Chapter 21

Plant Growth Regulators for Greenhouse Crops

(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.

Click on the following topics for more information on plant growth regulators greenhouse crops.

Topics Within This Chapter:

  • Cultural Factors Used to Control Plant Growth
  • Container Size
  • Plant Density
  • Irrigation Practices
  • Fertilization
  • Mechanical Conditioning
  • Pinching
  • Brushing
  • Light Quantity, Quality, and Photoperiod
  • Light Quantity
  • Light Quality
  • Photoperiod
  • Temperature Manipulation
  • Uses of PGRs
  • Regulating Shoot Growth
  • Enhancing Lateral Branching
  • Plant Flowering
  • Removal of Flowers
  • Other PGR Used in Greenhouse Production
  • Active PGR Ingredients
  • Factors that Affect Plant Response to PGRs
  • Plant Factors
  • Plant Species and Cultivars
  • Stage of Plant Growth
  • Plant Vigor
  • Plant Size
  • Environmental Factors
  • Temperature and Light
  • Growing Media
  • Water Quality and Amount
  • Physical and Chemical Factors
  • Residual Chemical Effect
  • Application Rates
  • Time of Application
  • Dosage
  • Chemical Uptake and Translocation
  • Coverage
  • Spray Droplet Size
  • Application Methods for PGRs
  • Sprays
  • Application Rates
  • Factors Influencing the Effectiveness of PGR Sprays
  • Spray Equipment
  • Soil-Active PGRs
  • Drenches
  • Application Methods
  • Watering-In
  • Sprenches
  • Plug and Liner Dips
  • Factors that Influence the Effectiveness of Liner Dips
  • Bulb Soaks