spider mites

Spider mites are one of the most prevalent indoor garden pests. It's likely at some point in your gardening life you’ll encounter a frustrating infestation of these almost invisible pests. 

While there is no danger concerning spider mites on humans, spider mites in soil, on houseplants, or in your flourishing indoor garden are a massive cause for concern. If left untreated, spider mites will wreak havoc across your entire crop and spread throughout the grow room.

If you see spider webs on plants, this is a big sign its time to get serious about spider mites. Spider mites may be one of the most common pests, but it doesn't mean you can't easily remedy the situation. With careful monitoring, a little due diligence, and all-natural pesticides, you can get spider mites under control before they take control.

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What do Spider Mites Look Like?

Spider mites are tiny pests and ones which aren’t always visible with the naked eye. The most common varieties are red spider mites, black spider mites, and the most prevalent, the two-spotted mite. It is often not until you have a full-blown infestation that you'll notice them, because your crop will start to show the effects.

The only way you’ll get a clear picture of what they look like is under the magnifying lens of a microscope. They resemble a small beetle with six distinct legs. Pretty obviously, their color gives away the specific species: black, red, and two spotted.

If you do see the signs of an infestation, you’ll likely be more concerned with exterminating them then their microscopic features. The most noticeable symptom of a spider mite infestation is the discoloration of the leaves.

If you notice a spotty light yellow patch on your plants, take a closer look. On the underside of the leaf, you may find a cluster of mite eggs, which might be easier felt with the tip of a finger than seen with the naked eye. Spider mites will appear like small dark dots surrounding their eggs.

Another critical sign of these pests is a build up of tiny webs in and around the branches, leaves, and flowers. Webbing is a symptom of a severe infestation. If you see webbing, take immediate action to rectify the issue before it spreads throughout the grow room.

Where do Spider Mites Come From?

Spider mites and their eggs are so adept at hitchhiking, the original source of the infestation isn't always apparent. Any outside source is suspect, from the air to the tools to the gardener. Most often, your outbreak will have come from another garden, carried into your home on used equipment, dirty tools, industrial materials, and even your clothing.

Making the innocent mistake of walking across the lawn, and then entering the grow room can bring the eggs into contact with your plants. It’s one of the reasons why commercial operations have such extensive protocols for entry into grow facilities.

The most common sources for a spider mite infestation include:

  • Contaminated soil or soilless medium
  • Containers and tools
  • Unfiltered HVAC inflow
  • Inside CO2 replacement tanks
  • Clothing, shoes, and the gardener

Something simple you can do is start with a high quality plant soil rather than mass-produced, lower-quality soil.

Spider mites might not don’t have wings, but they are light enough to float through the air. They are very active hitchhikers, and if given a chance will catch a ride on just about any surface until they get to your plants.

kill spider mites in soil

How to Prevent Spider Mites

The only real way to prevent spider mites is to put in the work before they infest your garden. This early work really cuts down on the risk of infestation. It’s well worth the additional initial effort to avoid issues later when the crop is nearing harvest.

Sterilize all tools

When you move tools and equipment from outside to inside the grow room, sterilize them with a mild mixture of soap (or alcohol) and water. Working between multiple indoor grow rooms? You’ll also want to clean the tools before they move between spaces. Better yet, keep duplicate items in each space to keep these tools separate. Always check for spider mites in soil, coco, or any new growing medium.

Isolate and clean clones

If you purchase clones (or move seedlings from one area to another), you should have a separate area designated for a period of isolation. Isolate for a week or more to see if the clones develop signs of pests or disease.

Whether or not you choose to isolate the clones, at the very least, you should prep and clean them before entry.  Wipe the leaves off with the same solution of mild soapy water using a damp cloth or sponge.

Gently wipe the top and bottom of the leaves and the stem to remove any lingering eggs or adult mites. This can seem like a painstaking process, but consider how much more effort it would take to clean the leaves of a mature plant.

Improve your plants environment

Spider mites thrive in hot, dry environments. Depending on your indoor crop, you might be able to lower the temperature or increase the humidity (slightly) to make the indoor climate inhospitable to these microscope bugs. If you grow your plant variety in the environment that it thrives in, with proper temperatures, humidity levels, airflow, and air exchange. In that case, they will more likely to naturally resist theses pests.

Spider mites also hate excessive air circulation, and air circulation is something almost all plants can benefit from. Add additional fans to up the air circulation in the under-foliage, where the mites generally like to hang out. If you have an HVAC system pulling air from the outside, you’ll also want to set up an air filtration system with a filter fine enough to prevent an external infestation from the airflow.

Consistantly monitor crops

Preventing spider mite infestation is most importantly about catching it early. Check your crop daily to look for the signs of spider mites and other diseases. A leaf-by-leaf inspection isn’t necessarily needed, but you can scan plants for spotty yellow leaves and webbing, and check for eggs or mites in the leaves, nodes, and buds. Catching an infestation early makes the cleanup process exponentially easier.

How to Kill Spider Mites

Spider mites are incredibly frustrating pests because of their capability to destroy entire plants. If your blooming plants are infected, it could be too late. But it's always worth trying to save them if you think there's time, and it can be done naturally! 

