What's your impact? Try my lawn care, the environment, and our ecosystem self-assessment.

Dear Avant Gardener, We converted our Kansas backyard to a low-mow, low-water sedge-like grass last year. Our gardener used the term “carex” to describe it. It was hard to get established (took three tries), but half the yard is looking pretty green as we come out of the winter. The other half still appears to be struggling. The half that is struggling is shadier and wetter – more trees on that side of the yard and it slopes, so water runs in that direction whenever it rains. Can you recommend variables we might consider in trying to assist the slow-growing half as we move into spring and summer? — Don, Fairway, KS

Excellent example of “right plant, right place!” Or, really, the converse, right plant, wrong place. No-mow Carex is among the best lawn options from both environmental and ecological perspectives, as you can see in the self-assessment chart below. Eliminating mowing mitigates climate change, because mowing accounts for an astounding five percent of air pollution in the United States. In addition, planting Carex helps our ecosystem by nurturing the insects at its foundation. (Note that the no-mow seed mix you linked to is not Carex; it is a mix of non-native fescues, which are less beneficial for native insects.)

There are hundreds of native Carexes, but I’m guessing your gardener planted Carex pensylvanica (Pennsylvania sedge), which has become popular as a lawn replacement. I used it in Brooklyn and wrote about it in “Love the Look and Feel of Grass? These Ground Covers Are for You.” In Mt. Cuba Center’s recently released four-year Carex trial, Pennsylvania sedge performed well in both sun and shade, in both dry and average moisture-content soil. The thriving half of your backyard fits this bill. However, Mt. Cuba does not recommend Pennsylvania sedge for the moist conditions in the other half of your lawn.

I suggest you try James’ sedge (Carex jamesii) where the existing Carex is failing. It is a top performer in the Mt. Cuba trial that thrives in shade in moist-to-wet soil, but also performed well in sun and average moisture. I value Mt. Cuba’s trial results based on controlled comparisons of landscape plants under various growing conditions, in contrast to the generally anecdotal — and often conflicting — information elsewhere.

Native to your county, James’ sedge looks similar to Pennsylvania sedge and will blend well with it. Its foliage feeds sedge grasshoppers, leaf beetles, and caterpillars of the eyed brown and Appalachian brown butterflies. The seeds feed many species of birds.

Your gardener can buy Carex jamesii plugs (and other locally native Carexes) at nearby wholesaler Taylor Creek Restoration Nurseries or you can order from them through Izel. You can also buy seed from Prairie Moon; it’s too late to stratify them outdoors in Kansas this year, but you can artificially stratify seeds in a fridge.

Happy no-mowing!

Dear Avant Gardener, I was told by a plumber to keep the grass short over my septic leach field (which is too small for the size of my house, per code) so the sun could help with evaporation and keep the system from getting too full. Is this the correct advice? — Zoe, Red Hook, NY

Your plumber is no ecologist, evidently, though his advice is fairly standard. In fact, your plumber’s comments about surface evaporation are worrisome. That’s not how drainage fields work. Before you consider planting options, please make sure your inadequate septic tank is not an environmental hazard.

Septic tanks and sea-level rise

As sea levels rise, more and more of America’s more than 20 million septic systems are threatening the safety of our drinking water, rivers and streams. In a properly functioning septic system, liquids from the septic tank percolate down through a few feet of filtering soil, where microbes and other biological processes remove harmful bacteria.

When this doesn’t happen, bacteria and parasites from human waste flow into drinking water supplies or recreational waters, creating a public health problem. Nitrogen and phosphorous, also a byproduct of the waste, pollute waters, creating oxygen-depleted zones in rivers and along the coast, closing shellfish harvests and killing fish. — Washington Post

For general information on caring for your septic system, as well as signs of failure, see the EPA’s homeowner’s guide to septic systems. Note that one way to decrease the load on your septic system is to divert some of your greywater — from showers and the washing machine, for example — to use in your garden; just make sure to keep it clear of the leach field.

Increased coverage and infiltration

George Loomis, co-author of Soil-Based Wastewater Treatment, told me that preventing erosion is the main function of ground cover over a drain field. Grass does a good job, but a multi-year study of groundwater runoff seepage troughs found flowering meadow provides superior coverage compared to turf (73 vs. 63 percent).

I would however avoid any plants with aggressive root systems that seek out moisture and "like wet feet.” Roots from woody trees and bushes can be problematic because many plants like moisture and nutrients (i.e., wastewater). — George Loomis

When not water-seeking, the deep roots of native herbaceous plants can actually benefit your drainage field by increasing infiltration, mitigating compaction, and absorbing nutrients. Beth Clawson of Michigan State University Extension recommends choosing plants suited for a dry prairie:

[T]he roots of dry prairie plants do not clog septic system pipes because they do not thrive in water saturated conditions. — MSU Extension

Replacing lawn over a septic drain field with meadow also minimizes mower and foot traffic over the area.

This compacts the soil, inhibiting its ability to adequately drain the water. It also reduces the pore space necessary for aerobic microbes that help to treat the wastewater. — MSU Extension

If you replace the current grass with a meadow of native dry prairie plants, make sure to minimize erosion and avoid watering by seeding or planting plugs directly into the grass in fall. You can choose plants from Beth Clawson’s list or use Prairie Moon’s Septic Safe Seed Mix.

— The Avant Gardener

Why, How, Wow!

Why?

Most American lawns are contributing to climate change, despite the ability of lawns to act as carbon sinks. That’s because the way we care for lawns produces carbon dioxide and other greenhouse gases. The two main culprits are gas-powered equipment and synthetic fertilizer.

Most lawn equipment is gasoline powered, typically being one of two types: two-stroke or four-stroke engines. To fuel this equipment, it takes about 800 million gallons of gasoline annually, with 17 million additional gallons spilled in the process. Two-stroke engines pose a unique environmental hazard because they do not have an independent lubricant system, so fuel and oil are mixed. Due to this, about 30 percent of the fuel does not combust completely, thus releasing toxic gases into the air. . . . Four stroke engines are also used in some equipment, and while they are slightly more environmentally efficient, in total, they are also harmful. A four stroke lawnmower operating for one hour equates to a vehicle traveling for 500 miles.
A sobering warning issued by the California Air Resources Board in 2017 reported the following: “By 2020, gas-powered leaf blowers, lawn mowers, and similar equipment in the state could produce more ozone pollution than all the millions of cars in California combined.” — Lawn Maintenance and Climate Change, PSCI

How

Wherever each of us is on our journeys toward more ecological, environmentally-friendly yards, we can do better. Fortunately, many of us have choices; my lawn itself falls into the “better” category below, but I’ve replaced much of it with diverse natives — a “best” practice. Where do your lawn care practices fall on the chart below?