This article is about dealing with common indoor plant pests.

You already know that you can improve the quality of your home when you add plants. That’s because they instill a sense of calm and peacefulness. Not unimportantly, according to NASA studies, indoor plants remove up to 87 percent of airborne toxins within a day. It’s no wonder people love to surround themselves with greenery.

But it’s not all clean air and sunshine in the indoor plant world. Although they don’t have as many pests as outdoor plants there are a handful of fairly common indoor plant pests you will want to consider.

Isolate New Plants Before Introducing Them into the House

Marcia Bundi of Bundi Gardens in Great Falls, Montana, says, “When you bring your plants inside, or bring new ones home, isolate them.” Marcia is a veteran horticulturist and greenhouse owner.

Keep new plants isolated for a few days to a week, including any outdoor plants you are moving indoors. It allows you to closely examine the leaves and soil. If you notice something flying or crawling around, eliminate the pest problem before placing them near other plants. It’s much easier to deal with an issue on one plant, rather than all of them.

Assess the Size of the Container

If there are roots poking out the drain holes, it’s time to repot your plant. Since this telltale sign isn’t always obvious, there are other hints that it’s time to give your plant a larger home. If the water sits on top of the soil instead of immediately soaking in, or if the plant seems to dry out excessively, both are good indicators that your plant requires more room. Although a larger space is beneficial, plants don’t require a ‘McMansion’ sized container either. Typically, going up one pot size will get the job done.

The Role of Gravel

Do not commit the cardinal sin of placing gravel in the bottom of a container. While it was a popular habit for a long time, in reality, it’s more harmful than useful. Originally the thought was the gravel keeps the roots from sitting directly in the water, but as long as there are drainage holes, the water runs out the bottom as it should. If there are no drainage holes, the gravel still doesn’t help. It simply creates a dead space that reduces the amount of soil. So leave the gravel in the driveway.

With that said, be sure to have adequate holes in the bottom of whatever container you use. Break out the drill with a masonry bit (preferably 1/4 inch or larger) and add a few drainage holes to whatever container you’re using.

New vs. Old Soil

Besides focusing on ample space, use new soil to reduce the potential for diseases or pests. Plus, fresh soil provides nutrients that have leached out of used potting mix. Learn more about potting soil.

Exercise Restraint When Feeding and Watering

Bundi also says, “I think the biggest problem with indoor plants is overfeeding and overwatering them.”

She says they don’t need feeding if they are not actively growing. In the middle of winter, when light levels are low, refrain from feeding. Then, when the days lengthen in spring, resume with a water soluble fertilizer.

“Water them when they are dry, but don’t let them sit in water,” Marcia says.

If they’re given too much water, she says the roots become water-logged, oftentimes rotting and ultimately killing the plant. The easiest way to prevent this is a little benign neglect, as she jokingly calls it. Instead of having them on a specific schedule, stick a finger in the soil to see if the plant actually needs water.

Know the Common Indoor Plant Pests

In dealing with common indoor pests first determine if there is a problem. It’s often easy to spot pests on your indoor plants since they are in front of you on a daily basis. It’s glaringly obvious when their leaves are brown or pocked, or when you see bugs flying around. While a couple of insects isn’t a cause for alarm, you’ll want to stay vigilant. It doesn’t take much of an infestation to be a problem in the confines of a home.

Fungus Gnats – Another Reason to Not Overwater

“Fungus gnats look like flies. They have spidery legs and clear wings,” says Marcia. They also have long antennae, which distinguishes them from flies or mosquitoes, and are rather delicate looking. They’re not strong fliers, so are more often seen flying close to the plants or scrambling over the top of the soil or on the foliage.

“Fungus gnats feed on algae that grows in the soil. The larvae eat the roots of the plants,” says Marcia. The adults aren’t a big issue as their life span is only 3 days, nor do they feed on the plants.

Fungus Gnats – photo by Amy Grisak

The best way to prevent a fungus gnat infestation is to not overwater. If the soil is not perpetually damp, algae is less likely to grow, and it won’t encourage these pesky guests.

