Having a green thumb means being naturally good at growing plants and keeping them healthy. Someone with a green thumb seems to know instinctively when to water, how much sunlight a plant needs, and what to do when leaves start turning yellow. Their gardens flourish, their houseplants thrive, and even finicky vegetables like tomatoes seem to grow abundantly for them.

The phrase doesn't mean their thumb is actually green, of course. It's an idiom that captures how skilled gardeners seem to have a magical touch with plants. If your neighbor's roses bloom spectacularly while yours struggle, people might say she has a real green thumb.

Some people develop a green thumb through years of practice and careful observation. They learn to recognize when soil is too dry just by looking at it, or notice the early signs that a plant needs help. Others seem to have an intuitive sense for what plants need. But even people who kill every cactus they touch can develop more of a green thumb by paying attention, learning from mistakes, and understanding that different plants have different needs.

The opposite might be having a black thumb, meaning plants tend to die in your care no matter how hard you try.