Dahlia leaves turn yellow because of Stem rot. This is the main reason and you’ll notice wilted leaves on the plant that soon turn yellow. Magnesium deficiency also causes the Dahlia leaves to turn yellow.
There can be other reasons for foliage yellowing. Let’s see what those reasons are and how to fix them.
Why are the leaves on my Dahlias turning yellow?
Improper watering is one of the main reasons why the Dahlia plant’s leaves turn yellow. Non-optimal soil pH is also one of the major reasons why Dahlia leaves yellow.
Stem rot also causes yellowing in the leaves of Dahlia. Check the plant for the symptoms of Stem rot and treat it accordingly.
Dahlias turning yellow and dying
Dahlia plants turn yellow and die when they are infected by stem rot/root rot. Stem rot is seen in the Dahlia plant when the soil around the plant is waterlogged. This is especially seen in poorly draining soils.
This disease is caused by soil-dwelling fungi. A white-colored crown forms around the stem where the plant touches the soil.
The entire root system of the plant rots in severe conditions destabilizing the plant. Cut off the infected plant parts with a sharp, clean knife.
To prevent
- Do not let old, dead leaves clog up your garden surface.
- To prevent waterlogged conditions, keep mulch away from the stems of plants.
- Mix peat moss in the soil to make it light thus preventing any future outbreaks of stem rotting.
Overwatered Dahlia Diseases
Excess watering leads to waterlogged conditions around your plant. It is crucial to water your Dahlia plant consciously.
Overwatering causes Dahlia tubers to rot. Dahlias are known to be very sensitive to root diseases. This makes it tough to grow them.
Signs of Overwatering Dahlias
Dahlias give out some signs when they’re being overwatered. Look out for them if you want to prevent root rot in your plants.
- Leaves turn yellow but they are limp and soft in the case of overwatering.
- The tips of the leaves turn brown. Overwatering signs quickly show at the tips of the leaves.
- You’ll see blisters forming on various parts of your Dahlias. These erupt and white warty growths are seen on the blisters.
Fix Overwatering in Dahlia
Check the soil with your bare fingers. If the soil is moist up to several inches, your Dahlia is probably overwatered. Let the soil dry out between watering sessions.
Soil with bad drainage creates waterlogged conditions around the plant. You can prevent this by adding compost to the soil.
Underwatering
Underwatering too can cause yellowing in the leaves of Dahlia. Underwatered leaves appear limp but dry. This is the way to distinguish them from overwatered plants.
Experts say drip irrigation is great for Dahlia. Water your plants once a week, when you do, water them deeply.
The rootball of underwatered plants gets dried up. You can fix such plants by making the rootball wet.
Add a layer of organic mulch if you think the issue lies in the soil. Mulch helps the soil to hold moisture better.
Tip: Water the plant when top 2 inches of the soil goes dry. By doing this you can make sure that you don’t overwater the plant.
Leafhopper
One leafhopper won’t affect a plant much but a large population can even kill a plant. They are tiny in size, green in color.
Leafhoppers cause discoloration which first appears in the margin of leaves. The leaves turn yellow initially but they turn brown and brittle eventually.
To prevent leafhopper infection spray the vulnerable plants with a mixture of insecticidal soap and seaweed extract.
You may want to spray a mixture of insecticidal soap and rubbing alcohol. This is proven to effectively control Leafhopper infestation.
Spider mites
Spider mites cause yellowing in the leaves of Dahlia too. These insects are small and live on the undersides of the leaves.
You can confirm a Spider mite infestation if you see webbings on the leaves. They cast web to protect themselves from potential predators.
Yellow spots are seen on the leaves of infected plants. If the infection becomes severe, the leaves turn yellow completely.
At this point, the plant gets stunted. You may want to hang yellow sticky cards around the plant to identify such pests early on.
To fix:
- Spritz the undersides of the leaves using a garden hose to dislodge these pesky insects.
- ‘Cinnamite’ is a natural pesticide that gets rid of adult Spider mites efficiently.
- You can use Neem oil to get rid of these pesky mites too.
Potted Dahlia leaves turning yellow
Potted Dahlia leaves turn yellow because of Stem rot. Waterlogged conditions lead to root and stem rot in plants.
You need to make sure that the pot in which your Dahlia has drainage holes. Make sure the soil drains out excess water.
