Dahlias are beautiful, but they can be tricky to grow. That’s because dahlias are susceptible to different diseases and pests that can leave them with yellowing leaves. Luckily, identifying the yellowing problem your plant is experiencing and treating it is easy. In this article, we’ll go over ten common causes of yellowing leaves in dahlia plants and how you can fix them.
Reasons Your Dahlia’s Leaves Are Turning Yellow
When it comes to the health and care of your dahlias, there are several reasons why you may notice that some of their leaves are turning yellow.
- Fungal Disease: This is a common problem with dahlia plants. The fungus spreads quickly, especially in warm climates or during humid summers. You can prevent fungal diseases by keeping your dahlias well-drained and watered while they’re growing; be sure not to overwater them as well.
You can also try planting your dahlias in raised beds so that water doesn’t pool around their roots. Fungal infections often cause small brown spots on the leaf surfaces as well. These spots may later turn yellow if left untreated.
- Improper Watering: Overwatering can cause root rot at any time of year—but especially during the summer months when temperatures rise above 80 degrees Fahrenheit (27 degrees Celsius). If this happens often enough, it can cause the plant’s roots to die off completely until only its stems remain green above ground level.
Avoid root rot altogether when watering your dahlias this way each day throughout the summertime months. Make sure there’s adequate drainage available for excess water after irrigation has occurred once per week up until fall. Watering is needed less in the fall due to cooler temperatures setting in around September through December annually here within North America.
Fungal Disease
Fungal diseases are caused by fungi, which are tiny, living organisms that can cause many problems for plants. Fungal diseases can be difficult to diagnose because they are not always visible.
The symptoms of fungal disease in dahlia leaves include yellowing leaves with brown spots or blotches on the leaves.
If you have noticed these symptoms in your dahlias, you need to treat them immediately. This way, the damage doesn’t spread throughout your garden and ruin other flowers.
Improper Watering
- Watering frequency. Dahlias should be watered every day or every other day, depending on how quickly the soil dries out. If you’re watering your dahlia once a week and it still seems to dry out quickly, try watering it more often—but don’t water excessively.
- Watering depth. To avoid drowning your plant’s roots with deep waterings, let the top inch of soil dry out between waterings before adding more water and filling the container up again.
- Watering in the morning (or evening). Some people recommend watering early in the day so that dew won’t form on leaves during night hours when temperatures are more relaxed than during daylight hours; others say that moisture from dew is good for plants’ health because it keeps them cool and prevents fungal infections from forming on their leaves’ surfaces.
Sunburn
If you have too much sunlight shining on your dahlia plants, they may develop sunburn. This can be caused by a combination of factors:
- Not enough water in the soil
- Too much fertilizer applied to the plant at one time (if this happens, use a leaf yellowing spray or foliar solution instead)
- Poor drainage in the soil
Over-Fertilization
Too much fertilizer or a fertilizer that is too strong can cause yellowing leaves, especially if applied when the plant isn’t actively growing. In the spring, fertilize dahlias when you first start seeing new growth appear. Avoid using synthetic fertilizers, as these are likely to kill your plants rather than help them grow.
Nutrient Deficiency
If your dahlia’s leaves are turning yellow, it is likely a result of nutrient deficiency. This yellowing can happen because your plant isn’t getting enough nutrients in the soil. The most common nutrients that dahlias need are nitrogen, phosphorus, and potassium. If you are unsure how much of these to give your dahlia plants, it’s best to test the soil before adding fertilizer.
- Nitrogen (N): promotes green growth on foliage and stems
- Phosphorus (P): encourages root development and flowering
- Potassium (K): promotes strong roots
Soil pH
Soil pH is the measure of acidity or alkalinity in the soil. It’s also known as “soil reaction” and can be measured with a testing kit. When it comes to dahlia plants, the pH of your soil should be between 6 and 7; however, most dahlias will tolerate a range from 5.5-7.5.
Soil pH can be adjusted by adding either lime (to lower soil pH) or sulfur (to raise soil pH). If you’re using compost on your dahlia plants, make sure that it’s balanced for the amount of organic material in it. Otherwise, you’ll need to add some lime to make up for its acidic nature before applying it on top of your existing soil mix.
Insects and Pests
An insect or pest infestation can cause dahlia leaves to turn yellow. If you notice that your dahlias are suffering from an infestation of insects or pests, there are several things you can do to get rid of them and prevent further damage to your plants.
