9 Reasons Why Lemongrass Turns Brown! (And How to Fix It!)
If you love Thai and a bunch of other Southeast Asian cuisines like I do, then you probably have some lemongrass growing in your garden like me! But why do they suddenly start turning brown sometimes? Is it a sign of a serious problem? I’ll share with you what I know!
Lemongrass can start turning brown because of 1) aging, 2), underwatering, 3), overwatering, 4), too little light, 5) too much light, 6) cold temperatures, 7) nitrogen deficiency, 8) pest damage, and 9) plant diseases. Once old leaves are trimmed and growing conditions are corrected, it will start producing new green leaves.
You can use lemongrass to create teas, soups, and many other savory dishes. To make that possible, you should have enough lemongrass to harvest. But that’s difficult to achieve if all the leaves have started turning brown. Find out how to stop browning in lemongrass!
1. Aging
Like most other plants, old lemongrass leaf tips will inevitably turn brown and dry due to old age and will fall off easily.
As with most things in life, lemongrass (Cymbopogon spp.) won’t live forever. They’ll eventually meet their demise unless they are regularly thinned and propagated for new plants.
You’ll typically notice this once their blades have reached over a foot (30 cm) in height. Then, in their place young shoots will start sprouting from the lemongrass base.
Lemongrass is a relatively tall grass that grows in clumps. Its blades can reach more or less 3 feet (91 cm) tall and one clump can grow as thick as 6 feet (182 cm)!
The older leaves will continue degrading and browning as the plant takes nutrients, water, and even chlorophyll, the green pigment. All of these will be transferred into the new growth.
For a good while after that, your plant will mostly stay green. Then the leaves will start getting discolored from the blade tips as this natural cycle of life begins anew.
Since they are originally perennial plants, you can expect this to happen for several years. However, if you grow it as an annual grass—whether for ornamental or culinary purposes—this should only happen once, by the end of the year.
Check out other types in our article on slow-growing grasses!
Solution
Simply trim part of the leaves that have turned brown to keep your lemongrass looking neat and lush. Do this regularly to promote the growth of new leaves.
Oftentimes giving them a yearly massive trim around the winter months would do. Just make sure to leave about 2 inches (5 cm) of the base so that new shoots can grow once it starts growing actively again.
2. Underwatering
Native to the tropical region of Asia, lemongrass leaves can start drying up and become brown. They require consistently moist soil and humid conditions to thrive.
If you grow them from store-bought bunches from the supermarket or grocery, they will almost always start turning brown all over before it starts showing vibrant green growth.
Admittedly, I panicked when I first experienced this. But after learning more about this grassy aromatic herb I came to understand that this was quite normal.
You see, lemongrass likes to be kept in moist soil. This, of course, is something that most—if not all—supermarkets can’t provide. So it’s quite common for them to start getting discolored over time.
Then, once you do put them in water or soil for propagation, lemongrass still needs a bit of time before they finally adjust to their new environment before they focus on growing again.
Besides that, they also prefer moderately high humidity (up to about 75–80%) so that their growing medium doesn’t dry out too fast. This may happen even more quickly if you grow them in containers.
However, when they finally get used to their new growing conditions and are provided with sufficient moisture, you’ll see your lemongrass shooting up rapidly!
Solution
Use trimmed brown lemongrass clippings as mulch so its soil retains much more water and it won’t easily get dry. For potted lemongrass, amendments such as perlite can be added to reduce the amount and rate of water loss.
If you live in a colder or more dry area, water lemongrass more frequently—even more so in summer. Don’t wait for its soil to become bone dry before giving watering it. But make sure to directly water the soil, preventing the leaves from getting wet. I’ll explain why later!
3. Overwatering
Although lemongrass needs moist soil, its leave will turn brown when watered too much. If kept in wet soil for long periods, it can develop root rot and ultimately die.
This might sound contradictory to the point I mentioned earlier but there is a clear distinction between wet soil and moist soil. Lemongrass prefers the latter.
Even in their native habit, lemongrass can suffer serious damage because of continuous heavy rainfall. This is why they are much easier to grow in containers.
Left to stay in waterlogged soil, its leaves will first start turning yellow and then brown. This is because it’s essentially drowning in such conditions. Its roots are likely to grow soft and slimy as well.
Discover more about this in our article on the causes of root rot.
Many other problems can arise when you overwater lemongrass.
This is a lesson that one of my friends had to learn the hard way. She had to get rid of her lemongrass in its entirety because she forgot to move it indoors before the summer monsoon started.
Solution
If you get heavy rainfall in your area quite regularly, then cut back on watering your lemongrass plants, or do not water them at all (as I do in the UK).
More importantly, if you notice that they’re getting more water than necessary in the area they’re planted in, opt to transfer them to a big and shallow container. By doing so, you can easily move them around when it gets too rainy for their liking.
