Greenhouse - Raising Media pH

Low media pH can lead to poor plant performance in the greenhouse. The following is a short article on correcting a low pH in a greenhouse crop.

So Your pH is Down!

We occasionally get calls when the pH of the substrate in a greenhouse has dropped to pH 4.0. Somehow, someone was not monitoring regularly and suddenly they are in the “got- to- act-fast” mode.

How do you deal with trying to raise this soil pH? The answer is liquid limestone. This is generally purchased in 2.5 gallon containers. Mix the contents of this container into a 5 gallon bucket of water, slowly adding the liquid limestone to the water and stirring to get the lumps of limestone into suspension. Take this 2.5 gallons of liquid limestone and 2.5 gallons of water mixture and add it to 95 gallons of water. Keep agitating the tank to prevent the limestone from settling out. This 100 gallon solution is applied as a drench to 1,000 ft2 of growing area. Be sure to wash off any liquid limestone from the foliage to avoid leaving a residue. If the pH is 4.0 then the pH should move up to 5.0 within 10 -14 days. If the pH is still too low the process can be repeated.

Article from the February 17, 2006 edition of the Greenhouse TPM/IPM Weekly Report from University of Maryland Cooperative Extension