Fungus gnats typically aren’t a huge problem, and the larvae only harm the plant if they occur in large enough numbers. However. if an infestation is significant, there are potential treatments. Yellow sticky traps placed on skewers and stuck into the soil around the plant will capture many of them. The natural bacteria, Bt (Bacillus thuringiensis) ,is also effective, although it should be applied according to the label directions for the best results.

What to Do About White Flies

“White flies like hot, dry conditions. And guess what our houses are like?” asks Marcia.

To remedy the situation, she recommends adding humidity in arid climates. Not only is it beneficial for the plants, it’s good for human health, particularly during the winter.  This might be as simple as placing a bowl of water near the plants or placing a pan of water on the stove (particularly if there is wood heat in the home).

“You can also spritz some water on them,” suggests Marcia.

They thrive in areas where there are no predators. White flies can proliferate to the point that they can cause significant damage by sucking out the juices of the plant.

White Flies – photo by Amy Grisak

Although they’re called flies, they’re in the same family as aphids, yet look like tiny moths. Unlike aphids or mealybugs (another relative) they have white wings with a somewhat waxy body. They’re often seen in clusters on leaves and stems of the plants.

As with the fungus gnats, sticky traps capture a fair number of the white flies. But for severe infestations, it is best to employ insecticidal soap. Bundi cautions to use an insecticidal soap and not a detergent of any sort since the latter is prone to burning the plant. Spray the underside of the leaves and stems since it’s easy for them to hide in the crevices of the plant. This may require several treatments.

Aphids Are Weak and Stupid

Related to the white flies, aphids are also vampire insects that pierce the leaves and stems of the plants. But they prefer a much different climate.

“They like damp, less dusty conditions,” says Bundi.

Outside gardeners are well acquainted with the dozens of different varieties of aphids, showing up in colors ranging from pinks, oranges, and reds. These same pests can plague indoor plants. Aphids don’t scurry out of view, so they’re easy to spot congregating on stems and the undersides of leaves. To make matters worse, the secrete honeydew, a sticky substance that is messy and makes the plant prone to fungal infections – which is what ants love on the outside plants.

Even though aphids can significantly damage plants, they are easy to kill. Horticultural oil coats and suffocates the insects, and a product such as an insecticidal soap (once again, don’t use sprays containing an actual detergent) kills them immediately.

But for most infestations, it never comes to needing chemicals. If there is a single stem with the aphids, simply snip it off and dispose of it. Alternatively, wash it off, scrubbing away the aphids.

“They’re little, they’re weak, and they’re stupid,” explains Marcia. She typically takes a squirt bottle with water and her fingers to squish and eliminate the problem.

Dabbing Away Mealybugs

Indoor pests are well-suited to the cushy life and warm conditions of house plants, and can proliferate to the detriment of the plant, if not spotted and checked. Mealybugs are an insect of the tropics that particularly thrives in this environment. Thankfully, they’re not fast-moving critters and are easily spotted so you can gain a handle on them.

Bundi says, “They look like cottony puff in the leaf axil.”

They are oval-shaped, and can be pinkish or have a poofy white appearance. They are most likely found in clusters, and being scale insects, they also produce the sticky honeydew. Not only do they damage the plant by piercing and feeding on the plant, the honeydew promotes fungal diseases, such as sooty mold.

On outside plants, the mealybug destroyer is a type of ladybird beetle. It cleans plants of mealybugs and aphids. But, who wants to introduce beetles into the house to wage a battle royal between pests and predators?

Instead, for relatively small infestations, Marcia says, “Take a cotton swab, dip it in rubbing alcohol, touch and kill them.”

It knocks out the individual insects, but you’ll most likely need to repeat this process every week until all of them are gone. But other than the direct application, general pesticides (such as pyrethroids) or systemic chemicals offer limited relief, partly dependent on the maturity level of the mealy bugs. Chemicals are more effective if the mealybugs are young because the mature insect has a thicker, waxy coating. 

Indoor plants are not immune to pests, but as long as you keep a close eye on the overall health of your plants, along with possible uninvited guests, you can enjoy a healthy array of green the entire year.