Problem Solving and Irrigation
For the month of August gardeners should focus on continuing to monitor for pests and diseases. Our Landscape Manager, Drew Stevens, recommends paying special attention to hydrangeas that may need fungicide applications to manage cercospora leaf spot and anthracnose. Gray leaf spot and chinch bugs frequently show up in St. Augustine (or Charleston) grass by August. Pests that have recently been brought into the nursery for identification are mealybugs on sweet grass and bamboo; also, root rot on boxwoods. Make that last yearly application of fertilizer to turf (if not done already) and pay close attention to irrigation needs. Continue to feed and groom summer annuals but start planning for cool season ones.
More on Irrigation:
Last August we experienced almost three weeks of daily rain at the nursery. That amount of rainfall can do a lot of damage to plants in pots especially with regards to root rot. If your soil does not drain well, plants in the landscape can suffer too. This year’s rainfall pattern for August could be very different so it’s imperative that you know what to do in any given rainfall scenario. Probably the most frequent questions that we receive at the nursery are about how much water or irrigation is enough. Most folks have difficulty in understanding how complex the answer can be.
When I first began working for Extension in 1996, the general rule of thumb was that plants in the landscape need, at least, 1 inch of water per week. That amount is still used but occasionally I’ve seen 1½ inches of water recommended. So, one way of answering the question of how much is enough is to simply set an irrigation system to supply 1-1½ inches of water per week. There are problems with using a general rule though.
Plants typically don’t have the same evapotranspiration rates (water loss through leaves) throughout the year. For deciduous plants that have dropped all their leaves for winter there may be no water movement at all. (If you ever wondered why certain places become waterlogged or boggy in winter, look around to see how many deciduous trees are nearby. In the summer they pull lots of water from the soil and none in the winter.) Some soils retain water better than others. A clay soil will hold water better than a loamy soil and both have a higher water holding capacity than a sandy soil.
Some plants are more xeric than others and may not need supplemental water at all; others may be especially water loving. With some plants such as turf, Extension specialist recommend waiting until the grass is slightly drought stressed before irrigating. The grass should have a blue-gray tinge, or you can see your footprint after you walk across the lawn before you irrigate. For some plants, though, waiting until they show symptoms of drought stress is not an option.
Below is a list of things that you can do to try to be more efficient and effective with your water applications:
• Group plants in your landscape according to water needs
• Use drip irrigation where possible
• If you have an irrigation system, know exactly how much water it puts out
• Use the can method for above (see Clemson HGIC 1802 factsheet below)
• Try soil moisture sensors (the human finger works really well)
• Mulch, mulch, mulch
Clemson’s HGIC website has a series of factsheets on irrigation that can walk you through many aspects of managing water in your landscape. Below is the series on Irrigation Management. There is also a series on Landscape Irrigation Equipment that you can search for at: https://hgic.clemson.edu/
Factsheet 1800, Landscape Irrigation Part 1: Water in the Landscape
Factsheet 1801, Landscape Irrigation Part 2: Determining When to Irrigate
Factsheet 1802, Landscape Irrigation Part 3: How Much Water?
Factsheet 1803, Landscape Irrigation Part 4: Winter Irrigation and Winterizing
Factsheet 1804, Landscape Irrigation Part 5: Irrigation Time of Day
Factsheet 1805, Landscape Irrigation Part 6: Soil Type and Irrigation Frequency