With container-grown lemongrass, only water it until all the excess spills out of its drainage holes. Make sure that its growing medium drains well without drying up too fast.
4. Insufficient Sunlight
When it doesn’t receive at least 6 hours of full sun exposure daily, lemongrass leaves can develop browning and start wilting. It can only tolerate light or partial shade.
If you’ve ever been to Thailand, Malaysia, or any other nearby country in the southeast, then you probably know firsthand how it’s sunny most of the time.
That’s the kind of environment lemongrass likes since it originated from there. For it to keep its elongated leaves looking lively and green, it should have at least 6 hours of direct sunlight—even if you grow them indoors.
Now, you can still grow it if you live further up in the northern hemisphere—say, Canada. But it will require supplemental lighting in such cases.
Otherwise, its colors will quickly fade until it finally turns dry and brown. It will also stop producing new green shoots if it receives little to no light.
Unless you provide it with enough light, be it natural or artificial, your lemongrass has little to no chance of surviving.
Solution
Make sure to place your lemongrass in an area that’s warm and bright during the day. For the most part, you want to have it in a south-facing garden or near a south-facing window.
Alternatively, you can set up a good quality grow light (like the one below from Amazon) 1–2 feet (30–60 cm) above it.
Leave that on for 12–16 hours a day if you’re growing lemongrass completely indoors and you don’t have a space that gets enough light.
5. Excessive Sunlight
Leaving lemongrass plants exposed to intense sunlight for more than 8 hours could lead to leaf burn. This causes their leaves to become dry, brittle, and brown.
One of the most common mistakes I see new gardeners make when growing lemongrass is leaving under the scorching sun all day, every day.
Plants like lemongrass are like to us in this sense. We need sunlight since it helps us produce more vitamin D but staying out for too long without protection can put us in danger.
In comparison, plants need sunlight to produce food for themselves. But if lemongrass gets too much sunlight, chlorophyll will start breaking down. As a direct result, its leaves will lose their bright green color.
Solution
Never leave your lemongrass under direct sunlight in the heat of summer for more than 8 hours. Move it to a shadier location if you have it in pots.
Alternatively, you can build a little shield of plastic around it—kind of like a mini greenhouse—so it gets direct sunlight only for a limited amount of hours.
You could also protect its long leaves and prevent browning from excessive sunlight by using shade cloths like this one from Walmart.
For potted lemongrass grown in planters using full-spectrum grow lights, make sure to have enough space between the topmost leaf tips and the light. Also, if you’re using fluorescent lights, switch to an LED bulb or tube instead. They produce a lot less heat when operating.
6. Cold Temperatures
Because they are tropical plants, lemongrass doesn’t tolerate cold temperatures below 50°F well. They can even die if left outdoors and exposed to frost.
In Southeast Asia, fall and winter temperatures don’t really get that chilly. At best, it can get quite cool. At such a time, lemongrass typically undergoes a short dormancy period.
However, I’ve only ever really seen it get reddish brown during the cold months of the year when it’s grown outside of its home region. More specifically, that can happen when they are grown in containers in America and Europe.
Lemongrass grows best with warm temperatures between 77°F and 86°F (25–30°C). Additionally, it can handle temperatures as low as 50°F (10°C) and as high as 91.4°F (33°C).
The fragrant lemongrass can be grown from hardiness zones 6 to 11. But they need to be overwintered for growth to resume once spring comes.
So here’s the thing—all the chlorophyll in lemongrass blades degrade as the temps continue dropping. Other than that, we usually get less sunlight and humidity during this time of the year.
All of these contribute to the discoloration of lemongrass leaves that eventually end up dying off. The plant itself can even succumb to frost. It will die with temperatures consistently under 40°F (4°C).
In the rare event that your lemongrass does survive through harsh winter conditions, it’ll likely have sustained significant damage already.
Solution
You can harvest all the leaves of live lemongrass plants before the first from it your area. Store them in air-tight containers so you can continue using them during the cold months. Properly frozen lemongrass can be kept frozen for up to 6 months!
Don’t wait for all the leaves before doing this. Otherwise, you’ll only have bland and brown lemongrass blades left.
If you want to keep it growing during the fall and winter seasons, keep it in an enclosed space where the temperature can easily be controlled. Maintain temperature within 50–60°F (10–15°C) so it can overwinter safely.
7. Nitrogen Deficiency
When grown in nutrient-poor soil, lemongrass can quickly decline and turn brown. Lemongrass plants need nitrogen-rich soil to continuously produce new green leaves.
Since it can grow thickly very quickly under the right conditions, many people seem to have the impression that lemongrass is a non-fussy, low-maintenance plant. There is some truth to that, but only to a certain degree.
During their active growing seasons (spring and summer), lemongrass needs a lot of nitrogen so that they can develop well and keep growing new green leaves.
