Taking care of houseplants can be tricky at times: you could have the hardiest plants in the world and still run into unexpected problems along the way, such as uncomfortably sticky leaves. Are sticky leaves on houseplants a cause for concern? And if so, how does one amadeal with them?
Some of the main reasons indoor plants get sticky leaves include:
- A pest infestation
- Nectar on the surface of the leaves
- Bacterial infection or fungal growth
- High humidity
In this article, we’ll discuss, in great detail, the five primary reasons that indoor plants develop sticky leaves. I’ll also tell you how to address these underlying problems and nurse your plant back to normal health.
1. A Pest Infestation
Unfortunately, a pest infestation is probably the most common reason indoor plants develop sticky leaves.
What makes matters worse is that the pests that cause this problem are often too tiny to be seen unless you examine the plant closely, so the first indicators of an infestation will be symptoms like sticky leaves.
There are a bunch of pests that can cause this problem, but the three that are most often responsible are scales, aphids, and mealybugs.
These insects latch onto plant leaves and feed on the nutrient-rich sap and nectar found within plants. This nutrient-rich sap is found in the phloem, a vascular tube that transports carbohydrates, such as sucrose, to the entire plant.
As these little critters feed on this sugary sap, they excrete a sticky substance called ‘honeydew.’ Yup, that’s right: honeydew is insect poop.
As disgusting as it may be to think about, if you touch your plant and feel it’s unusually sticky, it’s probably the honeydew causing this sensation.
Honeydew itself isn’t particularly dangerous to plants. The liquid is non-toxic. However, simply leaving it alone will lead to several problematic scenarios.
Honeydew attracts ants and other insects you don’t want to deal with while already fighting off an existing infestation.
It also creates the perfect breeding grounds for fungi. Sooty mold, in particular, is often seen growing on plants covered in honeydew. This black mold blocks off some of your plant’s access to sunlight and oxygen.
Fortunately, honeydew can simply be washed off with warm water and a cloth. You can also wash off sooty mold in this way. But washing is only a temporary fix.
The bugs themselves are the major problem here. The honeydew and mold will return as long as the bugs are alive.
Additionally, the nutrient-rich sap they feed on is food they’re stealing from your plant. Leave them to their own devices for long enough, and the host plant will end up malnourished.
Okay, so we know that pests are the likely culprit – how do we confirm this suspicion?
Here are a few general indicators – besides sticky leaves and sooty mold – that your houseplant is being attacked by pests:
- Stunted growth
- A change in leaf color (leaves turn brown or yellow when they lose too much sap)
- Spotted leaves
- Visible white webbing
You should closely examine the leaves of your plant. Make sure you check the underside of the foliage; that’s where pests tend to hide.
Here’s what you’re looking out for:
Scale bugs are stationary brown or black bumps most commonly found on the underside of the leaf, although they can sometimes be located on plant stems too. They are protected by a sea-shell-like coating.
Aphids are tiny bugs that are a little under 0.4 in (1 cm) in size. They come in various colors – white, yellow, orange, brown, and black. Aphids reproduce rapidly and can seriously damage plants. They can be winged or wingless.
Mealybugs are tiny white bugs that leave behind a conspicuous cottony material when reproducing. They also look like pieces of cotton.
Dealing With Infestations
When it comes to dealing with pests, you can either decide to put up a fight or isolate the plant and leave it to its fate.
Unfortunately, eliminating pests can be a long process because of how fast they reproduce. You’d have to kill off every single one to end the infestation.
I recommend checking out the scale of the infestation you’re dealing with. If it’s just a few leaves on a single plant, it’s quite likely that you’ll successfully be able to clean up the bugs with some insecticide.
On the other hand, if the plant is infested all over, you may just want to cut your losses and run, but be sure to separate the plant from other plants. You don’t want the infestation to move to your other plants.
Fortunately, severe infestations are seldom seen in indoor potted plants.
Here’s how to eliminate the offending pests.
Scales have a durable outer coating that protects them against most insecticides.
- Remove the scales from the afflicted leaf manually with a brush. This is only practical if the infestation is localized to one or a few leaves.
- Use rubbing alcohol. It dissolves the protective coating, making scales vulnerable to chemicals.
- Apply horticultural oil all over the affected leaf. The oil cuts off access to oxygen, causing the bugs to suffocate.
Clean your plant with an insecticide spray after the scales are removed. This will kill the larvae and younglings that are too small to be removed manually but haven’t developed their protective shells yet.
I recommend conducting this treatment weekly.
Unlike scales, aphids do not have protective shields.
