Gardening Myths

It’s easy to believe certain garden myths because they are ubiquitous; often passed down from previous generations or now found literally everywhere online. I am a scientist, trained to look at facts, and even I believed some of these myths until I thought to look deeper. Part of the reason it is easy to believe in gardening myths is that many of them are partially true or are based on facts. Below are some common garden myths I have come across, and I will continue to add more myths and references if you'd like further reading.

1. Myth: Adding rocks (or other large material) to the bottom of a pot improves drainage. Water does not move easily between different substrates of varying sizes, and this practice actually reduces drainage. Adding perlite to your potting soil (if it’s not already there) helps with drainage and aeration, while vermiculite helps retain moisture.
2. Myth: Goldenrod causes allergies in the fall. In fact, goldenrod pollen is heavy and cannot blow around in the wind. Instead, the pollen moves from plant to plant via insects. What is more likely causing fall allergies is ragweed, but ragweed has much less showy flowers (they are green and blend in with the rest of the vegetation) and is therefore less noticeable than the beautiful goldenrod flowers. That being said, my dog is allergic to goldenrod (and tons of other stuff), but he likes to run through our fields of goldenrod, likely getting the pollen all over himself. So, as long as you don’t roll around in a goldenrod field, it is not likely to be responsible for your allergies.
3. Myth: Peonies need ants to bloom. Although this is not true, ants are commonly found on peonies before flowering but not after, leading to this myth. Before they open, peony flowers secrete sweet nectar that ants feed on. The ants get food from the peony and, in return, the ants defend their food source, keeping other insects that may want to eat the peony at bay.
4. Myth: Adding coffee grounds to your garden increases the acidity of your soil. When you brew coffee, most of the acid comes out of the grounds and into the coffee you drink. Used coffee grounds are neutral pH; if you wanted acid, you would have to use fresh, unbrewed coffee grounds or the coffee itself to acidify the soil. That being said, coffee grounds are a great addition to your compost, just don’t expect a pH change.
5. Myth: Watering your plants when it is sunny will burn your plants where the drops remain because they act like a lens. If this is true, anytime the sun comes out after a rain shower, particularly in the very hot south, you would find burn marks all over the plant leaves. This rarely happens, but it turns out that in rare circumstances, particularly with fern leaves that have small waxy hairs that can hold a droplet of water above the leaf, sunburn can occur (see Reference 1 below). But sunburn exacerbated by water droplets is rarely the problem if you find marks on your plant leaves; instead, look for pests, chemical injury if you spray, or diseases.

References and Resources

1. ​1. Egri, A.; Horvath, A.; Kriska, G.; Horvath, G. Optics of sunlit water drops on leaves: conditions under which sunburn is possible. New Phytologist, 2010; DOI: 10.1111/j.1469-8137.2009.03150.x
2. 2. Enroth, Christopher. Are you falling for these gardening myths? University of Illinois Urbana-Champaign. May 16, 2025. https://extension.illinois.edu/blogs/good-growing/2025-05-16-are-you-falling-these-gardening-myths
3. Piskor, Steve. Debunking Garden Myths. Penn State Extension. July 5, 2023. https://extension.psu.edu/debunking-garden-myths