If, like I did, you sprayed your indoor plants with alcohol to clean or shine their leaves or to get rid of mealybugs (like I did, too), and you’re not sure what happens next, don’t panic. Here’s what you need to know.
Alcohol can be used as an insecticide to kill soft-bodied insect pests that attack plants. It can be used as a growth inhibitor or growth enhancer to control plant growth and development but only at adequate concentration. Alcohol can also be used as herbicide to kill off weeds and unwanted plants.
If you aren’t sure if alcohol is a safe insecticide for your indoor plants, you’ll find this article particularly useful. Read on.
Alcohol spray can kill soft-bodied insects that attack and destroy plants, slow or speed up plant growth, get rid of snails and slugs, kill weeds or competing plants, and even revive flowers.
On the other hand, be warned that alcohol can also harm plants. To prevent alcohol burns, dilute the alcohol with water and soap, and then test on a leaf or two before spraying your plants.
Alcoholic drinks containing ethanol can kill soft-bodied insects such as mites, aphids, scales, whiteflies, fungus gnats, and mealybugs. A dab of alcohol with a cotton bud is a spot treatment that is as effective as full spraying.
How does alcohol kill plant insects? In two ways: 1) alcohol has the ability to suck out water (desiccant) and 2) alcohol can penetrate and wet through their waxy skin (surfactant). The insect dies when the alcohol touches its body.
FACTOID: Adding some liquid soap to your alcohol spray can penetrate the waterproof coating of insects such as mealybugs.
You can use rubbing alcohol (isopropanol or isopropyl), although it is only very effective when it doesn’t contain additives. On the other hand, many gardeners claim that ethanol (grain alcohol) is more effective at killing insect pests.
PRO TIP: Make your own insecticidal spray by mixing equal parts of 70 percent strength alcohol (like this one on Amazon) and water. If you’re using 95 percent strength alcohol, mix 1 ½ parts water to 1 part alcohol. Always test on a leaf or two for up to 5 hours. If no leaf burn happens, repeat after a week until all insects are gone.
Alcohol is used by farmers to increase plant growth such as in vegetable farms and in orchards. On the other hand, some indoor gardeners use alcohol to inhibit or slow down the growth of indoor plants.
The most common types of alcohol include methanol, ethanol, isopropyl alcohol, as well as alcoholic beverages. They affect plant growth in different ways.
Methanol: Plants use methanol (also known as wood alcohol or methyl alcohol) like they use carbon dioxide. Simply put, methanol stimulates the growth of many types of cultivated plants. Researchers say that the best plant yields are achieved by applying a solution of 30 percent methanol and 70 percent water.
FACTOID: A spray of diluted ethanol and methanol (also called methyl) alcohol such as this one on Amazon can dramatically improve the growth of tomatoes, peas, and C3 plants (e.g., alfalfa, barley, eucalyptus, oats, potatoes, rice, sugar beets, sunflower, soybeans, wheat).
Ethanol: Do you want to avoid trimming overgrown indoor plants? Do you believe that plants feel pain when you’re pruning them? Here’s a quick alternative. Plant growth can be slowed down by applying a 5 percent solution of ethanol (the alcohol in drinks).
FACTOID: Plants stress out when given a 10 percent ethanol alcohol solution. However, a 25 percent ethanol solution can kill a plant.
Isopropyl (Rubbing) Alcohol: Watering your plant with rubbing alcohol will slow down growth, similar to the effects of ethanol. Likewise, a spray of 5 percent isopropyl alcohol with stunt plant growth. As well, treating a plant with more than 25 percent isopropyl alcohol will scar, damage, or kill the plant. When it’s not available in local stores or supermarkets, I usually buy on Amazon here.
FACTOID: Seventy percent isopropyl alcohol is sold as an antiseptic. This can be safely sprayed on plants to kill aphids and other soft-bodied insects.