When they’re grown in the ground around other plants that are regularly fed with organic nutrient sources like compost and chicken manure, you won’t really have to worry about it.
But when lemongrass is kept and grown in a container, its growing medium is much more likely to get depleted of nutrients quite quickly, especially with regular watering.
In other words, if you’re growing your lemongrass in a pot and its general growing requirements are met but you’ve never fed it even once, its leaves will still turn brown.
Solution
Apply a balanced or nitrogen-rich fertilizer to your lemongrass plants at half-strength. Do this weekly for potted plants, and monthly for ones grown directly in the ground.
For best results, have your soil tested first so you can better address its nutrient deficiency.
8. Pest Damage
Damage from pests such as aphids, mealybugs, and spider mites can result in brown scarring and speckling in lemongrass leaves.
Even though lemongrass is often used as a pest repellent around gardens and inside homes, it can still fall prey to pesky bugs.
Such pests include spider mites that leave discolored speckling on the grass blades as they feast on the plant.
The only good thing about these kinds of attacks on lemongrass is that they’re very rare. In some places, like the Midwest, they are even largely considered pest-free or pest-resistant.
You can thank lemongrass’s high citral content for this.
Besides giving it that distinct citrusy scent that’s a lot like lemon, this essential oil also has strong pest-repellent qualities. Citral protects lemongrass from insects, small rodents, and even reptiles!
Solution
Attach a high-pressure spray nozzle to your hose and use it over your infested lemongrass. This can generally dislodge unwanted guests from the plants.
To make sure they don’t take interest in your lemongrass again, get rid of them completely using insecticidal soaps and registered insecticides. A pre-mixed ready-to-use insecticidal like the one below from Amazon is a convenient choice.
9. Plant Diseases
Brown spotting on lemongrass leaf tips and margins is typically a sign of infection. The two most common plant diseases that affect lemongrass are leaf blight and rust.
The main way to differentiate leaf blight and rust damage is the discoloration they leave in their wake.
Signs of leaf blight infection appear as reddish-brown spots on drying leaves.
In contrast, damage from rust disease starts off looking more golden brown. You’ll likely notice this once it progresses into dying leaf tissue forming along lemongrass leaf veins.
Both of these fungal plant diseases can develop in overly humid and wet conditions. This is why I strongly warn against drenching lemongrass leaves whenever you water them.
Spores of the fungi that cause such diseases can stick to portions of the leaves that are moist or wet. If not addressed, there is a high chance of your lemongrass dying completely.
Solution
The main way you can stop your lemongrass plant from catching these diseases is by directly watering the plant’s growing medium. If it’s impossible to prevent this, just make sure they properly let the leaves thoroughly dry each time you water them.
Avoid planting or placing your lemongrass near plants such as onions, scallions, and garlic as these can also host fungi which can affect your citrusy herb.
More importantly, cut off any infected leaves with clean shears. Then, make sure to disinfect them once again after you’re done to prevent the further spread of diseases.
FAQs
Can you eat brown lemongrass?
Brown lemongrass is mostly considered safe to eat. That is, at least for human consumption. Even blades discolored due to rust disease can still be brewed for teas and used for cooking different savory dishes. Consuming brown lemongrass leaves doesn’t cause detrimental side effects in humans.
Why is my lemongrass turning purple?
Some varieties of lemongrass normally have a slightly purple base. Their leaves, however, are normally green in color and never purple. Reddish purple discoloration in lemongrass could indicate phosphorus deficiency. Commonly, this happens when they are grown in containers filled with a dry growing medium.
Is lemongrass toxic?
Lemongrass is generally known to be a non-toxic herb so it’s widely and safely used for cooking. However, consumption in large amounts can cause mild toxicity in animals. In cats and dogs, for instance, eating it can cause an upset stomach. Its effects are worse in horses, potentially leading to breathing difficulties, weakness, and even death.
Summary of Why Lemongrass Turns Brown
The old leaves of live lemongrass plants can start turning brown because of aging, making room for the growth of new green blades. Such a process is a natural and unavoidable part of the plant’s life cycle.
Mistakes under and overwatering can also lead to browning lemongrass leaves. Hence, providing moist but well-draining soil is key to preventing browning due to moisture issues. Lemongrass can also become brown due to lacking or excessive light exposure. Cold fall and winter weather can also lead to browning as it is a tropical grass.
Nitrogen depletion in its growing soil can also contribute to discoloration. Lastly, although not common occurrences, pests, and diseases can result in the development of brown marks due to plant tissue death.
Sources
- “Lemongrass in the Garden” by Terra Linse and Dan Drost in Utah State University Extension
- “Lemongrass, Cymbopogon spp.” by Susan Mahr in University of Wisconsin-Madison Division of Extension
- “Lemon grass” by n/a in PlantVillage
- “Rust of Lemongrass” by Scot Nelson in The University of Hawai’i
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