Dahlias are magnificent plants that exhibit large exotic flowers which can mesmerize any plant lover. It can sink your heart when you see the leaves of Dahlia turning yellow.
Reasons for Dahlia’s leaves to turn yellow include Incorrect Soil, Pests, Overwatering, Underwatering, Disease, etc.
To fix the yellowing leaves you would need to identify the root cause of the problem. Let us look at the causes with symptoms and solutions below.
#1 – Incorrect Soil
Dahlia has specific soil requirements. Here are three ways where incorrect soil can lead to yellowing leaves of Dahlia.
A. Alkaline Soil
Dahlia thrives in slightly acidic soil and well-draining soil. The ideal pH value for Dahlia is 6.5. If the soil is alkaline, the Dahlia leaves would start to turn yellow.
How to Diagnose?
When you see the leaves of Dahlia are yellowing and you suspect the acidity of the soil, it is best to test the pH. A reading above 7 means the soil is alkaline.
You would need to bring down the acidity of the soil to around 6.5. You can either apply aluminum sulfate or sulfur for the same.
B. Nutrient Deficiency
Also at times, dahlia leaves may turn yellow due to a lack of iron or nitrogen.
In Utah, in particular, plants are susceptible to a condition known as Chlorosis. It signifies that the plant is not able to produce enough chlorophyll and this causes the leaves to turn yellow.
How to Diagnose?
It can be seen by the yellowing of leaves along with a network of dark green veins.
Now how do you determine if the chlorosis is due to Iron or Nitrogen Deficiency?
In case of Nitrogen deficiency, leaves will start turning yellow from the base of the leaf blade. And the old foliage will start to turn yellow first.
Whereas, in case of Iron deficiency, Dahlia leaves will start to turn yellow from the top of the leaf blade. And the new leaves will be the first to turn yellow.
For Iron deficiency, add iron sulfate to bring up the iron levels in the soil.
For Nitrogen deficiency, apply suitable fertilizer with an NPK ratio of 4 10 10. We would recommend Lilly Miller Bulb & Bloom Food 4-10-10 4lb. You should use a fertilizer with less nitrogen and more potassium.
C. Heavy clay soil
They prefer loosened and well-drained soil. Heavier clay soil can lead to waterlogging.
How to Diagnose?
This water can devoid the root of the required nutrients and you will notice the signs of stress with the yellowing of leaves.
Heavy clay soil affects drainage. The soil would not dry out as soon as it should and this may result in water logging around the roots.
- If you notice waterlogging, stop watering until the top 1.5 inches of soil is dry.
- Adding compost and other organic matter can help change the composition of the soil over time.
#2 – Pests
Dahlia can be infested by multiple insects that can cause wilting and yellowing of the Dahlia leaves.
They are one of the most prominent pests that infest dahlia plants. Leafhoppers transmit a disease known as the “yellows” by feeding.
They are tiny green insects. They often attack the Dahlia plants in early spring.
Initial feeding injury can result in discoloration, sometimes called “hopper burn”. It is often reflected as v-shaped yellowing on leaf tips. continuous feeding can cause the leaf to turn brown and eventually brittle.
Spraying Garden Safe Brand Fungicide can help you control them.
They are small insects about 1 to 1.3 mm long and thrive in high humidity and average temperatures (23 to 28℃).
They have wings and hence can quickly spread. As they can cling on, water spray doesn’t help to control them.
Thrips feed on the leaves’ sap and due to the constant loss of sap, leaves start to curl and turn yellow.
Removing the weeds and disposing of the weeds regularly can help to avoid thrip infestation. Reduce weeds as they can influence thrip populations
In case, you do get an infestation, we would recommend spraying Bonide Insecticidal Soap.
They are also responsible for yellow dahlia foliage.
Heavily infested Dahlias with armored scale will appear weak having yellow leaves. Armored scales can kill Dahlias and must be controlled when their populations rise.
Armored Scales feed under the leaves but unlike other scales do not produce honeydew.
To find out, if you have an armored scale infestation, check at the lower side of the leaves.
Heavily infested plants are often covered with small, circular coverings, and underneath each covering is the scale organism feeding on the juices of the plant.
Due to the hard covering, they are difficult to remove. Water spray and common insecticides do not reach them.
We would recommend spraying Compare-N-Save Systemic Tree and Shrub Insect Drench to control them.
Spider mites are also tiny insects that live on the underside of leaves causing yellowing.
It is easy to check if you have a spider mite infestation. Just lookout for the web on the lower side of the leaves.
When the mites attack, you will initially see yellow spots on the leaves before full leaves turn completely yellow.
To control them, you should first look for Neem oil as it is considered one of the most effective methods to get away with mites for its pesticide qualities.
Neem oil chokes them. It can be mixed with castile soap and water and sprayed.
#3 – Overwatering
Overwatering is often the culprit when it comes to the yellowing of the Dahlia leaves. Dahlia is prone to root rot and hence you need to be cautious and should follow the watering schedule.
Overwatering causes waterlogging around the roots. This causes a lack of nutrients for absorption through the roots.
How to Diagnose?
You would notice that the yellow leaves of Dahlia are also limp and soft. Tips of the leaves would also start to turn brown.
- When you notice your Dahlia leaves turning yellow due to overwatering, you should immediately stop watering until the soil gets dry.
- Check the soil if it is draining well else add compost and other organic matter.
- Water the plant twice a week only when you see the top 1 to 1.5 inches is dry.
#4 – Underwatering
Though overwatering is often the cause, underwatering also can make the Dahlia leaves turn yellow.
How to Diagnose?
You would notice that the yellow leaves of Dahlia are limping but dry.
- When you notice your Dahlia leaves turning yellow due to underwatering, you should water the plant whenever the topsoil is 1.5 inches dry.
- Adding mulch to the soil would help to retain the moisture for a longer time.
#5 – Disease
Some fungal problems result in yellowing of leaves including Root rot, Stem rot, Mosaic Virus, and Verticillium Wilt.
Root rot / Stem rot – Overwatering promotes fungal growth that results in the root or stem rot. This will initially lead to yellowing of the leaves then brown and eventually the plant will die.
Mosaic Virus – This is a deadly virus that is spread by aphids who carry them. It will reflect as irregular yellow spots on the leaves. Further, the plant will have stunted growth.
- Remove and dispose of the infected part of the plant.
- Disinfect your garden tools
Though it is not a must, but we would recommend you to cut them off.
Potted dahlia leaves may turn yellow due to Incorrect Soil, Pests, Overwatering, Underwatering, Disease, etc.
We would recommend checking the reason why they are yellowing and then taking suitable corrective measures as we have penned down in this article.