Factors Affecting pH and E.C. of the Growing Media

Many questions are coming in regarding speckling of lower leaves of geraniums.

This is how it starts.  Picture on your left hand show early symptoms of light color speckling and a dull green color.  It slowly progresses and speckles merge with each other and then become necrotic.  The picture on your right hand side is when pH is below 5.0 and entire plant is not sale-able.  Look at the economic loss if you are not able to diagnose the problem early enough. Geraniums naturally cause growing medium to become acidic as they grow and combined with the use of acidic fertilizers, the pH starts dropping.  With pH going on acidic side, the uptake of trace elements is considerably increased and toxicity occurs. This is attributed to iron toxicity.  Let us look at factors which affect the pH of the growing medium:

• Potting media components and amendments.  Peat moss and pine bark are acidic, vermiculite and perlite are neutral and limestone added to counteract acidic components.
• Plant species grown. Species that increase the pH of the potting medium include petunia, pansy, African marigold, annual vinca, zinnia, becaopa. Species that decrease potting media pH include geranium, begonia, celosia, dianthus, tomato
• High nitrate fertilizers raise pH, while high ammonium fertilizers lower pH.
• Irrigation water with higher levels of bicarbonates increases pH

Media Electrical Conductivity (EC)

• EC is a measure of soluble salt contents in a growing medium, water or solution and is a good tool to mange crops.  The sources of soluble salts in a growing medium include irrigation water, fertilizers, media components and amendments and fungicidal drenches.

• Monitor EC on a regular basis especially during the rapid growing time of April.
• Higher EC ranges would cause water deficiency symptoms in bedding plants.
• Lower EC ranges would reflect nutrient starvation.