Jan 6

Written by: bugmaster
1/6/2010 4:29 PM 

Bug Master Bulletin for Fall-Winter

Proper Winter Irrigation

One of the most misunderstood aspects of landscape management for homeowners is irrigation management. Specifically, how often should you run your irrigation system. Below are a few basic facts and recommendations on how to properly irrigate during cooler months. These are simplified guidelines as proper water management combines the complex interactions of soil, water, and plant sciences. No two landscapes and irrigation systems are exactly alike. These recommendations apply to established lawns and landscapes.

PLANTS DON’T WASTE WATER, PEOPLE DO!
The amount of water a plant requires is equal to that lost through plant growth. Plants transpire (lose) water through tiny openings in the leaves called stomates and this loss is directly related to temperature (air and soil), day length and sunlight intensity. Water use and loss peaks during the summer months and continually declines as temperatures cool. The colder it gets, the less water plants need. Water is absorbed through the smallest root structures called “root hairs”, these water and nutrient absorbing roots grow best in oxygen rich environments, thus most are in the top 12-24 inches of our soil. Since water displaces oxygen in the soil, waterlogged soils reduce root growth and function having a negative impact on plant health. Rainfall or irrigation is stored in the soil and is lost only through percolation, evaporation or removal by plant roots. Large fibrous root systems are the key to overall plant health and drought tolerance.

Cold temperatures mean plants are using very little water and supplemental irrigation should only be applied as needed. If your grass only needs mowing every two weeks, then it doesn’t need water 2-3 times a week. Shrubs and trees require a quarter or less of the water required for turf areas.

Take Control:
Irrigation controllers are nothing more than clocks that open and close valves based on a pre-set timing schedule. They do not measure any of the factors related to water needs such as plant growth, soil moisture, air and soil temperatures, sunlight or rainfall. Improperly set controllers are the main cause for excessive water use and waste and are only useful if continually reset based on current conditions.

The BEST way to run your irrigation from now until March is to turn it OFF and only run it if the grass shows signs of wilt. We usually get rain every 10-14 days during the winter as cold fronts move through the area. Behind these fronts are colder temperatures which minimize plant growth rates. Most systems have an “ON” and “OFF” setting, simply turn the system to the “OFF” position, the clock will still keep the time and all settings will remain. If and when supplemental irrigation is needed, turn the system “ON” and it will run on the next cycle. After the system has run, turn it off again. Before turning the system on, check the weather to see if rain is forecast during the next several days, as it NEVER hurts to wait a few days for rain during this time of year. If you must keep the system on during the winter, water no more than once per 7-10 days. The easiest way to test for soil moisture is to stick your finger in it, if you feel wet soil, you don’t need additional water. If you pay for irrigation water, you will see a SUBSTANTIAL SAVINGS on your water bill by watering only as needed.

Detrimental Effects of Overwatering:
Maintaining high soil moisture conditions during the late fall and winter can produce detrimental affects that far outweigh the affects of under watering. A little wilt never hurts any plant; the same is not true for too much water. Excessive irrigation keeps the soil waterlogged since there is little evaporation or plant water use to remove the water. This can cause root rot, root diseases, leached nutrients, weed problems such as dollar weed and sedge and fungus problems, such as Brown Patch. It also means any rainfall will be lost to runoff since the soil cannot hold any more water. Mowing these wet soils increases compaction, leads to rutting and tears the grass up when mowers turn. Keeping soils below maximum water holding capacities encourages deep healthy roots, improving drought tolerance and water and nutrient uptake capabilities. The above ground parts of a plant are only as good as the root system below ground.

Annual Flowers:
Annual flowers planted this time of year may need some additional water until well rooted, but running an entire irrigation system to water only a few plants makes no sense. Take a few minutes to water small annual beds by hand, or for larger areas, adjust the irrigation controller so only those areas are irrigated as needed. As the plants mature, reduce the water. Remember many annuals are highly susceptible to fungus problems caused by excessive moisture. Pre-plant fungicide applications to annual beds can help prevent fungus problems from occurring. Geraniums like a dry to moist soil and Impatiens prefer a moist soil. Wet soils are not recommended for any flowering annual variety.

Cold Nights:
Make sure the irrigation is turned off when freezing or near freezing temperatures are forecast. Ice will damage most of our southern landscape plants, wetting plants on these cold nights only causes more damage. Irrigating crops during freezes like you see on TV for agricultural crops is done only when the irrigation can be run continuously during the night until the temperatures rise above freezing the next day. If the irrigation goes off during the night, the entire crop is lost. Do not try this for landscaped areas. Watering plants before a freeze can help protect them. A wet soil will absorb more solar radiation during the day than a dry soil. This heat is then radiated back during the night. To be effective the irrigation should be run the night before allowing as much daytime solar radiation to be absorbed as possible, make sure to turn the system off again.

If you would like any further information on this subject, please contact our office and I will be happy to discuss your particular situation.


Written by:
Brian Combs, General Manager, M. Ag. CPH, CCA, CPO,
Certified Professional Horticulturist - Certified Consulting Arborist
Member of the American Society of Consulting Arborist

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