Greenhouse - Common Greenhouse Crops that Develop Iron Deficiency

The following is information on common greenhouse crops that develop iron deficiency if the pH is too high.

High pH and iron deficiency in Calibrachoas, Bacopa, Diascia, Scaevola, Verbena, and Petunia

For this group of plants (Calibrachoas, Bacopa, Diascia, Scaevola, Verbena, and Petunia) make sure to keep the pH between 5.3 and 5.8 to avoid problems with iron deficiency. We often see plants with interveinal chlorosis show up in the growing season. One of the approaches is to use an acidifying fertilizer such as 21-7-7 or 18-9-18. If you have high alkalinity water sources then the first choice should be sulfuric acid injection to lower the pH level. Keeping the pH low is the best way to prevent iron chlorosis but sometimes additional iron may be needed – apply as iron chelate or iron sulfate (always rinse foliage when using iron sulfate to prevent foliar burn). The pH can be lowered using iron sulfate at 1 - 3 lbs per 100 gallons. Apply chelated iron such as Sprint 138 or 330 as a drench at 3-5 oz per 100 gallons.

Reprinted from the March 20, 2009 edition of the Greenhouse TPM/IPM Bi-Weekly Report from the University of Maryland Cooperative Extension Central Maryland Research and Education Center.