If the soil holds more water than needed, add compost to it to make it suitable for the plant.
How often do you water potted dahlias?
Water your Dahlia consciously. You can check if the plant needs water by inserting your finger into the soil. If the soil is dry, water it!
You need to water your Dahlia plant once a week. Water deeply when you water the plant. Drip irrigation works wonders for Dahlias.
Dahlia Mosaic Virus: Yellow spots on dahlia leaves
Yellow spots on Dahlia leaves are seen when the plant is infected by Dahlia Mosaic Virus. Aphids carry this virus and spread it when they drink the sap of new plants.
Symptoms
- Yellow streaks are seen along the midrib or veins.
- Twisty, rolled or cupped leaves are seen in infected plants.
- Black spots are often seen near the midrib. The growth of the plant is stunted.
To control
- The best way to prevent this disease is by controlling the aphid population around these plants.
- Dispose of the infected plants/plant parts as soon as you see them. Don’t divide/propagate them.
- Disinfect tools immediately after using them on infected plants.
Dahlia Nutrient Deficiency
Dahlia leaves turn yellow when the plant doesn’t get the nutrients it needs to produce chlorophyll. Both Iron deficiency and Magnesium deficiency can cause the leaves to turn yellow in Dahlia. This condition is called Chlorosis.
Dahlia Magnesium Deficiency
Dahlia leaves turn yellow when the plant doesn’t get enough Magnesium. The leaves turn yellow due to Chlorosis.
You can add Epsom salts to the soil/potting mix to improve the Magnesium content. Mix a teaspoon of Epsom salt in 9 liters of water.
Older leaves turn yellow before the newer growth when the plant doesn’t get enough Magnesium. Get a soil test done before amending the soil.
Dahlia Iron Deficiency
Iron deficiency causes the leaves to turn yellow in Dahlia. The leaves turn yellow while the veins remain green due to iron deficiency.
The newer leaves turn yellow before the older leaves when the plant doesn’t get enough iron. Your plant can’t absorb iron if the soil pH is above 6.5.
Get the soil tested. See if the soil really lacks iron content or if it’s not acidic enough. You can amend the soil to make it acidic.
Dahlia leaves turning yellow due to insects
Dahlia leaves turn yellow when insects like Thrips, Aphids, Leafhoppers, and Spider mites infest the plant. Slug and Snail damage also cause the leaves to turn yellow.
These sap-sucking insects cause yellow spots on the affected Dahlia leaves. Insect infestations happen when you don’t follow proper cultural practices.
Remove leaf debris whenever possible to keep the pests from flourishing. You can read in detail about the pests that infest Dahlia.
Dahlia’s leaves drooping and turning yellow
Dahlia leaves droop when the plant is watered improperly. Dahlia plants turn yellow and droop when it gets too much sunlight. Dahlia leaves also droop when the plant is given more fertilizer than needed.
Dahlia leaves turn yellow and eventually brown due to fertilizer burn. Leaves appear as if they’re scorched.
Dahlia leaves turn yellow and wilt when the plant gets more sunlight than required. Sometimes the leaves might turn brown. Try to ensure the plant is getting some shade in the afternoon to protect it from the harsh sun.
Verticillium Wilt Dahlia
Verticillium wilt is a fungal disease that wilts the leaves on one branch initially. The leaves of this branch may turn yellow. Eventually, the disease affects the entire plant.
The yellow leaves turn brown/black after a few days. Verticillium wilt is seen in those regions where the temperature fluctuations are dramatic.
A plant that’s infected by Verticillium wilt can not be saved. Dig out the plant and dispose of it carefully. Replace the soil if possible.
You can treat the soil infected by Verticillium wilt by using techniques like soil fumigation and soil solarization.
Can Dahlias get Aster Yellows?
Yes, Dahlias can suffer from Aster Yellows. Aster yellows is a bacterial disease that causes the leaves and stems to turn yellow.
Extensive deformities are seen when Dahlias are infected by Aster Yellows. Flowers will turn green and become leaf-like structures.
Shoots get deformed and give the plant a witches’ broom appearance. Sometimes bulb-like structures are formed instead of seeds.
Once a plant is infected by Aster yellows there is no way of saving it. Remove and destroy all the infected parts of the Dahlia plant.
Happy Gardening 🙂