Nonchemical height control strategies for greenhouse crops: Part II

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

In the previous Greenhouse Alert, we discussed several environmental strategies for height control of greenhouse crops. In this issue, we focus on a few cultural strategies that can be used to control plant height. In most situations, experienced growers will utilize a mix of cultural, environmental and chemical techniques to produce crops within their height specifications.

Cultivar selection
The first step in controlling plant height begins with selecting the cultivars that meet your needs. Each year we are inundated with catalogues and advertisements showcasing the newest genetics. In addition to flower characteristics and disease or insect resistance, breeders are also selecting new plants that have a compact growing habit. Remember to consider this attribute when choosing a new cultivar.

Plant nutrition
Fertility can also influence stem extension and plant height. It is easier to produce compact finished plants when starting with compact plugs. This can be accomplished by limiting the amount of fertilizer (particularly nitrogen and phosphorus) applied to young plants. To learn more about plug fertility, check out an article posted on the North Carolina State University website:

Another nutrient strategy to help control plant height is to use a fertilizer that primarily contains the nitrate form of nitrogen. In commercial fertilizers, nitrogen is available in different forms including ammonium, nitrate and urea. When selecting a fertilizer, keep in mind that ammonium and urea forms of nitrogen can promote elongated growth that may produce more leggy plants.

As with plugs, limiting the amount of phosphorus can inhibit stem extension after transplant. Application of a fertilizer solution containing 10 to 15 ppm of phosphorus at every irrigation is sufficient to meet the needs of most plants without excessive elongation. Be careful not to take this to an extreme; if plants are not provided with any phosphorus, they may show deficiency symptoms such as overly stunted growth and purplish leaves.

Water stress
Limiting water availability to plants can be a useful tool for controlling plant height. A plant subjected to water stress will have a slower rate of growth and stem elongation. When using this technique to control plant height, be careful not to let your crop become too wilted. An experienced grower will know how much water stress their crop can tolerate before reaching the permanent wilting point, which is when plant damage occurs. Also, some greenhouse crops recover from wilting much better than other crops.

Cold water on shoot tip

Recent research at the University of G uelph has shown that the use of cold water can be very effective in controlling plant height when applied to the growing tip of Easter lilies. Unfortunately, most bedding plants studied have not shown a similar response to cold water. The only responsive species were begonia, impatiens, sweet potato vine, and zonal geranium. For more information on using cold water to reduce stem extension, visit:

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