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

How Dirty Is Your Water? Ready Research Results

During summer 2009, we collected irrigation water samples from 24 greenhouses and nurseries across 11 states in the United States as part of the Young Plant Research Center program. We evaluated physical, chemical and biological water quality and determined whether current treatment practices were maintaining water quality within recommended guidelines. Table 1 summarizes our results

Understanding Plant Nutrition: Managing Multiple Species

Multiple species are often grown in the same greenhouse section, or even in the same container.    Often, these species have different acceptable pH ranges and iron requirements (Table 1), which can lead to growing difficulties that affect plant quality. In this final article, we give tips on managing multiple crops in the same greenhouse.

Understanding Plant Nutrition: The Complete Series

An Introduction Read about the basics on essential nutrients for plant growth, uptake of nutrients and pH’s effect on nutrient solubility.  Nutrient Sources 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 be added to soilless media? It’s all

Understanding Plant Nutrition: Geranium Nutrition

Seed and zonal geraniums are iron-efficient crops that are prone to iron/manganese toxicity when the media-pH gets too low. Once plants show toxicity symptoms of necrotic spots and marginal burn (Figure 1), the affected leaves do not completely heal. The only options become shipping lower-quality plants–to take additional time to produce healthy new growth that

Understanding Plant Nutrition: Calibrachoa

Calibrachoa are often described as a “high feed” or “high iron” requiring crop. This is not exactly true. Calibrachoa are an iron-inefficient crop and are prone to iron deficiency because they lack the ability to take up iron from the soil solution if the media pH is too high. Once iron deficiency sets in, calibrachoa

Understanding Plant Nutrition: Stock Plant Nutrition

Nutrient management for stock plants is similar to other long-term crops. We have worked with several leading stock plant growers both in the United States and overseas over the past decade. Together, we have found the keys for success are fairly straightforward: have an organized plan that includes media and fertilizer selection, organize crops into

Understanding Plant Nutrition: Poinsettias

Profit margins are extremely tight for poinsettias, so minimizing shrinkage that results from crop losses is essential. If nutritional stress occurs, you will be struggling from that point onward to produce a high-quality plant for sale. Poinsettias hang around your greenhouse for several months, much longer than short-term spring crops. Therefore, a preventative approach that

Understanding Plant Nutrition: Environmentally Induced Plants

Most nutrients are actively taken up by the plant from the soil solution. With active uptake, the plant roots use energy to scavenge the root environment for soluble nutrients. For nutrients that are taken up actively (like nitrogen or phosphorus), their concentration in the root medium (as measured with soil tests) tends to correlate well

Understanding Plant Nutrition: Common High Media-EC Problems

High electrical conductivity (EC) in the growing medium makes it harder for roots to take up nutrients and water–it is like trying to grow plants in sea water and can result in “salt burn” (damage to sensitive root tips) and toxicity symptoms in foliage (Figure 1). In this article, we will discuss the causes and

Understanding Plant Nutrition: Low Media-EC

When growers talk about “lack of feed” or “hungry plants” (Figure 1), the issue is usually insufficient supply of fertilizer nutrients. The easiest way to measure fertilizer level in the root media is with an electrical conductivity, or “EC,” meter. What is Media-EC? Electrical conductivity (also know as conductivity, EC or soluble salts) is a