Planning to dig a hole? To plant a tree, set a fence post, make a water garden, build a deck? Wait! There might be something down there.

“Roots aren’t the only thing in the soil of your yard,” said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum in Lisle. “In city and suburban areas, there are lots of underground utility lines that you can easily damage with a shovel or a backhoe.”

Underground pipes and conduits bring services like natural gas, electricity, water, internet, cable TV and phone lines into your house and carry sewage away. It’s all too easy, when you dig a hole, to accidentally hit something important.

Fortunately, utility companies and municipalities make it easy to steer clear of gas and electric lines. You make a phone call or enter a request online and a locator will come and mark the positions of those lines in your yard with spray paint or flags. The call and the service are free.

Within the Chicago city limits, call 811 or 312-744-7000 or visit ipi.cityofchicago.org/digger to enter your request online. Elsewhere in Illinois, call 811 or 800-892-0123 or visit juliebeforeyoudig.com to enter an online request with JULIE (Joint Utility Locating Information for Excavators), a not-for-profit founded by Illinois utility companies to avoid line damage.

You need to place the request no more than 14 days before you start your project, but you also must allow a minimum of two business days for the locator to do the work, according to David Van Wy, damage prevention manager for JULIE.

It’s a good idea to have utilities located early in your planning process. It will help you choose the best site for a new tree or structure. After you’ve settled on a safe location, you can select an appropriate tree species for that site. However, you will need to call for utility line location again a week or two before you actually start work, because the official location is only valid for 14 days.

The locator will only mark gas and electric lines that were installed by the utilities or the municipality. Any lines added by the homeowner, such as a gas line connecting to an outdoor grill or an underground electrical conduit to a shed or garage, won’t be marked. “The utilities don’t even know about them,” Yiesla said. It’s up to you to keep a clear record of any private gas or electric lines that you or a previous owner has installed so you can avoid damaging them.

Van Wy suggested having utility lines located as soon as you move into a new home, before you start any gardening. Keep a record of those locations and be very careful whenever you dig within 18 inches of them, he said. Utility lines may be in the top foot of soil, so even routine gardening risks disturbing them.

The consequences of digging without locating utilities can be severe. Cutting electric lines can cause power outages. Even worse, breaking a gas line filled with natural gas at high pressure can set off an explosion and fire. In May 2021, a fire started when a homeowner in McHenry County struck a gas line while digging in the backyard. In 2019, a gas explosion and fire caused by digging destroyed five buildings in San Francisco, less than a decade after a similar error in nearby San Bruno leveled 37 houses and killed eight people.

Many home projects, not just tree planting, involve digging far enough down to strike gas or electric lines. If you’re building a deck, the footings for the support posts need to be set at least 36 inches deep. Landscape projects such as patios, paths and water gardens need excavations to make space for the underlying gravel layers. Regrading to change the slope of a lot may also endanger utility lines.

“Learning what is underground is part of assessing the conditions in your home landscape,” Yiesla said. “For example, if you want to plant a tree in a particular site, you need to know about the sun and soil conditions. You need to look overhead to see if the tree would run into power lines as it grows. And you need to be sure there isn’t anything important below the soil that could be damaged when you dig the hole.”

For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or plantclinic@mortonarb.org). Beth Botts is a staff writer at the Arboretum.