In gardening and agronomic terminology, a volunteer is a plant that grows on its own, rather than being deliberately planted by a farmer or gardener. Volunteers often grow from seeds that float in on the wind, are dropped by birds, or are inadvertently mixed into compost. Some volunteers may be encouraged by gardeners once they appear, being watered, fertilized, or otherwise cared for, unlike weeds, which are unwanted volunteers. The action of such plants — to sprout or grow in this fashion — may also be described as volunteering.

Volunteers that grow from the seeds of specific cultivars are not reliably identical or similar to their parent and often differ significantly from it. Such open pollinated plants, if they show desirable characteristics, may be selected to become new cultivars.