Low pH and high pH growing media

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.  

I have noted a number of pH problems in the last month from area greenhouses, and I need to remind you to check your media pH before you use it. Growers have reported both high pH over 7.3 and low pH below 5.8 problems and many times it was because the media came in without a lime charge or with too much lime. Do not assume that the second or third batch of media you ordered is the same as the first. By rights they should be if the supplier is doing their job, but I have seen mistakes made that result in the grower having to deal with a problem that came from the supplier. Check pH every time you get a shipment and save a sample of the media in a ziploc bag for reference later on if there is a problem.

Also be sure your injector is working properly and providing the correct amount of fertilizer for your crops. A malfunction could result in a pH problem that is the grower’s fault. Check your injector’s calibration with the fertilizer table on the back of the bag.

Also if you have a shallow well 50 feet or less, your water quality can change with the seasons. We have had a lot of rain in some areas of west Michigan and that can impact the water quality (alkalinity, etc.) and change your media pH. Get a complete water analysis; do not rely on the one from three years ago.

For more assistance on greenhouse media pH management, contact your local MSU Extension greenhouse educator.

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