A reader recently asked me why their raspberry plant’s leaves are curling. I’m familiar with some causes of leaf curl, but I wanted to do more research to get them a complete answer. Here’s what I found.
Raspberry leaves curl from insufficient water and nutrients, excess heat, and aphids. For best results, only water when the first 2-4 inches of soil is dry and apply compost and mulch. Aphids transmit leaf curl virus to raspberry plants, so manage aphids with water, neem oil, or ladybugs when possible.
While raspberry plants get leaf curl from several causes, how can we identify the issue causing it, and how can we fix it?
1. Under-Watered
The main reason raspberry leaves curl is from a lack of water. The curling is a natural response to hold more moisture within the leaf. If left for too long, the leaves dry, brown, and drop from the plant.
You can tell if your raspberry plant is under-watered if its soil is bone dry. I like to check this by pushing a finger into the soil, under the plant’s drip-line or canopy.
Fortunately, there’s a rule for watering that avoids both under and over-watering.
Only water when the first 2-4 inches of soil is dry. When you do water, deeply water down to 2 feet as the majority of the plant’s roots are found within this depth.
Similar to blueberry roots, and other fruiting plants, 90% of raspberry roots grow within the first 2 feet of soil. By deeply watering, we’re allowing all of the plant’s roots to absorb water and promoting deeper roots.
Remember: shallow watering leads to shallow roots. Short roots cause plants to become highly dependent on frequent watering and unstable in winds or other events. Deep watering promotes greater drought survival (accessing deeper water) and better anchorage in the soil.
Additionally, provide raspberry plants with 2 inches of compost every 1-2 months and 4-12 inches of mulch every 3-6 months.
Compost provides valuable nutrients and greatly retains soil moisture. It does this by improving the soil’s richness or organic matter, with every 1% increase leading to an additional 20,000 gallons of water held per acre.
Mulch also provides nutrients, but is great for reducing evaporation, regulating soil temperature, and preventing erosion. Since raspberries evolved as understory plants in forests, they’re used to plenty of mulch in the form of fallen leaves and branches.
As permaculture guru Geoff Lawton says, a forest grows on a fallen forest.
Even if your raspberry plant is watered properly, strong heat and dryness also cause leaves to curl.
2. Excess Heat and Dryness
Raspberry plants that are too hot and dry get curling 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, brown, and drop in a matter of days or hours.
Ideally, grow raspberry plants in USDA zones 2-8, depending on the variety. This is generally between -50ºF 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 -50ºF, we’re going to focus on what to do in hot weather.
But first, it’s helpful to know how raspberry plants cool themselves so we can expand on it.
Raspberry 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 raspberry plants cool.
Tips for Hot Weather
- Compost and mulch – as mentioned above, compost and mulch are two of the most important practices in any garden, especially regarding water retention and soil temperature control.
- Partial shade – Since raspberries are natively understory plants, they prefer partial shade from the hot afternoon sun. You can create shade by using umbrellas, shade sails, or other plants. The best direction to shade from is the western sun as it’s the hottest.
- Plant Density – To boost transpiration, create as much plant density around your raspberries. This raises the humidity and provides partial shade to the raspberry and its soil, significantly cooling it. A good way to do this is with companion planting.
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 |
Certain nutrient deficiencies cause raspberry leaves to curl. The above table shows how you can identify the most common deficiencies for raspberry plants.
However, it’s not always obvious which nutrient is deficient in the soil. For this reason, applying a regular boost of a complete nutrient profile is recommended.
The Best Way To Fertilize Raspberry Plants
The two main ways to fertilize raspberry plants are chemical fertilizers and compost. While chemical fertilizers have nutrients in quantity, they often lack quality and cause issues such as dry soil and reduced soil health.
As a result, many gardeners are finding that compost is replacing their fertilizers. As mentioned in the watering section, use 2 inches of compost every 1-2 months around your raspberry’s drip-line. Keep it at least 3 inches from the stem to avoid mold.
Either one you choose—you can check out the fertilizers and compost I recommend on my recommend fertilizer page.
However, nutrients aren’t everything.
Soil pH
While nutrients are important, they cannot be absorbed by the plant properly if the soil pH is too acidic or alkaline.
Raspberry plants prefer a soil pH of 5.6-6.2.
The reason why most plants prefer a slightly acidic soil pH is because this is the pH that dissolves the nutrient solids. Only then are they accessible to the plant’s finer roots.
The best ways to check your soil’s pH are with 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. Transplant Shock
If your raspberry plant 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 raspberry 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
5. Leaf Curl Virus (Aphids)
Aphids are small bugs that suck the sap from underneath the raspberry plant’s leaves. This loss of sugar and moisture causes the leaves to curl, discolor, and drop. They also cause raspberry leaf curl virus.
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.
The best ways to get rid of aphids (and mites) on raspberry 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.
Other bugs can also cause leaf curl on raspberries, including:
- Leafhoppers
- Leafrollers
To learn more about raspberry leaf virus, and the pests that cause raspberry leaves to curl, check out this Berry Diagnostic Tool by Cornell University.
