Farmers and gardeners use plant hormones to control how plants grow. Many of the hormones they use are made artificially, so they are called synthetic, and they can be sprayed on plants or used as powders.
A selective herbicide kills some plants but not others. Synthetic auxins are used on lawns and cereal fields. Broad-leaved weeds take in the auxin and grow too fast in an uncontrolled way, so they die. Narrow-leaved plants such as grass and cereal crops are not harmed much.
A cutting is a piece of stem cut from a plant. If the end of a cutting is dipped in rooting powder that contains auxin, it grows roots quickly. Each cutting then grows into a new plant that is identical to the parent.
Fruit normally develops after pollination and fertilisation, and it contains seeds. If auxin or gibberellins are applied to unpollinated flowers, the fruit develops without seeds. This is called parthenocarpic fruit, and seedless grapes are an example.
Hormones can also change dormancy and timing. Gibberellins break dormancy, so that seeds germinate when the grower wants. Fruit is often picked unripe so it does not spoil on the journey, and is then ripened with ethene when it reaches the shop.