Many people think their herb is dead when its leaves turn black, but that’s only because they don’t know how to fix thyme leaves turning black!
You can avoid thyme leaves turning black by reducing moisture, offering protection against cold/frost, providing adequate sunlight, preventing/curing fungal diseases, limiting exposure to extreme heat, avoiding high-Nitrogen fertilizers, and frequently pruning your thyme.
Also, don’t forget that thyme leaves turning black could be due to aging and a sign that your thyme is dying naturally.
Also read: How to Fix Thyme Leaves Turning Brown?
1. Reduce Moisture
The most common reason behind thyme leaves turning black is excessive moisture that saturates the plant, making it rot and the leaves turn black, and possibly dying thereafter.
Usually, an excess of water immediately affects the roots, concentrating on the lower extremities of the plant. Roots happen to be the most important part of the plant and if they are compromised, the entire thyme plant’s leaves can turn color and the plant can die.
The most likely ways your thyme plant will get excessive water are:
- Poorly draining soil
- High air humidity
- Lack of sunlight exposure
What to Do?
Solving excessively wet environments depends on first finding out what the cause is. But, making adjustments in every aspect is important.
- Start by reducing watering and avoiding evening watering, especially if you are currently in a season or location with poor sunlight.
- Next, ensure your thyme is getting enough sunlight and is in the right spot. A sunny period between 6 and 8 hours will suffice, if not more!
- Uproot the plant and assess the roots for root rot damage. Trim off damaged parts and repot them in inappropriate soil.
- Amend the soil if it is holding back too much water. Ideally, the soil should be more sandy than rich with organic matter. The material of the pot also plays a part in this, so, ensure that it dries fast.
- Make sure your thyme isn’t bushy or crowded, assuring that enough air currents are surrounding the plant.
- If you are approaching a rainy season, relocating your thyme so it is out of the rain is essential.
Usually, a combination of all these points helps in fixing an overwatered thyme plant with black leaves.
2. Protect Against Cold and Frost
Thyme is not a cold-hardy herb and actually originates from a hot climate. So, understandable, frost can be one weather element that can kill your plant! Not to mention that when the frost thaws out, it can leave your thyme plant with too much water.
Other reasons why your thyme may be dying and turning black in winter frost is due to the lack of sunlight and possibly the high air humidity as well.
NOTE- Winter frost leaving thyme leaves black or dead is not always permanent! The plant will start regrowing in spring.
What to Do?
It’s no secret that thyme is not cold-hardy and especially needs protection during the cold and frosty winters. There are several ways you can do this, but if your plant is still young, or potted in a small pot, you’ll want to bring it indoors immediately.
Other ways to protect your thyme plants from frost include covering them with a cloche, fabric, or mulch, or placing them in an outdoor greenhouse.
A few thyme varieties are more cold-tolerant than others and you could confirm which one you have and whether you will experience frost in your area. But, the best way to fix thyme leaves turning black is to protect your thyme plant in advance of frost and cold setting in!
Related read: Can Thyme Survive Winter? Tips to Protect Thyme
3. Provide Adequate Sunlight
Sunlight is the main building block when it comes time for a thyme plant to synthesize food. Sunlight, chlorophyll, and water are the essential elements helping your thyme plant to synthesize food.
A lack of sunlight can make thyme leaves turn black as they will not be able to synthesize food matter, ultimately resulting in moist conditions that will lead to discoloration of the leaves.
Lack of enough sunlight usually occurs when thyme plants are in the wrong spot (shady location), watered excessively, or are passing through a season with poor sunlight.
What to Do?
Immediately move your thyme plant out of the shade and into the sun. This will help to remove all moisture in an attempt to resuscitate the plant. Your thyme should get over 6 hours of sunlight to recover but to grow it would need more!
Chances are that the current season you are in only offers poor sunlight. Or maybe your geographic location is not popular for having a lot of sunlight.
The solution to these problems that are otherwise out of your control is to get a grow light. Grow lights act as an excellent replacement for sunlight except it is an artificial source and come in handy when sunlight is too weak or limited.
4. Prevent and Cure Fungal Diseases
The thyme herb is susceptible to diseases, particularly fungal diseases such as Botrytis and Root Rot. Although spores of the causative fungus of these diseases may be present in the air, water, or soil, it is certain conditions that allow their numbers to multiply.
Conditions favoring fungal growth are:
- Overheat watering
- Night watering
- High humidity (lack of air circulation)
- Soils with poor drainage
- Excessive watering, not allowing the soil to dry out completely
- Season or lack of sunlight to dry out the soil
What to Do?
It is clear an overly moist environment is allowing fungal populations to thrive! This must be changed immediately if you want to stop the discoloration of your thyme plant and especially if you want to fix thyme leaves turning black.
But first, you must assess the damage! Uproot your thyme plant to see how badly the roots of the plant are affected. You will have to try your best to trim off the infected portions to avoid the spread of the disease (assuming it was soil-borne.)
NOTE- If damage is too extensive, your thyme plant may not be salvageable! In that case, you must remove the plant and all the infected matter so it does not spread.
