During the spring crop production season growers often use plant growth regulators (PGRs) to manage plant vigor during the grow-out stage.
The objective it to slow stem stretch while still allowing the plant to grow. Low rates of PGRs can be used for this purpose. With low rate applications, the PGRs can be reapplied as needed to control growth. Any of the commercial PGR products can be used at this stage but of course not all species respond the same to any one material.
These Profusion zinnias in this photo (April 20) were planted end of February and treated twice with low rates of Bonzi (paclobutrazol). First application was made on April 4 (15 ppm) and second application (25 ppm) made two weeks later.
Refer to current issue of New England Greenhouse Floriculture Guide for information on proper use of plant growth regulators and also non-chemical methods for managing plant height.