Uses of Plant Hormones

Plant hormones are used to control plant growth. They can be used in areas such as agriculture and horticulture for many reasons, including increasing yield, obtaining desirable features, and lowering costs.

Three hormones used to promote plant growth in agriculture and gardening are:

  • Auxins
  • Gibberellins
  • Ethene


The main functions of auxins are to help plants grow and stimulate plant cells to elongate (get longer). So they are typically used:

  • as weed killers
  • as rooting powders
  • in tissue culture

Weed killers

Although auxins stimulate growth, if there is a very high concentration, it can disrupt the growth of a plant, which kills it.

Weeds are pests that compete with crops for water, sunlight and nutrients. Some weeds even release harmful chemicals that kill crops. This reduces the efficiency of farming.

Most weeds are broad-leaved, which means that their leaves have a flat, relatively broad surface. Weed killers contain auxins and many are selective weed killers, so they only affect broad-leaved plants. This means that weed killers can be sprayed on a large variety of crops, but they will only kill the broad-leaved weeds.

The increased amount of auxin causes the cells to elongate and grow too rapidly, which kills the weed plant.

Rooting powders

Plants with desirable features are often cloned, resulting in more plants with the same characteristics.

Cuttings are small sections of the plant that are cut off. Plants can be cloned by taking a cutting from the original plant. Root cuttings give rise to new stems, and stem cuttings develop new roots.

Stem or leaf cuttings are dipped in rooting powders which contain auxins and placed in the ground. The cutting will produce roots then it will start growing into a new plant.

  • The auxins encourage root growth

To promote growth in tissue culture

Plants can be cloned using tissue culture. Cells from the plant are taken and they are placed in a growth medium containing lots of nutrients. Hormones such as auxins are added and the cells begin to form roots and shoots.

  • Auxins are typically used to promote growth


Gibberellins have three main uses:

  • Initiating seed germination
  • Growing larger fruit
  • Inducing flowering

Initiating seed germination

If a seed is in soil without the right conditions, it will not germinate (grow and put out shoots). It requires the right amount of water, oxygen and warmth. We call the time before growth dormancy.

Farmers can expose the seed to gibberellin, which can induce germination at times of the year when it would not normally happen. This allows farmers to cultivate multiple crops simultaneously and throughout the year.

Growing larger fruit

Gibberellins can enable plants to produce larger and heavier fruit, which increases yields.

Inducing flowering

To induce flowering, there also needs to be optimal conditions. Gibberellins can induce flowering in plants. This means that plants can be grown to produce more flowers, which can also be bigger.

  • Gibberellins encourage flowering plants to flower at a faster rate


Ethene is a hydrocarbon gas that stimulates the ripening of fruit, so it is often used in the food industry. It works by stimulating an enzyme that causes fruit to ripen. If you observe how different fruit ripen at different rates, you can see how useful it is to be able to control the ripening of fruit.

It can take many weeks to ship fruit around the world before it reaches a consumer. So fruit can purposely be picked when it is not ripe. It is firm, so during transport, it gets less bruised and damaged. When ready to be sold, the fruit is exposed to ethene and warmer temperatures, causing it to ripen quickly.

Since plants often produce their own ethene, its effects can be suppressed during transportation to prevent premature ripening. This reduces wastage because more fruit is suitable to be sold, as it does not ripen too early.

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