It would seem grass is quite good at spreading, so why are there still thin spots and bare patches on your lawn? Conversely, how can you limit grass from showing up where it’s not wanted? Let’s look at the ways grass can spread and how to get great results with your specific lawn.
Grasses may spread through above-ground runners called stolons, underground rhizomes, or seeds. Tillering increases the number of blades on a single crown. A species can use several methods. Lawn care affects spreading: proper watering, mowing, and fertilization can increase growth and thickness.
Overview Of How Grass Spreads
The way your grass spreads determines how well it thickens and fills in bare spots, as well as how aggressively it invades your flowerbeds. Not all varieties are the same – some species spread quickly while others sit in place like a potted plant.
There are three basic ways grass spreads:
Seeds – This is the traditional method we’re most familiar with. Grasses typically produce a seed stalk that dries and releases its cargo into the wind, spreading to any friendly ground it lands upon. Random seed dispersal doesn’t necessarily spread evenly and tends to form clumps.
Runners – This is the fastest method to fill in a bare patch naturally. It involves stem-like shoots that spread laterally from the parent with nodes that can produce identical children. Runners may grow either above or below the ground. The new plants are independent and will eventually send out runners too.
Tillering – Many grasses produce additional stems next to the original shoot called tillers. These multiple new stems feature normal, segmented blades that help the plant fill in laterally and make a dense tuft.
Artificial Spreading: Sod, Sprigs, and Grass Plugs
In good conditions, most grass will spread quickly after being planted in sprigs or plugs. Runner-growing species rapidly start filling in the gaps; bunch grasses soon begin tillering.
Laying larger pieces of sod over prepared ground works well with many warm-season grasses. This can provide an instantaneous lawn, especially when using tightly interwoven grasses like St. Augustine.
Spreading Through Seeds
Grasses naturally produce seeds, but you may never see them if you mow regularly. The usual process is for the grass to send up a seed stalk late in the season; once it ripens, the seeds are scattered by the wind or otherwise disbursed.
- Depending upon the time it takes the grass seed to germinate and mature, this can be a very slow method of spreading.
- Seeds are formed by sexual reproduction through pollination: the child grass may be different than its parents.
- It’s better to evenly sow the seed yourself. If you rely upon nature to spread your grass, it’s subject to random, patchy coverage.
Spreading By Runners
There are two kinds of runners: stolons and rhizomes. These root structures don’t absorb nutrients or moisture – their only mission is to spread the plant. It is a form of vegetative reproduction that produces new, independent clones.
This is the way most warm-season grasses spread. Some species produce both types of runners as well as seeds. Though it isn’t unsightly, stolons produce crisscrossing undergrowth that some aficionados dislike.
This is a runner you can actually see above ground. It’s a long, slender, stem-like shoot that a mature crown sends out to root a short distance away. A new plant develops along the end of the shoot.
Grass isn’t the only plant that spreads through stolons: strawberries are another example. Stolons form a network of runners beneath the grass blades that eventually creates a thick mat of grass. Their rapid growth and dense habit can produce a uniform, lush lawn that chokes out weeds.
Each new plant is independent of the mother plant once rooted – you can cut the stolon and its young plantlets will grow just fine.
Rhizomes are thick underground shoots formed by the roots. They travel beneath the surface until they hit a likely patch of moist soil, emerging a short distance from the original plant.
Rhizomes are a bit slower-growing than stolons but, since they carry additional reserves, the shoots they send up are quite sturdy. If you see a fully-formed blade emerging from the soil near healthy grass, it’s likely to be a new rhizome shoot.
Happy Grower … Or Invasive Weed?
The same grass prized by some gardeners has others reaching for an herbicide. It’s all in the eye of the beholder. Windblown seeds and wandering runners from desirable lawn grass become uninvited weeds in your planters and manicured beds.
Weeding and trimming keeps a typical lawn within its bounds, but one kind of grower does cross the line (any line) pretty emphatically: the indeterminate rhizome.
Many popular grasses like Bluegrass will send out runners locally to find a friendly spot of ground, but indeterminate rhizome grasses send out shoots in all directions without discrimination – and without stopping. The stuff of nightmares.
Indeterminate rhizomes usually don’t terminate until they reach an impassable obstacle – and, since they’re underground, you never know what they’re up to. Johnson grass and Quackgrass are in this category, and so is rambling Bermuda grass: now you know why it’s growing over the driveway, in the gutter, on the porch steps…
How Specific Grasses Spread
Lawn grasses are labeled either warm- or cool-season according to when they grow best.
These grasses grow fastest in the summer and usually go dormant when the weather turns cold. They often have stolons and can spread quickly:
St. Augustine – This shade-tolerant stolon factory rapidly produces a lush carpet with the right care. It lacks underground rhizomes. St. Augustine produces seed if you don’t mow it, but some strains are infertile.
Bermuda (Wiregrass, Couch Grass, Devil’s Grass) – This well-loved/badly hated grass spreads everywhere with its indeterminate growth pattern using both stolons and rhizomes – it will seed, too, if you don’t keep up with mowing.
Common Bent (Colonial Bent, Browntop) – A popular moorland grass that produces both stolons and rhizomes. It takes effort to establish and spreads slowly but makes a beautiful dense turf.