Pests, such as thrips and aphids, can cause your dahlia leaves to turn yellow. Thrips are tiny insects that suck the juice out of plant tissue. Aphids are pear-shaped bugs that feed on the sap of plants. They leave behind a sticky residue on the leaves and stems of your dahlia plants. The damage may cause blotches on the leaves, which will eventually turn yellow or brown.
Low Light Levels
If your plant isn’t getting enough light during daylight hours (for example, if it’s being grown indoors under fluorescent lights), its growth rate will slow down considerably—and this means less photosynthesis happening in each individual leaf. When this happens, the chlorophyll production process starts slowing down as well, which means less green pigment in each leaf cell and eventually yellowing leaves as a result.
Poor Soil Texture
Dahlias are shallow-rooted plants, so their soil should have good drainage and plenty of organic matter. If you’re planting in a pot or raised bed, adding compost or well-composted manure will help improve the soil texture. You can also improve the quality of your garden soil by using a rototiller to break up clumps and make it looser.
Winter Dormancy
- Dahlias are native to the South American Andes, where they are grown as annuals. They are not hardy in cold climates and will die if temperatures fall below freezing.
- Dahlias can be overwintered in a frost-free location such as a greenhouse or conservatory, but many gardeners choose to bring them indoors for the winter. Indoor lighting is more intense than outdoor lighting, allowing your plants to grow more rapidly during the long nights of winter.
Viral Disease
Viral diseases are caused by viruses, i.e., tiny, infectious particles that attach themselves to the cells of living organisms and cause illness. There is no cure for viral diseases, though they can be prevented in many cases by avoiding contact with infected people or animals.
Viral infections are detected with a blood test or other diagnostic testing. In some cases, antiviral medications may be prescribed to help manage symptoms and prevent complications from developing. You should also avoid close contact with others with similar symptoms; this will help keep your disease from spreading further than necessary.
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How to Fix Dahlia Leaves Turning Yellow
The following are some tips you can use to treat your dahlia plants:
- Rotate your plants every three months so that they do not remain in one position for too long
- Ensure that there is enough space between each plant so that they don’t compete for nutrients or sunlight
- Prune your plants often to remove dead or diseased leaves
- Water only when necessary (once or twice per week)
If your dahlia leaves have turned yellow, it could be due to several reasons. One common cause is the plant contracting fungal disease, and another is nutrient deficiency.
To deal with dahlia leaves turning yellow due to fungal disease, you must treat the plant thoroughly with a fungicide approved for use on dahlias. The second remedy for this problem is watering deeply but not too often. Watering frequently will make your soil moist, allowing fungi and bacteria to survive for longer periods in the soil. This new growth will attack your plants’ roots easily when they grow from them during the winter months or rainy spells when moisture levels are high in garden beds.
If there’s any nutrient deficiency in soil due to improper chemical composition (too much nitrogen), add bone meal fertilizer at about one tablespoon per square foot. Add the fertilizer around each plant after planting them back into containers or flowerbeds again in the fall.
You can also add lime according to the directions on the label before planting starts next springtime again. Adding lime will ensure plants have sufficient nutrients throughout the growing season.
To deal with dahlia leaves turning yellow due to insects and pests, Remove any dead or dying foliage immediately. The sooner you remove these infested areas, the less likely they are to spread disease to other parts of your dahlia plants.
Spray insecticidal soap directly onto any aphids or thrips you see feeding on your dahlia plants’ leaves or stems with a hand sprayer every seven days until harvest time in early fall. Insecticidal soap kills soft-bodied insects like aphids and thrips but is harmless to humans and other mammals when used as directed.
To deal with dahlia leaves turning yellow due to poor soil texture, the first thing to do is to ensure that the soil is well-drained and not compacted. If it is, you need to break up the soil and add some more compost or manure.
You should also remember that if you have used artificial fertilizers in the past, these can kill off all your beneficial bacteria in the soil, which are needed for healthy plant growth. So, if your plants have been treated with artificial fertilizers in the past, you may need to add some compost or manure before adding any more fertilizer.
Our Final Thoughts
Even for seasoned horticulturists, figuring out why dahlia leaves are yellow can be difficult. The ability to observe is your most powerful weapon in the fight against plant distress. It might be simple to forget to check beneath the hood when loud blossoms capture your attention left and right. However, you can generally stay ahead of problems by setting aside some of your maintenance time for leaf inspection, following best practices, and knowing what to look for. We hope you found this article helpful. If you are interested in learning more about flowers, check out our other posts on how to care for them.