How to convert cool-season lawn into native plantings

Peter Arnold, Virginia Tech School of Plant and Environmental Sciences, Arnold Classic Farms

David N. Bellangue, Virginia Tech School of Plant and Environmental Sciences

Jenna Beville, Virginia Tech School of Plant and Environmental Sciences

Forrest Brown, Virginia Tech School of Plant and Environmental Sciences

Dillon P. Golding, Virginia Tech School of Plant and Environmental Sciences, Hoot Owl Hollow Farm, Woodlawn, VA

Joseph D. House, Indiana Army National Guard

J. Leighton Reid, Virginia Tech School of Plant and Environmental Sciences

Jonathan O. C. Kubesch, Virginia Tech School of Plant and Environmental Sciences, Arnold Classic Farms, Country Home Farms, Pembroke, VA, Kentucky Native Plant Society

The majority of turf and pasture species in Kentucky are cool-season species from the Old World. In suburban yards, these species might include Kentucky bluegrass (Poa pratensis), orchard grass (Dactylis glomerata), and tall fescue (Schedonorus arundinaceus). These grasses rose to prominence because they tolerate the mowing, fertilization, and usage regimes of most pastures and yards. Weekend games and parties in the backyard are hard on the soil surface, and thick sods can reduce soil erosion.

Cool-season lawns have limitations. In many yards, the amount of foot traffic doesn’t justify maintaining a thick green lawn. Fertilizer, gas, and mower repair might be money better spent on other activities around the house. Additionally, intensively managed lawns can add pollutants into the wider environment. Finally, while all grasses produce wind-pollinated flowers, these flowers do not necessarily support the pollinators in decline across eastern North America.

More people are eager to convert lawns and pastures to native species, primarily wildflowers, grasses, and small woody plants. These native plantings can replace traditional garden beds, take up dedicated areas, or even replace the entire backyard lawn. Native plantings reintroduce native species back into suburban areas. These native plantings provide a great introduction to our natural heritage for young children as well as a proving ground for restoration of natural plant communities at larger scales.

How do we convert cool-season lawn and pasture into native plantings? Cool-season grasses tolerate a fair deal of abuse, which can make them challenging to kill. A stepwise planning and planting process can help with killing lawns as well as planting native species. A fair deal of technical and popular literature is available to help guide interested homeowners and landowners to make the switch, but here’s a quick guide to help frame your conversion.

Step 1. Assess the site and set your goals for the planting

Site assessment should precede any action. Without an idea of the resources, site condition, or a plan, a native planting is less likely to succeed in meeting your goals. This assessment should consist of a soil test and a composition assessment. Soil testing should be in accordance with guidelines from the University of Kentucky soil testing lab. The routine soil test can determine basic soil fertility, and the organic matter test can decide whether additional amendments, such as compost or straw or wood mulch, are required.

If such amendments are added, please consider the Carbon to Nitrogen (C:N) ratio. Carbon will tie up nitrogen making it unavailable to the plants, meaning additional nitrogen will be necessary to ensure proper microbial breakdown of amendments and proper growth for the plants. Plant species need to be selected based on soil acidity.

Most American lawns are a mixture of cool-season grasses, introduced legumes, and native as well as non-native broadleaf forbs. Getting an idea of the yard composition can be as simple as walking the yard and at 100 points determining the plants nearest to a boot tip. This step point method is quick and effective. This assessment does not need to be overly formal: grass, clover, and broadleaf weeds. This initial composition can determine the efficacy of different conversion strategies.

Homeowners Associations and other regulatory bodies may not like how these stands look, especially considering that most native plants are not subject to regular, short mowing. Be as pragmatic as possible, not fanciful. Evaluate your situation and act in the most effective way to meet your goals. These organizations could be persuaded to be more supportive of these actions if the yard can advance conservation, environmentalism, and biodiversity protection. After confirming approval, native plantings should be planned appropriately.

Goals for native plants depend on what you expect from your site. Producing native blooms for pollinators might favor a semi-natural wildflower bed, whereas a meadow mix might be more appropriate for wildlife. A native lawn may not be a possibility right away, but native areas with walking paths or native beds might be a great way to move toward a wilder yard.

