Stock plant nutrition for cutting success

Poor rooting percentages from stock plant cuttings may be due to nutrition.

Posted on March 25, 2015 by Kristin Getter, Michigan State University Extension, Department of Horticulture

The main portion of a chlorophyll molecule, demonstrating how important nitrogen (N) is in chlorophyll's design.

Have you ever had poor rooting percentages from cuttings off of your own stock plants? One potential problem may be the stock plant nutritional status. Consider the following scenario from Michigan State University Extension.

An experienced grower buys non-patented Vinca major cuttings each year, roots them and then uses those rooted cuttings as stock plants. For the past 10 years, this grower has realized nearly 100 percent rooting success from the original (bought) cuttings and secondary cuttings from the stock plants. This year, the grower buys in the plants, roots them successfully, but then the cuttings taken from the stock plants have very non-uniform and low percentages of rooting. What may have happened?

In the absence of any visible or obvious cause to the problem, the grower sent samples to Michigan State University Diagnostic Services. The lab found no pathogen or insect issues and thus ordered a plant nutrient tissue analysis from a third party laboratory. The results showed the micro- and macro-nutrient contents of the sampled tissue, as well as recommended ranges for “foliage plants (general)” (see table). Since the lab’s recommendations were for generic ornamental plants, I also provided the grower with recommendations from the “Plant Analysis Handbook III” (Bryson et al., 2014) for vinca specifically. Notice the lab’s recommendations and Bryson et al.’s recommendations are not always similar.

 A portion of the plant nutrient tissue analysis lab report for Vinca major cuttings exhibiting poor rooting percentages.

No matter which recommendation was used, nitrogen (6.28 percent), phosphorus (0.64 percent) and potassium (6.47 percent) levels were all high. Based on these results, the high levels of N-P-K were believed to be the source of the vinca rooting problems.

Of particular concern in this report is the nitrogen. Nitrogen of course is extremely important for a plant as it plays a large role in synthesis of chlorophyll (see figure), amino acids and proteins, and is a constituent of its DNA. It is very mobile, meaning that if the plant is lacking nitrogen for growth, it can move nitrogen from one part of the plant, such as older leaves, to where it needs it most, such as root or shoot growing points. However, excessive nitrogen in plant tissue can inhibit (prevent) rooting of cuttings.

Phosphorus is found in all cell membranes and plays a large role in plant metabolism. Phosphorus should also be limited in stock plants used for cuttings, but not to the point where there are obvious (purpling) signs of a deficiency, as moderately low phosphorus can improve rooting.

Potassium’s role in the plant is to balance charge within the plant. Potassium is also an enzyme activator and helps to regulate stomata, which regulate air and water vapor to pass into and out of the plant. Most fertilization regimes recommend potassium be provided in a 1:1 nitrogen:potassium ratio. However, for management of stock plants, research at North Carolina State University showed that for stock plants of New Guinea impatiens, the best fertilizer regime tested was 3:1 nitrogen:potassium.

Further resources

• Plant Analysis Handbook III by Gretchen Bryson et al.
• Stock Plant and Cutting Nutrition, Greenhouse Product News

This article was published by Michigan State University Extension. For more information, visit http://www.cnchemicals.com/. To have a digest of information delivered straight to your email inbox, visit http://bit.ly/MSUENews. To contact an expert in your area, visit http://www.cnchemicals.com/, or call 888-MSUE4MI (888-678-3464).