Aspirin Spray for Tomatoes and the Vegetable Garden

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Robert Pavlis

Do you want to grow great tomatoes? Most gardeners do and they are on a constant hunt for magical concoctions that will create the best yield and most flavorable tomato. The latest craze involves the use of aspirin. Just mix a few aspirin in water and spray your plants. Spraying tomatoes or any other kind of plant with aspirin will make them grow better, have less diseases and ward off insects.

My regular readers will know that I love to find the origin of a myth, and I think I know how this one got started. Lets have a closer look at how some science can result in an online sensational cure-all.

Aspirin Spray for Tomatoes and the Vegetable Garden
Aspirin Spray for Tomatoes and the Vegetable Garden

Aspirin Reduces Insect Pests and Diseases in the Vegetable Garden

Do a quick google and you will find headlines such as these.

  • Aspirin Increases Growth and productivity
  • Aspirin Prevents Blight in Tomatoes
  • Aspirin Wards Off Insects

Reading these posts you quickly realize that almost none of them reference any kind of scientific study to support their claim. Occasionally you will see mention of work done by Martha McBurney, a Master Gardener at Rhode island University, but no real data is presented. I have followed up on many of these links and I think I’ve tracked down the series of events that has led to this popular internet solution of using aspirin.

Science Looks at Aspirin in Plants

The science did not really look at Aspirin; they studied the role of salicylic acid (SA). Early work on tobacco plants showed that higher levels of salicylic acid helped plants fend off diseases, including mosaic virus. Similar results were found in cucumber plants. It should be noted here that this worked looked at natural salicylic acid levels in plants – plants were not sprayed.

Compost Science for Gardeners by Robert Pavlis

Work by the U.S. Department of Agriculture found that spraying tomato seedlings with salicylic acid, before they were exposed to a phytoplasma, reduced the incidence of disease from 94% to  47%. They suggested that “the treatment triggering systemic acquired resistance (SAR), a kind of general readiness state that primes plant defenses against pending microbial or insect attack”. This work was all lab work.

Another study found that both acetylsalicylic acid (Aspirin) and salicylic acid induced stress tolerance to heat, chilling and drought in bean and tomato plants, by either soaking seeds or as a soil drench.

Foliar application of SA in greenhouse experiments showed better growth and fruit development.

Fast forward a few years and SAR (systemic acquired resistance) is better understood. When a pathogen infects a plant, SA is produced by the plant at the infection site. Some of this SA is transported to uninfected parts of the plant, where it turns on the plant’s defenses. SA does not fight infection directly, but it triggers plants to fight the infection. “The activation of SAR provides a broad-spectrum resistance against a wide range of related or unrelated pathogens.”

A summery of the science on this subject, dated 2019, had the following to say, ” Exogenous application (ie spraying) of SA are reported to activate the defense responses including SAR. However, rapid glycosylation of SA and its phytotoxicity has prevented the efficiency of SA as a plant protection chemical”.

To paraphrase this, SA has a short life in plants and it can be toxic, which makes it impracticable to use.

Aspirin vs Salicylic Acid (SA)

A lot of people assume these are the same, but they’re not.

The active ingredient in aspirin is acetylsalicylic acid. When it is dissolves in water it produces salicylic acid and acetic acid. It is quite possible that the SA produced from aspirin will have a similar effect on plants as pure SA, but none of the scientific work tested aspirin.

Building Natural Ponds book, by Robert Pavlis

Citizen Science on Aspirin and Plants

I mentioned Martha McBurney, a Master Gardener at Rhode island University. Her work is routinely used in social media to validate the use of aspirin on plants. In the summer of 2004, after seeing some of the above science, she applied aspirin to vegetable plants; tomatoes, cucumbers, beans and basil. It is reported that Martha said, “by the end of the season, the plants in the raised beds with the aspirin water looked like they were on steroids! The plants were huge, and green and with no insects. We even saw some disease problems that reversed themselves. We think we got a virus on the cucumbers, and the aspirin water seemed to reverse it. The cucumbers ended up being very healthy. Seed sprayed with aspirin water gave 100 percent seed germination, compared to spotty germination in the other trial beds.”

Note the lack of any real detail of either the experimental setup or the results. I have not been able to find any documentation of this work.

The following year, Dr. Rebecca Brown, Plant Sciences at the University of Rhode Island worked with Martha to repeat the experiment in a more controlled fashion, including replicates. They tested Early Girl tomatoes with two concentrations of aspirin and a commercial product called Messenger.

The conclusion from this work is, “Aspirin and Messenger will not decrease fruit yield under low-disease conditions if used to trigger systemic resistance in tomatoes. Messenger and Aspirin applied at the rate of 250 mg per gallon of water may actually increase the number of fruit. We cannot make any conclusions as to the efficacy of these compounds in reducing disease, because of the lack of disease in the study. Variation among plots was quite high, perhaps because of edge effects resulting from the lack of border rows. It would be beneficial to repeat the study under conditions more favorable to disease development, and to use larger plots with border rows.”

