Wednesday, February 18, 2009

Greenhouse - Monitor Your Media pH

The following is a short article on pH issues with greenhouse media and plant deficiencies.

Media pH

Most plants have an optimal pH range in which they perform best. Some plants may prefer slightly acidic media while other plants can tolerate a much lower or higher pH. The pH of the media influences the uptake and availability of all nutrients. Growing greenhouse plants in media with a pH lower than the optimal range can result in poor uptake of macronutrients (in particular Calcium, Magnesium, and Phosphorus) and increased uptake of some micronutrients (e.g. iron toxicity). On the flipside, micronutrient deficiencies generally occur on plants growing in media with a pH higher than the optimal range (e.g., iron or manganese deficiencies).

Iron Toxicity in Marigold probably due to low media pH. Photo by Tina Smith, UMass.

Iron deficiency in petunia probably due to a high media pH. Photo by Tina Smith, UMass.

Written information from the Michigan State University Greenhouse Alert Newsletter March 4, 2008.


Misty said...

this is a problem that I have recently encountered with Garden Center purchased bluberries in 1 gal containers.
Apparently by the time I had purchase d them the ph had begun to increase to a point that plants were beginning to suffer. My PH meter readings were between 6.5 to 7.0...MUCH too high for blueberry or rhododendron. I Had fed with azalea food previous to this affirmation of high PH......and noticed a spike in growth...pale green growth as shown in your petunia picture....which if induced by large uptake of Nitrogen could draw in the aphids!!
MY remedy: lower the PH of current planting media, stop feeding with azalea foods, switching to "holly tone" once plants show signs of recovery. And using a foliar iron and micronutrient supplement.....
I am wondering if I chose to do the right thing??

Gordon Johnson said...


You did the right thing in lowering the pH of the media and applying foliar iron. You need to find out what caused the rise in the media pH. Do you have high alkalinity water? That would be my first thing to check.