Pre-conditioning "Toughening" Lawns
For many years there have been spirited debates about whether frequent, shallow watering or deep, infrequent watering of lawns is best. A connection is often attempted to be made to rooting depth which is primarily genetically determined. Research shows that irrigation practices affect turf's ability to tolerate heat and drying conditions, but hasn't shown that irrigation practices effect rooting.
Irrigation and other turf care practices (fertilization and mowing for example) affect both the plant's physiology and anatomy. Frequent and heavy irrigation causes lush growth. A minimalist approach toughens the grass. The leaf cells of toughened plants can tolerate more drying and the plant's physiology withstands more drought and heat stress. Toughened (pre-conditioned) plants are likely to be more resistant to summer diseases and recover more quickly in fall when cooler temperatures return.
Irrigation practices at the beginning of the growing season play a large role in this pre-conditioning. A rainy June with higher humidity (for Colorado) before July heat allows for minimal toughening. This is especially so if people add irrigation applications to nature's June water bounty. "Brown-outs" and diseases such as Ascochyta may be more common as a result, particularly where irrigation coverage is insufficient in hot, dry weather.
While excessive irrigation creates low oxygen conditions that promote shallow rooting, the primary effect of irrigation on turf heat and drought tolerance is due to influencing the physiological and anatomical makeup of the grass.
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Updated Friday, April 19, 2013