I’ve been researching raspberry plants lately, and I saw they commonly get brown leaves. There wasn’t a great answer about this issue out there, so I did some more digging. Here’s what I found to identify and treat brown leaves.
Raspberry plants get brown leaves from improper watering, climate, nutrients, as well as pests and diseases. To prevent brown leaves, only water when the top 2-4 inches of soil is dry, apply compost and mulch, and grow in zones 2-8.
Let’s take a closer look at how to identify what’s causing brown leaves on raspberry plants(and how to fix it).
1. Under-Watering
By far the most common cause of brown leaves on raspberry plants is a lack of water. Raspberry plants that don’t have enough soil moisture develop issues such as leaves curling, drying, browning, and dropping.
Curled leaves are one of the early signs of under-watering as a plant’s leaves curl to conserve and hold onto any remaining moisture.
If you catch the leaves at this stage and provide the plant with sufficient water, the curled leaves will recover. However, if the plant is left without water for much longer, its leaves will turn brown and drop.
Fortunately, since watering is one of the climate factors that we can control best, it’s not too difficult to adjust.
The best way to water raspberry plants is to only water when the first 2-4 inches of soil is dry. I like to check this by pushing a finger into the soil, under the plant’s canopy. Aim to soak the soil down to at least 2 feet as the majority of the plant’s roots grow at this depth.
Additionally, apply 2 inches of compost and 4-12 inches of mulch.
Compost provides valuable nutrients and greatly improves the water retention of the soil. Every 1% increase in the soil’s organic matter leads to an additional 20,000 gallons of water held per acre.
Mulch reduces evaporation, regulates soil temperature, and prevents soil erosion. Since raspberry plants evolved as understory plants in forests, they’re used to plenty of mulch in the form of fallen leaves and branches. So, don’t toss your fallen leaves. Use them to boost your garden!
As permaculture guru Geoff Lawton says, a forest grows on a fallen forest.
2. Excessive Heat and Dryness
Under-watering is made much worse if the weather is extremely hot and dry. Even if you’re properly watering your raspberry plant, its soil can dry in a matter of days or even hours if the conditions are hot enough.
One of the best ways to help your raspberry plants grow well is to make sure you’re growing your variety in its proper hardiness zone.
Aim to grow raspberry plants in USDA hardiness zones 2-8. Avoid temperatures below -50ºF and above 90ºF if possible.
While it’s not always possible to control the weather, you can influence it. Gardeners are finding this out more and more each day and creating microclimates in their backyards and properties.
Microclimates are a difference in a local climate compared to its greater climate. It can mean using the shade of a single tree, or the shade of a mountainside. Sunlight, wind, moisture, and other factors influence microclimates.
A successful and extreme example is how an oasis can grow in a desert (and no, they’re not mirages!).
Here are some ways you can reduce the effects of heat and help raspberry plants stay cool.
- Compost and Mulch – providing compost and mulch are two of the best practices anyone can use in their garden. The effects of their moisture retention, nutrient quality, and erosion control are unmatched.
- Partial Shade – while most plants require full sun (6+ hours a day), that doesn’t mean they can tolerate a hot sun. Aim to provide your raspberry plants with partial shade if temperatures get above 90ºF. Shade from the hot, afternoon (west) sun is most beneficial.
- Plant Density – planting raspberries densely with companion plants not only provides them with benefits such as soil coverage and partial shade, but protection against wind, pests, diseases, and more. It also dramatically retains moisture from transpiration.
Remember, plants (including raspberries) stay cool by sending moisture from their roots to their leaves and through a process called transpiration. Just like humans, plants exhale moisture (transpiration), and this is why a thick, jungly canopy feels more humid than an open one.
By covering the soil, creating shade, and capturing transpiration, we’re drastically influencing the microclimate for our plants and giving them the best chance to grow.
To learn more about microclimates, and how you can create them in your backyard, check out this video by Gardener Scott.
3. Improper Nutrients
Excess Nutrients
If you’ve been properly watering, and your climate hasn’t been extreme, the next potential issue to consider is improper nutrients.
Excess nutrients are caused by over-fertilizing. Typically, this is from chemical fertilizers as compost isn’t potent enough. Fast-release fertilizers in particular cause excessive nutrients to be released quickly.
