Aspirin in the Garden

Aspirin in the Garden pic SG

We joke about doctors telling us to take two aspirin and call in the morning. But aspirin in the garden? Oh, yes, according to research performed at my alma mater, the University of Rhode Island (URI).

Dr. Rebecca Brown, a professor of plant science at URI, found that a foliar spray of aspirin water applied to tomatoes (or any plant) helps them to resist disease. After reading about her research, I was intrigued. And, as all my readers know, when I’m intrigued, I hit research mode.


First, let’s look at what aspirin is. Chemically, aspirin is acetyl salicylic acid, which is salicylic acid that humans can tolerate taking orally. (My retired-chemist father would roll his eyes at my oversimplification, but we’re gardeners, not chemists.)

Salicylic acid is the ingredient in aspirin that acts as a pain killer when we humans take it. Originally, it was derived from the salicin found in the bark of willow trees. (Now, it’s made in the lab.) It’s the salicylic acid in aspirin that is so helpful to plants.


Salicylic acid is a plant hormone derived from the metabolism of salicin. Basically, it’s a signal molecule within the plant. The most important role of salicylic acid is its involvement in a plant’s defense against pathogens by means of systemic acquired resistance.

Systemic acquired resistance begins when one part of a plant is attacked by a disease or infection. Salicylic acid (and other biochemicals) are then produced by the plant as a signal to activate certain genes that create resistance to the spread of that infection. (This signal can also move to nearby plants when the salicylic acid is converted to methyl salicylate. It’s the botanical equivalent of “Danger, Will Robinson!”) Basically, salicylic acid activates the plant’s immune system. Unfortunately, in many cases, the plant doesn’t recognize its attacker in time to produce sufficient salicylic acid to prevent spread of the infection to the entire plant.


This is where we gardeners can help. Just as we humans take extra Vitamins C and D as a preventative during cold and flu season, we can give our plants extra salicylic acid to boost their immune system and help trigger their natural defense against harmful bacteria, viruses, and fungi. This is done by applying an aspirin water foliar spray.


  • 1 aspirin tablet of 250 – 500 mg (More than 500 mg will burn the foliage)
  • 1 gallon fresh water
  • 2-4 squirts of insecticidal soap or other horticultural soap
  • 32 ounce spray bottle

1. Crush the aspirin tablet into powder. Add to the gallon of water and mix well.

2. Pour aspiring water into the spray bottle and add 2-4 squirts of insecticidal/horticultural soap and shake. The soap will help the aspirin water spray stick to the leaves where the plant can absorb it. (If you use a different size sprayer, adjust the amount of insecticidal soap used.)

3. Apply to all leaves liberally every 2 to 3 weeks as a preventative measure; once disease has struck, it may be difficult to stop its progression.

I sprayed my garden with aspirin water (using a 325 mg tablet) last weekend. One gallon sprayed almost my entire garden – and that’s a lot of plants! So, one bottle of aspirin will last me for quite some time. What an inexpensive way to help my plants be healthy.


Using aspirin to help my plants fight the diseases of the South – such as Septoria Leaf Spot, Powdery & Downy Mildew, and blight – is a major win for my garden. But here’s yet another way aspirin can help. Martha McBurney, a Master Gardener at the University of Rhode Island, experimented with spraying seeds with aspirin water before planting. She found that doing so gave her almost complete germination!

I guess this makes sense, since many old-timers steeped willow bark in a bucket of water that was later used to soak the roots of transplants. This helped the transplants form new roots.

I wish I’d known this before I planted my seeds this spring. But, I guarantee you I’m going to try this when I plant later this summer and fall.


I’m looking forward to seeing how the aspirin water foliar spray helps my garden, especially my tomato plants. I had a rough time with disease last summer, so I’m excited about something that can help my plants fight the bad guys and thrive. I’ll keep you posted on how it’s going.

Have you used aspirin water in your garden? Please comment below how it’s worked for you.










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