A review of the effects of atmospheric humidity on the growth of horticultural crops

SummaryHumidities between 1.0 kPa and 0.2 kPa vapour pressure deficit (vpd; 55 to 90% r.h. at 20°C) have little effect on the physiology and development of horticultural crops. Humidities lower than these lead to plant water stress and thus reduce growth, whereas higher levels encourage disease and may cause disorders of growth and development. In some conditions, e.g. in polluted atmospheres, high humidity may contribute to further damage to the crop. There may, however, be occasions when a high humidity is desirable, e.g. in generating root pressure to avoid calcium deficiency in fruit or young leaves; when using pathogenic fungi to control insect pests; and in the propagation of plants from leafy cuttings or in tissue culture.