Science vs Anecdotal Information

We can learn a lot from the above experiments.

Notice the very different conclusions reached in 2004 and 2005. In 2004, the results were not properly measured (as far as we know) and there were not enough replicates (confirmed by Dr. Brown). The results are anecdotal and the opinion of the person doing the work.

When that same person repeated the work under stricter conditions, the conclusions were vastly different. The two years might have been very different disease wise – that is one reason these types of experiments are usually carried on for several years. Results in a single year can be an anomaly.

The use of replicates allows one to apply statistics on the data providing a standardized way to measure results. This is always part of any published study, and never part of anecdotal information.

Martha reported her 2004 results to media and they have been published in a few places. When the 2005 results became available, showing no disease control, they did not become published in the media, and the previous reports of success have still not been corrected. That is very common. The media and much of the public only care about sensational stories, not the facts.

Consequently, the general public is only exposed to the initial anecdotal report showing positive results. Anecdotal reports are of limited value.

Aspirin and Insects

What about keeping pests off plants? There is no real evidence of this. One thing that happens a lot is that when a product does one thing in the garden i.e. prevent diseases, it is automatically assumed it will do even more. Claims get exaggerated as they get repeated.

Others feel that since aspirin makes plants healthy, they will naturally develop defenses against pests. Unhealthy plants do tend to have more pest problems, but that does not mean spraying healthy plants with aspirin will keep pests off the plant.

Does Aspirin Work?

Based on the science, there is a logical explanation as to how aspirin could help control diseases. The problem is that the science is all lab work, and none that I found proved anything in the field. SA is effective if applied before a disease attacks, but will not do much once the disease is there because it triggers defense mechanisms in plants, it does not fight disease.

All of the research, except the report from Rhode Island University is with SA, not aspirin and this one report did not show disease control.

It is also not clear which diseases are affected. The chemical mechanism involved does seem to be generic, but it still needs further study to fully understand it. So claims that it will prevent blights in tomato might be true, but I have not found evidence that this works.

Aspirin is also toxic to plants and the concentration of any spray should be tested before use. There is limited information about toxic levels on different kinds of plants.

Will aspirin work as an insecticide? There is no evidence for this.

Will aspirin make plants grow better? If a plant is stressed, aspirin may help the plant deal with the stress. In such a situation it might grow better, but I found little evidence that spraying non-stressed plants makes them grow better. Some limited research indicates tomato yields may be higher.

Aspirin might work to prevent diseases but it needs to be used before the disease attacks.

Most of the scientific studies looked at spraying the plants directly, but a few looked at soil drenches, which also seemed to work. However, this was lab work in potted plants. Trying to treat plants in the field using soil drenches is much more complicated. If you decide to try this method, foliar spray would be a better option.

Aspirin might help plants grow better, but the evidence is limited and until we know more, it is probably best for gardeners not to use it.

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

61 thoughts on “Aspirin Spray for Tomatoes and the Vegetable Garden”

  1. Robert Pavlis, have you dine any research on the matter? Would you be willing to do some experimentation? My anecdotal observation is that it helps my tomatoes and peppers with the heat. I haven’t really seen any difference in pest pressure.

  2. Does coated or uncoated aspirin make a difference? I’ve seen other articles that specify uncoated but doesn’t give an explanation why.

  3. Robert, great reading for the lay person. You should know though that the quality of a literature review is using good studies. You seem to hybridize popular Google science and a very cursory review of research. Get into the chemistry and plant physiology along with standardized trials. Then simplify it, it will allow you to make sound conclusion. Thanks for your work and if you’d like to test some of these product and treatments I’ll set up field trials. Kuddos

  4. Loved this article. It’s funny how many old school gardeners get butt hurt when the methods they “know and love” are challenged. Totally unwilling to accept tan alternate theory based on science. I’m all for experimentation in gardening as everyone should be. Keep up the great work!

  5. Thanks so much for this information!

    I’m a garden blogger and saw a garden “hack” on Instagram guiding people to water their tomato plants with aspirin-water. It sounded kinda legit and thought it would make for a good article, but it’s important to me that the content I create is accurate and not just good for clicks. I now have a better understanding why people think this might work (and who knows, for some it might…but my college statistics and bio classes have taught me that without controls, *anything* could have been thing to help, not the aspirin). The science just isn’t sound enough for me to promote this as an actual thing to do.

    I know that a lot of gardening is experimentation and following advice from the old-timers, but the Internet makes it too easy to start a game of telephone with shaky info. Thanks again!

  6. I read an article from daily mail .co .uk thats states scientist are saying to spay tomatoes with aspirin. Just saying

    • Then I suggest you stop reading this source of misinformation.

