Are coffee grounds effective against aphids?
Written by
Paul Reynolds
Reviewed by
Prof. Samuel Fitzgerald, Ph.D.Coffee grounds are frequently referred to as aphid deterrents, but this has been challenged by field trials within the past year and laboratory research on potential effects. The only substantial effect seen is a slight soil acidification (pH drop of 0.3-0.5) and grounds do not repel or kill aphids. For example, a recent tomato trial concluded that the infestation rate of coffee-amended plants was identical to control plants.
Ineffective Home Remedies
- Coffee grounds: No repellent properties observed
- Banana peels: Attract fruit flies instead
- Cinnamon sprinkles: Temporarily deters ants, not aphids
- Eggshell barriers: Ineffective against winged aphids
Proven Alternatives
- Castile soap sprays: 90% aphid reduction in 48hrs
- Lacewing releases: 1,500 larvae/1,000 sq ft efficacy
- Garlic-chili sprays: 5-7 day repellent effect
- Diatomaceous earth: Kills aphids within 6hrs of contact
Although coffee grounds help conserve soil structure, adding them only has a minor effect on pH levels, and as most vegetables prefer a pH range of 6.0-7.0, we recommend testing your soil before making amendment decisions. For example, I added 12 lbs. to my kale bed and only dropped the pH by 0.4 points. As the local cooperative agent suggested, it would have been easier to spray with sulfur.
Effective Practices
- Test soil pH every 60 days
- Use sulfur for intentional pH reduction
- Apply compost tea for balanced nutrition
- Rotate crops to disrupt pest cycles
Read the full article: Natural Aphid Control: 12 Safe Solutions for Plants
