Why can't lawns and gardens just get along?

When Lawns Attack
Keeping Grass Out Of Gardens
by Jim Kohut, Staff Writer

The relationship between gardeners and lawn grass can best be described as “love-hate”. Nothing seems to give the homeowner more pride than a lush, green newly-mowed lawn, and yet nothing drives the die-hard gardener inside more crazy than trying to maintain a garden space within that lawn. It’s almost an expected right of homeowners to have both magnificent lawns and fabulous gardens in and adjacent to them. While we want great grass in our lawns, we definitely want that grass out of our gardens.

Unfortunately, our turf grass doesn’t seem to share our views. It almost seems to be a monthly ritual whereby gardeners labor over their garden borders, edging and re-edging, tearing out newly developed clumps of grass which have encroached on the garden, pulling the runners that probe deep into the garden spaces. No matter what one does, it seems as though the grass is on some kind of mission to assimilate the gardens. Keeping the grass out of your gardens is an ongoing chore that never seems to end, and only the most avid of gardening fanatics would label this activity a good use of their time.

There are ways, though, to keep grass in check and out of the gardens, and thus to minimize the ongoing maintenance requirements. The key is to understand the characteristics of lawn grass and then design boundaries which work around the factors that make it so persistent.

It’s All About The Grass

So why does your lawn seem so intent on annexing your gardens? Why can’t the two just get along?

	Grass spreads by underground rhizomes

It’s the very attributes of grass which make it ideal as a groundcover that make it a real nuisance for gardeners. Most cool-season turf grasses used in the North spread naturally by underground runners called “rhizomes”. These are wandering, tenacious roots which are able to break through even the most compacted of soils. At periodic intervals, these rhizomes themselves set root and send up new shoots, starting a new plant, which again spreads by sending out its own rhizomes. Even if the original rhizome is severed, the remaining plant continues to grow independently of the “parent”. Some are so resilient that they can sprout a new plant even if a small root piece is left in the soil. It’s these rhizomes that are so successful at crossing the boundaries between our lawns and our gardens.

Different grasses are more or less effective in spreading. Kentucky bluegrass is a popular cool-season lawn grass which spreads relatively easily, making it ideal to fill in a lawn area quickly and effectively. Some grasses are downright invasive, such as the dreaded crab grass or quack grass, the bane of many gardeners around North America. A small piece of root with only one dormant bud is often enough to start a new plant. Others, such as rye grass and fescue, spread very little if at all.

It’s also important to consider seeds as a significant method of propagation. Just as the ubiquitous dandelions enter most gardens by seed carried by the wind, many grasses arrive in your gardens by seed as well, particularly wind-blown species such as foxtail and broom grass. Seeds can also arrive with new soil, or even be tracked in on muddy shoes.

Management and Planning

The first key to keeping grass out of your gardens is to ensure that grass is not already present in the garden areas. If you’re starting a new garden, there are a few things you’ll want to keep an eye on. If you’ve excavated a plot out of existing lawn, you’ll want to be sure that there are no remaining roots or root pieces lingering in the remaining soil. Make sure that you cut the edges of the lawn with a sharp tool such as a lawn cutter or a good spade; make the cuts into the sod as vertical as possible, and be sure not to accidentally “mash” any rhizomes into the garden plot.

If you’re bringing in new soil, you can safely assume that the soil will have some grass seed already present (plus all kinds of weed seeds as well). The only way I have ever found to manage this is to accept that there will be weeds and grass sprouting the first year; one or two diligent weedings will pretty well take care of this, and the grass and weeds won’t return. In years following, a light layer of organic mulch will help to keep new weed seeds from contacting the soil and keep the ongoing maintenance to a minimum. Trying to force the seeds to germinate prior to planting the garden is somewhat futile; only the seeds on the surface will germinate, and when the garden is disturbed or tilled later to accommodate the intended plants, new seeds will sprout again.

If you are attempting to renovate an existing garden, it is important to eradicate all traces of grass already in the garden. For this, there is really no substitute for a good old fashioned manual tilling, where you break the soil up into a loose loam and then use your hands to feel out and remove all clumps and runners. However, I realize that this is difficult in a perennial garden to say the least, and pretty well impossible in a shrub border. If the existing problem is troublesome enough, the only solution may be to dig out the old garden, along with all the plants and shrubs and grass, and start over again, only this time doing it right from the start.

You can also try killing the grass using an all-purpose herbicide such as a glyphosate, but from my experience, unless you have very clear access to all of the grass, you’ll either not kill it all, or you’ll end up killing the entire garden along with the grass! I’ve had friends tell me to “paint” the glyphosate on with a paintbrush, but I do remain skeptical…

Don’t overlook the great opportunity afforded by garden location at the design stage. If you’re planning a new garden, examine possible ways to naturally separate the lawn from the garden with inhibitive barriers. For example, plant a garden between a sidewalk and the house, where contact with the lawn is kept to a minimum. Likewise plant gardens near driveways, patios and other man-made features which inhibit plant growth and offer a border other than lawn grass.