To eliminate aphids:
- Cut off heavily infested parts of the plant. Aphids multiply rapidly – it’s too late to save parts of the plant that are overrun.
- Don’t delay treatment. Aphids are notorious for their ability to carry and spread plant-killing diseases.
- Use neem oil or insecticidal spray to kill off the bugs effectively.
- Wash the plant thoroughly.
Keep up treatment until no more aphids inhabit your plant. This may take several weeks.
To get rid of mealybugs:
- Brush off visible mealybugs from the plant.
- Use neem oil or insecticide spray as an effective cure.
- Repeat treatment until no more bugs are visible.
- Keep the plant isolated, as mealybugs can easily travel from plant to plant.
In all three cases, I recommend using neem oil over full-strength, commercial insecticide. Unlike synthetic chemical insecticides, neem oil is all-natural and won’t hurt your plants.
This addresses a major problem associated with insecticide use: in killing the pests, it inadvertently damages the host plant too.
Don’t shy away from using insecticide when dealing with larger infestations, though.
2. Nectar on the Surface of the Leaves
If you’ve examined for pests but haven’t been able to find any despite searching meticulously, don’t worry. There are plenty of other reasons your plant leaves might feel sticky to the touch, some of which are non-threatening to the plant.
Nectar is another sugary substance produced by plants. It’s essentially sugary water that plants use to attract pollinators.
The presence of nectar on your plant leaves may be what’s causing them to feel sticky. But how did the nectar get on the leaves – isn’t it only present in flowerheads?
Some Leaves Have Extrafloral Nectaries
Typically, you only find nectar in flowerheads because that’s where reproductive organs rest. However, some plants have extrafloral nectaries.
Nectaries are glands that produce nectar. Extrafloral nectaries are nectaries that don’t take part in the pollination process. You might wonder why they even exist if they don’t contribute to pollination.
You may be surprised to learn that extrafloral nectaries are a clever defense mechanism built to discourage plant-eating animals (herbivores) from approaching and eating the plant, but this isn’t done straightforwardly.
The excess nectar secreted by these extrafloral glands attracts carnivorous insects, such as ants and ladybugs. The presence of these insects then keeps dangerous herbivores at bay.
Extrafloral nectaries are typically found on plant stems, leaves, and flowers. Sometimes, excess nectar leaks onto the foliage, which may be what’s causing it to feel sticky.
If nectar is what’s causing your plant leaves to become sticky, you probably don’t have anything to worry about. Sometimes, non-pollinator insects will feed on this nectar, but that’s only natural and to be expected.
Flowers Generate Nectar When They Bloom
Flowers use nectar to attract pollinators. However, some plants – usually ones that grow lots of flowers – produce a lot more nectar than others.
Sometimes, excess nectar from blooming flowers can drop off onto other plants.
To deal with the stickiness, you can wash off the nectar and keep your plants further apart so that they don’t collect nectar from each other.
The loose nectar will instead drop off into the potting mix, or potentially, onto the floor.
Clean Your Plants From Time to Time
You don’t necessarily have to clean the nectar immediately, but doing so will get rid of the unpleasant stickiness. When it comes to plants that have extrafloral nectaries, you may have to give them a thorough cleaning from time to time to prevent a build-up of nectar.
But that’s something I recommend you do with all your houseplants anyway.
Occasional washings get rid of dirt, insects, decomposing matter, waste, and other undesirable things on the surface of your plants. It’s a great way to keep your collection hygienic, clean, and disease-free.
You don’t have to soak your plants in the sink to get satisfactory results, either. You can use a spray bottle and a damp cloth for cleaning purposes.
If you want more anti-pest and anti-disease benefits, consider mixing a tiny amount of lime or vinegar into the water. Add only a little bit, though. Our primary goal here is to give the plant a physical cleaning.
Some Plants Have Sticky Leaves for Evolutionary Purposes
If a plant suddenly turns sticky, that’s certainly a reason to be alarmed. However, some plants are naturally sticky.
Plants in sandy environments, for example, use their sticky exterior to coat themselves with sand. This helps them regulate internal temperature, deflect excess sunlight, and protect themselves from small insects.
You should look up your plant species to know what’s normal and what’s not.
3. Bacterial Infection or Fungal Growth
It is rare, but sticky leaves can be caused by a bacterial or fungal infection.
You may see the symptoms of such an infection in the form of spotted leaves. Other symptoms include an unpleasant smell and root rot.
If an otherwise healthy plant is turning black above the soil, the possibility of a bacterial or fungal infection is high.