A general plant community is a great way to frame a native bed or area in the yard, and here are a few questions to help you get started:

• Will this plant community be grassy, flowery, or woody?
• Are there any priority species for your area?
• Will the area be a series of managed beds, or a semi-natural meadow with walking paths?
• Are trees and woody plants part of the native planting?
• Is shade a factor of the area?
• Will you need to consider how much light is needed for desired native plants?

Increasing the diversity of species in the planting can improve plant growth and competition against weeds, as well as reduce pest pressure. Native plants come with different management requirements than cool-season grasses and limitations. These species grow from March to November and then go dormant, leaving brown stubble. Native turfs are being evaluated in the eastern USA, but low-growing western natives are not necessarily native to Kentucky nor do these species compete well with weeds when water isn’t limited.

If you’re seeking to create a landscape similar to what existed pre-settlement, consider using regional plant and seed suppliers, and ask Kentucky Native Plant Society officers about what might work in your geography. Consider building a plant community that might resist extreme climatic events.

Step 2. Plan a timeline to convert the site

Cool-season grasses grow most aggressively in the spring and the fall (hence the name “cool-season”). That means that killing these grasses during these periods (March-May and September to early November) can be extremely challenging. The best time to kill these grasses is when they are already struggling (early March, early June, or late August) to grow or by challenging the grass with intense stress (intense mowing, herbicide, tillage). An extreme stressor, such as mowing the grass shorter than normal, would cause the grass to exhaust its stored carbohydrates. In this state, the grass would be very vulnerable.

Many native species respond well to cold stratification either naturally (dormant-season seeding) or to planting out of competition with cool-season grasses (June planting).

Step 3. Pick a conversion strategy

Cool-season grasses are popular in the Upper South because they tolerate the regular mowing, use inputs quickly, and can form thick sods.

Mowing

Most mowing regimes seek to remove more than ⅓ of the total grass height and keep the grass at 3-4” tall. This regime preserves the energy reserves of the grasses. However, regularly cutting and lowering the mowing height can kill these grasses. Start by cutting a lawn at the normal cutting height and then drop a setting with the mower every cut until the stubble is ½ to 1” tall. Keep cutting the grass to this height and then prepare to seed or plug native plants into the stand.

Mowing works well for plants that grow above the soil surface. Low-growing species, such as thistles, can evade the mower by positioning their leaves almost at ground level. Mowing could work well with mulching for plugs or light tillage for seeding.

Mulching

Mulch can be any material that is used to cover the soil surface. Mulching can improve water retention, reduce soil surface temperature in the summer, and increase soil surface temperature in the winter. In smaller areas, mulching can smother an existing lawn simply through an extremely thick layer (>8”). Horse or poultry owners might pile soiled bedding on a site. This old bedding needs stirring in order to kill weed seeds. Tree leaves raked into a pile can kill the grass underneath as well as support overwintering insects.

Mulching works well to control cool-season grass and low-growing broadleaves. Mulching can be ineffective when trying to plant a meadow mix. Mulching reduces seed germination for weeds but will do the same for small native seeds.

Herbicides

Herbicides should be used judiciously following all instructions and guidance. Herbicides can be a part of a conversion strategy but should be considered in concert with some of these other strategies. Herbicides fall into two categories: selective and non-selective.

For a yard with more grass than broadleaf weeds (>75% grass), a grass selective herbicide can kill turfgrass while allowing any native weeds (e.g., wild violets) to remain during the conversion process. If there are no desirable native grasses or forbs already present, then a nonselective herbicide can be used to completely kill the existing vegetation.

When selecting a herbicide, it’s important to select one without any residual effects as this might cause issues with germination in new stands of native plants. In many lawns, a nonselective herbicide can effectively eliminate weed competition during the first month of planting.

All herbicides need to be used with the consultation of a local Extension agent or licensed applicator. Herbicides should be part of a plan rather than the sole conversion strategy for converting a yard.

