Everything About Perennial Ryegrass

Perennial ryegrass is known for its ability to germinate quickly. However, it is much more than that. It’s a strong, quick-growing, beautiful grass that can naturally overpower weeds. It’s also capable of preventing erosion when grown on steep surfaces like ditches and roadways.

Due to its beautiful dark green hue, it has attained the honor of being the main part of the turf of Wimbledon Tennis Club and August National Golf club (home of the Masters).

Published: October 21, 2022.

What is Perennial Ryegrass?

Perennial ryegrass (Lolium perenne) is a cool-season perennial grass belonging to the family Poaceae. It has no connection with the cereal rye.

It originates in Asia, northern Africa, and Europe, but today it’s cultivated across the world for various purposes including a pasture grass and lawn grass on residential and commercial areas, golf course tees, fairways, rough areas, and other sports fields. It was released in the USA in the early 1960s.

Perennial ryegrass does well in areas with moderate summers and cool winters. It prefers full sun but can bear low levels of shade.

Although it prefers fertile and well-drained soil, it can survive in a variety of soils. It’s often included in mixtures of slower sprouting grasses like Fine Fescues and Kentucky Bluegrass to increase traffic tolerance of the turf and to help stop soil erosion during turf establishment. However, if used in higher proportions in the mixtures, it dominates the entire area since it is extremely competitive.

Perennial ryegrass has a bunching growth habit. The plant is densely tufted and multi-tillered and grows up to a height of 0.3 to 1 meter (1 to 3.3 feet).

Its leaf blades are dark green with conspicuous parallel veins on the upper surface, whereas the lower surface is smooth and glossy. Most perennial ryegrasses have a red tinge at the bottom of the leaf sheaths.

It also grows flowers in the form of spikelets in the corners of a rachis (flower stem) in a zigzag pattern. The grass spreads through vertical stems called tillers and not by rhizomes (underground stems) or stolons (above-ground stems).

It has a shallow root system, i.e. it sits in the upper 6 inch surface of the soil. However, the grass forms a very dense sod that sprouts fast but spreads slowly. The shallow root system, however, makes the grass less heat- and drought-resistant than tall fescue and zoysia grass.

But, researchers have developed more drought-resistant varieties of perennial ryegrass. These cultivars also have increased stress tolerance, enhanced mowing quality, higher insect and disease resistance, more uniform leaf texture, higher shoot density, and darker green color.

The other type of ryegrass is annual ryegrass (Lolium multiflorum). Although annual ryegrass grows quickly and strong, it will die off at the end of the season and will never return, whereas perennial ryegrass keeps coming every year for around 3 to 10 years.

There is still another variety of ryegrasses named Darnel (Lolium temulentum). This variety is poisonous as it contains a fungus species, neotyphodium. It’s dangerous for grazing animals and pets.

Symbiosis with Endophytes

Perennial ryegrass too can be purposefully exposed to Neotyphodium (endophytes) fungal infection.

The fungus lives intercellularly in the tissues of the stem, leaf, and sheath.

Due to these endophytes, perennial ryegrasses get increased stress tolerance. Cultivars containing endophytes can suffer less damage from insects like sod webworm, chinch bugs, and billbugs since the endophytes produce toxic alkaloids.

Endophytes are transferred to offspring via seed hence seed should be stored carefully under cool, dry conditions to retain this useful fungus. However, children, animals, and pets should be kept away from such endophyte-infected perennial ryegrass lawns.

Diploid and Tetraploid Perennial Ryegrasses

Perennial ryegrass is of diploid and tetraploid types.

The diploids have two sets of chromosomes and hence they are smaller in size than the tetraploids which have four sets of chromosomes.

Diploids have finer leaves, are more densely tillered, and therefore look aesthetically more pleasing whereas tetraploids have wider leaves, and long tillers and seed heads. Their varieties are taller and less dense.

Since their sod is more open, they are suitable to be planted in combination with legumes such as red clover, alfalfa, and white clover. They also have higher levels of water-soluble carbohydrates i.e. higher sugar levels and hence more palatable to grazing animals. By far, diploids are more preferred for lawn application.

Cultivars

Cultivars of turf-type perennial ryegrass are some of the most versatile grasses available today.

They have qualities like improved traffic tolerance, quicker establishment, and deeper green color.

Still, researchers are trying to achieve traits like increased disease resistance, cold hardiness, heat and drought tolerance, ability to survive under snow sheets for prolonged periods and salinity tolerance.

Some of these cultivars are Evolution, Fastball RGL, Pangea GLR, Xcellerator, Stellar 3GL, Pizzazz 2, CHT, Rinovo, Metolius, Karma, Wicket, Grand Slam GLD, Apple SGL, Manhattan 6, Sideways, Dasher 3, Benchmark, Saltinas, Phenom, Home Run, Triathlon, Harrier, Zoom, Estelle, Protégé, Mighty, Allstar 3, Fiesta 4, Palmer IV, Soprano, Fusion, Regal 5, Revenge GLX, Fiji and many more.

