Are you irrigating or irritating your plants?

Published 3:16 am Wednesday, June 28, 2006

By Staff
Staff report
Several years back my brother was teaching a junior high social studies class. On an exam he asked about the economy of a Middle Eastern country.
One of his students responded to the question by explaining that the country was relatively poor and that they produced few crops and the ones they did produce had to be irritated. The dry weather we have experienced locally over the past few months brought this story to mind.
As I travel and meet with home owners about lawn and landscape problems, I wonder if people are intending to irrigate plants or irritate them. I often see inadequate and poorly designed systems and poorly timed and managed applications of water to lawns and landscapes that, in some cases, cause harm to the plants they are intended to help.
These irrigation mistakes fall into the categories of too little water, poorly distributed water, and water at the wrong time.
Too little water can be caused by undersized pipes and sprinkler head design. To a certain extent, homeowners can divide the lawn into small areas or circuits that can be watered in sequence to reduce the size of the pipes required.
Typically, the sprinkler heads need to placed so that the water from adjacent sprinkler heads totally overlap (throw from head to head) to assure adequate distribution. One way to test both the quantity and distribution of water is to place open containers like coffee cans over the area being irrigated.
Allow the system to run long enough to catch one inch of water in the cans. Check to see if the cans are catching water at the same rate.
This time of year, it takes about an inch of water twice per week to keep turf growing at its best. If it doesn't rain the deficit can be made up from irrigation. As a matter fact, most years, irrigation is only helpful a couple of times per season, and faulty designs will not be apparent. However, this year poorly designed systems are easy to see.
The positive side of dry weather is that it reduces the likelihood of fungal diseases. Fungal diseases of plants are much worse when the foliage is wet.
Unfortunately, these diseases can be made worse by both natural afternoon and evening showers and by irrigating late in the day. Basically, the longer water is beaded up on the plant, the longer the fungus has to reproduce.
Watering programs should be timed so they don't increase the amount of time the leaves are wet. Dew falls in the evening and dries in the morning. Irrigation applied in the late afternoon or evening wets the plant and increases the time interval that he plant is wet.
Likewise, water applied to the plants just as they are drying in the morning also increases the length of time the plants are continually wet. Therefore, late afternoon and mid morning irrigation is not recommended. The best time to irrigate is the early morning hours. If this can't be done, mid afternoon watering that allows the plants to dry before dark is acceptable.
It is important to apply adequate amounts of water evenly over the irrigated area when it will not increase to length of time the plants will be continuously wet.
If you want to learn more about irrigation, I recommend the Texas A&M University irrigation web site at
It connects to a number of commercial and university resources related to home lawn and landscaper irrigation.

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