In greenhouses artificial illumination may be used, although unless the crop is especially valuable this may be too expensive to be practical. They are frequently used in conjunction with each other to improve the appearance or usefulness of plants. Familiar examples include trimmed privet hedges and Japanese dwarf potted trees, known as bonsai. Plant growth may be regulated through use of plant hormones, auxins, which may stimulated budding, flowering and fruit set and growth. Other hormones and chemicals promote ripening of fruit and inhibit sprouting in onions and potatoes.
Soil management is essential in horticulture.
Plants are dependent upon soil for 13 of the 16 minerals necessary to their growth. Carbon, oxygen, and hydrogen are derived from air and water, but N, P, K, Ca, Mg, S, and various trace elements must be present in usable form in the soil for plants t survive and grow. The acidity or alkalinity of the soil also influences plants. Extremes of soil acidity or alkalinity are toxic in themselves, but even slight variations from neutrality affect availability of soil nutrients and must be corrected. Soil structure determines the plant's supply of water and oxygen, the ease of root growth and the availability of nutrients.