Author Archives: Paul Fisher

About Paul Fisher

Paul Fisher is an associate professor and Extension specialist in the Environmental Horticulture Department at the University of Florida. You can eMail him at

Understanding Plant Nutrition: High ph Problems

High media-pH (above 6.4) induced iron deficiency is the most common nutritional problem for certain iron-inefficient crops (Figure 1), including calibrachoa, diascia, nemesia, pansy, petunia, scaevola, snapdragon and vinca. Plants only take up dissolved nutrients through their roots. When the media-pH is too high, micronutrients (especially iron) are less soluble and unavailable for uptake by

Understanding Plant Nutrition: Correcting Low Media pH

Iron/manganese toxicity is a common problem when media-pH drops below the ideal level in certain crops, including geraniums, marigolds, lisianthus, and pentas. As media-pH decreases (meaning the pH becomes more acidic), iron and manganese become more soluble, resulting in higher concentrations in the soil solution. For each drop in media-pH by one unit, for example

Understanding Plant Nutrition: The Series

Understanding Plant Nutrition: An Introduction Read about the basics on essential nutrients for plant growth, uptake of nutrients and pH’s effect on nutrient solubility. Nutrient Sources: Media Cation Exchange Capacity The authors take a look at the myth that cation exchange capacity is important to soilless media. Limestone and pH Why does limestone need to

Understanding Plant Nutrition: Managing Media EC

High fertilizer levels can be too much of a good thing, leading to excess growth, nutrient toxicity and potential runoff of nutrients into the environment. Conversely, low fertilizer levels can lead to nutrient deficiency symptoms. A basic goal for a nutrition program is to supply nutrients to the crop within an acceptable range for healthy

Universities Uniting by Paul Fisher

Writing this essay reminded me of “A Christmas Carol.” There are different futures for Extension depending which path we collectively choose to take. When the Agricultural Extension Service was created by Congress in 1914, agriculture was a dominant player in the U.S. economy. Recent trends in global food supply, biofuel and sustainability have led to

Understanding Plant Nutrition: Managing Media pH

Managing the pH of container media is a challenge in the greenhouse and nursery industry. Many growers face problems associated with their media pH either drifting up or down to levels that result in loss of crop quality and sales. In this article, we will discuss how the factors that we have discussed in previous

Understanding Plant Nutrition: Controlled- And Slow-Release Fertilizers

Using controlled-release (CRF) and slow-release (SRF) fertilizers allows growers to supply nutrients for an extended duration without the specialized equipment needed to apply water-soluble fertilizers. These fertilizers are added to the media at mixing or applied to the media surface after planting. Nutrient runoff can be reduced using CRF and SRF, especially compared to applying

Understanding Plant Nutrition: Fertilizers And Micronutrients

Micronutrient (iron, manganese, zinc, copper, boron and molybdenum) nutrition is different from managing macronutrients, such as nitrogen, in three fundamental ways. First, the solubility and plant availability of micronutrients is affected by media pH to a much greater extent than is macronutrient solubility. Second, the difference between acceptable concentrations of micronutrients and concentrations that are

Understanding Plant Nutrition: Fertilizers And Macronutrients

When you select a water-soluble fertilizer, the primary goal should be to supply plants with a sufficient amount of essential plant nutrients for good growth and flowering. In this article, we will focus on macronutrients (nitrogen, phosphorus, potassium, calcium, magnesium and sulfur) supplied by water-soluble fertilizers. We will discuss macronutrient sources, fertilizer formulations and the