It's absolutely okay to grow just one plant, especially if space is limited. While some plants benefit from companionship, like certain herbs or pollinator-attracting flowers, others, like tomatoes, can thrive on their own. The Galahad tomato, specifically bred for container gardening, should do well in a 15-gallon container. Just ensure it gets adequate sunlight, water, and nutrients.

The 15-gallon container you're considering provides a decent amount of space for root growth. As long as you provide proper support for the tomato plant as it grows, regular watering, and appropriate fertilizer, it should flourish.

If you're looking for more information on growing tomatoes in containers, read this article.

https://coirmedia.com/blogs/growing-...-in-grow-bags/