Temperature regimes, irrigation and fertilization practices, and photoperiod may be manipulated to accelerate or retard plant growth. The most common type of chemical growth regulators used on bedding plants are growth retardants. Growth retardants are used primarily to control plant height, but may also be used to promote early flowering or increase branching. Growth retardants registered for use on bedding plants. Bedding plant species vary considerably in their response to the different growth retardants.
Some species respond to only one growth retardant, whereas others respond to several.
Rate of application. Most recommendations specify rates of growth retardants for plants that have recently been transplanted to cell-packs or pots. It should be noted that seedlings in plug trays normally require lower application rates of growth retardants to control stretching compared to seedlings transplanted into cell-packs or pots. Refer to New England Greenhouse Pest Control and Growth Regulators Recommendations for application rates of growth retardants on bedding plants. A recent trend among growers is to decrease the application rate but to increase the number of applications.