The top question we get from our grower customers each season is about plant nutrition. For example, what fertilizer blend is best for the plant, at what rate (ppm nitrogen) the plants should be fed, or how often to fertilize the plants, writes Dennis Crum, Director of Growing Operations at Four Star Greenhouse.
A more complex question often asked centers on plant nutritional issues caused by soil pH levels that are either too high or low to make certain nutrients available to the plant at proper levels. The most frequent such problem is iron deficiency symptoms (yellowing of new growth) in lower soil pH-loving plants, such as Supertunias (petunias), Superbells (calibrachoa), and Bacopa (sutera). When soil pH levels rise much above 6.0- 6.2, the most sensitive varieties in these groups will begin to show yellowing of new growth due to a lack of iron uptake, even though there may be ample levels of iron in the soil and fertilizers. At higher soil pH levels, iron will not be available to the plant.
Many growers we speak to know the pH of their water and often also the pH of their soil. What is confusing to many growers is when the soil pH is too high, even when using a soil mix that is 5.8 – 6.0 out of the bag or hopper, water pH may seem to be at a manageable level, and they are feeding with an acid fertilizer. Everything written above is important information, BUT one very important factor is missing: the growers usually do not know what the total alkalinity of their water is.
Water total alkalinity is listed as CaCO3 and, in simpler terms, is a measurement of the "liming" effect of a given water source when applied to a grower's crops. A water supply with high alkalinity will cause soil pH to rise over time if not addressed properly, and one with too low total alkalinity may lead to a soil pH drop that also causes nutritional issues. The target range for optimal total alkalinity is roughly 60-140. Many greenhouse water supplies fall within this range. But many areas experience water supplies that are either well above or below these optimum levels.
For better crop consistency and to avoid potential crop quality issues caused by nutritional problems, the easiest and most logical step is to have the growers' water supply tested before the next growing season. There are many sources for testing irrigation water; agricultural suppliers, universities, county extension offices, and independent labs are all available for such testing. What is needed is an irrigation supply water test that looks at the major and minor elements needed by plants: pH, EC (soluble salts), and total alkalinity. Such tests usually cost in the range of $40 -$75. At this price, water testing is a very wise investment to ensure the success of future crops and to avoid any undue "growing headaches."
Testing water equips growers to make better decisions when selecting soil mixes, purchasing a fertilizer blend that best addresses the water supply used, and possibly considering further steps to help make the water supply work FOR the grower and not AGAINST them. Broker salespeople, county extension agents, and university staff can all help explain the test results to growers and help them to develop a plan of action for their crops.
For more information:
Proven Winners
111 E Elm St Ste D
Sycamore, IL 60178
www.provenwinners.com