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Diagnosing Indoor Plant Problems

Mike Gary
Mike Gary
3 min read
Diagnosing Indoor Plant Problems

Getting rid of pests on your indoor plants is one of the most vexing aspects of owning plants. I can remember feeling so frustrated that I contemplated (but didn’t!) discarding all of my houseplants. So often, I followed treatment instructions only to have the pests reappear again a month or two later and I would have to start treatment all over again!.

It is possible to successfully eradicate most indoor plant critters safely. The secret to success is not WHAT you use to treat them, but HOW you apply that treatment.

Pesticides: Why or Why Not?

Pesticides contain chemicals that are often potent and very effective in treating plant pests. Most pesticides have a residual effect. That means that the residue left after treatment will last long enough to kill any pests that escaped the original treatment. The downside of pesticides is that they are toxic substances that can be harmful to people, pets, and the environment. This is especially true in enclosed indoor spaces. For that reason, I do not use or recommend the use of chemical pesticides. I understand that is a personal choice. Fortunately, there are safe alternatives.

Safe alternative treatments work only when they make direct contact with all of the pests. They do not have the residual effect that pesticides do. That means that safe treatments must be applied thoroughly enough that the spray makes direct contact with every single critter. If you miss a few, they will survive, reproduce, and the infestation will return. It is the failure to get complete coverage that is the primary reason such treatments fail.

So, the key to treating indoor plant pests effectively is to get complete coverage of all leaf and stem surfaces of the infested plant. That means spraying thoroughly enough that all of the leaves and stems are dripping wet as the spray solution washes over the plant surfaces. If you miss even a few of the nearly invisible juvenile pests, they will survive, reproduce, and the infestation will return. This is a messy task best done outside if possible.

For spider mites a solution of plain water mixed with a squirt of liquid dish soap is effective. For mealybugs and scale insects, mix 5 parts water with one part alcohol and a squirt of dish soap.

Fungus gnats are usually introduced with contaminated packaged potting soils that are used when people repot their plants. This is a common problem as packaged potting mixes are not regulated. The best solution is to not repot. Gnat larvae in the soil will mature, develop wings and fly out.

To treat fungus gnats, first remove and discard all loose soil from the top surface that is not in immediate contact with the roots. Doing so will also discard many of the larvae that live in the uppermost portion of soil and it will allow the soil in the root zone to dry out sooner. Letting the soil dry as deep as possible without harming the plant is the best solution because the gnat larvae require moisture to survive.

Mosquito Bits are a natural solution that can sometimes help. Yellow sticky traps help detect where the gnats are coming from. But the winged adults only live for about a week before they die of old age. Eradication of the larvae in the soil is the key. Sand, cinnamon, and diatomaceous earth, and other folk remedies are of very limited value in treating the gnat larvae.

Most other critters found in the soil are harmless and most will gradually die off on their own.

Of course, preventing pest problems in the first place should be an important goal. None of the treatments mentioned above is effective in preventing pest problems. Many years ago, I realized that I was finally having very few pest problems. I realized that as I had learned how to care for my plants better, there were fewer pest issues. That is because, like people, healthy plants have an excellent natural resistance to low-level pest and disease problems. A healthy, well-cared-for plant rarely will have pest problems.

The other side of that coin is that when you discover a pest on a plant, it is a good indication that that plant is under stress for other reasons, usually improper light or watering. It is quite possible to successfully treat a pest problem but the plant dies anyway; not because of the pests, but because of the underlying condition that was not corrected. So, whenever you discover pests on your plants, be sure to take that as a sign that your plants may have another underlying problem that needs to be corrected.

DiagnoseGardeningPlant Problems

Mike Gary

Garden Expert