Brown Spots on Spider Plant (Causes and Treatment)


Brown spots on Indoor potted spider plant leaves

The spider plant is a timeless favorite in the world of houseplants, and for good reason. I appreciate that they are effortless to grow, endure most levels of light, and they’re not too finicky about water. But they can be prone to some issues, including developing unsightly brown spots.

The most common causes of brown spots on spider plants are Fungal diseases and fertilizer burn. In addition, physiological disorders like edema, nutrient deficiency, scorching can cause this problem. To revive your Spider plant eliminate severely diseased parts and apply fungicides if needed. 

I understand that finding brown spots on your otherwise lush, beautiful, and colorful airplane plants can be rather disconcerting.

But don’t panic. I’ll show you how to troubleshoot the problem and baby your houseplant back to health. Plus, look ahead for ways to prevent it from occurring in the first place.

What Causes Brown Spots on Spider Plants?

When brown spots emerge on your houseplants, that’s always a telltale sign that something is off with your spider plants.

They may develop differently depending on the cause, severity, and period of browning. They may vary in size, texture, and even shade of brown.

Brown spots appear primarily on the tips of the plant but can spread across the entire foliage. Some spots become progressively bigger, while others remain barely visible. They usually appear as blisters at first then turn into dry lesions.

In either case, knowing the exact cause of the brown spots on your spider plant will help you combat the predicament more effectively.

You’ll want to inspect your houseplant closely to pinpoint the problem. It also pays to think about the conditions your houseplant has been subjected to of late.

I’ll walk you through how to identify each of the common causes of brown spotting in spider plants. You’ll also learn how to remedy each of these typical issues that cause your houseplant to turn brown.

Algal Leaf Spots

If you park your houseplant in a warm, humid area, sometimes it can be infected by parasitic algae called algal leaf spot. It’s usually spread from one plant to the next by rainwater but can be blown indoors by the wind.

If your spider plant has an algal leaf spot disease, you’ll find rough, mesh-liked brown to greenish-brown blotches on the afflicted leaves.

The diameter of each blotch measures roughly half an inch. But several blotches can bleed into one another to create what appears like a bigger blotch.

I have found that algal leaf spots appear primarily on softer, younger foliage. You can also see a stunted appearance on tips, stems, and other parts. They often start as small, pale green round spots before blossoming into large reddish-brown lesions.

How to Fix This

Most cases of algal leaf spots barely become more than a cosmetic issue, as they make your houseplant look unsightly.

However, they’re rarely fatal unless the infestation is so severe it covers nearly the entire spider plant. You should be able to get rid of the algal leaf spot disease using non-chemical methods, such as:

  • Avoid watering for a while – moist conditions fuel an outbreak of algal leaf spots. So, you’d want to keep your houseplant foliage as dry as possible. If you must water, do so at the base of the plant. Space out your houseplants to improve ventilation.
  • Eliminated severely affected plant materials – Get rid of any dead or heavily-diseased foliage to reduce the spread of the algae.
  • Maintain proper potting soil health – Stay on top of soil drainage, fertilize & water as required.
  • Chemical use – If you must control a wide-spread infestation, use copper fungicides. Apply after every 10-14 days until you’ve ridden the houseplant of the leaf spot disease.

Fungal Diseases

If you keep your spider plants in overly humid and hot conditions, the cause of the brown spots is almost always a fungal disease.

They typically start out as light green spots, especially on the leaf tips, and gradually turn brownish. In some cases, the spots can turn fully black.

Here are the most common fungal diseases that may cause brown spotting in spider plants:

Downy Mildew 

This fungal disease is caused by algal-like parasitic organisms. It appears as a soft, fuzzy-looking brown growth. It’s mostly noticeably on the lower foliage of a spider plant but may manifest other symptoms like leaf mottling, leaf drooping, or stunted growth.

