it can kill the plant. Already weakened plants from drought, over-watering, and other stressors are more likely to become infected from Verticillium wilt.
This fungal disease affects blackberry branches closest to the soil and works its way up the plant. The branches or canes appear blueish-black and die during the summer when the plant fruits.
There’s no cure for verticillium wilt, but proper water management can prevent and limit the disease. Drying out the soil can starve the fungus.
Root Rot
Root rot, also called Armillaria or Phytophthora Root & Crown Rot, is a root fungus that causes a blackberry bush’s leaves, blossoms, and fruit to droop, yellow, brown, and drop.
This disease typically occurs in areas with poor drainage.
Avoid using sprays for root rot as it’s not effective.
There is no chemical control available for crown and root rot in the home garden. The most important control strategy is careful water management.
Clemson University Cooperative Extension Service
To prevent root rot, only water when the top 2-4 inches of soil is dry and promote well-draining soils.
To treat root rot, transplant your plants to an area with fresh, drier soil. Potted blackberry bushes with root rot should be repotted with fresh potting soil. Raised beds are also helpful in improving soil drainage.
For example, my potted Kaffir lime tree had root rot recently, which I was able to tell from the sopping wet soil and swampy smell. Fortunately, after repotting the tree with fresh potting soil and waiting a few days, the tree made a full recovery!
Sources
- https://ucanr.edu/sites/SoCo/files/27140.pdf
- https://ipm.ucanr.edu/PMG/GARDEN/FRUIT/blackberries.html
