Scott Cailteux mows his yard at his west Lawrence home in this April 2010 file photo. Like many Lawrence residents, Cailteux bags his grass and uses the city’s yard waste pick-up service. “If you don’t bag it, it is just messy,” Cailteux said.

To Omaha and back. That’s how far — about 415 miles — that Lawrence sanitation crews drive every Monday from March to November to pick up grass clippings and other yard waste that residents set out along their curbs.

City crews do this in large trash trucks that get about three to four miles to the gallon and emit diesel fumes with every turn of their wheels.

Since 1993, the city has been doing this in the name of helping the environment, largely because grass clippings will produce harmful methane gas when deposited in a landfill. But those clippings don’t produce such gas if you just let them lie in your yard.

Now, some wonder whether the city is being so environmentally friendly after all.

“It is hard for me to say that it is good for the environment,” said City Commissioner Mike Dever, who is an environmental consultant by trade. “My gut tells me the program has good intentions, but I’m not sure it has a net positive effect on the environment.”

Let it lie

What seems clear among horticulturists and environmentalists is that the program isn’t doing your lawn any favors. For folks who want a picture-perfect yard, grass clippings are your friend, not your enemy.

“It is actually much better for your lawn to let them lie,” said Jennifer Smith, the horticulturist for the Douglas County Extension Office. “They’ll help you save water and money.”

Basically, about 60 to 80 percent of a grass clipping is water, Dever said. When the clippings decompose, some of that water evaporates but some of it goes back into your lawn. Same thing for any fertilizer that the blades of grass absorbed before they were cut.

“Anybody who knows how a lawn works will tell you that it makes 100 percent sense to let it lie,” Dever said. “A lot of times people just bag it because that is what they always have done.”

Busting the thatch myth

But what about thatch, that carpet of dead grass that smothers your lawn? Bagging your grass has to help prevent that. Smith says no. In fact, she said it might make it worse.

That’s because people misunderstand what creates thatch. It is not the dead clippings from the lawn. Those largely decompose. Instead, thatch is more a symptom of yards that are overwatered and overfertilized. Basically, it is a sign that your lawn is growing too rapidly.

The way it works, she said , is that grass not only grows up. It also grows sideways, sending out runners or shoots. The lawn mower cuts what grows tall. But the sideways growth doesn’t always get cut and often times turns into thatch.

Letting your clippings lie can help because the clippings will help preserve water in the lawn. That should cut down on the times you need to water, making it less likely that you’ll overwater.

“I tell people that fertilizer companies must have invented lawn mower bags, because they want you to do more with your lawn than you need to,” Smith said.

But let’s be fair. Everybody has seen yards that look like a cow pasture golf course, in part because there are big clumps of grass clippings everywhere.

Dever said that definitely can happen. But it usually happens because people are mowing their grass too short — creating too large of clippings. Or letting it grow too tall between mowings, again creating large clippings. So, don’t do that.

But if you are still not convinced, there’s one other group that says bagging on a regular basis is a bad idea: the people who run the lawn waste program. That’s right. City leaders run a program to pick up yard waste, but they would just as soon you not use it regularly, at least not for lawn clippings.

“From an efficiency standpoint, it is far better to leave. That is absolutely the best management practice,” said Tammy Bennett, the city’s assistant public works director who oversees the program. “But that doesn’t mean that is what the customers of Lawrence want to do.”

Ah-ha.

Cutting back?

The program is popular among many. On average, city crews pick up yard waste at 3,000 households per week. The households that use the program aren’t the same every week, so the total number of households that use the program during the course of a year is much higher, although city officials don’t have firm figures for that.

The yard waste program also is a big reason why the community’s recycling rate is at or above the national average on a regular basis.

“It definitely would be a big change in service that we would hear about, if we stopped doing it,” Bennett said.

Scott Cailteux might be tempted to object. He was out bagging his yard recently, and said there are all types of reasons to collect those clippings.

“If you don’t bag it, it is just messy,” Cailteux said. “The dogs track it in the house and when the kids are running through the yard they track it in.”

Baggers and clean freaks everywhere, put down the phones. Don’t call Commissioner Dever quite yet. Dever said he isn’t ready to say that the program should be discontinued. It does serve some important needs, he said. In the fall, the program picks up large quantities of leaves. Leaves, if left on your lawn, can hurt it. Plus, blowing leaves aren’t the best for neighborly relations. And, Dever said he can understand why people may want to bag their grass during parts of the spring when weeds are beginning to emerge and seed.

But Dever does want the city to give some thought to reducing the frequency of the program, perhaps to every-other-week. Another option may be to create a demand response service, where residents schedule a time for city crews to pick up the waste.

Dever thinks the issue is a perfect one for the city-county sustainability coordinator — a new government post that begins in May — to study.

“I think we need to really try to measure the true carbon footprint of the program,” Dever said. “We need to see what the true costs of ownership are. I think that’s the fair thing to do.”

Dever said that discussion could happen this summer, when the city is crafting its 2011 budget.