Well, it is summer in Memphis and this winter and spring have been one of the wettest on record. Now, with the increased heat, it means increased water demand by your plants. Plants move a great deal of water through their systems. A mature oak can absorb as much as 400 gallons of water a day when the air temperature nears 100°. Remember also, the root zone of that oak is approximately 2 ½ times the canopy width, so all your grass, shrubs, perennials, and annuals nearby are competing for the same water. The oak has thousands of miles of roots and feeder roots, so is there any doubt about who wins the competition for water?
“How much do I water?”
We should be applying approximately 1-2 inches of water per week to keep plants healthy. Watering should be infrequent, but thorough. To accurately set up your sprinkler system, place a couple of empty soup cans at different distances in the pattern, and let it run for an hour. This will show you how much water is applied in an hour and if you are getting even coverage. Try to apply between ½ and 1 inch of water each time you irrigate. Some gardens will require more water because of the soil type.
“When is the best time to water?”
Watering early in the morning is best. It allows for maximum absorption and less evaporation. However, watering anytime in the day before 4 PM is good. This allows enough time for the foliage to dry. That is important in Memphis because we grow so many plants prone to leaf diseases. However, if you are like me and work 10+ hours a day, six days (or more) a week, evening is the only time I have to water. Mother Nature waters 24/7, so if it needs water…water it. There is no evidence backing the claim that watering in in the sunshine causes burning. Some trees and shrubs begin to slow down when soil temperatures begin to increase in the summer. Heat and wind dry the foliage faster than the root system can resupply due to the slower metabolism so we see some evidence of leaf burn. We see this more often in Japanese Maples, especially lace leaf varieties.
“How do you feel about irrigation systems?”
Irrigation systems are a testament to the fortitude of plants. Unless you change it, it puts out the same amount of water regardless of the temperature, whether it is raining or not, and it totally disregards the needs of different types of plants. Plus, it does not compensate for new plantings. As we said above, the average root zone on a plant is 2½ times the canopy. If you have an established 3’ wide plant, the root zone is about 44 sq. ft. If you plant a new 3’ plant from a 5-gallon container, its root zone is less than 1 sq. ft. There are not any roots outside the root ball. The established plant is receiving 44 times the water that the new plant is getting, and they probably need the same amount. Quite often we have customers that do not understand why their new plant, under irrigation, dies. “It’s getting watered!” yes, but not nearly enough!
That said, a properly designed irrigation system does an excellent job if it is programmed to water deeply and the proper spray heads are used based on the needs of the plants. Watering deeply is critical. Frequent shallow watering requires more water because of evaporation, and it causes roots to stay near the surface. This makes them more prone to drought stress, which occurs year-round, and winterkill.
“So how can I tell if I need to water?”
Nothing beats the finger test. Pull the mulch back and check the soil about knuckle deep. If it feels moist, do not water. If it is dry, water. Pretty simple. Some plants will tell you by wilting, but that can be misleading. Young hydrangeas will wilt in the sun even with moist soil. They have lots of large leaves and the transpiration rate in hot, windy weather, can exceed the root absorption rate. Once they are in the shade, they pump back up. Once established, which can take several years, that should stop.
Some plants recover quickly from wilting, but some do not, so you should avoid letting them wilt repeatedly. Some do not wilt, they just shed leaves. Some drought stressed plants often shed the internal foliage. This decreases the amount of water it loses. It is just the plant’s way of protecting itself… it does not want to die. And then some plants show no signs of drought stress until they turn brown, so waiting for a plant to show stress is not always the best idea.
“Can I over water in this heat?”
Yes you can! Often, we see plants stressed, or die, in the spring from excessive rain during the winter. In the spring, the air temperature rises quickly and plants flush with new growth. But the soil temperature is cool, and it is usually wet, so there is minimal root development. As the summer progresses, the top growth slows down and there is an explosion of root growth in the warm soil. Many plants will not survive the warm soil being overly saturated in summer, especially plants that are not native to our area and need better drainage. Plants take in water through microscopic roots. If these roots rot off, the plant cannot take in water and it dries up and dies in wet soil. If these roots dry up from lack of water, the plant cannot take in water and it dries up and dies in dry soil. The net result is the same… dead plant. Dry plants need water to grow new roots. Wet plants need air to grow new roots, but chances are good, whatever the reason, YOU WILL WATER A WILTED PLANT. It may need air, not water.
So, a wilted plant needs water…………..but it may not need watering.
Because of our extremely wet winter and spring, we need to pay close attention to our landscape, especially the trees and shrubs that have been planted in the last 2 years. These trees and shrubs are still becoming established in their new environments and are highly susceptible to root problems. Using root stimulators will help plants recover from root loss due to sitting in wet soil for 6 months. Also, feeding with a good organic fertilizer like Milorganite, or plant specific Espoma products, will improve soil health and drainage. Even though most plants appear healthy right now, the stress of heat and summer drought could make that what seems like a healthy plant, become severely distressed. A little preventive care can go a long way to keep your landscape looking its best.
As always, if you need advice……just pick up the phone…..we are here for you.
Happy Gardening