Dahlia’s come in a range of different varieties, some are good for ornamental flowers to cut and keep in the home. Whereas, others are better for attracting insects and keeping your garden healthy.
Too much water, not enough water, poor soil health, or the incorrect amount of sunlight can cause dahlia to die. To revive dahlia water it when the soil is 1-2 dry from the top. Provide nutritiously and draining soil along with 4-6 hours of direct sunlight. Also, make sure the pot has drainage holes and the plant is free from disease or pests.
In this article, I will explain everything there is to know about the causes of dahlias dying so that you can save them. Or, learn a valuable lesson that you can take with you into the new planting season.
Too much water causes root rot
Keep them moist but not sitting in water. A common beginner mistake with dahlias is to over water in the spring. When dahlias have just started to grow, they don’t have a lot of foliage. Therefore, the demand that dahlias have for water at this stage in their growth isn’t very high.
In moderate climates, expert dahlia growers recommend not to water them until the summer, when they have a large amount of foliage, and the temperature is much higher. This is when the water demand is the highest. However, this does depend on how hot the spring is in the climate where you live.
- Brown dry leaves
- Edges of the leaves are brown and dry
- Flowers are brown on the edges
- Tubers have soft wet areas – noticed when dug up
- Mold growing on the surface of the soil, and stems
- Do not water dahlias every day in the spring when they are just planted
- Water dahlias once a week in the spring when they are new
- Keep the soil lightly damp but not soaked
- Avoid having your dahlias sitting in water for long periods – being waterlogged
Not enough water
Dahlias are very easy to overwater when they are still small and don’t have a lot of foliage. But, once they are starting to grow and/or when the temperature is very hot, they DO need a lot of water. If you have a fully grown dahlia, the soil should still not be soaked. However, you need to ensure that the soil is damp.
This very much depends on your climate and the type of soil you have. The signs of overwatering and underwatering are very similar. But, on closer inspection, you can tell whether they need more water.
- Soil is completely dry to the touch especially in summer, and in hot climates
- Leaves have yellow spots or are completely yellow
- Leaves and flowers are crispy, brown, and dry
- Dahlias didn’t bloom
- Put a finger 2 inches (5 cm) into the soil, it should be damp if not water them
- Water your dahlias twice a day – morning and evening in the summer
Not enough or too much sunlight
Different varieties of dahlias need different amounts of sun. Some can grow perfectly fine in complete shade. Whereas, others need partial or complete sun.
If certain varieties of dahlias don’t get enough sun, they will grow very tall as they reach out looking for more sunlight. They can also have limited growth as they don’t have as much energy to convert into growth. Some varieties of dahlias will die and show signs of dying if kept in full or partial shade.
- Dahlias growing extremely tall – they’re trying to reach for more sun
- Leaves are shriveled and brown
- Leaves are yellow, partly yellow, or have yellow spots.
- Only a few flowers, and flower buds
- Find out how much sunlight your dahlias need based on the variety they are
- Replant them in an area where they will get the amount of sun they need
- Move potted dahlias into a different area where they will get less or more sun
- Experiment with planting them in different locations to see how much sunlight is ideal
- Thin out trees and shrubs around them to let in more sunlight
Poor draining soil
Poor draining soil can cause dahlias to become waterlogged. But, sandy soil that drains too much causes the soil to not retain enough moisture. The pH of the soil is too high or too low can also cause dahlias to die. These are easily fixed, by adding various products to the soil. As well as, changing how high or low you plant your dahlias in the ground, explained below.
- Leaves browning at the edges – soil is too rich, too much fertilizer is used
- Leaves are completely brown, drying out, and falling off
- Flowers brown on the edges
- Dahlias growing poorly, less growth than the typical height the variety grows to
- For poor draining soil replant them above the soil, to form a mound above the soil
- For soil that is too free-draining replant them further into the ground
- Test the soil pH, using a soil testing kit – the ideal pH is 5.8 to 6.2 for most varieties
- Soil that has a pH that is too high – add aluminum sulfate or sulfur
- Soil that is too low – add limestone or hydrated lime
Pest insects can eat dahlias until they die
Flea beetles, earwigs, slugs, snails, black bean aphids, and thrips can feast on dahlias damaging the stem and leaves. When this happens not enough sunlight can be absorbed by the dahlias and they can begin to die. Some are easy to identify, whereas others are very small and hard to spot.
- Holes in the leaves – can be very small and appear as spots, or can be large
- Missing parts of the stems on new (green) growth
- Small bite marks
- Visible insects on the surface of the plant, and in and around the soil
- Leaves wilting and dying
- Stunted growth – the plant doesn’t grow to the typical height of the variety
- Plant a diverse range of plant species where your dahlias are planted
- Some leaves being eaten and stem damage is normal and won’t kill a dahlia plant
- Use slug and snail pellets
- Use sticky traps to trap insects when the numbers are too large
Various diseases can affect dahlias and cause them to die. If the problem occurs on all of the leaves then it’s more likely a soil quality, watering, insect infestation, or sunlight issue. However, if it’s limited to only some of the leaves it’s more likely a disease.
Also, if it occurs suddenly such as overnight or over a few days it’s much more likely a disease. Rather than being caused by a nutrient issue in the soil. Or, too much or not enough watering. Mold spores are the most common disease that can occur. This can be solved with a simple home-based spray made from 1 teaspoon of vegetable oil, 3 tablespoons of baking soda, mixed in 1 qt (1 liter) of water.
- Yellow spots on the surface of the leaves
- Small black spores on the underside of the leaves
- Dead spots of brown and dry areas on the leaves
- White residue on the top side of the leaves
- Leaves dying and falling off
- Non-uniform damage to the leaves
- Spray the plant after sunset with the spray mixture described above
- Use a natural mold killing spray
- Move potted dahlias indoors or outdoors when you notice the issue