Plants that absorb alcohol via their roots are severely damaged. This is because the alcohol content causes severe dehydration (as discussed in the case of the soft bodied insects).
FACTOID: Foliar sprays of triacontanol (also known as melissyl alcohol or myricyl alcohol) increases the growth and yield of tomato, sweet pepper, sugar beet, cotton, tobacco and potato plants.
Alcohol can help plants when sprayed on the leaves. However, it can be deadly when it gets into their roots. As a natural herbicide, alcohol can kill off weeds and other plants that rob your prized herbs of essential nutrition. However, most gardeners say you should not use this method.
Yes, it’s true. You can pour your expensive whiskey, your imported vodka, or your prized armagnac through concrete sidewalk cracks to kill weeds. You can also water your potted plants with rubbing alcohol to kill unwanted plants – but I don’t recommend this.
First of all, it’s an expensive herbicide. Second, you can’t grow anything in alcohol-infused soil. In other words, even the good plants that you’re protecting will change colors, die of thirst (water loss), turn into shades of brown or black, and die.
PRO TIP: Water your plants before spraying them with alcohol. Also, spray alcohol at night, and never in direct sunlight. But if you want to kill off weeds, spray in direct sunlight. Even better, irrigate the roots with alcohol, but bear in mind that nothing will grow in alcohol-soaked soil
FACTOID: Drinking alcohol or rubbing alcohol are effective weed killers, particularly liquids with very high alcohol concentrations such as absinthe vodka or undiluted rubbing alcohol.
The most common types of alcohol are ethanol, methanol, isopropyl alcohol, and denatured alcohol.
Ethanol (EtOH) is pure, organic alcohol that is also known as ethyl alcohol or rubbing alcohol. It is fermented from grains, so it’s also called “grain alcohol” and is often found in almost all alcoholic beverages from beer and wine to whiskey.
Scientists found that flowers watered with a 5 percent solution of ethanol grow slower than usual, so it is used as a growth retardant to control the size of indoor plants, delay the maturity and wilting of commercial flowers, and so on.
Ethanol is also commonly used in producing antiseptics, disinfectants, cleaning agents, colognes, mouthwashes, plastics and polishes. In the medical field, ethanol is used as an antidote in cases of methanol overdose or ethylene glycol poisoning.
For indoor herb growers who use rubbing alcohol as an insecticide, test various concentrations of water-alcohol mixtures before spraying plants to kill insects. In cases of serious pest infestations, be cautious when using undiluted alcohol such as this one on Amazon.
Methanol is often used as a solvent, as fuel for racing cars, and in increasing crop yields. The growth of many cultivated plant crops can be stimulated by the right application of methanol spray.
Studies indicate that a 30 percent methanol solution is very effective in increasing plant yield. You can check out methyl alcohol such as this one on Amazon.
However, although foliar spray of methanol or ethanol has been proven to increase the growth of tomato, tobacco, and rockcress (arabidopsis) plants, watering plants with alcohol (irrigation) can damage roots and kill plants.
FACTOID: Methanol is often used as a solvent as well as fuel for racing cars.
Isopropyl alcohol in antiseptics (also called rubbing alcohol) can be used as a spray to kill aphids on plants. To slow down plant growth, use isopropyl alcohol at 5 percent concentration.
Note, however, that when it is used in undiluted form, rubbing alcohol can burn the leaves plants, particularly in bright light. To prevent burning, dilute with liquid soap and water. To prevent scarring on leaves, rinse each plant thoroughly after spraying with alcohol.
One effective insecticide formula is 70% rubbing alcohol (isopropyl alcohol) such as this one on Amazon. Mix 1 part to 7 parts water to get rid of aphids, mealybugs, thrips, whiteflies, and other insect pests on plants.
Denatured alcohol is ethanol with additives or chemicals that make it taste bad or smell bad so that nobody drinks it. Remember, ethanol is poisonous if it is consumed in large quantities, so ingredients such as methyl ethyl ketone, acetone, and denatonium are added to make sure that doesn’t happen.