Tillage

Tillage can be controversial for native plants. Presettlement soil disturbance would have included wildlife hoof action, wind and water disturbances, and perhaps even Native American agriculture. In the 19th and 20th centuries, excessive agricultural tillage has damaged many soils in eastern North America. However, tillage can be appropriate with the following conditions:

1. Area is a flat surface at a distance from streams and water sources
2. Soil is not rocky
3. Site does not have a lot of tree roots

Tillage varies in the depth and the degree of disturbance to the soil profile. Conventional tillage involves moldboard plowing, followed by disking and/or harrowing. Readers in Louisville might be familiar with the Cub Cadets of the 1960s and the Brinly Hardy single bottom moldboard plows. Garden tractors can prepare smaller areas for conventional tillage. In some cases, garden tractor hobbyists are willing to come and run their tractors for free at a property.

Rotary tillers — rototillers — usually use a machine to completely mix all the soil to a certain depth. Many vegetable gardeners use rotary tillers to prepare gardens. Rototillers are commonly available at garden centers. Harrowing often loosens the top fraction of the soil surface. Horse owners and pasture managers often use drag harrows to spread manure and overseed pastures. Homeowners might use a dethatching rake or a pull-behind dethatcher to similarly prepare the soil surface for small native seed.

Tillage should be conducted as close to planting as possible in order to minimize soil erosion risks or should be followed by a cover crop to protect the soil prior to planting natives. Fall tillage was popular in eastern North America previously because clumps and clods could break down during freeze-thaw cycles. A potential fall tillage-spring planting might work like this: Till the spot around Labor Day, immediately plant a cover crop such as wheat, and then kill the cover crop in spring ahead of planting the desired native plants.

Step 4. Seed or plug the desired native species into the yard

Seeding or plugging these native species into the prepared bed or area is the exciting part of many native plant projects. The area goes from an unremarkable Kentucky bluegrass into purple coneflowers, black-eyed Susans, or even Indian grass (Sorghastrum nutans).

Seeding is useful when the area is large, species grow easily from seed, or labor limits the ability to plug plants. Seed often increases the number of species that can be included in a seed mixture, because seed is generally cheaper than plants. Plugging plants is useful when the area is small, plants can be challenging to grow from seed, and labor is not limiting. Plugs often jump start a planting by 2-3 months over seeding and can help with weed control early in the life of a planting. Seeding and plugging need not be mutually exclusive in a yard. Mixing planting methods can provide a staggered establishment that looks good in the first season and fills in more fully in subsequent seasons.

Step 5. Maintain and monitor your planting over time

Native plants can be less labor intensive than introduced species, but they still require stewardship. After buying a seed mixture, one would hope a homeowner would want to know whether a native planting succeeded. In a native grassland seeding, these criteria could be considered roughly as follows:

• Successful is >20 plants per square yard
• Adequate is 10-20 plants per square yard
• Unsuccessful is <10 plants per square yard

These targets come from building a grass-wildflower community, and might need to be adjusted to your conditions. Ground cover might be a goal for a rain garden, and so a stand >70% cover is desirable to avoid soil erosion. For plugs, a certain % survival might be ideal (x plants survived out of y total plants). These plantings should be evaluated a year after planting to provide a conservative estimate of which plants should persist.

Very often native plantings are ugly in the first year, but these plants are working to build strong root systems rather than competing with weeds. Keeping native plantings cut to 6-8” as weeds overtop native species can improve native plant growth. At the end of the first growing season, old growth can be left standing or cut to 8” after a few hard freezes.

The lawn is a conceptual, biological, and mechanical landscape that allows nonnative grasses to dominate a large portion of suburbia. Converting lawns to native species is a step toward conservation and appreciation of our natural heritage. Assessing conditions, timing conversions,  preparing sites, planting natives, and keeping up native plantings should improve the success of native plantings, as well as provide a rewarding experience for all involved.

Acknowledgments

This article was possible thanks to fruitful discussions and restoration attempts under the direction of Dr. Reid. The present article was motivated by some work to develop, maintain, and conserve native plants in the modern landscape. Kubesch thanks his wife, Sarah Grace, for encouraging native plant experiments at Country Home Farms.

References

This article was written with as many open-source publications as possible, and those links have been embedded throughout the text.

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