7/20/2021 - By Lynn Griffith

I recently returned from a week of nursery consulting in New Mexico and Arizona. Obviously, being in the desert Southwest in late June, it was quite warm. In fact, in Phoenix, the temperature reached 118° two days in a row, with humidity around 9%. While the weather may not be that extreme where you are, much of the country is dealing with potentially record high temperatures, as well as significant drought in some areas.

These conditions create a lot of stress on plants in our nurseries and landscapes. However, there are a few tricks growers, landscapers and turf managers can use to help their plants deal with the heat. One farm we visited was growing plants in 17-inch black plastic pots. The head grower was concerned about high soil temperatures stressing his plants, reducing growth and negatively impacting root systems. I suggested he either try to find the same pot in white, or else grow with a pot within a pot. I also pointed out that I use inexpensive little meat thermometer probes, from the grocery store, to monitor soil temperatures.

As temperatures soar to near triple digits or higher, keeping root systems healthy is critical. Most potting media are phosphorus deficient. It is said that the corn plant needs two thirds of its phosphorus in the first one third of its life. I think most plants are that way. Harrell’s Phosphorus Plus is a great way to help the root systems of young plants to take off. It can be applied as a drench or through liquid feed, as well as foliarly. Keep in mind that phosphorus is leachable in soilless container media.

EarthMAX® Organic applications are another way to keep root systems abundant and healthy., Many growers have seen EarthMAX® Organic impart positive effects on root systems. Harrell’s Root Enhancer contains chelated iron, fulvic acid and kelp extract, all of which are known to, well, enhance root systems. Foliar sprays with Title Phyte® can also help keep root systems strong and active.

Good potassium nutrition is also critical for plants in hot weather, as potassium helps regulate the opening and closing of the stomates. Heat stress combined with potassium deficiency is a dangerous combination. Potassium leaches readily from both field soil and container media. POLYON® controlled-release fertilizer is of course a great way to keep plants supplied with controlled-release potassium. Foliar sprays with liquid or soluble potassium sources are also helpful in maintaining good potassium levels to help with heat stress.

Harrell’s also has a very extensive line of wetting agents and surfactants to aid in moisture penetration and retention. Antitranspirants can help slow moisture loss from foliage. Many growers like to syringe their plants on hot afternoons with brief bursts of irrigation, to help reduce both media and leaf temperatures. The rapid drying conditions in hot weather help minimize the risk of disease when syringing, keeping your plants both healthy and cool. All of these techniques and products can help plants make it through the long, hot summer.