Over-fertilized raspberry plants often get symptoms such as leaves curling, drooping, browning, and dropping. Sometimes, green leaves can drop from the plant. With too much fertilizer, the raspberry plant can die.
If you believe you’ve over-fertilized your raspberry plants, the best way to treat it is by leaching. Leaching is when you water the soil enough that a large amount of nutrients gets pushed further down into deeper soil layers, out of the reach of the raspberry plant’s roots.
A 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 |
Raspberry plants that lack nutrients most often get yellowing, browning, and dropping leaves. Fortunately, different types of yellow leaves can help narrow down the specific deficiency (see the table above).
However, it’s not always possible to determine which nutrients your soil is lacking (unless you have it tested), so the best way to treat your soil is to provide it with a fertilizer with a complete nutrient profile.
The Best Fertilizer for Raspberry Plants
The two main ways to fertilize raspberry plants are chemical fertilizers and compost. Generally, while chemical fertilizers have nutrients in quantity, they often lack quality and can lead to long-term damage to the soil. This is why more and more gardeners are finding that compost is replacing their fertilizers.
However, chemical fertilizers can have their place, especially if we use them as a short-term solution and not the endgame.
For fertilizers, aim for a balanced NPK (nitrogen, phosphorus, and potassium, the three main nutrients of plants) and apply as directed on the package.
For compost, apply 2 inches every 1-2 months. Mulch also assists with nutrients (among other benefits), so applying 4-12 inches every 3-6 months works incredibly well.
Either route you go, you can see which fertilizers and compost I recommend on my recommended fertilizer page.
Soil pH
While nutrients are essential, plants cannot absorb them sufficiently if their soil has an imbalanced pH.
As with most plants, raspberries prefer a slightly acidic soil pH (5.6-6.2). This is because a slight acidity 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
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 raspberry’s soil pH is too acidic (below 5.6), apply alkaline amendments such as wood ash, biochar, or lime.
For soil that’s too alkaline (above 6.2), apply acidic amendments such as sand, peat moss, and coffee grounds.
4. Pests
- Aphids – Small dot-like bugs that suck the sap from underneath the raspberry plant’s leaves. Treat by spraying water, neem oil, or releasing ladybugs (a natural predator). Spraying them with a jet of water worked for my potted Kaffir lime tree.
- Spider Mites – Similar to aphids, mites suck the sap from leaves and can be treated in the exact same ways.
- Japanese Beetles – Feeds on leaves and sometimes berries. You’ll likely notice them visually or see evidence of holes in leaves. Treat with soap and water, neem oil, or physically remove them from the leaves (bonus points if you feed the beetles to your chickens!)
- Leafrollers – Small caterpillars that feed on berry leaves, flowers, and green fruit. They use their silk to curl the leaves and hide in them. Treat with pheromone traps and by encouraging natural predators such as spiders. Sprays are not recommended.
5. Diseases
- Root Rot – a root fungus that causes leaves, blossoms, and fruit to droop, yellow, brown, and drop. Typically occurs in waterlogged soil and those with poor drainage. No chemical control is available. Repotting my potted Kaffir lime tree with fresh potting soil treated its root rot.
- Verticillium – a fungal disease in soil that causes leaves to yellow and brown, and can lead to the raspberry plant dying. Already weakened plants from drought, over-watering, and other stressors are more likely to become affected.
- Cane Blight – a fungal disease that wilts and browns leaves, and kills part or all of a raspberry plant. Usually starts from a wound on the plant. Treat by promoting airflow and sunlight, and pruning infected canes. Sprays are rarely necessary.
- Fire Blight – a bacterial disease that appears as scorched leaves (hence the name). Affects the rose family (apples, pears, berries, and more). Treat with pruning and sprays including vinegar and essential oils. Some chemical sprays may be effective.
- Rust – a fungal disease that turns raspberry leaves a splotchy red-brown. Treat by pruning and using organic sprays.
To learn more about the pests and diseases raspberry plants get, check out these resources:
- Raspberry Insect Pests, University of Minnesota Extension
- Raspberry Diseases, Government of Alberta
- Raspberry Cane Diseases, University of Minnesota Extension
