B-Nine is the most commonly used growth regulator for controlling height in pot mum production. The amount and the timing of B-Nine applications are dependent on the cultivar, temperatures and light intensity.
Generally, B-Nine is applied about 2 weeks after the pinch, or when new shoots are 11/2" to 2" in length. A second application may be needed in 2 or 3 weeks. The last application of B-Nine should be no later than the center bud removal stage to avoid deleterious effects on flower form or color.
B-Nine rates range from 2,500 to 5,000 ppm depending on the variety and time of year. Higher rates are used for tall-growing varieties and during the warmest, brightest growing seasons. Bonzi and Sumagic are two other growth regulators registered for height control of pot mums. However, they are not as easy to use as B-Nine.
Spraying techniques are much more critical with Bonzi or Sumagic. Coverage of stems is necessary, since leaf application is less effective. Therefore, higher spray volume is needed. Also, uniform application becomes more critical, since all stems must directly receive the chemical. In general, multiple applications of lower rates with thorough stem coverage are necessary with Bonzi or Sumagic.
Spray rates to use on a trial basis are 31 to 125 ppm for Bonzi and 5 to 10 ppm (2.5 to 5 ppm in low light) for Sumagic. First apply whenever you would normally apply B-Nine. However, fewer repeat applications may be needed since these chemicals appear to have a greater retardation effect than B-Nine. Sumagic may be especially useful to trial in summer when high temperatures diminish B-Nine's effectiveness. Bonzi has also been used by some growers as a 2 ppm drench to hold plants at a given height with little to no effect on flowering.
| The following guidelines are a suggested starting point for B-Nine applications on pot mums: |
| |
Number of B-Nine Applications |
| Short Tmt. varieties |
0 to 1 |
| Medium Tmt. varieties |
1 to 2 |
| Tall Tmt. varieties |
2 to 3 |