The numbers game has Kansans watering at every extreme -- too little and too much ... too often and too close to never.

The Kansas State University horticulturist said the numbers game is why some sprinkler systems operate like clockwork, even during rainfall. It also is why some people have such disappointing results, even though they work hard on lawn care.

The numbers are formulas based on the amount of moisture lawns should get each week, Fagerness explained. In general, for example, the formulas for typical Kansas lawn turfs call for 1 inch of moisture – through rain or irrigation – every week of the growing season.

But that doesn’t account for some make-or-break factors:

* How widely state soils vary in water-handling ability.

* How turf needs to grow, to stay healthy through Kansas’ weather extremes.

* How air temperature and relative humidity can affect soil’s moisture loss.

* How widely sprinklers range in ability to distribute water evenly.

* How inaccurate homestyle rain gauges can be in measuring a whole lawn’s average precipitation.

The way around these problems is fairly simple, Fagerness said. Instead of trying to measure the amount of moisture that they and the growing season weather apply, homeowners should measure how deeply moisture "percolates" into the soil.

"An inch of water in sandy soils may not be nearly enough," he said. "In heavy clay, it may be too much for the soil to absorb all at once, so water may puddle or run off. You’d do better applying the moisture in increments."

One approach to assessing soil moisture depth is to use a shovel to slice straight down into the lawn. Then push the shovel forward and examine the dirt that’s exposed.

Another is to push a screwdriver or piece of rebar into the soil. When it hits dry dirt, it will move no further. Homeowners can then mark ground level with thumb and forefinger and pull the metal rod up to see how deep it went.

"You need to do that in several places, to get an idea of your lawn’s average moisture depth," Fagerness said. "About 6 inches of moist soil is a good job of watering."

Kansans’ favorite lawn turfs – tall fescue and Kentucky bluegrass – can get into serious problems with shallow watering, he warned. They’re cool-season turfs that perform best in spring and fall. For minimal health while under summer’s stresses, they need strong, deep root systems in place.

"You can’t spoil grass. You’ve got to make it work, to develop its version of muscle," the horticulturist said. "For example, if you irrigate 10 to 15 minutes every day, you may have a lush lawn this spring. But you’ll just be watering the top inch of soil. So, you’ll have top-heavy turf with lots of leaves to maintain. But when summer comes, the roots will all be in that top inch, where the soil dries out quickest."

Deep watering often requires running sprinklers for an hour, Fagerness added. As a result, most lawns don’t need watering more than once a week, except during hot, dry spells.

"If we have good moisture this spring, they won’t need watering at all," he said.