How do I slow plant growth?

Growers have asked, “What can be done to slow growth on crops during times of low demand? “ —A great question. Let’s look at the available options.


If you find your crops growing under lower light levels, warm temperatures and heavy fertilization, excessive growth or stretching can occur. Excess growth can be slowed by growing crops cooler with increased spacing and using less water, a term called growing “harder.” If space allows, increase plant spacing and if crops can take colder temperatures in the 60º F range, you may want to consider this approach. The use of negative DIF (difference between daytime and nite time temp.) is also a growing technique useful during finish and can help reduce plant height.

OHP Plant Growth Regulators (PGRs)

Chemical plant growth control is a standard tool for growing many crops and is used during early plug, liner, and early to mid-finish production. Late application of PGRs to plants can offer growth control for a short period of time or stop growth in order to hold a crop for a long time. Such applications are done with a drench of triazole-based PGRs such as OHP’s Pac O. Below are suggested OHP products and rates that can offer late growth control.

B-Nine® WDG

A spray application at 2500 to 3750 PPM (mums) or 5000 PPM can offer growth control on a number of plants. Zinnia, coleus, mums and other large leafed plants respond well from B-Nine WDG foliar applications. Apply early in the morning and do not overhead water for 24 hrs. The lower rate of 2500 PPM is less risky but users may need to make a couple of applications. A tank-mix of B-Nine WDG at 1250 or 2500 PPM plus Cycocel at 1000 PPM will increase effectiveness. DO NOT use Cycocel rates over 1200 PPM.


We do not recommend the use of Cycocel in late finish as the rates needed for growth control may produce a yellowing. Cycocel is best used early to mid-cycle in crop production.

Pac O™ (Spray applications)

Foliar applications can vary wildly depending on the crops involved. Remember that viola, geranium, and begonia are VERY sensitive to Pac O. Sprays could range from 2 to 5 PPM. For other herbaceous crops use the mid to higher rate recommendations making sure to cover stems as best as possible; consider rates of 15 to 30 PPM. If crops have more leaves than stems showing you should consider B-Nine WDG sprays.

Pac O™ (Drench applications)

Drench applications are very effective in holding crops over. Consider using from 1 to 4 PPM using the correct drench volume for the pot size. A 1 PPM drench is like a 10 PPM spray. This 10:1 ratio can help you to determine what drench rate to use. Petunia baskets that are up to size will hold well using a 4 PPM drench.

Woody ornamentals are probably best held in check by using high spray rates or moderate drench rates of Pac O. Plants like azalea and other woody plants would use 100 to 150 PPM as a spray or 10 to 15 PPM as a drench. Lantana or other smaller plants respond well to a 2 PPM drench.

Generally speaking, one drench application should hold for 4 weeks or possibly longer. Drench volume is very important and users should follow the container drench volume rates in the label.

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