Gardeners beware. That strip of green space between the sidewalk and the curb — officially known as a terrace — is not your property. It might be right outside your door, but that slice of earth belongs to the city of Madison.

However, that hasn’t stopped many a homeowner from adding rows of flowers, raised beds, planters, Little Free Libraries and even rock gardens to terraces. Much of this urban landscaping is perfectly legal. But it isn’t hard to find terrace gardens that fall outside the letter of the law. In order to avoid becoming a scofflaw green thumb (or having your terrace garden scrutinized), here’s what you need to know.

Until recently, policy on city-owned terraces was mostly about turf grass, reflecting the near ubiquity of grasses like Kentucky Bluegrass alongside streets and sidewalks. There was (and still is) a requirement in Madison that residents maintain the land by keeping grass on terraces below eight inches in height. But as awareness grows about the environmental toll of a finely manicured lawn, it has become more increasingly common for residents to get creative with this quasi-public space.

So in 2014, city officials clarified the rules on terrace gardens with an official “treatment policy.” It spells out the do’s and don’ts of permissible landscaping in terraces (although there is still wiggle-room in the law). City officials are largely tolerant of terrace gardens that aren’t technically in compliance with a hodgepodge of city ordinances.

Landscaping features like mulch meant to protect “approved plantings” (we’ll get to that later) are allowed as long as they are stable and easy to remove. So are temporary wire fencing, lattices and vegetable cages. A street terrace permit is required for putting in permanent structures like retaining walls, raised beds, benches, large planters and other “privately placed” items. Not many people apply for a street terrace permit, according to building inspector George Hank. Yet terrace gardens are easy to find. And because enforcement of the rules is “100 percent complaint-driven,” it’s unlikely an inspector will come knocking.

“We aren’t going out there looking for violations,” says Hank. “Our philosophy is to educate first, enforce when necessary. We really don’t like writing tickets.”

The most common complaint the city does enforce is when plants get in the way. If leaves, vines or flowers start encroaching on sidewalks, driveways or the street, the city will typically send an official notice informing residents to get their plants under control. If even some progress is made but the issue isn’t fully resolved, the city will grant additional time. Only when it’s “absolutely necessary” will a citation be issued.

And there are complaints about terrace gardens. Hank says his office frequently finds itself in the middle of a dispute between neighbors.

“Beauty is often in the eye of the beholder. We get complaints from people that their neighbor’s [terrace] is overgrown. Other times, someone has clearly put in years cultivating some kind of garden and the neighbor just wants to see grass,” says Hank. “We don’t really pay attention to what type of plants are there. It’s all about whether it’s in compliance with the code.”

Whether it’s just a bed of tulips or a raised bed, a terrace garden also can’t interfere with on-street parking. Plants need to be placed two feet back from the curb to accommodate people getting in and out of cars. Plants in terraces also cannot be taller than 30 inches for a four-foot-wide area parallel to a driveway apron.

“This is about visual clearance for people pulling in and out of driveways and for pedestrians,” says Hank. “These areas provide you a chance to see either someone on the sidewalk or in the street.”

But fair warning: Hank says there is one big caveat to terrace gardens, whether a resident seeks permission or not.

“Any time you do anything in the terrace, you are doing it at the risk that the city might come through and tear it all up,” says Hank. “They won’t put anything back or compensate you at all for it. Permit or no permit.”

And that might be the most exciting part of terrace gardening. You might come home one day and it’s all gone.

The 2014 treatment policy grants homeowners wide latitude in what types of plants are allowed in terraces. Flower gardens, vegetables, hostas, basically all non-woody plants are permissible. Plants with bark are another matter.

“What is heavily regulated on terraces are shrubs and trees. They have to be under 24 inches in height. So that pretty much eliminates planting trees,” says Phil Gaebler, a city engineer. “I’d stick with plants that you can easily cut back so you have a clean slate each spring.”

Madison Forestry, part of the city’s Parks Division, is responsible for maintaining 96,000 trees along Madison’s 700 miles of city streets. Not only does the city not allow residents to plant trees, they don’t want you messing with their trees either. It’s against the law to cut, prune or remove a city tree. The treatment policy even forbids plantings within a five-foot radius of a terrace tree, although it’s pretty easy to find yards where terrace trees are ringed with hostas.

A handful of plant species have been deemed health hazards and could lead to a $20 ticket if not eradicated. In January 2017, Ald. Ledell Zellers shepherded an update to Madison’s noxious weeds ordinance. It outlines 14 plant species that aren’t allowed on terraces (or anywhere else, for that matter). These include poison ivy, stinging nettle, giant hogweed, wild parsnip, Canada thistle, plumeless thistle, musk thistle, marsh thistle, common and cutleaf teasel, purple loosestrife, Japanese knotweed and common reed grass.

Language was also included in the updated noxious weed ordinance to encourage residents to use plants native to Wisconsin in their gardens. Doing so would “eliminate or significantly reduce the need for fertilizers, herbicides, water and lawn maintenance equipment.”

“Native plants are also beneficial because they help reduce air pollution because they do not require mowing,” reads Section 23.29 of the Madison General Ordinances. “They attract a variety of birds, butterflies and other pollinators. And their use promotes biodiversity and stewardship of our natural heritage.”

For a list of plants native to Wisconsin, the UW Arboretum’s website has a guide that provides detailed information on dozens of flora including the best species for attracting butterflies, hummingbirds and other pollinators.

Terrace tips

• To avoid electrocution or an awkward visit from a utility worker, give Digger’s Hotline a call. Just dial 811.

• If you have questions, contact the city engineering department at 608-266-4751.

• Permission is needed to add a “Little Free Library” to a city terrace. But there’s no permit or application fee.

• The city is generally laid-back about terrace gardens (just don’t mess with city trees or irritate your neighbors).