You’re enjoying a lovely, peaceful day at home when you suddenly smell something foul. You search high and low for the source of the stench, only to realize it emanates from your beautiful houseplants. What can be causing the smell, and what can you do about it?
Your houseplants may smell due to overwatering, poor soil aeration, fungal and bacterial growth, rotting roots, and insufficient light. Solutions include draining the excessive water, creating drainage holes in the plant pot, exposing the plant to indirect sunlight, and changing the potting mix.
In the rest of this article, I’ll take you through the causes of odors in houseplants. I’ll also discuss how to eliminate the foul smell and safeguard your indoor plants. Let’s get started!
1. Overwatering
Most indoor plants are perennial tropical species. For this reason, they need sufficient water for survival.
However, overwatering is a common cause of odorous indoor plants. In most cases, the problem arises from the “more is better” thinking of new plant owners. Although it’s natural to think that overwatering your indoor plants will benefit their growth, this can actually suffocate the roots and cause them to rot.
The presence of yellow leaves is an easy way to know your plants are receiving excessive water.
It’s worth noting that, unlike their outdoor counterparts, indoor plants are not exposed to considerable water loss. Overwatering outdoor plants is never an issue since these plants lose more water through:
- Soil seepage
- Evaporation
- Transpiration
How To Fix
The solution is to drain any standing water in the pot or tray and ensure proper drainage by creating holes at the bottom of the pot.
Keep in mind, however, that overdoing drainage holes can deprive your plant of the water it needs to survive by draining too much water. Three to four 1/4-inch (0.64 cm) holes at the bottom of each pot are sufficient. Apart from over-draining the water, larger holes will also drain the potting mix and deprive the plant of essential nutrients.
You can add a layer of broken pottery pieces or gravel at the bottom of the pot before topping up with the potting mix to prevent excessive water loss.
Finally, you should stick to a regular watering schedule and only water when the soil is dry to the touch. To check whether the soil is dry, place your finger about an inch (2.54 cm) deep into the soil. If the mix feels moist, wait a few days before watering.
2. Poor Soil Aeration
If you often forget to water or wait too long before watering your plants, the potting mix can become compacted, and air cannot flow through it effectively. Poor aeration creates an anaerobic – instead of aerobic – soil environment.
An anaerobic soil environment reduces the activities of soil microbes that promote soil aggregation. The potting mix relies on these microbes for:
- Phosphorus solubilization
- Nitrogen fixation
- Pathogen and pest suppression
- Decomposition of organic matter
Needless to say, anaerobic soil creates a conducive environment for anaerobic bacteria. These bacteria are harmful to houseplants and contribute immensely to the foul smell.
It’s also worth mentioning that poor soil aeration eliminates air pockets. Your plant needs these air pockets to breathe.
Insufficient oxygen absorption from the soil due to fewer air pockets leads to the death of root cells. Consequently, the plant loses vigor and dies.
How To Fix
You can improve soil aeration by mixing perlite or sand with your potting mix. These materials promote better drainage and prevent soil compaction.
You can also regularly turn over the top layer of the potting mixture, fluffing it up to improve air circulation.
This problem also points back to overwatering. Therefore, you should water your plant adequately to facilitate sufficient aeration.
3. Fungal and Bacterial Growth
As previously mentioned, fungi and bacteria thrive in moist, dark conditions with poor air circulation. These organisms can cause foul odors and harm your plant’s health by causing root rot or leaf spot disease.
Fungi use their enzymes to break down organic matter, leading to the release of foul-smelling gasses.
Knowing when your potting mix has fungi and bacteria that affect your plants can be challenging. Therefore, you need to be aware of the conditions that are unfavorable for fungi survival and ensure the potting mixture meets these conditions at all times.
How To Fix
You can prevent fungal and bacterial growth by ensuring proper aeration in your potting mix and avoiding excess moisture.
Fungal diseases are also easily transmitted through contaminated pruning tools or potting mix. As such, you must sterilize your tools before each use and buy a high-quality potting mix.
Although using a fungicide can also address fungal growth in your potting mixture, it’s best to prevent the problem from occurring in the first place.
4. Fertilizer Application
Although fertilizers contain essential nutrients for plant growth, they can release foul odors if applied incorrectly. Fertilizers with a high nitrogen concentration can cause the release of ammonia gas, leading to a strong, unpleasant odor.
Over-fertilization can also lead to salt accumulation in the soil, especially in potted plants where the soil cannot readily flush out excess nutrients.
How To Fix
The best way to solve this problem is by dumping the over-fertilized potting mixture and repotting the plant. An already over-fertilized potting mix will take longer to fix, yet you want to restore a fresh smell in your house.
