Warm spring prompts question: Is it time to water trees, shrubs and turf?

By David Ostdiek, Communications Associate - UNL Panhandle Research and Extension Center

One of the warmest and driest Marches on record has many western Nebraskans running sprinklers on their lawns, trees and shrubs already.

Not so fast, advises Scotts Bluff County Extension Educator Jim Schild. Some trees and shrubs need water now, some do not, and some landscapes should be checked to see whether or not they do, according to Schild.

“What people should be watering are any evergreen trees and shrubs, because with all the wind we’ve had and the lack of moisture, evergreen trees and shrubs will be highly stressed this spring,” Schild said. Evergreens generally require about 1 inch of moisture a month during winter, he said.

Also, the turf underneath, or in the root zone adjacent to, evergreen trees and shrubs will be stressed because the trees have been depleting that moisture, according to Schild. But deciduous trees and shrubs, which dropped their leaves in the fall, have not been using the moisture over the winter. Those that went into the winter in good shape moisture-wise are probably okay, especially if they’re in mulch beds, Schild said.

As of the 24th, March 2012 has been the fourth-warmest March since 1872, according to the National Weather Service at Cheyenne. For average daily high temps, it ranks 2nd. And it is tied for the driest March on record.

Schild said another landscape area that might be water-stressed are lawns with a fairly good slope that face south, where the direct sun angle may have dried more than other parts of the lawn (areas of compaction or limited soil, for example).

Other areas of the lawn may or may not need water, depending on how much snow they caught during the winter months, Schild said. To determine whether they do, Schild advises poking a long, flat-headed screwdriver into the soil in about 10 different areas of the lawn.

“If you can poke down five to six inches, there’s enough moisture that at this point in time they don’t need to be watered,” Schild said. “However, if you have difficulty getting it into the ground, look at applying one-half inch of water to the turf.”

A lawn’s soil moisture should be checked weekly, Schild said. “If we start picking up spring moisture, typically bluegrass lawns will be okay during April, then sometime during May we need to start thinking about routine watering or turning on the sprinkler system.”

Schild issued a caution about using sprinkler systems this early, when a frost is still very possible: “Treat it like fall irrigations, and make sure the water is shut off and the anti-siphon portion of the system drains.”

Unless it gets extremely cold, homeowners shouldn’t have to worry about valve boxes below the soil line freezing. Soil temperatures during the last week of March were in the upper 40s and low 50s.

“We shouldn’t have to worry unless night-time temperatures get into the single digits, which historically it has done at this time of year,” Schild said. The record low temperature for April 1 was minus 5 degrees Farenheit in 1975.

The biggest concern associated with the extended warm period is what it has done to tree and shrub species, Schild said.

“Soil temperature is what usually initiates leaf development on trees. With this extended warm period the soil temperatures are a good 10 to 12 degrees above normal for this time of year, and a number of the tree species are responding to that and starting to leaf out. Heavy freeze could cause some damage to some of these species, especially trees that are not quite hardy for this area.”

So selecting trees and shrubs for the landscape is important, Schild stressed. Even though the Scottsbluff area is now in Zone 5 of the USDA Plant Hardiness Zone map (one step warmer than it used to be), homeowners should consider planting trees that have a little more winter hardiness and those that tend to break bud at a little later date.

Schild said the warm March also has prompted people to wonder whether they should be applying fertilizers and pre-emergent herbicides earlier. “My response is no because we can still go through some fairly cold temperatures,” he said. Crab grass is a warm season grass, and a night-time freeze will kill what has germinated. And fertilizing turf this early will promote growth. That means more watering and mowing earlier, and the early demand on the turf’s root system could make it especially vulnerable to mid-summer heat stress if it’s not maintained properly.

The Panhandle Research and Extension Center is on the World Wide Web at panhandle.unl.edu.