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6 Reasons Why Dahlia Is Dying (And How To Revive)

Dahlias come in a wide array of varieties. Some are perfect for cutting and adding a splash of color to your home, while others excel at drawing in insects, helping to keep your garden thriving.

Giving dahlias too much water can lead to trouble, making them wilt and sag. Overdoing it with water, whether by overwatering or because the soil doesn’t drain well, can cause the tubers to rot. This, in turn, might make the leaves turn yellow or develop spots.

In this guide, I’ll cover everything you need to know about why dahlias might be dying, helping you save your plants or learn important tips for your next planting season.

1. Root Rot

Dahlia is dying because of overwatering

Dahlia is dying because of overwatering.

Make sure the soil around your dahlias is moist but not waterlogged. A common mistake among beginners is to overwater them in the spring. At the early stages of growth, dahlias don’t have much foliage, which means they don’t need a lot of water yet.

In areas with moderate weather, seasoned dahlia growers suggest waiting until the summer to start watering more frequently. This is when dahlias sport a lot of leaves, and the weather heats up, increasing their need for water. But, this can vary depending on how warm your spring is.

Yellow leaves and brown, dry edges are telltale signs of root rot—a result of too much water.

Here’s what to do:

  1. Avoid watering dahlias daily right after planting them in spring.
  2. Water them once a week during spring as they start to grow.
  3. Aim to keep the soil slightly damp, never drenched.
  4. Prevent your dahlias from being in soggy conditions for too long to avoid waterlogging.

2. Not Enough Water

Dahlia is dying because of underwatering

Dahlia is dying because of underwatering.

Dahlias are prone to overwatering, especially when they’re young and have sparse foliage. However, as they begin to grow or during very hot weather, their water needs increase significantly. Yet, even for a fully matured dahlia, the soil should not be waterlogged.

The need for water greatly varies depending on the climate you live in and the type of soil in your garden. It can be tricky because the symptoms of both overwatering and underwatering look quite similar at first glance. But with a closer look, you can determine if they’re thirsty for more.

Common signs include leaves with yellow spots or entirely yellow leaves. Leaves and flowers might also appear crispy, brown, and dry.

Here’s what to do:

  1. Stick your finger about 2 inches (5 cm) into the soil to check for moisture. If it isn’t damp, it’s time to water.
  2. Use 1-3 gallons of water per plant, adjusting based on size and soil dryness.

3. Not Enough or Too Much Sunlight

Dahlia is dying because of not enough sun

Dahlia is dying because of not enough sun.

Different dahlia varieties require varying levels of sunlight. While some thrive in full shade, others need partial to full sun exposure to flourish.

Lack of sufficient sunlight for certain dahlia types leads to them stretching unusually tall as they search for more light. This can result in stunted growth due to their inability to generate enough energy for development. Additionally, some dahlia varieties may not survive if they’re placed in too much shade, showing signs of distress and eventual decline.

Signs that your dahlias are seeking more sunlight include excessive height and leaves that are shriveled and brown.

Here’s what to do:

  1. Research the sunlight requirements for your specific dahlia varieties.
  2. Relocate them to a spot that meets their sun exposure needs.
  3. For dahlias in pots, move them to a location with more or less sunlight as needed.
  4. Try planting them in different spots to find the perfect sunlight balance.
  5. Prune nearby trees and shrubs to increase sunlight accessibility.

4. Soil

Dahlias struggle in waterlogged conditions caused by poor-draining soil, but soil that’s too sandy can drain excessively, preventing moisture retention. Additionally, soil pH levels that are either too high or too low can harm dahlias. Fortunately, these issues can be resolved by adjusting the soil composition and modifying planting depth as outlined below.

Here’s what to do:

  1. If your soil drains poorly, consider relocating your dahlias to an area with better drainage.
  2. Use a soil testing kit to check the pH level; dahlias thrive best in a pH range of 5.8 to 6.2.
  3. To lower a high soil pH, incorporate aluminum sulfate or sulfur into the soil.
  4. To raise a low soil pH, add limestone or hydrated lime.

5. Pests

Dahlia is dying because of pest infestation

Dahlia is dying because of pest infestation.

Flea beetles, earwigs, slugs, snails, black bean aphids, and thrips are all pests that can target dahlias, causing damage to the stems and leaves. This damage can hinder the plants’ ability to absorb sunlight, potentially leading to their decline. While some pests are easily spotted, others are quite small and more challenging to detect.

Signs of infestation include holes in the leaves, parts of the stems missing on new growth, and small bite marks.

Here’s what to do:

  1. Introduce a variety of plant species around your dahlias to create a more balanced ecosystem.
  2. A certain amount of leaf and stem damage is normal and shouldn’t fatally harm your dahlia plants.
  3. Employ slug and snail pellets to control these mollusks.
  4. Use sticky traps to catch insects when their population becomes overwhelming.

6. Diseases

Dahlias can fall victim to a range of diseases that may lead to their demise. If you notice issues across all leaves, the cause is likely related to soil quality, watering habits, insect problems, or insufficient sunlight. On the other hand, if only a few leaves are affected, it’s probably due to a disease.

Look out for yellow spots on the tops of leaves, small black spores underneath, and areas on the leaves that are brown, dry, and dead.

Here’s what to do:

  1. Apply a fungicide to the affected plant.
  2. Consider using a natural solution to combat mold.
  3. Ensure there’s adequate air circulation around your dahlias.