Aloe vera plants, known as true aloe, are known for their thick, succulent, green leaves with toothed margins. When those leaves start to turn brown, not only does it ruin their appearance, but it’s a sign that something is wrong.
There are multiple causes of browning on aloe leaves, and while most of them can be resolved, allowing your plant to continue to survive and eventually thrive, being able to identify the cause is crucial.
Watering issues are the most common cause of browning, but too much sun or fertilizer, or disease pathogens can also cause problems that will turn the plant brown.
Causes of Browning Aloe Vera
Each cause of an aloe turning brown looks slightly different from the others. Carefully examining your plant will allow you to determine the cause so that you can address it.
In any case, the brown leaves won’t recover, and they’ll act as a drain on the plant. Remove them as close to the base as you can. If the browning is just spotting from a disease or sooty mold, the leaf can remain so long as you treat the disease.
Not Enough Water
The most common cause of aloe leaves turning brown is watering problems. Not enough water is typically less of a problem than too much water, but it can happen. The easiest way to determine if underwatering is the issue is to look at the leaves. Are they dry and brown? Does the brown start at the tips of the leaves and work its way toward the base?
If the answer to both of those is “yes,” you should suspect underwatering.
Next, stick a finger in the soil. If it feels dry as deep as you can feel, your plant is probably not getting enough water.
Aloes can tolerate dry conditions for quite a long time, but, of course, they still need water. This is particularly true of plants in full sun exposure or in a dry climate.
The solution is easy. Increase your watering schedule. Water anytime the soil feels dry at three inches deep.
Too Much Water
Even more than underwatering, overwatering is a frequent issue. Well-meaning plant owners offer their succulents more water than they need in an effort to keep them healthy. But aloes do better with less moisture than you might think.
Unless the plant is in direct sun in a dry climate, watering once a week is probably too much.
When overwatering is the issue, instead of turning dry and brown, as happens with underwatering, the leaves will turn brown and mushy. They’ll be soft to the touch. The browning might start at either end of the leaf.
If you touch the soil, does it feel soggy or wet at all? Even after you water, the soil shouldn’t ever feel soggy. The terms “wet,” “moist,” and “soggy,” can be a bit nebulous, so it helps to imagine a sponge.
If you wet a sponge thoroughly and felt it, that’s soggy soil. If you gave it a single squeeze, that’s wet. If you wring that sponge out really well, that’s moist. You could also ball up a little bit of soil in your hand. If you squeeze it and water comes out, that’s soggy. If you squeeze it and it sticks together, but water doesn’t squeeze out, that’s wet. If you squeeze it and it falls apart when you open your hand, that’s moist.
You want the soil to feel moist to wet right after you water it. By the next day, it should feel moist, at most. Don’t water again until the soil has dried out three inches deep. A moisture meter can help you determine when the soil has reached the right level, but you can also simply use touch.
If the leaves are already turning brown due to too much water, it means that the roots in the soil are drowning in too much water and can’t access the oxygen they need. Remove the plant from the pot and dump out all the old soil. Make sure the drainage hole isn’t clogged.
Wipe the pot clean and refill it with fresh succulent or cactus mix potting soil.
Wash all the soil away from the plant and look at the leaves. Remove any that are black and mushy using a clean pair of scissors or a knife. Re-pot the plant in the fresh, clean soil. Then, reduce your watering schedule and take care only to water after the soil has dried out appropriately.
Keep in mind that plants need even less water during the dormant season, so don’t assume that you can water on a regular schedule. You should always check the soil.
Too much water can also promote basal stem rot, which is caused by pathogens in the Fusarium genus. In this case, the leaves, the base of the plant, and the lower leaves will turn brown and soft. There is no cure, but you can take cuttings for propagation from the plant above the location of the rot.
Too Much Sun
Aloe plants like a lot of sun, but in some cases, there can be too much of a good thing. Direct sun during the heat of the afternoon in a region that experiences high temperatures can cause sunscald on the leaves of the plant.
Sunscald looks like patches of brown, usually at the center of the leaf rather than on the edges or tips.
To verify that this is the problem, watch your plant throughout the day and note how much sun it’s receiving. If it is being hit with direct sun in the afternoon, move it somewhere it will be protected during the hottest parts of the day.
If you can’t move it, consider installing curtains or closing blinds during the afternoon heat.
One of the nice things about aloe is that they don’t demand a lot of food. If you regularly re-pot your plant in fresh soil, as you should, you won’t need to add much in the way of food.
They only need to be fed three times a year, with no food during the dormant season. A mild, balanced, water-soluble houseplant fertilizer with an NPK rating of 3-3-3 to 5-5-5 is ideal. It should be given in the spring, early summer, and mid-summer.
As with overwatering, well-meaning houseplant growers often over-feed in an effort to grow healthy, big plants. Too much food burns the roots, which will make the leaves turn brown, as well.
Even if you stick to a thrice-yearly feeding routine, be careful not to use food that is too strong. Anything over 5-5-5 is too strong and should either be diluted or avoided.
While rare, fungal pathogens can infect aloe plants. Aloe rust, caused by the fungi Phakopsora pachyfhiza and P. meibomiae, is more common on plants outdoors, but the spores can travel on tools, other plants, or humans to infect indoor plants.
The pathogen finds an opening in the outer rind. It attacks the phenols in the rind, causing oxidization. These oxidized areas turn brown and black, typically with an oval or circular shape. If you touch the spots, they will feel hard.
The disease thrives in temperatures between 60-82°F and needs moisture to breed and spread.
Remove any heavily infected leaves and spray the plant with a copper fungicide once every three weeks until no new symptoms develop.
Sooty mold, which is attracted to the sticky honeydew left by sap-sucking insects like aphids and mealybugs, can also cause similar brownish-black spots, but these can be wiped off with a wet rag. These spots can be resolved by eliminating any pests on the plant.
If the leaves are developing reddish brown spots with tan centers, it’s likely anthracnose, caused by Colletotrichum gloeosporioides. As with rust, this can be dealt with using a copper spray every three weeks until no new symptoms develop.