Borders and Edging

Stone edges may look nice, but are a challenge to maintain

Once you have a truly grass-free garden space, the next most important method of prevention is in the boundary between the lawn and the grass. The simplest of all borders is a natural transition between the garden and the lawn. While this is certainly the easiest and cheapest to install (which can be the only explanation for why so many gardeners use this “method”), it virtually guarantees a lifelong battle with the lawn for control over the garden space. Be prepared to edge and re-edge on a monthly basis with a religious zeal, because your garden won’t be very forgiving if you let some grass get in and take hold.

Many gardeners understand that some nature of a physical border is required to keep the lawn out of the garden with any success. I most often see three methods by which gardeners try to edge their gardens; “homemade solutions” they create themselves, manufactured border and edging materials, and more advanced professional borders which require much effort and expense. Let’s have a look at each.

There are numerous innovative ways that gardeners have employed to bound their gardens; rocks, bricks, railroad ties, cut wooden posts, even old beer bottles (don’t get me started…). Many of these work for a while, but are ultimately doomed to failure. The key is that given enough time, grass roots will eventually find every opening in the border between the lawn and the garden, no matter how small or widely spaced. Since virtually every “homemade” edging is not continuous but has some breaks through to the garden, they are all eventually going to fail in this manner. If you have a short-term window for your garden (3-5 years) and intend to fully dig it up and replace it with some frequency, then this solution might work for you. However, this wouldn’t be a very good idea for a shrub border!

Grass roots run deep, and rhizomes can happily run 4-5 inches below the surface for quite a distance. I have personally seen crab grass runners at more than a foot below grade! It is essential that any border barrier penetrates at least 5” below grade to keep the aggressive roots out. Another useful technique is to wrap the edging material in a high quality professional landscape fabric, extending from slightly above grade down the outside (lawn side) of the edging material, underneath and then into the garden for at least 2’. Be careful not to perforate the fabric, or the grass will find your mistake!

Many gardeners simply lay their border materials onto the surface at ground level, thinking that grass won’t go “where the sun don’t shine”. I’m not sure where this gem of advice originated, but it is a gross misunderstanding of the persistence of grass that will ensure failure, and likely in the first year! You can safely bet that “threatening” grass by laying a landscape tie on the ground isn’t going to work; if you’re counting on a barrier surface to inhibit the plant’s upward growth, it had better extend 2’ or more from the lawn and be absolutely impenetrable, like a concrete sidewalk or professional landscape fabric.

Degradation of the border material is another consideration. Wood will eventually decay and rot, providing new pathways for the grass to penetrate the garden. Bricks eventually crack, and frost can heave and separate even the most permanent of materials like stones set in mortar! Again, given time, grass will eventually find all of these nooks and crannies.

The more professional “pre-manufactured” lawn edgings are designed specifically to mitigate these factors. The better ones will resist degradation for a very long time, and are designed to be installed with virtually no paths for grass rhizomes to get through into the garden. Many, although not all, handle frost movement well without compromising their integrity.

The most common edging by far is black plastic lawn edging. When selecting manufactured edging, make sure it will extend at least 5” below grade, and has some form of barb or other means of securing it against frost heave. Proper installation is critical, and preparation of the lawn edge is of the utmost importance; it must be a clean, vertical cut, extending the depth of the edging or even a little deeper. Keep the top of the edging exactly at grade level, and use garden soil to hold it down, tamping it well to secure it. Again, wrapping the edging with landscape fabric as I described above will help guarantee that it keeps the lawn out of the garden for a long time.

	Custom brick borders add a touch of class

Advanced Borders

For the most committed of gardeners, there are other highly effective means of keeping your lawn out of your garden which have the added benefit of enhancing your landscape appearance. Concrete curbs cast in place work wonders, and are completely impenetrable when installed properly. The catch is, you will pay for them up front, and usually pay handsomely.

One of my favorite techniques is to use bricks, paving stones or precast stone blocks as a border; they look great, and work extremely well when properly installed. Again, the installation is the trick; they must be set upon crushed rock (like a 3/4 down) which has been put in the bottom of a trench twice as wide as the bricks and at least 8” deep, and covered on all 3 sides by a continuous run of landscape fabric. Once installed flush with grade level, these add a very natural look and are super easy to maintain; you can run your lawnmower right over them! If enough of you are interested in this technique, I could actually write a whole article about how to install it yourself!

If you’ve taken the steps of preparing the garden to be free of existing grass and provided a solid, impenetrable barrier as an edging, you will be well on your way to a harmonious coexistence of your lawn and your gardens, which means less maintenance work for you, and even more “oohs” and “aahs” from your admirers!

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