Growth Regulators
Some garden mum varieties tend to get too tall.
If these varieties are needed, they can be kept more compact with the use of growth regulators. B-Nine is the most traditional growth retardant
for garden mums. Effective use of all growth regulators is more of an art than a science.
Stage of the crop, concentration used, uniformity of application, and the weather after the application will all factor in to the level of control seen. Growers will need to learn how to adjust applications to fit their own needs and, therefore, accurate records are needed to be able to learn from crop to crop and year to year.
If most or all the varieties in your crop require growth regulators, a later plant date should be considered to reduce growing time and, therefore, plant size. Also, plant size can be held after the plant structure has been built (generally after the first 28 to 35 days from planting a rooted cutting) by reducing the fertilizer concentration and frequency, and by allowing plants to wilt between irrigations. It is important that these activities do not occur during the critical first 4 to 5 weeks after planting, as plants may not reach the desired size.
B-Nine can be used on garden mums grown for spring, summer or fall crops. For fall crops, a starting point would be to spray with 2500 ppm (.25%) B-Nine solution two weeks after the last pinch. On No-Pinch crops, an application should be applied when the breaks are 1-1½" long depending on experiences with the vigor of each variety. This could be repeated in two weeks on those varieties that still appear to be stretching. The rate of B-Nine may need to be increased to 3750 to 5000 ppm with higher temperatures or rapid, vigorous growth. Usually no B-Nine is applied after the buds have reached pea size to avoid flower discoloration and delay.
For spring pot production, 2500 ppm B-Nine is typically applied to medium and tall varieties 2 to 3 weeks after the pinch, when new shoots are 2" to 2½" in length. Short varieties may not need any B-Nine.
Garden mums sold as green plants in the spring can be sprayed with B-Nine to help keep them compact while in cell packs or small pots. For non-pinched green plants, use 2500 ppm (.25%) 10 to 14 days after planting. For pinched green plants, use 2500 ppm (.25%) 10 to 14 days after the pinch.
Bonzi is quite effective in height control, but must be used carefully
to avoid excessive stunting. Some growers use a 2 ppm Bonzi drench or a 30 to 50 ppm Bonzi spray to hold their crop at a given height. Sprays must be directed to stems and growing tips rather than leaves to be effective. Late applications have not delayed flowering.
Sumagic is also very effective, but results have been quite variable. Spray rates are 2.5 to 10 ppm and sprays must be applied to the stems, as done for Bonzi. Drench rates are only 0.1 to 1 ppm. Use Sumagic on a very limited trial basis only.
Florel has been promoted by some for three uses on garden mums: 1) to prevent premature budding, 2) to increase branching and 3) to stagger/delay flower dates of the same variety. However, because of the unpredictability of the Florel effect with different varieties and different environments, Florel use is not part of our recommended cultural practices.
Premature budding is best prevented with the use of long-day lighting, optimal temperature, optimal irrigation and optimal fertilization. No-Pinch crops with optimum cultural conditions produce excellent, well-branched plants. We suggest the use of variety selection to stagger flower dates.