Although denatured alcohol is not fit for consumption, it is safe when used in sanitizers, moisturizers, and in skincare products that include fatty alcohols that are derived from fruits and plants (e.g., cetearyl alcohol, cetyl alcohol, stearyl alcohol, etc.):
You can also use denatured alcohol such as this one on Amazon as a spray on houseplants to get rid of them of insect pests such as aphids or mealybugs.
FACTOID: Root or foliar sprays of triacontanol, natural fatty alcohol, enhances crop quality and increases vegetable production in millions of hectares of farmland and agricultural fields.
Can alcohol damage leaves? Yes, High-strength, high-concentration, or undiluted alcohol can burn and scar the leaves of your plants.
Is it OK to spray rubbing alcohol on plants? Yes, it is. Before you spray the entire plant, however, test one or two leaves first, then wait two to five days for signs of alcohol burn or damage on the leaves.
Can plants get drunk? No, plants can’t get drunk because they don’t have a brain, bloodstream, or nervous system like humans.
What happens if I water plants with alcohol? Alcohol makes it difficult for plants to absorb water, so the plant suffers from water stress. The lack of water may reduce the growing of leaves and stems. If you accidentally watered your plants with alcohol, get rid of the soil, wash the roots, and hope it ends well. Otherwise, get ready to get replacement plants.
Can I spray alcoholic drinks on plants? Dilute hard drinks (whiskey, vodka, and so on) if you want to limit the growth of your plants. At the same time, never apply wine or beer to your plants. The sugar in these beverages can grow fungus and bacteria that can seriously damage plants and cause strong odors.
Use a natural alcohol insecticide: To keep food safe, herb gardeners don’t use commercial insecticides. They use alcohol spray to kill insects that attack your plants, such as mealybugs, mites, aphids, scales, whiteflies, and fungus gnats.
Diluted alcohol is safe to use: Most plants can tolerate a half-and-half mixture of alcohol and water. To be sure, test a small part of an infested plant to make sure that the mixture does not damage the leaves. Spray late afternoons or early evenings when there is no direct sunlight. Finally, rinse away all alcohol, as much as possible.
Control growth with alcohol: Alcohol is also used by commercial growers and indoor gardeners either as a growth inhibitor or as a growth enhancer. For instance, to prevent indoor plants from overwhelming the interior decor, alcohol can be used to control the growth and development of leaves and branches.
Don’t use alcohol as herbicide: Finally, alcohol can also be used as a herbicide to kill off weeds and plants that are competing with your plants for nutrition. However, this is not recommended as it can poison the soil.
Congratulations to go through such a massive article on how to use alcohol spray on your plants. Happy gardening!
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- “Denatured Alcohol” by Healdsburg Tribune in California Digital Newspaper Collection
- “Effect of a long chain aliphatic alcohol (triacontanol) on growth and yield of different horticultural crops” by C. Kapitsimadi & S. A. Vioryl in International Symposium on Quality of Fruit and Vegetables: Influence of Pre-and Post-Harvest Factors and Technology
- “Effects of foliar and root applications of methanol on the growth of Arabidopsis, tobacco, and tomato plants” by I. Ramírez, et al in Journal of Plant Growth Regulation
- “Effects of foliar and root applications of methanol or ethanol on the growth of tomato plants (Lycopersicon esculentum Mill)” by R. N. Rowe, et al in New Zealand Journal of Crop and Horticultural Science
- “Fact or Fiction?: Vodka and Citrus Sodas Keep Cut Flowers Fresh” by C. Curtin in Scientific American
- “Global Alcoholic Beverages Market Report (2020to 2030) – COVID-19 Impact and Recovery” by Research and Markets
- “Triacontanol: a potent plant growth regulator in agriculture” by M. Naeem, et al in Journal of Plant Interactions
- “What Is Denatured Alcohol and Why Is It in My Skincare Products?” by J. Amable in Healthline