The Dahlia plant is a beautiful perennial tuber native to Mexico and Central America. Aside from being aesthetically pleasing, these lovelies can be used in pharmaceuticals, cosmetics, some food and as a coloring material used in dyes.
Dahlias are reasonably easy to grow but can succumb to certain diseases if not maintained correctly. One of the strongest visual indicators you will notice as the disease takes over is the dahlia leaves turning brown.
Brown leaves on dahlias can be disheartening for gardeners who are passionate about their plants. These vibrant and beautiful flowers deserve to be at their best, but when their leaves start to turn brown, it indicates an underlying issue that needs to be addressed.
This is usually due to over or underwatering, pest infestations, disease, incorrect sunlight or poor soil quality.
The most common diseases include bacterial disease and wilt, soft rot, aster yellows, powdery mildew, gray mold, Verticillium & Fusarium Wilt and smut.
If your plant is affected by one or many of these, I have a few simple steps you can take to bring your dahlia back to life.
Table of Contents
Dahlia Leaves Turning Brown: Reasons and Solutions
Let’s look at why Dahlia leaves start to turn brown and what you can do to correct the problem and heal your plant. Have no fear; most issues can be fixed as long as they are discovered early.
Some methods can shock the plant, but a little extra care whilst healing is better than a dead plant!
Overwatering/Underwatering
Overwatering your Dahlia plant will cause root rot. Especially in the early growth stages when there is minimal foliage, the plant won’t be able to keep up with excess moisture. The water will sit in the bottom of the pot and form a pool for the roots to lay in.
The roots won’t suck up the moisture, and they’ll go mushy and grow mold. The mold will grow up the stem and into the leaves.
If you notice that the edge of the leaves or flowers starts to dry out and turn brown, your dahlia plant needs attention. Some other signs are the tubers having soft wet edges or the soil and stems growing mold on top.
Under Watering your Dahlia plant also requires attention. However, the complications created due to a lack of water aren’t as severe. In extreme cases, you may notice spotty yellow or even crispy, dry brown leaves. Additionally, the flowers may not bloom.
The best schedule for watering a dahlia is once per week during initial growth and spring, when the plant may not absorb as much moisture. Try not to saturate your dahlia; instead, top it up as it starts to dry. The best test is by sticking your finger into the soil down to your second knuckle.
If it comes out dry, it’s a good sign to give your plant some water. As the plant becomes fully established, a potted dahlia should receive water 2-3 times per week. If your dahlia is planted in the ground, then 1-2 times a week is an adequate amount of water.
How to Cure Overwatered/Underwatered Dahlia?
Overwatered Dahlias can be revived by ensuring the pot has proper drainage. Sometimes the holes can get clogged up, causing a build-up of moisture around the roots. You can add a clay pebble mix around the root system to allow extra airflow around the tubers.
This will assist their ability to build strength within the root system. An underwatered Dahlia can be corrected by keeping a close eye on the moisture supply.
Try to make sure that the soil is damp but not soggy. If all else fails, the best action is to completely remove the plant from the pot and soil, clean the roots and replant with new soil.
Inappropriate Amount of Sunlight
Another reason your Dahlia could be forming brown leaves is the amount of sunlight it receives. Depending on the species, some dahlias need more sun than others.
Most types generally prefer 6 hours of full sun per day, though. They can do with up to 8 hours if grown in milder climates.
Too much sun or heat will make a Dahlia wilt. The leaves will dry out and burn. As a result, they will turn brown and need some immediate attention.
Some other signs of too much or not enough sunlight are the leaves growing as tall as they can to access sunlight were not available. Also, yellow leaves or spotted leaves with a yellow color and minimal flowers and buds.
What is The Solution?
The first actionable step you should take is finding out which species of dahlia you have. By working this out, you can research how much sun that particular species should receive. Sometimes it’s easy to just receive plants or buy on a gut feeling without knowing how to grow the damn thing!
Once this step is complete, the simplest solution is to move the dahlia into a shaded area regardless of whether it is a full sun plant. Try to control the amount of sunlight it receives in the first 10-14 days to allow it to recover, then test the 6-hour full sun position again.
If it seems to have recuperated, leave it be. If not, give it intervals of 3 hours in the sun and 3 hours in the shade until it has the strength to continue in full sun again.
Planting them in a shady garden area is another great idea as it will help offer some respite from the times they are soaked in the sun’s rays.
Poor Soil and Nutrients
Soil to a plant is its lifeforce. It contains all the food in nutrient form and regulates the water supply. Making sure that your dahlia has optimal soil conditions is vital to ensure it can grow and thrive. Soil temperature is just as important as the quality.