      The reason this is a myth is that there are many unreliable sources that recommend it.

  7. I find all of your comments very interesting but while you may write scientific articles for gardeners, it does not seem as if you are actually a gardener yourself. Perhaps before you attempt to disprove something through science, you should try it yourself and have firsthand knowledge on whether it works or not. Otherwise, all I’m reading is blah blah blah — I’d much rather have the trials and tribulations of a gardener tell me ‘it worked for me last year but not so good this year’ than have someone tell me that ‘there is no science to back up these claims’

    • 1) I have been gardening for 45 years!!!!

      2) If you want to listen to anecdotal information from gardeners, you can get that from any social media site. This site is for people who actually want to know the truth!

  8. How many producers are scientists, I don’t know. How many scientists are gardeners? Gardeners experiment all the time, when they find something that works for them they keep using it whether it’s scientifically stamped or not. I experimented with aspirin this year in southern Indiana. My tomatoes look healthier and stronger then I have ever had, bar none. There may not be definitive scientific data backing aspirin use in the garden but there is not scientific data proving it’s a myth either. So we’re left with personal experiences.

    • The idea of using Aspirin didn’t just come from nowhere – it has filtered down from scientific knowledge and observations – and experimentation. This is very common – in everyday life not just gardens.
      Sometimes it ends up in the hands of gardeners a bit prematurely – before the science has tested the validity etc. Humates and Biochar for eg. The jury is still out on some things.
      In this case there is good evidence building up that certain functional analogues of salicylic acid can assist plants to deal with disease/pathogen control and chilling/drought stress.
      It’s still fairly early days and there’s still more work to be done – but I don’t have a problem with having a go myself either.

      I am really looking forward to seeing if it can assist my young mango trees with bacterial apical necrosis (BAN) caused by Pseudomonas syringae….which is on the plants anyway but until we have near-frost events, it doesn’t cause any problems. (google this)

      I can’t wait for the science to catch up – so I have nothing to lose by testing it myself ….it’s not like I am going to be using some nasty, non degradable chemical instead – of which none cure BAN anyway (at present there is no cure for BAN)
      My trees will end up dying otherwise.

    • “Plants grown from seeds imbibed in aqueous solutions (0.1–0.5 mM) of salicylic acid or acetyl salicylic acid(ASA) displayed enhanced tolerance to heat, chilling and drought stresses.”

      How does this translate into growing seeds by gardeners? No idea. Most gardeners don’t stress their seedlings.

      Show me a study where aspirin – not pure chemical – is sprayed in the garden and there is a real world effect – like increased yield.

      • There us actually quite a lot of research being done on asprin (ASA) and plant growth – but my particular interest has been with it being a possible aid with chilling stress in my sub tropical plants that are chill-sensitive below 10C and develop chlorosis (or the “winter yellows”) after 5C nights and bright sunny days (photo-oxidative stress)
        Google Scholar has plenty of reading on the topic.

      • Gardeners might not stress their seedlings and plants but the weather and soil type certainly can, as can disease/pathogens.

        SA is a well known signalling molecule in plants and a major player in plants defence systems against pathogens. Healthy plants are going to be more productive.
        Now the research is looking to ASA – which is a derivative – as SA is nasty stuff and can cause severe burns etc…not something I would be wanting to make up stock solutions from, at home.

        I don’t really understand why this all such a big deal really….but the second link here should help you…

        “New Curtin research has shown how a readily available, cheap and safe-to-use product found in the medicine cabinet of most homes could be the key to better ecological restoration practices with major benefits for the environment and agriculture.”

      • Robert, if this covid19 ‘pandemic’, and the recent release of Pfizer’s vaccine data, has proven anything, it’s that anecdotal evidence is indeed much more accurate than ‘scientific’ evidence. It has also proven that clinging to ‘scientific’ evidence with a death grip (as you do here with your own ‘research’), and completely discounting anecdotal evidence can indeed be detrimental.
        I have been gardening for 39 years, longer if you include the years I helped my father and grandparents in their gardens. I have personally done the tests, with controls, growing from seeds in a garden. I ran these tests for five consecutive years, in the same garden plot, using the same methods (i.e. fertilization, watering schedules, etc…).

        • This is a science based blog. If you want to believe in non-scientific facts – feel free.

          If you want to discuss the topic – give us a link to some science.

  9. Hmm I feel like this is biasing more towards missing detection of the effect (Type II error) without having a really good reason (i.e. high cost outcome for Type I error). We’re not searching for new subatomic particles or putting lives in danger for getting things wrong here. So why have such a high bar for conclusive evidence? There’s plenty of anecdotal evidence to support use of aspirin in gardening, enough for the cost of using it times the possible benefit to outweigh the cost of potential harm, which is what? a few bucks and an hour of your time?


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