When Dahlia leaves are turning yellow, it is usually a sign that is something wrong with the plant. Healthy Dahlia leaves are dark green, and anytime their leaves turn yellow or brown it is an indication that the plant is sick or stressed out. If your Dahlia has only a couple of yellow leaves, then there isn’t much to worry about, but if there are more healthy leaves turning yellow every day, then you might have a serious problem.
One of the most common issues with dahlias is improper watering, either overwatering or underwatering. Both can result in yellow leaves and serve as a catalyst for other problems. Excessive watering can promote fungal infections, pest infestations, and the development of root or stem rot.
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It is not uncommon for Dahlia leaves to turn yellow, even under ideal conditions, usually, these leaves will go from yellow to brown and then simply dry out. Usually, the plant does this when it wants to get rid of one of its leaves, simply put the leaf is no longer productive and the plant will rather focus on keeping and maintaining its other leaves. This can be easily observed if the Dahlia plants are overcrowded, oftentimes the bottom leaves will turn yellow and fall off, but otherwise, the plant is healthy.
On the other hand, if more and more leaves are turning yellow, then you have to find out why they are and address the issue as fast as possible. If your Dahlia leaves are also curling then check out my recent article Dahlia Leaves Curling ( Top 8 Reasons ).
Dahlia Leaves Turning Yellow
When dahlia leaves turn yellow, it can be a sign of various issues affecting the plant’s health. One common cause of yellowing leaves is overwatering, which leads to waterlogged soil and root rot. On the other hand, underwatering can also cause yellowing as the plant lacks sufficient moisture and nutrients. Nutritional deficiencies, such as a lack of nitrogen, iron, or magnesium, can manifest as yellowing leaves. Another possible cause is fungal or bacterial diseases, such as powdery mildew or leaf spot, which can result in yellow patches on the foliage. Environmental factors like excessive heat or cold stress can also contribute to yellowing.
Poor Soil
The most common reason why Dahlia leaves turn yellow is due to compacted or poorly draining soil. Compacted soil can get the Dahlias root bound, they will simply not be able to penetrate the soil to absorb nutrients. This usually tends to happen in clay soil, especially if you had a couple of weeks without any rain. Clay can compact extremely fast especially when it dries out, once it is compacted and dried out, no amount of watering will help, as the water will simply run off.
Clay soil contains a lot of nutrients and minerals, and as long as it is not compacted it will provide the Dahlias with everything they need from the soil. If you have compacted clay soil, then the easy fix is to mulch it, grass clippings are ideal as it breaks down relatively fast. The grass clippings mulch will retain water and will stop the soil from baking and compacting. As the grass clippings are decaying they will attract bugs and worms that will loosen up the soil. If your Dahlia leaves are also turning brown then check out my recent article Dahlia Leaves Turning Brown ( Top 8 Reasons ).
Overwatering
The main killer of most Dahlia plants is overwatering, while they need a little bit more water when they are flowering but way too many people go overboard when watering their Dahlias. Overwatering can cause significant problems to Dahlias, their tubers and roots can rot, and mold can even start growing and feeding on them. Generally speaking, rotting Dahlia tubers will have pale green or yellow leaves.
Even if the Dahlia plant had some large healthy leaves, these will turn yellow if the tubers are rotting, in some cases, even the stem of the plant can start to rot. In this case, you should dig up your dahlias, throw away any soft tubers, and only replant the healthy ones.
Sunburn
Under rare circumstances Dahlia leaves can be sunburned, these leaves will have a pale green color with yellow dots, or turn completely yellow. Although Dahlias grow the best under full sun conditions, but only if they get plenty of water. During hot summer days, Dahlia plants will lose a lot of water through their leaves, and if they do not get more water they will slowly start to get sunburned.
Sunburned Dahlia leaves are yellow, and look wilted, there might develop some brown spots as well, at which point the damage to the leaves is fairly serious. Sunburn can also happen if you water your Dahlias improperly, like in the middle of the day and watering the entire plant rather than just the stem. Small water droplets on the leaves will magnify the sun, thus causing small sunburn spots.
To fix this issue you should water your Dahlias every day during hot summer days, but only in the evening and from the bottom.
At The End Of The Season Dahlia Leaves Will Turn Yellow
It is extremely important when the Dahlia leaves actually start getting yellow, if it is in early spring or mid-summer then the plant has some issues. On the other hand, if the end of the Dahlia growing season is near then you will see more and more yellow leaves. This is a normal process and nothing to worry about, once the growing season is over the Dahlia plants will start to prepare for their dormancy period.
This means that the leaves will start to turn yellow, and brown, and then fall off. There is nothing to worry about it as this is the natural life cycle of the plants. If the Dahlia buds are not opening then check out my recent article Dahlia Buds Not Opening ( Top 5 Reasons ).