If the temperature of your dahlias soil endures fast, severe swings (cold to warm and visa versa), they can succumb to diseases such as Verticillium & Fusarium Wilt.
This funghi will produce streaky brown or black roots on your plant. They tend to block the dahlias water system, which wilts the plant.
Unfortunately, the plant needs to be deported and destroyed if this disease establishes itself. The roots and stems can rot due to overwatering if the soil has poor drainage and/or air circulation.
As a result, the leaves will turn brown and even black in more severe cases. They can also turn yellow and brown due to a lack of magnesium and iron in the soil.
Dahlias prefer loosened well, drained soil. Sand and peat are great additives to help loosen clay mixes. Avoid mulches or anything else with sharp edges that can destroy the tubers growing beneath the soil. When it comes to fertilizer, low nitrogen is best suited to dahlias.
Something with a high percentage of potassium and phosphorus is optimal. Bloom foods and/or vegetable-type fertilizers have the mentioned nutrients in a balanced blend.
We recommend using an all-purpose 5-5-5 fertilizer when you first plant and when they start to bloom. Proceed with the same blend 1-2 times per month after that.
If you want to strengthen up the tubers, bone meal is an amazing additive. It’s an organic form of phosphorus that promotes a strong root system.
Banana peels can also be added for that little bit of extra phosphorus and potassium. Try cutting the peels down with some scissors, so they compose faster.
Another great organic material worth considering is chicken manure. Simply mix with compost and add to the top 1 inch of your dahlias base.
Lastly, eggshells can be used to give a calcium boost. The calcium will promote strong, healthy roots and also help aerate the soil.
How to Cure?
As soil is a delicate factor in getting right, the best way to correct any issue is to remove the plant and repot. Simply take the plant out of the pot, gently rinse the tuber root system and trim away any mushy, decomposed limbs.
Once this is complete, check over your dahlia to ensure all is green and healthy.
Then add some fresh soil with a starter fertilizer and set in your dahlia plant again. It may take up to a week or so for the tubers to establish themselves. Try to get the pH of the soil to between 5.8 and 6.2.
Dahlia Diseases
Necrotic Spot Virus
Necrotic spot virus is one of the most damaging diseases a dahlia can get. It starts out turning the leaves a spotty creamy yellow color, then fades into brown. Once the spots turn completely brown, the disease spreads to every minuscule piece of the leaves, turning them brown also. As a result, the flower wilts and dies. They are generally caused by migrating thrips (plant-sucking insects).
Fungal Disease caused by Verticillium Wilt
These types of fungi establish themselves in the dahlias xylem. As they grow, they block the plant’s water supply. Your dahlia may start to produce yellow leaves, which eventually lead to darkened stem tissue near the base of the plant and, in dire cases, streaky brown or black roots. These types of diseases occur with fast swinging temperatures.
How to Cure Dahlia Diseases?
Sadly, the necrotic spot virus is extremely hard to cure. You would have a tough task eradicating every single thrip, which is difficult to spot. They can hide between small folds of leaves and flower heads and burrow into the soil.
It’s best to cut your losses and remove the plant completely. Try to keep them away from other plants to stop the infection from traveling.
Much like necrotic spot virus, verticillium wilt ensures a similar result. As the water system is affected, it’s cutting the plant off its life supply of water. The dahlia plant will suffer a slow and painful death. It’s best to remove the plant and do so away from other plants to avoid them also becoming affected.
Pest/Insects
When pests and insects roam free on your dahlias munching everything in their path, they can cause some serious damage to the stems and leaves in the process.
As a result, insufficient sunlight is absorbed, and the photosynthesis operation halts completely. This causes stunting and reduced nutrient intake resulting in deficiency which leads to browning of the leaves.
Some pests such as the thrip bring diseases like the necrotic spot virus. This virus destroys the plant leaving the whole plant to become deep brown/black as it decomposes. The worst offenders for pests and insects are flea beetles, earwigs, slugs, snails, black bean aphids, and thrips.
How to Get Rid of Insects?
One of the best pest removal remedies is fighting fire with fire. Plant species of plants introduce other insects that feed on these pests. Insects such as butterflies, ladybirds, bees and hoverflies will eat those little buggers for breakfast.
Dill, fennel, parsley, coriander, lovage, angelica and flowering carrots are great for attracting these ‘protector’ insects. Alternatively, you can use snail and slug pellets or an insecticidal soap spray to kill them on site or scare them away.
Nutrient Deficiencies
Brown leaves can also be a result of nutrient imbalances or deficiencies in the soil. Insufficient nutrients can lead to poor growth and discoloration of the leaves.
