Dahlias tend to be a bit more sensitive than other plants, they are often targeted by pests, and diseases and have other problems like not flowering or even their leaves turning brown or black. For the most part, healthy Dahlia leaves look green or dark green, and the larger the plant is the bigger its leaves will also be. Under certain conditions the Dahlia leaves will turn brown, this is not always fatal but it could be if the plant is not treated.
Excessive sun exposure can lead to browning and dry leaves in dahlias, resembling sunburn. To address this issue, ensure that your dahlia plants are receiving adequate water and the right amount of sunlight. It’s important to strike a balance between sunlight and shade to prevent leaf damage. Additionally, inspect the plants for any signs of disease or pest infestation that could contribute to the browning of leaves.
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It can be extremely infuriating, struggling to grow a couple of Dahlias only to see their leaves turn brown once the plant is mature. If a couple of their leaves turn brown it shouldn’t be a big problem, but the more brown leaves the Dahlias have the higher the likelihood is that the plant will simply die off. Dahlias that have brown leaves, or their leaves are just about turning brown are less likely that they will flower.
Oftentimes it is not just one thing that can make the Dahlia leaves turn brown, but a combination of several things, which will slowly start to damage the leaves. If your Dahlia buds are not opening then check out my recent article Dahlia Buds Not Opening ( Top 5 Reasons ).
Dahlia Leaves Turning Brown
When dahlia leaves turn brown, it can be a sign of various issues affecting the plant. One common cause is fungal diseases such as powdery mildew or botrytis blight, which thrive in humid conditions or when plants are crowded. These diseases can cause browning, wilting, and eventual death of the leaves. Overwatering or poor drainage can also lead to root rot, which manifests as brown, wilted leaves.
Additionally, exposure to extreme heat or sunburn can cause leaf scorching and browning. It’s important to diagnose the exact cause of the browning leaves to implement the appropriate treatment. This may involve adjusting watering practices, providing better air circulation, applying fungicides if necessary, or relocating the plant to a more suitable environment.
Overwatering
If the Dahlias get way too much water then they can be negatively affected. Usually, overwatered Dahlias will rot away, although the plant also becomes more prone to diseases like the Necrotic Spot Virus, and Verticillium Wilt which will also cause their leaves to turn brown. If the Dahlias are being overwatered for a long period of time, then their leaves will slowly turn brown, to the touch they will feel mushy.
Overwatering is not always caused by watering the Dahlias too often, but by the soil not draining fast enough, which will have the tubers sit in the water where they will start to rot and affect the entire plant. If your Dahlias are not flowering then check out my recent article Dahlias Not Flowering ( Top 7 Reasons ).
Necrotic Spot Virus
One of the main reasons why Dahlia leaves turn brown is due to Necrotic Spot Virus. This virus will slowly turn the leaves of the Dahlias to yellow, then brown and they will eventually turn black or simply fall off. This virus is caused by thrips, and as they are slowly sucking the plant sap they will infect the plant. The good news is that if you get rid of the thrips, you significantly lower the chance of the Dahlias getting the virus.
The bad news is that if the Dahlia leaves have turned brown due to Necrotic Spot Virus then they are extremely unlikely that they will survive. If this is the first time you are planting Dahlias then check out my recent article What To Do With Dahlia Tubers In Spring? ( Top 6 Chores ).
Verticillium Wilt
Verticillium Wilt is a fungal disease that can affect Dahlias, oftentimes their leaves start to curl up and turn yellow, brown, or even red in certain cases. The Verticillium Wilt will infect Dahlias through their roots, from where it will slowly start to spread. This wilt can be found in almost every type of soil, but they do need a lot of moisture in order to survive. Soils that are poorly draining can have this wilt affecting not only Dahlias but other plants as well.
Fungicides do work against Verticillium Wilt, but it is best to try and avoid the situation where your Dahlias might get them. Make sure to plant your Dahlias in a well draining soil, and do not overwater them.
Frost Damage
Dahlias are extremely sensitive to frost, while a couple of days of frost will not kill the entire plant but it will damage the leaves. At the end of the growing season, most Dahlias look pretty bad, most of their leaves have turned brown or fallen off, and this happens due to the temperatures getting lower. On the other hand, they can even get frost damage during the summer, usually during hail storms or unusually cold nights.
Stem Or Tuber Rot
Once the stem or the tuber of the Dahlia starts to rot the leaves will eventually turn brown, provided that it has actually sprouted. Most Dahlias will die in the soil without even sprouting if they are affected by rot. Although if the tuber or the stem of the plant starts to rot after the plant has matured then it will start to slowly die off, beginning with the leaves browning. The sad news is that once the Dahlia tuber starts to rot there is nothing you can do.
On the other hand, if only the stem of the plant is starting to rot, then you can still cut it down and the tuber should not be affected. Usually, stem and tuber rot is caused by excess water, poor soil drainage, and low air circulation.
Underwatering
Dahlias tend to be thirsty plants, especially on hot summer days when they are blooming. Usually, the plant will start to wilt if it doesn’t get enough water, although this process can happen relatively quickly and you might only notice the brown leaves. In this case, the Dahlia leaves will turn brown and will be brittle to the touch. Simply touching the leaves will make them crumble, just like any other dried out leaves would.
The easiest way to treat this issue is to give the Dahlias more water, preferably in the evening. On the other hand, brown and dried out leaves will not be able to recover, so simply cut them off.
Sunburn
Dahlias are full sun loving plants, however, this excess sunlight can be devastating for the plant under certain conditions. On hot summer days, the leaves of the Dahlias can get burned, oftentimes small brown spots will form on the leaves. Eventually, these brown spots will become larger and the entire leaf will turn brown. To avoid this situation make sure to water your Dahlias from below, as even a couple of drops of water on the leaves will be able to make small brown burn marks on them.
On the other hand, if the Dahlias do not get enough sunlight their leaves can turn brown and eventually fall off. While Dahlias can grow in partial shade, but the bigger the plant gets the more light it will need, once it gets to a point where the sunlight isn’t enough it will slowly start losing some of its leaves, usually these will turn brown just before falling off.
Poor Soil
Dahlia leaves can turn brown if the soil conditions are not good enough, this can be anything from available nutrients in the soil, to how fast the soil is draining. Although Dahlias grow the best in a well draining soil, but they can grow relatively well in clay soil as well. As long as the clay soil is not compacted, the Dahlias can really benefit from the abundance of nutrients that are found in the typical clay soil.
If your local soil is relatively poor in nutrients, such as sand, you might want to amend the soil or grow the Dahlias in pots. No matter in what kind of soil you are growing your Dahlias it is usually a good idea to fertilize them before they start flowering. Just do not go overboard with the fertilizer as you might end up with Dahlias full of leaves and no flowers due to the increased nitrogen.
Key Takeaways
- The main reason why Dahlia leaves turn brown is due to too overwatering, excess water can start to rot the tubers and the stem of the plant, and the first sign of it happening is the leaves turning brown. In addition to this, Necrotic Spot Virus and Verticillium Wilt can also cause the Dahlia leaves to turn brown and eventually fall off. Dahlias can get sunburned, in this case, the leaves will turn brown and crumbly, in this case watering them in the evening does help a lot.
- Dry and brown Dahlia leaves are usually a symptom of not enough water, while wet, soggy, and brown leaves are signs of disease.
- Cold nights can turn the Dahlia leaves brown.