These pansies were first thought to be nutrient deficient due to the light green color of the foliage. An electrical conductivity (EC) test revealed high soluble salts. High growing medium EC can injure or inhibit the growth of plants. Common causes of high EC include: excess fertilizer (too high level or too frequent application), subirrigation, root disease, or restricted drainage. A soil test is almost always needed to confirm a soluble salts problem.
Fact Sheets
Basic Fertilizer Programs for Containerized Greenhouse Crops
pH and Fertility Review for Vegetatively-propagated Annuals
Root Diseases of Greenhouse Crops