Chlorosis
Chlorosis is not an actual disease as some might think, it is actually an iron deficiency. This doesn’t necessarily mean that the soil doesn’t contain enough iron, if the PH of the soil is above 6.5 then it is considered acidic, and this higher PH will stop the Dahlia plants from absorbing iron. Chlorosis manifests in yellow leaves and in most cases, the veins of the leaves will still remain green. If you have a well draining soil, that is poor in nutrients then the plant is less likely to get enough iron from it.
On the other hand, if you have clay soil, then it is more likely that the PH of the soil is way too high for the Dahlias to absorb the iron, ( clay soil tends to contain a lot of iron ) thus the Chlorosis. If only your Dahlia plants are suffering from Chlorosis then you are probably using the wrong kind of fertilizer for them. In this case, you should replant the Dahlias as fast as possible, ideally into compost or a high quality potting mix that doesn’t raise the PH levels.
Dahlia Leaves Turning Yellow Due To Increased Competition
Overcrowded Dahlias tend to suffer, especially if the nearby completion is a fast growing weed. Weeds tend to absorb nutrients and water a lot faster than Dahlias do, thus also growing a lot faster. If you have a lot of plants around your Dahlias then these can simply suck the surrounding soil dry of nutrients and water. Usually, in this case, the growth of the Dahlias will be stunted, however, if the plant is larger and doesn’t have access to enough nutrients or water some of its leaves will turn yellow, then brown.
Caused By Slugs And Snails
If you can grow Dahlias in your garden without worrying about slugs and snails, then I am envious. Dahlias tend to be one of the favorite food sources for slugs and snails, especially while they are sprouting. These pests will eat every new Dahlia shoot to a point where the tubers do not have enough energy to sprout anymore thus killing the entire plant. Mature Dahlia plants have fewer problems with these pests but they can still munch on their leaves.
If the yellow Dahlia leaves look like they are being eaten by a slug or snail, then you have to protect the plant. There are different types of slug pellets on the market, but no matter which one you choose make sure to follow the indications.
Due To The Size Of The Container
Way too often people tend to plant their Dahlias in way too small containers, the smaller the containers are the more likely it is that the Dahlias will have some issues. These issues can be anything from, lack of nutrients, overwatering, and underwatering to stunted growth. The main thing that turns Dahlia leaves yellow in containers is the lack of nutrients, Dahlia plants tend to be relatively hungry plants and if the potting mix doesn’t have enough nutrients then the leaves will turn yellow and slowly decay.
Make sure to get a large enough container when potting your Dahlias, especially important that the tubers do not actually touch the side of the container as this could lead to damaged tubers.
Potato Leafhoppers
Potato Leafhoppers are small insects that suck the sap out of the Dahlia leaves, usually, the leaves will be contorted and discolored. Serious Potato Leafhopper infestations can kill off an entire Dahlia plant in a matter of days, so make sure to get rid of them as fast as possible. Check the underside of the Dahlia leaves for the Potato Leafhoppers, as these usually feed on the underside of the leaves.
The biggest problem with Potato Leafhoppers is that they tend to hop from one leaf to another, and if you have several Dahlias close together then I have bad news for you. You can get rid of the Potato Leafhoppers by spraying the underside of the leaves with a water and dish soap mix, or an insecticide.
Aphids
Aphids are small insects that feed on the sap of the plant, sometimes directly from the stem, while other times from the leaves. Aphids can literally suck an entire Dahlia plant dry if there is a serious Aphid infestation. In addition to yellowing leaves, the Aphids can also deteriorate the entire structure of the leaves, making them look odd or contorted. Most people will simply try to spray off the Aphids but this is not an ideal way of getting rid of them.
Natural predators can be a solution, but your Dahlias do not have time until they show up and fix the issue. Instead, a dedicated insecticide against Aphids is usually the best solution.
Thrips
Thrips are another type of insect that will simply suck dry the Dahlia leaves. As the Thrips are feeding on the sap of the leaves the Dahlia plant will not be able to replace the lost nutrients and sooner or later the entire plant will start to go downhill. Thrips will cause Dahlia leaves to go yellow, and once they do they will not be able to bounce back, usually they will change color to brown and then fall off.
As usual, there are a lot of home remedies that you can find online against Thrips, although I wouldn’t experiment with these as until you find out what actually works your Dahlia plant might be already gone. Get a dedicated insecticide against Thrips and make sure to follow the indication.
Key Takeaways
- The main issue that causes Dahlia leaves to turn yellow is poor soil both in terms of nutrients and drainage. Dahlia leaves will turn yellow if they can not access enough nutrients, because the soil is compacted, or lacks nutrients. If the soil PH is above 6.5 then the Dahlias can develop an iron deficiency, because iron is not soluble at that PH, and it will result in yellow leaves with green veins.
- Pests that tend to suck the sap of the Dahlia plants can turn their leaves yellow.
- If your Dahlia plants are not getting enough water then they might get sunburned and their leaves will turn yellow.