Otherwise, solving the problem can be done with a few extra steps:
- Monitoring watering and waiting till the soil is dry
- Ensure the humidity is not too high
- Using soil that is well-draining (sandy soil or soil amended with perlite)
- Ensure your thyme plants get enough sunlight to dry off soil and excess water on the plants
- Sterilize utensils such as shears before using them on your thyme plant
5. Limit Exposure to Extreme Heat
The thyme herb originates from a hot and arid land but that doesn’t mean extreme heat and drought won’t affect it.
Thyme that is not as drought-tolerant or not equipped for soaring temperatures will start to show its displeasure if temperatures become intolerable. The first signs are drooping followed by discoloration to multiple colors, eventually reaching a dark brown or occasional black color.
What to Do?
Here are a few steps to combat black thyme leaves due to excessively hot summers.
- Try to ensure your thyme plant’s soil isn’t bone dry during heat waves.
- Ensure that your thyme is out of the sun during the hottest time of the day if it is very dry.
- Water more to compensate for evaporation and transpiration occurring during this time.
- Also, you can prune back growth to keep the plant compact and lose less moisture.
Usually, thyme plants can bounce back from such a scare when temperatures ease.
6. Avoid High Nitrogen Fertilizers
Excessive amounts of fertilizer can discolor your thyme plant’s foliage. But, it’s not the whole fertilizer to blame.
High amounts of Nitrogen are known to cause discoloration in your thyme plants. Choose to use a basic fertilizer that is not high in Nitrogen. Or, be cautious about how often you use fertilizer on your thyme plants.
Check your fertilizer’s nutrient profile and check to see if the nutrients are completely balanced. High nitrogen fertilizers will also lead to leggy and unappealing growth that will throw off the appeal of your thyme plant.
What to Do?
Thyme usually can survive with a yearly application of slow-release fertilizer. But, even then, you will have to make sure it is not a high Nitrogen fertilizer.
- If you are using fertilizer, make sure it is at the right time which is in spring, the beginning of the flowering season. Otherwise, growth initiated from fertilizer use may make the plants more susceptible to damage and possibly even death.
- You can also choose to dilute your fertilizer to half-strength using water. This is especially easier with a liquid fertilizer.
- Alternatively, you can choose to use a fertilizer with lower Nitrogen content than the other components Potassium and Phosphorus.
7. Frequently Prune
Thyme leaves turning black due to a lack of pruning seems like an unlikely cause for such a dire problem. However, it is possible and a problem you may be forced to deal with if you don’t prune or incorrectly prune your thyme.
When in its element and flourishing, thyme can become very bushy and woody to say the least. Unfortunately, some areas of the thyme will not have access to sunlight and adequate air currency, leading to overly moist conditions and thus favoring fungal growth!
With warm and moist conditions, fungal infections are bound to arrive in no time at all. Making changes to your plant will only worsen the situation, especially if the thyme is still growing. Fungal infections then lead to your thyme leaves turning black!
What to Do?
Luckily overly wet conditions are easier to tackle than most fungal infections. Start by uprooting your discolored thyme plant to see how bad the damage is. If roots are unsalvageable and have undergone extensive damage, you will have to remove them (or start anew!)
- Next, you will obviously want to do some extensive pruning to your thyme plant to ensure all areas have access to sunlight and steady airflow.
- If this isn’t enough, you will have to rotate your plant (if potted) to ensure adequate sunlight to all parts of the plant.
- If planted in the ground, ensure surrounding plants are not blocking out sunlight from your thyme plant.
8. Natural Death!
If thyme leaves turning black have happened rather fast or overnight, it could be a sign that your thyme is dying! Not because the plants are ailing but just because it has lived out their full lifecycle.
Thyme plants are perennial ones that will die down or remain dormant during the winter. But in spring these plants will shoot back to life. This happens for 4 to 5 years before the plants experience natural death.
Unlike the other problems on this list, there is no solution for natural death except for replacing it with a new plant.
No one likes to say goodbye to their thyme plant, especially when it is on bad terms such as thyme leaves turn black! So, to help you out we have all the solutions.
You can fix thyme leaves turning black by:
- Reducing moisture
- Offering protection against cold/frost
- Providing adequate sunlight
- Preventing/curing fungal diseases
- Limiting exposure to extreme heat
- Avoiding high-Nitrogen fertilizers
- Frequently pruning your thyme
NOTE- It isn’t always possible to save thyme with leaves turned black. But, you can always get another thyme plant.
Have a recipe that includes thyme but in the measurement of a “sprig”? How Much Thyme in a Sprig?
Why is my thyme plant turning woody?
Thyme plants can turn hard and woody when they are not being looked after properly. Pruning is essential to ensure your thyme plant stays neat and that older parts of the plant are removed before they die off. Woody stems are also a sign of maturity and your thyme plant becoming old!
How does thyme get root rot?
Root rot is induced by overly wet conditions that make it nearly impossible for the roots to function and provide nutrients to all the other parts of the thyme plant. Your thyme is at risk of root rot if you overwater it, place it in a shady location. Also, season matters as watering should reduce when coming out of summer.