Zoysia – This versatile grass spreads by both stolons and rhizomes. Considered a warm-season species, Zoysia handles colder temperatures than most in this category. It grows slower than many grasses and can form a dense, almost weed-proof carpet.
Bahia – A heat-loving South American grass that spreads using both low-growing stolons and thick rhizomes. It’s hardy in drier regions, where its runners form a thick mat.
These grasses prefer cool weather and go dormant or die in high temperatures and hot sun. They can be excellent for overseeding lawn that goes dormant each winter.
Fescue – This hardy, cool-weather grass comes in many varieties of two subspecies: Tall and Fine. These versatile bunch plants typically spread through seeds and tillering, so they aren’t good at quickly filling in bare spots.
Creeping Red Fescue – This special Fescue variety does spread through short rhizomes. It doesn’t spread quickly, though; hence the name.
Bluegrass – This versatile grass spreads through rhizomes and by tillering. It fills in bare spots quickly under the right conditions. A less-desirable cousin called Rough Bluegrass spreads from stolons instead … it’s a common way to tell the difference.
Ryegrass – There are a number of rye species, but Annual and Perennial Rye are the most popular for lawns. Often mistermed ‘Winter Rye’ – another variety altogether – these runnerless grasses germinate quickly and thicken by tillering.
Helping Your Grass Spread
If you’re trying to fill in a bare spot, check how your type of grass spreads. Runner grass will eventually do the job, but you’ll have to reseed a tillering bunch species like Ryegrass to see results. Plant with plugs or sod for a quicker solution.
Regardless of whether you’re seeding a patch or waiting for runners, you can speed the process:
Reduce Soil Compactness
Grass grows and spreads best in soil that drains well and has enough structure to allow roots to breathe. Lawns with compact soil generally spread poorly because the fledgling roots can’t dig in. The same goes for struggling seedlings.
Physical aeration is one of the best things you can do for a lawn with hard-packed soil. It involves a machine that pokes holes in your lawn or – much better – physically removes small, deep divots of earth and thereby loosens the soil.
- Aerate when the soil is moist: water the day before if necessary.
- Go back over any highly compacted ground multiple times.
- Let the plugs dry, and then crumble them with the back of a rake to fill in the holes.
- If your soil is very compact, consider adding a thin layer of sand before raking.
- Aeration for warm-season lawns is best done in late spring to allow time for the grass to adjust. Cool-season grass benefits from either a spring or fall aeration.
- Aerate before overseeding in autumn or whenever you’re preparing ground for sowing.
Pro Tip: Sow before back-raking: seed that falls in the aeration holes is protected and can germinate in nice, loose soil.
Maintain Moist Soil
Water generously during your lawn’s growing season to maximize growth. A good soak is better than a sprinkle: you want the water to penetrate deeply. Light watering only moistens the surface and encourages roots to turn upward, where they are more subject to drying and damage.
The ideal moisture level for your soil varies by species. Many lawns go dormant if they suffer a drought. Cool-season species tend to like moisture in the soil but aren’t immune to root rot if the ground stays too wet.
Cut back on watering during the cool months.
Mowing regularly at the proper height for your lawn helps stimulate spreading. The grass will adapt and thicken or spread more quickly.
A good rule is not to mow more than the top 1/3rd of the grass at one time. This leaves your grass with enough reserves to spread and thicken.
The exception is new grass: mow it high until its root system has developed. Note that stolons generally grow too low to damage by mowing.
Proper soil nutrition is another key to a full, thick lawn—but be careful not to overfeed. Too much fertilizer can burn grass and actually stifle growth.
Pro Tip: If you suspect an overfertilized lawn, water it heavily to flush away salts.
The best times to fertilize warm-season grass are at the beginning of spring, summer, and fall. If you intend to overseed for winter, consider going easy or even delaying the fall application until then.
The important time to fertilize cool-season grasses is in early fall. Perhaps reapply two months later. Some lawn-owners fertilize in the late spring after the shoots have come out to avoid overly rapid growth.
A fertilizer with a higher proportion of nitrogen is good for blade growth. It turbo-charges tillering if done at the right time.
Keep the root system strong by alternating with a well-balanced blend. Organic fertilizer is especially good for soil and roots.
Keep Weeds at Bay
Weeds are an impediment to your lawn, both for the nutrients they consume and the sunlight they block. Pull them out regularly!
Weeds become a diminishing problem as your grass spreads and creates a thick carpet of runners and tillers … but lend a helping hand until then.
How to Limit The Spread Of Grass
Sometimes you want to stop your grass from spreading. Here are some recommendations:
- Mow regularly to keep seed stalks from ripening. This controls most seed-spreading grasses.
- Herbicides are available, but be cautious. These toxic agents can start a cycle of unexpected problems – and replacing your soil is a costly and labor-intense operation.
- Deprive unwanted grass of light by placing a board or other solid material over soil you wish to make grass-free.
- Place a barrier between the offending grass and the space you want to preserve. Bury it six or so inches deep to stop rhizomes from invading. How high and wide the barrier should be varies: Bermuda will travel three feet across a paved path before giving up, but most grass is less ambitious.
- Bake the soil to kill grass and seeds by spreading a sheet of 2 to 4 mil clear plastic over the area you’d like to sterilize. Wait six to eight weeks.