Regular fertilization is essential for healthy dahlias. Use a balanced fertilizer with equal amounts of nitrogen, phosphorus, and potassium.
Apply it according to the recommended dosage and frequency, taking care not to exceed the instructions. Incorporating organic matter, such as compost, into the soil can also improve its nutrient content.
Why does Frost Damage May Cause Dahlia leave to Go Brown?
During the colder months, frost can give dahlia leaves frost burn. It’s possible that the plant can die as a result, especially if the season is long and harsh.
It’s not always the case but specifically during hard frost periods. If this does happen, the leaves will scorch to a crisp and turn brown.
Dahlias will often survive most outdoor winters as long as the soil is well drained. In addition, giving the tubers some extra insulation in the form of very small to fine cuts of mulch. A thick 1-2 inch layer around the tubers is optimal.
How to Cure?
Frost damage is usually curable; it’s not a disease that can spread throughout the plant. The simplest way to correct a frost-burnt dahlia plant is to trim the dead areas with a sanitized cutting tool.
The best time to prune is as spring turns to summer. This will allow the dahlia to use a decent amount of the sun’s rays to create enough energy to sprout out during summer.
How to Care for Potted Dahlia?
Dahlias are a great plant to have in pots. They are generally low maintenance and don’t require conditions that are out of the ordinary. The biggest issue with growing dahlias in a pot would be keeping the balance of moisture. They tend to soak in their water quickly, leaving the soil dry.
They love a good drink, but too much water can rot the tubers and cause major issues down the track. You can water them frequently, even more so in the drier months or under drought-like conditions.
Fertilizing during the growing season is recommended to build a strong frame that helps to hold up their flowers.
Low nitrogen fertilizers with high percentages of potassium and phosphorus suit this type of plant. Aim to have the pH of the soil between 5.8 and 6.2. The levels can be leveled out toward alkaline by using well-rotted manure and wood ashes as compost mixed into the soil.
They may need to be staked early to assist with the structure holding up the weight of the buds. Dahlias enjoy around 6-8 hours of sunlight per day. At the same time, afternoon shade will help prevent the leaves from burning.
How to Care for Grounded Dahlia?
Planting Dahlias in the ground is similar to using a pot to grow them. All the conditions are pretty much the same. The biggest difference with growing in the ground would be how the soil needs to be prepared.
As dahlias have tubers instead of roots, it’s important to aerate the soil where you want to have the plant.
Tubers require more of a sandy/peat mix in their grow area to navigate through the soil and establish themselves. The tubers are much thicker and need those air pockets to allow them through. Dahlias love a good drink, so give them plenty of water without flooding them.
A moist but not soggy soil is optimal. Fertilizing is extremely important, especially when new growth starts to appear.
Dahlias need a fertilizer with low amounts of nitrogen and high percentages of potassium and phosphorus. This combination encourages strength and helps build a structure to assist in holding up the heavy buds/flowers soil’s pH should be maintained at between 5.8 and 6.2.
This can be assisted by using rotted manure and wood ashes blended into the top 1-2 inches of the plant’s soil.
You can stake the stems for extra stability during the early stages. Try to plant them in an area where they receive between 6-8 hours of full sunlight. If you don’t have any shady spots, you can plant something larger next to it to offer some relief in the warmer/drier seasons.
FAQs
Why are my dahlia buds facing downwards?
Dahlia buds facing downwards can occur due to various reasons, including genetic traits, environmental conditions, or insect damage. While some dahlia varieties naturally have downward-facing buds, environmental factors such as excessive heat or wind can cause the buds to face downwards.
Can over-fertilization cause brown leaves on dahlias?
Yes, over-fertilization can lead to brown leaves on dahlias. Excessive amounts of fertilizer, particularly high nitrogen levels, can cause leaf burn or nutrient imbalances. Use a balanced fertilizer and follow the recommended application rates to prevent this problem.
How can I prevent brown leaves on dahlias during the winter months?
Dahlias are sensitive to cold temperatures and should be treated as tender perennials in colder climates. Before the first frost, dig up the tubers and store them in a cool, dry place. Remove any remaining foliage and inspect for signs of disease. Store the tubers in peat moss, sawdust, or perlite until spring, ensuring they are kept frost-free.
Conclusion
Dahlia leaves turning brown can either be an absolute disaster or manageable with some simple maintenance procedures. They can succumb to various diseases via either excess water or specific pests that can unknowingly wreak havoc.
Luckily, if you see the warning signs as soon as they occur, you have a better chance of saving these beauties. We hope this information has helped you understand the issues that can occur with dahlias and how to correct them.
