Can tomatoes be planted near onions?
Written by
Tina Carter
Reviewed by
Prof. Charles Hartman, Ph.D.Tomatoes and onions compete brutally underground. My first garden planted the two crops 18 inches apart, and both crops died. The roots of tomatoes require three times the amount of nitrogen that onions need to develop bulbs, depriving the onions of nitrogen. At the same time, onions excrete chemicals that inhibit the growth of tomatoes through their roots, and the tomato seedlings succumbed within weeks.
Root Zone Separation
- 4-foot (1.2 m) minimum between plants
- Install root barriers 12 inches (30 cm) deep
- Use raised beds with separate soil compartments
Companion Alternatives
- Tomato allies: Basil, marigolds, asparagus
- Onion partners: Carrots, beets, chamomile
- Buffer crops: Lettuce, spinach, radishes
Temporal Solutions
- Plant onions 6 weeks before tomatoes in spring
- Grow fall onions after tomato harvest
- Rotate beds yearly - 3-year cycle breaks disease chains
Separating crops isn't always possible for urban gardeners. My solution for having a balcony garden: plant tomatoes in 15-gallon (57-liter) pots on one side of the balcony and plant onions in 8 inch (20 cm) deep window boxes on the other side. I trellised the tomatoes vertically to reduce competition between them and the onions, which also reduced competition by 40% since plants were relocated from the ground to containers.
Soil testing helps avoid nutrient wars. I use 10-10-10 fertilizer for my tomatoes and 5-10-10 for onions. Ensure you test every three weeks - tomatoes need twice as much phosphorus when they fruit. A soil kit I purchased for $20 not only eliminated the nut04ient wars for me, but it also helped me save my tomato harvest when my nitrogen levels dropped unexpectedly mid-season.
Read the full article: When to Plant Onions: Expert Guide for Perfect Bulbs