Regenerating Perennial Ryegrass (RPR)

Researchers have developed a new variety of perennial ryegrass that is more durable and pest-resistant than the traditional varieties.

This is known as Regenerating Perennial Ryegrass (RPR). It has creeping stems (pseudo stolons) that enable the grass to regenerate without reseeding.

It’s also more resistant to pests than the regular varieties and can withstand a wider range of climatic conditions. Thus if someone doesn’t want to choose perennial ryegrass for their lawn just because of its reputation as high-maintenance, they can choose RPR.

Perennial Ryegrass Growing Zones

Perennial ryegrass flourishes well in the US Department of Agriculture growing zones 3 to 9.

It is popular as a lawn grass in the interior parts of the Pacific Northwest (mainly in western Oregon), western Washington, and lower parts of western British Columbia in Canada.

It’s also often used in the southern parts of the United States for overseeding dormant lawns, golf courses, and athletic fields.

At present, Pacific Northwest produces around 85% of the perennial ryegrass seed used in the United States and around 40% of the world supply.

When to Plant Perennial Ryegrass

The gardener can get two occasions when they can plant perennial ryegrass – once in late summer or early fall and second in the early spring.

The gardener should prepare the seedbed at least 6 months before their planned planting date to ensure any soil amendments they add will get time to react. Amendments should necessarily have an organic fertilizer with high nitrogen content.

Fall Planting: By far, early fall is the least risky period for planting since the days are still warm and suitable for germination, while nights begin to get colder.

The dropped temperatures of nighttime protect seedlings from diseases. Additionally, humidity during this period is also just suitable for faster germination. As such, the optimal climatic conditions for perennial ryegrass to germinate are when the daytime air temperature ranges from 60 to 75 degrees F and the soil temperatures are reduced to 50 to 65 degrees F.

If the grower waits till late fall, the risk increases since the first frost is around the corner. If seedlings have to undergo even a few days of frost, they can be killed. Therefore, it’s advisable to schedule things in such a way that the grass attains maturity when the first frost strikes the area.

Spring Planting: The next best opportunity to sow perennial ryegrass seed is spring. Although experts strongly recommend fall planting, growers may need spring planting to fill out bald spots or thinning lawns.

The best conditions for spring planting are when the temperatures become 60 degrees F and start to rise from there. This roughly corresponds to around 2-4 weeks after the last frost. However, if the temperatures increase too fast, the seedlings may get damaged or even killed.

Overseeding: While overseeding a cold-season turf with perennial ryegrass, it’s good to start planting by late September to early October for the Upstate regions and late October for the Midlands and coastal areas.

If the grower wants to overseed a warm-season turf, they should wait till the existing warm-season grass goes dormant before sowing perennial ryegrass seed. Beginning too early will expose the seeds and seedlings to temperatures that are warmer than required.

Moreover, it will cause the two varieties to compete for oxygen and nitrogen and perennial ryegrass will lose the competition. Therefore the gardener should wait till the existing warm-season lawn (such as Bermuda grass lawn) to go completely dormant.

Once the warm-season grass starts turning tan from green and its blades appear limp, the gardener can be sure that there is no threat to the seedlings of perennial ryegrass.

How to Plant Perennial Ryegrass

Soil Test

To start with, the gardener should test their soil. Perennial ryegrass prefers well-drained fertile soils. Phosphorus and potassium should be in a medium range.

It prefers a soil pH of 5 to 8. If the pH is below 5, the lawn cannot survive. In that case, the gardener should add lime to the soil. Mechanical incorporation of lime during seedbed preparation is important for best results.

Preparing the Soil

For preparing the soil, the gardener should rototill the upper 6 inches of soil. This will add oxygen to the soil and will break any compacted soil for improved water absorption and root growth.

They can even run an aerator attachment over the soil to provide a space for the seeds to establish their root system and for air and water to penetrate. Then they have to clean any rocks, sticks, and other debris.

Then they should till in organic matter such as compost, shredded yard waste (grass clippings, leaves, etc.), black topsoil, or an organic matter-based, slow-release fertilizer. They should also till in any other amendments according to the soil test results.

Now the gardener should level the ground using a rake. For larger areas, a lawn tractor with a rake attachment can be used.

Addition of Fertilizers

When perennial ryegrass seed is planted along with legumes, there is no need to add nitrogen to the soil. When not planted with legumes, perennial ryegrass will need around 4 pounds of nitrogen per 1,000 sq. feet.

The gardener can even use an all-purpose fertilizer and spread it uniformly over the entire area.