Alternaria 

Most severe in warm, humid conditions, this fungal leaf blight affects mostly mature foliage. They usually begin as tiny brown spots with yellow halos then turn into irregular brown spots (around ¾-inch). Each severely impacted leaf may wither, get wrinkled, or even fall over.

Anthracnose 

Leaf spots caused by Anthracnose often start as small yellow or brown spots that grow into dark brown spots.

Septoria Leaf Spot 

These fungal leaf spots begin on the undersides of mature foliage as somewhat round spots with a gray center and dark brown margin. If you don’t treat it for a long time, the leaves will turn yellow and wither.

Powdery Mildew 

As an amateur (that was a long time ago!), I used to mistake powdery mildew with downy mildew. The latter thrives in cool, moist conditions.

Powdery mildew is characterized by spots that start as white patches that eventually turn into yellow-brown spots, often seen on the upper sides of the leaves.

How to Fix This

You can use numerous strategies to treat fungal diseases:

  • Avoid watering the plants for a while to get rid of excess moisture that fuels the growth of the leaf spots.
  • Place your houseplants in an airy spot and space them out.
  • Avoid overhead watering. You should keep the leaves fairly dry by applying water at the base.
  • Use copper-based fungicides at the very first sight of the telltale signs of fungal disease. I’ve discovered that fungicides that contain chlorothalonil, neem oil, myclobutanil, lime-sulfur, or mancozeb can do the trick.

For the treatment of Fungal diseases. Here are the fungicides i recommend:

Name of The FungicideAmountAmount of Water
Garden Safe Brand Fungicide32 tablespoons (1 fl oz) 1 gallon of water
Bonide 811 Copper 4E Fungicide1-4 tablespoons (.05-2.0 fl oz)1 gallon of water
Southern Ag – Liquid Copper Fungicide3-4 tablespoons1 gallon of water

Bacterial Diseases

If you notice sunken, watery brown, or black lesions/spots on your spider plant, you may be dealing with a bacterial disease.

Your houseplant will likely develop bacterial leaf spots if you keep it in a poorly ventilated area. Overwatering and too much humidity can exacerbate the disease. 

How to Fix This

There’s no cure for houseplants affected by bacterial leaf spots. You can spray with a baking soda solution and use sulfur-based or pyrethrum-based sprays. They’ll stop the spread, but not heal diseased parts.

Bacterial leaf spots can be fatal to your houseplant. If the bacterial disease is systemic, you should get rid of diseased parts before they spread to healthy foliage.

Parking your houseplant in a brightly-lit and well-aerated spot can go a very long way. Avoid overhead irrigation, as well.

Nutrient Deficiency

If your spider plant has brown spots, the houseplant may be suffering from a lack of nutrients. This may be due to root rot, wrong light, or poor soil nutrition.

Leaves of spider plants low in nitrogen often turn yellow before developing brown spots. If everything else looks good except for browning on the leaf tips, this could mean that your houseplant is iron deficient.

Deficiency in zinc or magnesium is usually manifested in the form of brown spots on foliage near the center.

How to Fix This

Ideally, you should apply fertilizer to your spider plant every month in summer and spring. A water-soluble fertilizer is highly recommended. Avoid over-fertilization as fertilizer burn will also cause brown spotting.

If the brown spots are indicative of nitrogen deficiency, try placing your houseplant in a brighter area to see if the spots will disappear. For iron deficiency, just one dose of iron-containing fertilizer should be enough.

Edema

More common than most gardeners are willing to admit, edema is a condition in which the houseplant takes up more water than it can use. This causes the leaf cells to engorge and rupture.

The rupturing often results in watery blisters, bumps, or spots, especially on the undersides of the leaves. They’re often crusty, wart-like raised blisters that may turn necrotic. You may confuse them with bacterial or fungal leaf spots.

