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Common pH Problems in Retail Greenhouses

Thu, May 6th, 2021, created by Beth Scheckelhoff

Many retail greenhouses and garden centers are gearing up for Mother’s Day weekend – the traditional start to the spring sales season here in the upper Midwest.

While most commercial production facilities identify and correct pH-induced nutrient disorders before product is shipped for finishing or retail, some issues still crop up once plants reach their final destination. Two issues commonly seen at the retail level are iron and manganese toxicity in zonal geranium (see e-Gro Alert 6.01) from low media pH and iron deficiency in calibrachoa from high media pH (see e-Gro Alert 7.06).

Make sure all garden center employees are trained to keep an eye out for plants that begin to look a little “off” from surrounding plants or other cultivars of the same species. Suspect plants may show discoloration, leaf or flower deformations, overall stunting, or other abnormal characteristics. These plants can indicate larger issues with plant nutrition, the environment, or pests.

One of the most inexpensive devices a greenhouse or garden can invest in is a handheld pH meter. For tips on different types of meters see e-Gro Alert 8.27.  This is a must for every greenhouse and garden center and will easily pay for itself over a short period of time.

A quick check of growing media can reveal whether the media pH and EC are too high, too low, or in the correct range. For example, a recent visit to a retail establishment identified two separate issues in close proximity. 

First, zonal geraniums were suspected to have a root pathogen as one variety discolored foliage and browning of leaf edges. Inspection of the root system showed healthy roots concentrated at the bottom of the containers and not throughout the growing media. Foliage discoloration was uniform across a handful of plants and beginning to show throughout additional plants in the greenhouse – though only in this one cultivar. A pour-thru media sample showed the pH to be at 4.8, well below the desired range of 5.8 to 6.4 for zonals.

In the neighboring greenhouse section, a single variety of calibrachoa began to exhibit yellowing leaves with green veins, a common sign of iron chlorosis when media pH rises above 6.2. The pH of the media was 6.8.  

These common nutritional issues need to be revisited annually in garden centers and greenhouses with high employee turnover. Teaching employees to spot changes in growth and development, followed by separating suspect plants, determining the cause, and identifying corrective action is key to success – now and in the future. 

About the Author:

Beth Scheckelhoff

Extension Educator, The Ohio State University

Beth Scheckelhoff is an Extension Educator for Greenhouse Systems at The Ohio State University. Beth provides Ohio greenhouse vegetable and ornamental growers with research-based information and recommendations for crop production, pest management, business management, and produce safety topics via educational programs, individual consultations, and publications.

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