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.

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

Topics Within This Chapter:

  • Plant Hormones
  • Characteristics of Plant Hormones
  • Classes of Plant Hormones
  • Abscisic Acid
  • Auxins
  • Cytokinins
  • Ethylene
  • Gibberellins
  • Factors Affecting Plant Growth Regulator Performance
  • Plant Factors Influencing Plant Growth
  • Plant Species and Cultivars
  • Stage of Plant Growth
  • Plant Vigor
  • Plant Size
  • Environmental Factors Influencing Plant Growth
  • Temperature and Light
  • Growing Media
  • Water Quality and Amount
  • Physical and Chemical Factors Influencing Plant Growth
  • Residual Chemical Effect
  • Chemical Uptake and Translocation
  • Coverage
  • Dosage
  • Spray Droplet Size
  • Cultural Factors Used to Control Plant Growth
  • Container Size
  • Plant Density
  • Scheduling Greenhouse Crops
  • Irrigation Practices
  • Fertilization
  • Mechanical Conditioning
  • Brushing
  • Pinching
  • Light Quantity, Quality, and Photoperiod
  • Light Quantity
  • Light Quality
  • Photoperiod
  • Temperature
  • Plant Growth Regulators
  • Ancymidol
  • Benzyladenine BA
  • Chlormequat Chloride
  • Daminozide
  • Dikegulac Sodium
  • Ethephon
  • Flurprimidol
  • Methyl Esters
  • Paclobutrazol
  • Uniconazole
  • Application Methods of Plant Growth Regulators
  • Spraying
  • Applying Drenches
  • Sprench
  • Plug and Liner Dips
  • Bulb Soaks
  • Plant Growth Regulator Application Considerations
  • Application Rates
  • Relative Potency of PGRs
  • Time of Application
  • Directions for Mixing Plant Growth Regulators
  • Wetting Agents
  • References