Watering

After fertilizer application, the gardener should water the lawn with a sprinkler to get the most coverage. They should make sure a good soaking, but should not water excessively so as to form mud and puddles.

Sowing Seed

Now the gardener should seed with a seed spreader to ensure uniform distribution and prevent bare spots. They will need around 10 lbs. of seed per 1,000 sq. feet of area.

Lawn experts recommend spreading a thin layer of straw on top of the sown seeds. This will hide the seed from birds, prevent soil from running off and keep the seed in place.

Watering Again

After sowing seed, the gardener should water the area again thoroughly, but not excessively to form mud or puddles. They should watch the soil carefully to see how fast the water is soaked into the soil so they can know when to stop.

The new perennial ryegrass lawn needs to be watered once a day until it starts germinating. This should be around 7 days after the plantation. Once germination starts, the gardener should water 4 times a week for a few weeks.

Mowing

Experts recommend not mowing the young grass while the lawn is still establishing until it’s quite tall and thick. When the young seedlings are allowed to grow tall, they develop a strong root system.

Once the lawn establishes itself well, the gardener should mow the grass to a height of 1 ½ to 2 ½ inches to keep the growth dense and look pleasant.

How to Take Care of Perennial Ryegrass Lawn

Perennial ryegrass does need maintenance to look its best. Although it’s resilient and usually can perform well on its own without much care, the gardener will have to do some things to make their lawn look healthy and keep it free from diseases.

Also, perennial ryegrass tends to clump due to its growth habit. Hence maintenance is also necessary to prevent it from looking tangled and messy.

Soil Test

Soil pH, particularly in the upper 2-inch surface, reduces as a perennial ryegrass lawn ages. Therefore regular soil tests to monitor soil pH should be conducted for established lawns.

If the test indicates that pH has fallen below 5.5 in the upper 2-inch surface, the gardener should add lime.

Watering

The gardener should water their established perennial ryegrass lawn to about 1 inch per week, including rainfall.

They should water thoroughly and deeply to promote deeper root growth. By September, they should gradually reduce watering.

Including supplemental rainfall, it’s fine if the lawn gets 1 inch of water every 10 to 14 days.

Mowing and Dethatching

Once the perennial ryegrass establishes, it can grow even up to a meter in height if not mown regularly. During the growing season, it should be kept at around 2 to 2.5 inches in height.

In the hot summer months, however, it’s essential to allow the grass to be taller as tall blades will keep the ground shaded which will create a moist and healthy environment and protect roots.

The growth of roots is directly dependent on the height at which this grass is mown.

Mowing perennial ryegrass to only one inch will highly reduce its ability to photosynthesize. This in turn will keep the roots much shallower and they can be easily damaged by extreme heat and drought.

How to Mow: It’s important to keep the direction of the mower changing with each pass while mowing the perennial ryegrass lawn.

This will make sure the blades will stand straight up and make it easier to get a clean cut with each pass. Also, the mower’s blades should be very sharp to protect the grass from getting torn as torn grass blades are susceptible to diseases.

Fertilizer Application

Perennial ryegrass requires fertilizer in much higher amounts than some other types of grasses. During its active growing period, it needs 4 pounds of nitrogen per 1,000 sq. feet. The gardener has to provide this from February through June, and again in October through December, as needed.

Perennial ryegrass, like most other grasses, needs potassium, phosphorus, and nitrogen in larger quantities than what naturally occurs in the soil.

The gardener should apply fertilizer around 4 to 8 weeks after germination. By far a fertilizer like 18-1-18 is best for an existing lawn. Gardeners should strictly avoid over-fertilization, as that can kill the grass.

Controlling Weed, Insects, and Diseases

Perennial ryegrass tends to suppress weeds due to its aggressive growth pattern and a habit of releasing chemicals into the soil that kill weeds.

So, weed shouldn’t be a big problem with a perennial ryegrass lawn.

However, any sick grass can die back and that part of the lawn can have weed infestation. The gardener should work quickly with a weed killer or hire a professional to deal with this problem.

One of the insects that affect perennial ryegrass commonly is billbugs. These are beetles that make holes near the stem and then feed on stems and leaves. They usually attack in June and because their damage can imitate browning due to heat and dry conditions, many gardeners make a wrong diagnosis of the problem. Using an organic lawn insecticide is a solution.

Perennial ryegrass can be affected by certain diseases too. It’s commonly affected by gray leaf spots which can be easily identified by leaf spots and blights that kill the lawn. The affected blades get twisted.

Other common diseases are pink patches, rust, and snow mold. Gardeners should apply fungicides to treat them.

Growing a perennial ryegrass lawn can be a joyful experience because the gardener will be rewarded with a beautiful lush green soft and dense lawn to please their eyes and feet.

With the development of improved varieties, it’s also possible now to grow perennial ryegrass virtually in any region. So, the gardeners that love lawns should give perennial ryegrass a try.