If you have been keeping your plants in an optimal environment, and doing your due diligence monitoring the health of them, you can catch the spider mites before it gets out of control.

Prune and destroy

If the infestation seems restricted to a few stems and leaves, aggressively prune out the majority of the nests. If the infestation is more severe you might consider destroying the entire plant.

Hose down the plants

Buy a safe, organic pesticide or make one yourself. Hose down the plants with a mild solution, covering both the undersides and topsides of each leaf.

Use natural pesticides

Spider mites dislike many common household ingredients, like alcohol, essential oils, carrier oils, and soap. Mix any of these into the water, in a mild dilation, and you have an affordable and uncomplicated natural pesticide. There are also many commercially available natural pesticides in garden stores and online.

Introduce beneficial insect predators

Some growers, usually within large commercial operations, find it more useful to introduce a natural predatory - like the ladybug. Adding more creatures into your garden is an excellent idea if you farm for a living, but maybe a bit of overkill if you are farming as a hobby.

How to Make Homemade Spider Mite Spray

Despite how prevalent spider mites are in the indoor gardening industry, they are relatively easy to treat with natural home-made solutions. If you notice a small infestation, try treating it naturally to avoid pesticide contamination on the final product. You can easily make a number of home-made solutions with easy to find ingredients.

  • 2 tsp Neem Oil (essential oil)**
  • 1 quart Water
  • ½ tsp dish soap

Combine all ingredients into a spray bottle and dose all plants within the infested room. Spray both the tops and bottoms of the leaves, the stems, and the soil (if growing with soil).

Repeated every day until well after the infestation subsides.

**Citrus, peppermint and eucalyptus oils are also natural pesticides. Mix with the neem oil, or use separately. Keep in mind essential oils are very aromatic; it may not be an ideal solution for pest control during the flowering stage. The aroma and flavor may ultimately affect the final product.

You're in flower and need something now?

There are some organic pesticides that you can use safely up until the last day before harvest. 

With all of the regulations, it's best to stay with those that are actively supplying the commercial hemp farms with pest control solutions that go through all of the additional testing for heavy metals and other contaminants, as they are still around because they're safe and they test as such. 

Grower's Ally Crop Defender 3, Safer - Insect Killing Soap, and Doktor Doom- Spider Mite Knockout, are all some examples of products that are tested and safe to use a day before harvest. 

Quickly tackle large areas with a PetraTools Electric Backpack ULV Fogger.

Why Treat Spider Mites in Soil Naturally?

By now, you must have read about the controversies surrounding the contamination of medicinal plants from harmful pesticides. From California to Canada, the news is filled with medicinal plants testing positive for non-approved chemical pesticides. The fact that pesticides often linger after curing, processing and packaging is a strong argument for using natural methods to combat spider mite outbreaks. Chemical pesticides may be sufficient for killing spider mites, but they are not for human consumption. Furthermore, there are additional concerns if are inhaling the final product.

According to those in the know, the pesticides at grow supply shops make up nearly 30 percent of retail sales. They are popular because they are cheap and easy, but that doesn’t make them healthy. There is also a growing theory that spider mites are evolving to be resistant to the most common pesticides.

Natural solutions to a spider mite infestation are just as effective, even if you’ve got to do a bit more upfront work.  With a bit more elbow grease, you maintain a natural product that is safe to consume, and even inhale. If you've recently brought home a ration of few clones, purchased used tools and equipment, or accepted plants as a gift - do a little bit of groundwork to prevent a total-grow room infestation.

Next time you turn over a leaf and notice the troubling signs of a red spider mite, black spider mite, or two-spotted infestation don’t panic. You’ve now got the know-how to treat it.

With a few new skills in your belt, you’ll be able to manage the risk before it enters into your grow room. You also now know what to do should any spider webs on plants begin to appear. Finally, instead of shelling out your hard-earned cash on a chemical pesticide, which might cause issues in the final harvest  - use a homemade pesticide instead.


Spider mites might seem like the end of the world - but they are easily treatable with a little due diligence. The most important part is to be on the lookout before they reach the grow room, inspecting your plants daily, and keeping them in the optimal environment.

Author | Chris McDonald

With two decades of expertise, Chris leads Happy Hydro in redefining sustainable gardening and delights in backpacking adventures, mind-expanding journeys, and creating memories with his loved ones.

1 comment



Interesting article about spider mites. I have 5 oleander bushes on my terrace at my holiday home in Greece &, whilst the insecticides kill or prevent the common yellow oleander aphid, it does NOT do anything about the spider mite.
Your article said it was like a beetle with 6 legs. Not true. As your pic shows, a spider has 8 legs & is, therefore, NOT an insect &, seemingly, immune to insecticides !! I’ve been pruning, spraying & treating with insecticides for months now, but to no avail. Because of this, 4 of my 5 oleanders have big infestations. I’m now going to cut them right down & treat with lemon juice, vinegar & washingup liquid. But I worry about eggs still being in the soil. It’s heartbreaking – some of the plants are 10yrs old & have flowered beautifully over the years.

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