Auxins were the first class of plant hormones to be discovered. Their main function is to help plants grow and auxin stimulates plant cells to elongate. The tips of the growing stems and roots (apical meristem) of a plant is one of the main places where auxin is produced. The apical meristem is also the location that all other parts of a plant grow from - the stem, leaves and flowers.
Auxins are one specific group of hormones that are used:
Selective weedkillers kill some plants, but not others. This can be useful for getting rid of dandelions in a lawn without killing the grass, or weeds that compete with crops such as wheat. The selective weedkiller contains a growth hormone that causes the weeds to grow too quickly and die. Because most weeds have broader leaves than grass or wheat, the weedkiller is absorbed in larger quantities by the weeds.
Selective weedkillers kill plants that some species of animals rely on as a food source. This can result in a reduction of biodiversity.
Plant cuttings can be dipped in hormone rooting powder before planting.
Synthetic plant hormones are used to control plant growth. For example, rooting powder contains growth hormones that make stem cuttings develop roots quickly.
Tissue culture is a technique used to grow whole new plants from small sections of a parent plant.
Hormones are used to stimulate cell division and elongation.
When pollen has fertilized the egg cells in flowers, fruit develops with seeds inside. Some people prefer eating fruit without seeds. One method of making fruit grow without seeds inside is to spray the flower with hormones such as auxin or gibberellin. This is called parthenocarpic fruit development.
Dormancy stops seeds germinating until conditions are ideal for growth. Hormones can be used to remove the dormancy of a seed so it can germinate at all times of year.