Chapter 18

Plant Growth Regulators for Greenhouse Crops

(draft book excerpts)

Plant growth regulators (PGRs) are chemicals that are designed to regulate or control some aspect of plant growth. They are applied for specific purposes to bring about specific plant responses. These include stem length, rooting, flowering, leaf abscission, fruiting, and cold hardiness. Most of the PGRs used in the greenhouse function as “growth retardants.” These PGRs reduce plant height by inhibiting the production of gibberellins, which are the hormones responsible for cell elongation. Their effect is primarily on stem, petiole and peduncle elongation. Leaf expansion may be reduced too, resulting in smaller, thicker leaves with darker green color leading to reduced water requirements due to lower transpiration rates. Although there is much scientific information on using PGRs in the greenhouse, it is not an exact science. Achieving the best results with PGRs is a combination of art and science— science tempered with a lot of trial and error and a good understanding of plant growth and development.

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