How to Fix This

There are various ways you can treat spider plant brown spots caused by edema depending on the actual cause:

  • If the culprit is poor watering habits, stop watering for a few days or until the top inch of the potting soil is fairly dried out. Remove water trays and ensure large pots are well-drained.
  • Improve air circulation and water when the sun’s up and warm. Gradually move your houseplant to a brighter spot.
  • Do a soil test and adjust soil pH and nutrients accordingly.

Excess Light/Scorching

Exposure to excessive light can bring temperature stress to your spider plant. Your houseplant should be exposed to part sun and parked in a reasonably bright spot. Don’t rush your plant from a poorly-lit area to a sunny spot.

For optimum growth, your spider plant should be kept in temperatures between 70°F (21°C) and 90°F (32°C). Too much light will not only shock your houseplant may cause tissue damage, often presented as brown spots.

How to Fix Brown This

The answer is simple: relocate your houseplant away from the scorching conditions. Move your spider plant to a spot that receives bright, indirect light. Avoid direct sunlight at all costs because it can cause scorching.

Frost Damage

As with scorching or excess light, cold drafts can also damage your houseplant’s tissue and cause brown spots to develop. This is usually seen during the start of winter.

If your houseplant is located near the window, see if there’s a cold draft, particularly at night. This is also common for spider plants in unheated conservatories and sunrooms.

How to Fix Brown This

Again, relocating your plant to a warmer spot will do the trick. Make sure your spider plant is adequately insulated or keep the room warm. Simply turn on the heating system, but maintain the temp in the 70°F (21°C) and 90°F (32°C) range.

Low Humidity

Spider plants do well in moderate humidity (somewhere in the 30% to 50% range).

Too high and too low humidity can spell doom for your spider plant. On the one hand, excessive humidity, especially when coupled with warm conditions, is a recipe for bacterial, algal, or fungal diseases.

On the other hand, low humidity means the leaves of your spider plant will wilt and turn browns on the tips.

How to Fix Brown This

Low humidity is a common problem during the winter months. To rectify the issue, place your houseplant in a medium-humidity room. You can mist around the plant occasionally.

Insect Infestation

Even though spider plants are typically hassle-free, they’re sometimes troubled by aphids, scales, spider mites, mealybugs, whiteflies, and other insects. They usually drill holes in the leaves and suck out juices, leaving brown spots.

How to Fix Brown This

First, you must inspect your spider plants for any signs of insect infestation. If any of the insects mentioned above invade your houseplant, wash the bugs off outside or in the shower with a strong spray of water.

Watering Problems

Brown spots on spider plants are usually a sign that you need to reconsider your watering habits. If you overwater your houseplant, then leave it to completely dry out before the next irrigation, that’s a recipe for brown spotting.

Excessive watering generally leaves the potting soil waterlogged. This makes it difficult for the houseplant to absorb nutrients and oxygen. Instead of drenching it in water, maintain a consistent watering routine.

A spider plant thrives when the potting mix dries out slightly between irrigation. Check the soil after every four to five days.

If the soil mix is a bit dry to the touch, water the houseplant properly. Make sure that the water runs out of the bottom of the pot.

How to Fix Brown This

A spider plant thrives when the potting mix dries out slightly between irrigation. Check the soil after every four to five days.

If the soil mix is a bit dry to the touch, water the houseplant properly. Make sure that the water runs out of the bottom of the pot.

If the soil is waterlogged, inspect the root system for root rot. Remove disease roots and apply some anti-fungal to the rest.

Transfer the houseplant to a bigger pot and leave the waterlogged mix until it dries out a bit. Repot your plant and maintain a good watering habit from then on.

Fertilizer Burn

Brown spots on the leaves of your spider plant are often a sign of over-fertilization. This indicates an accumulation of salts from excessive application of fertilizer. It can also be caused by softened water.

Spider plants require a little fertilizer to boost growth. But, as with the human body and vitamins, too much can do more harm than good.

How to Fix Brown This

Water your houseplant until it comes out of the holes in the bottom. This will help drain out salts that have accumulated from excess fertilizer. If the fertilizer burn is too severe, you might want to repot with fresh soil.

