why is my dahlia yellowing

Dahlia Leaves Turning Yellow? (Here’s Why and How to Fix It!)

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.

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 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 stems of plants.
  • Mix peat moss in the soil to make it light thus preventing any future outbreaks of stem rotting.


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.
  • 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 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.


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

Do you see yellow spots on Dahlia leaves? This is because of a virus that specifically attacks Dahlia plants. It is aptly named Dahlia Mosaic Virus.

Aphids carry this virus and spread it when they drink the sap of new plants.


  • 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.

Happy Gardening 🙂