A volunteer plant is a plant that grows without the gardener planting it. The original plant went to seed. The seed was dropped or was carried by the wind. Or the fruit matured on the plant and dropped. Either way the gardener did not deliberately plant the seed.
Volunteer plants could be wonderful or awful.
The original plants could have been from a plant that produces seed identical to the parent plant. Or not. If that heirloom flower met up with a bee that came from another variety it could be a great discovery. Or not. These I tend to be patient with and see what happens. I also have the space to do so.
The original plants could have been hybrids and the seed they produce reverts to an undesired plant. Or not. Did you want to chance allowing it to grow on a prime piece of garden real estate? It might be something we don't like. Personally I won't waste my time if I know it was a hybrid parent plant.
Why we are told to destroy volunteer plants.
Most of us ignore the volunteer plant. We don't pay it any special attention. However that plant might be harboring disease or insects that will infect our intentionally planted crops. This is why it is recommended that you yank out volunteers.
If you are going to allow volunteer plants to grow, treat them as you would any other plant in your garden.
Above photo is of ONE volunteer everglades tomato plant that is happy as can be. It is about 12 feet in diameter and still growing. It has shown no signs of disease or insects but if/when it does it will be removed.
