The usage of plants is quite common in various industries. Some plants are used in the manufacture of perfumes, though they have been largely replaced by chemically manufactured products. The oils of lavender, thyme, and rosemary are largely used in the perfume industry. Flowers are also used to a certain extent as drugs. The examples of such plants are arnica and cannabis, the essential substances are taken from the flowering tops of plants.
The nectar of flowers is used by the bees to make honey. But the most important value of flowers for people is the admiration for their beauty and the fruits which follow them. Great business enterprises deal with seeds, the breeding of young plants in nurseries, and the sale of trees, shrubs, and flowering plants as well as cut flowers.
It is possible to make flowers bloom all year long by planting in greenhouses and through the artificial forcing. For example, growing tulips as potted plants to make the bloom for Easter celebration. They are kept at a low temperature for a considerable period and then at a higher temperature to promote growth and flowering. For other plants is more important the length of light exposure. For example, chrysanthemums can be forced to bloom earlier and faster by covering them with black cloth so that they receive light for only 10 to 12 hours a day. On the other hand, poppies bloom only when the light exposure periods are rather long. Also, for a greater amount of bloom, plants should not be given the excess of nitrate fertilizer.
Growing potted plants can sometimes be increased by planting them in rather small pots in order to limit the root growth. Growing shrub plants can be increased by pruning so that the remaining branches become lighter. But it needs to be done with special care in order not to remove too many leaves thereby decrease the entire plant development.