After repotting the plant, stick to the fertilizer packaging’s recommended application rate and frequency. You should also consider using slow-release fertilizers because, as the name suggests, they release nutrients into the soil slowly. These fertilizers also reduce the risk of leaching nutrients out of your potting mix during watering.
Although houseplants have slightly different fertilizer requirements, studying the needs of each species can be tiresome. The good news is that most houseplants have almost similar fertilizer needs. Therefore, treating them in a singular way should be enough to satisfy their nutrient requirements.
Here are general fertilizer guidelines for most indoor plants:
- Apply liquid fertilizers more frequently: Since these fertilizers have a lower concentration of nutrients, your plant needs more of them regularly. It’s suitable to use them every 1-2 weeks during the growing season and once a month during the dormant period.
- Apply slow-release fertilizers less often: These fertilizers break down slowly, releasing nutrients over a longer period. Therefore, you can typically apply them once every 3-4 months during the growing season.
- Apply granular fertilizers less frequently: While they have a higher concentration of nutrients, you should apply them once every 2-3 months during the growing season. Over-fertilizing with granular fertilizers can cause fertilizer burn.
5. Decomposing Organic Matter
Houseplants need organic materials in their potting mixture for healthy growth. These materials include compost, manure, or peat moss. However, these materials can release foul odors when they start decomposing.
The decomposition of organic matter in the soil is mainly caused by the following:
- Too much water that creates a moist environment for decomposers
- Lack of aeration in the potting mixture
- Overfeeding with organic materials.
How To Fix
To address this problem, you want to ensure proper drainage and aeration in your potting mix. Mixing perlite or vermiculite in the potting mix is the best way to create a well-drained and aerated mixture.
Other fixes for this problem include:
- Avoid overfeeding with organic matter: Excessive organic matter in the potting mixture can lead to excessive decomposition and odor release. Thus, it’s advisable to stick to the recommended amount of organic materials on the potting mix packaging or consult a gardening expert for advice.
- Remove dead leaves or plant material from the mix: Dead leaves in contact with water and oxygen can start decomposing and release foul odors. As a result, removing them from the potting mixture is essential to prevent this issue.
- Consider the source of your organic material: Before using any organic material, you should check to ensure it’s not likely to cause a poor smell. Manure from predatory animals and some plant materials, such as trimmings from a tomato plant, can cause foul odors. If you must use such materials, it’s advisable to compost them before use in your potting mixture.
- Adding activated charcoal: Activated charcoal is an effective way to control odors since it absorbs them. Mixing 1/3 cup of this charcoal into every four quarts (about four liters) of the potting mixture can help reduce odor release from decomposing organic matter.
6. Rotting Roots
The roots of indoor plants can rot for various reasons, including over-watering and fungal infections. These rotting roots will release a putrid smell as they break down in the soil.
Signs that your plant has rotting roots include:
- Wilting or yellowing leaves
- Mushy and discolored roots
- Stunted growth
I’ve specifically written an article about the particular smell of root rot. Read it to learn more: This is What Plant Root Rot Smells Like
How To Fix
The best solution for this problem is prevention, mainly by avoiding over-watering.
Overwatering is the main culprit for root rot since it creates a conducive environment for fungal growth. Moreover, it reduces aeration in the soil, making it impossible for the roots to breathe.
You should only water the plant when the top two inches (5.08 cm) of soil are dry to the touch. Alternatively, you can use a soil moisture meter to confirm the right time to water the plant.
Here are the steps to getting the correct moisture readings using a soil moisture meter:
- Push the meter’s metal probe into the potting mixture. You should ensure at least ⅘ of the metal probe’s length is in the soil. Don’t force the probe into the soil to avoid breaking it.
- Let the moisture meter stay in the soil for about 30 to 60 seconds. This is the amount of time the meter needs to get an accurate reading of the moisture content.
- Read and record the moisture level. Check and record the displayed moisture level. Remove the probe and clean it with a dry cloth before inserting it into a different spot in the soil. Read the results for the new spot and record them. Repeat the process until you cover the entire pot.
- Interpret the results. The meter’s scale can be on the dry or wet side. Use the scale on the package for interpretation.
Here’s a video to take you through the above procedure:
If you notice rotting roots, take immediate measures to address the problem. Here are some effective remedies:
- Remove affected roots: Cut the rotting roots using sharp and disinfected scissors.
- Repot the plant: Transfer the plant to a fresh, well-draining potting mix.
- Improve aeration: Remove compacted soil and mix in perlite or vermiculite to improve drainage and aeration.
- Fungal infections: Apply fungicide according to package instructions to prevent further rotting and fungal growth.
