Greenhouse - Geraniums, Soil pH, and Fertility

The following is an article on the effect of soil pH and fertility on geraniums in the greenhouse reprinted from the Greenhouse TPM/IPM Weekly Report by University of Maryland Cooperative Extension.

Geraniums- soil, pH and fertility

Growers should be using a medium to high drainage soil mix and feeding with 300 ppm nitrogen. A pH of 6.0- 6.3 for zonal geraniums and 5.5- 5.8 for ivy geraniums is recommended using the pour-thru method. If the pH drops below 5.5 - 6.0 on zonal geraniums, you can get iron and manganese toxicity which causes a bronze speckled necrosis on the lower leaf margins. You can raise the pH with liquid lime or calcium nitrate fertilizer if the pH is not extremely low. If the pH gets up to about 6.5 on ivy geraniums, you will start to see an iron deficiency (yellowing of the new leaves). You can lower the pH with sulfuric acid or ammonium nitrate fertilizer. Sprint 330 or 138 can be added to correct an iron deficiency- don’t forget to rinse off the leaves.

Reprinted from the February 8, 2008 edition of the Greenhouse TPM/IPM Weekly Report from University of Maryland Cooperative Extension.