It’s hard to pinpoint exactly what may have caused your plant to contract an illness – there are numerous possibilities.
Unsanitary cutting tools, for example, can cause bacteria to spread into exposed incisions. Diseases can spread via pests, such as aphids. They can simply jump from plant to plant if the two are close enough.
Dealing With Pathogens
Unfortunately, we don’t have ‘medicine’ for plants the way we do for humans.
While there’s no chemical cure, there are a few things you can do to help your plant fight the disease:
- Cut off the infected part of the plant immediately. This is perhaps the most important thing you can do, as it will prevent further spread.
- Isolate the plant. You don’t want the disease to spread to other houseplants.
- Avoid using the diseased plant or potting mix as compost.
Beyond that, you can only hope for the best.
Preventing Future Infections
Prevention is better than cure.
You can reduce the likelihood that one of your houseplants contracts an infection in the future by:
- Sanitizing your cutting tools before pruning or deadheading plants.
- Not using garden soil for potting mix. Garden soil is unsterile and laced with bacteria and fungi.
- Giving your plants more sunlight. Many microorganisms, especially fungi, can’t handle intense UV rays from the sun.
- Taking care not to overwater your plants. Overwatering causes your plant’s roots to rot, which is certain to attract a lot of unwanted guests.
- Cleaning your plants every once in a while.
- Checking your plants frequently.
- Addressing pest-related issues promptly. Pests can carry diseases.
- Cutting off damaged body parts from your plant. Frost damage, for example, is irreversible and will lead to rotting.
Plants have an immune system. A healthier plant will be better able to fight off infections.
Here’s everything you need to know to keep your houseplants healthy all year round: How To Keep Indoor Plants Healthy (9 Essential Tips)
4. High Humidity
When the humidity is high, things naturally feel moist and sticky.
If you’re only getting a mildly sticky sensation when touching your houseplants, high humidity might be why. Keep in mind that the local humidity around your plants is likely slightly higher than the room’s overall humidity.
This is because plants and the soil they’re planted in constantly lose water to the air via transpiration and evaporation.
If your plants are bundled together, placed in pebble trays, or the surrounding air is poorly ventilated, evaporation is enough to create a localized region of high humidity around the plant.
Is High Humidity Undesirable?
If high humidity is causing your plants to feel sticky, should you get rid of it? Well, there’s a bit more to it than that.
See, most plants actually prefer being in high humidity. That’s what they’re used to in the wild, and it helps them retain the water inside their body for longer.
This also translates into less frequent watering, something you may value if you’re not enthusiastic about watering your houseplants every other day.
Except for a few drought-tolerant species, such as cacti and succulents, most plants will thrive if you let them sit in high humidity. Some plants, such as ferns and orchids, will even lose foliage when the humidity is too low.
Poor ventilation equates to an increase in indoor humidity, generally speaking. However, it’s still something you need to address. The drawbacks of poor ventilation far outweigh the benefit that the marginally increased humidity levels will have on you and your plants.
If you’d like to lower the humidity around your plants, here are a few ideas:
- Separate your plants. Don’t keep them huddled up.
- Improve ventilation and airflow.
- Avoid keeping your plants in bathrooms and kitchens – these rooms are naturally humid.
- Run a dehumidifier.
- Fix any water leaks.
Overwatering can cause your houseplants to develop wet, mushy leaves that feel sticky to the touch. Unfortunately, that’s only the tip of the iceberg.
Overwatering brings with it numerous problems, such as:
- An increased risk of fungal growth in the soil
- Root rot
- Wilting leaves
Simply put, overwatering is not something that should be taken lightly.
Overwatering in indoor plants is usually seen in pots without drainage holes. I strongly advise using pots with drainage holes for your houseplants for this very reason.
You can learn more about plant pots and drainage holes here: Should All Indoor Plant Pots Have Drainage Holes?
Here are the primary symptoms you should look out for:
- Mushy leaves
- Droopy foliage that doesn’t perk up when watered
- Waterlogged soil
- An unpleasant smell from the soil
- Root rot
To find out for sure, dig a few inches (5+ cm) deep into the soil and examine the roots. Black, soggy, or decaying roots are a clear indicator of overwatering.
Remedy and Prevention
Unfortunately, there’s not much you can do about overwatering other than readjusting your current watering cycle.
Keep in mind we tend to overestimate how much water plants actually need. Less frequent but thorough, deep waterings are preferable to more frequent, shallow waterings.
You should also let the soil dry out in between each watering. This ensures your plant’s roots don’t stay standing in water perpetually.