7. Insufficient Light
Like any other plant, indoor plants need sunlight for photosynthesis. However, the good thing about most indoor plants is that they can tolerate low light conditions, a characteristic of the indoor environment. Still, your indoor plants need access to partial indirect light.
The light requirement condition doesn’t benefit the plant alone; the soil also needs light to remain fresh.
Keeping the soil in a cool space, away from sunlight, creates a suitable environment for mildew and mold growth. These microorganisms release a musty smell that can ruin your indoor plants’ scent.
How To Fix
The solution for this problem is straightforward: provide enough light for your plant and its potting mixture. For example, you should place the plant at least three feet (90 cm) away from windows or in areas where it can receive indirect sunlight for about 4-6 hours daily.
If the plant is already affected by mold or mildew growth, remove the top layer of soil and replace it with a fresh potting mixture. You may also introduce beneficial microorganisms in the form of compost tea to improve the overall health of your houseplant’s soil.
8. Old Potting Mix
An ammonia, or excrement-like smell signifies an old potting mixture. You may also smell traces of sulfur (which smells like rotten eggs), indicating bacterial activity.
This smell is not a good sign as it means that the potting mixture has broken down, losing its ability to retain water and supply nutrients for the plant’s growth.
Although the potting soil doesn’t go bad, its additional components do. For instance, peat moss has a lifespan of one to two years. When this component expires, it reduces the soil’s water-draining ability, and the potting mixture may produce a foul smell.
How To Fix
Repot the plant regularly with fresh potting mix within the period recommended on the package. Most indoor plants need repotting every 12 to 18 months.
If the mix is already affected, remove the top layer of the expired mixture and replace it with fresh potting. You may opt for a soilless mixture since garden soil is prone to waterlogging and compaction.
You must also buy original indoor plant potting mixture from reputable gardeners or nurseries. Avoid using an old potting mix from other plants, as it may contain diseases, pests, and harmful microorganisms that can affect your indoor plant.
9. Under-Processed Manure
Manure processing is vital in removing harmful microorganisms and weed seeds. If the manure is not processed correctly, it can release ammonia which smells like cat urine or rotten eggs.
Apart from the smell, the type of manure you use affects the plant’s quality. Fresh manure is the last thing you want to go for when planting indoor plants. Such manure may contain bacteria that can affect the health of your plant.
How To Fix
Avoid using unprocessed manure as a fertilizer for your indoor plants. Instead, opt for organically-composted manure with minimal odor, such as kelp meal or fish emulsion.
If you have already used unprocessed manure, remove it and replace the top layer of soil with fresh compost or organic fertilizer to improve your plant’s health and eliminate foul odor.
10. Insect and Pest Infestation
Indoor plants are not immune to pests and insects.
Stink bugs are the worst when it comes to odors in plants. These insects are sap feeders that are attracted to the plant’s sap. When under attack, they release a putrid smell similar to pungent cilantro as a defense.
Aphids and mealybugs also produce an unpleasant odor when squashed or disturbed. These pests damage the plant by sucking its fluids, leaving behind sticky honeydew conducive to mold growth.
Snails and slugs produce a musty and fishy odor when they crawl through the soil. These pests have voracious feeding habits that create holes in the leaves and stems of plants like ZZ plants.
How To Fix
Inspect your plants regularly for any indications of pest infestation. Common signs that your plants have been infested include:
- Presence of sticky honeydew
- Holes in the leaves
- Damaged or wilted leaves
- Discoloration and distortion of new growth
If you notice any of the above signs, spray your plant with organic insecticidal soap or horticultural oil. Alternatively, you can introduce beneficial insects such as ladybugs to manage pests naturally.
11. Chemical Pollutants
Most indoor plant owners prefer to use insecticides and pesticides to keep pests and insects away. However, some of these chemicals can harm your plants and release a strong odor.
Apart from insecticides, other household chemicals such as chlorine and bleach can also cause damage to indoor plants if accidentally spilled on the soil or leaves.
How To Fix
Avoid using chemical pesticides and insecticides as much as possible. It’s advisable to use organic solutions such as insecticidal soap or horticultural oil to manage pests.
If your plants have been exposed to chemical pollutants, flush the soil with clean water and trim off any damaged leaves or stems.
Summary
Odorous houseplants signify a mess that must be addressed urgently. If left unchecked, the condition will worsen and make your house inhabitable.
A foul smell can be a sign that your plant is slowly dying from problems like root rot and suffocation.
If you notice your houseplants don’t smell right, inspect them for waterlogging. This is the leading cause of odors in indoor plants. The presence of yellow leaves confirms that your plants are overwatered.