From here, fertilize your houseplant sparingly, only once every month in summer and spring. Water-soluble fertilizers are best suited for spider plants.

You May Also Enjoy: Why is my Spider Plant Dying? (Causes and Solutions)

How to Prevent Brown Spots on Spider Plant?

As you might expect, preventing brown spots from appearing in the first place will depend on the potential cause. I will touch on how to prevent each problem from causing brown spots on your spider plant.

Algal Leaf Spot

Although algal leaf spot is seldom dangerous to your houseplant, you’d want to keep it at bay using the following strategies:

  • Ensure your spider plants are robust, as healthy houseplants are less prone to algal leaf spots. Fertilize, water, and care for your plant as needed.
  • Place your plant in a well-aerated and brightly-lit spot.
  • Avoid areas with high humidity. Space out your plants, too.

Fungal Diseases

  • Fungal diseases thrive in warm and highly humid conditions, so avoid them.
  • Keep house plants apart to prevent a buildup of humidity.
  • Make sure your plant is in an area that has good circulation.

Bacterial Diseases

Because there’s no known cure for systemic bacterial leaf spots, you must remove severely diseased plant materials immediately to prevent further spread. Use any technique that decreases wetness on leaves, improves air circulation, or lowers humidity:

  • Place your plant in an open, airy spot.
  • Create ample space between houseplants.
  • Water your plants at the base to avoid leaf wetness.
  • Don’t overhang other houseplants over your spider plant.

Nutrient Deficiency

Studies have shown that a water-soluble fertilizer with an NPK ratio of 19-6-12 or 2-1-2 is ideal for the spider plant’s optimum growth.

Park your plant in a bright, indirect sunlight spot to prevent nitrogen deficiency. A fertilizer rich in iron, zinc, and magnesium should be applied once.

Fertilizer Burn

On the same note, you should avoid over-fertilization. Applying a water-soluble fertilizer once every month or so in summer or spring should be OK. Avoid fertilizers that contain boron or fluoride.

Edema

  • Use well-drained potting mix and avoid over-fertilization.
  • Reduce watering during low-growth periods and colder months.
  • Increase spacing between houseplants to improve light intensity.

 Excess Light

Avoid direct sunlight because it can scorch the foliage. For best results, station your spider plant in an area that receives bright, indirect light.

Frost Damage

Make sure your houseplant is well-insulated. Park it in a warm area or keep the room warm. Seal off any windows or vents that may bring in a cold draft.

Low Humidity

If the room is very dry, give your spider plants a daily misting. Alternatively, you can set the pot on top of a shallow water tray with pebbles.

Insect Infestation

Bright (indirect) light, adequate water, and proper air circulation should prevent most insect pests from invading your spider plants.

Watering Problems

Spider plants love the potting mix to dry out a bit between watering. Check the potting mix every 4-5 days to see if it’s dry a bit to the touch. Water your plants consistently to avoid overwatering.

Last Words

Brown spots on spider plants are a common issue for these houseplants. They’re normally caused by a disease, be it bacterial, fungal, or algal. Environmental stresses like excess light, low humidity, frost, and too much humidity can also cause leaf damage and brown spots.

Over-fertilization, overwatering, edema, and nutrient deficiency may also play a role in the development of spider plant brown spots.

If everything seems OK but there are still brown spots, check for insect pests like whiteflies, mealybugs, spider mites, scales, and aphids.

Treating the brown spots will depend primarily on the cause. However, good air circulation, humidity control, adequate water, and bright light should prevent them from getting a toehold on your precious houseplants.

Arifur Rahman

I'm the owner of gardenforindoor.com. After completing my bachelor of science in agriculture, I'm serving as a civil service officer at the Department of Agricultural Extension, Bangladesh. I started Garden For Indoor to make your indoor gardening journey easy and enjoyable.

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