Blue Oat Grass Plant Profile

Blue oat grass (Helictotrichon sempervirens) up close

Drew Avery / Wikimedia Commons / CC BY 2.0

Standing out among ornamental grasses for its blue-green foliage, the blue oat grass plant offers a unique aesthetic and easy maintenance for gardens and landscaping. This perennial grass plant is evergreen or semi-evergreen in regions with mild to moderate winter seasons, providing visual interest even after the growing season has ended.

A clumping plant, blue oat grass has been described as dramatic and yet well-behaved. It produces abundant shoots of blue-green grass stalks during the spring, but rarely self-seeds and doesn’t have the reputation of taking over in a garden. In summer, spikelets of tiny blue-green flowers bearing seeds appear at the top of the tall grass stalks in groups called panicles. These gradually turn to wispy brown plumage as fall approaches—imitating the appearance of oats. 

Blue oat grass in garden
Mark Turner / Getty Images
Botanical Name Helictotrichon sempervirens
Common Name Blue oat grass
Plant Type Perennial
Mature Size 2 to 3 feet tall and 2 to 3 feet wide
Sun Exposure Full sun
Soil Type Dry and well-drained
Soil pH Slightly acidic to neutral
Bloom Time Summer
Flower Color Blue
Hardiness Zones 4 to 9
Native Area Europe

How to Grow Blue Oat Grass

Blue oat grass is a great option for planting in your garden, since it is not invasive and requires little regular maintenance to maintain its beautiful appearance. These plants require just average to dry soil moisture conditions, rarely self-seed, and just require occasional cleaning of dead growth by hand or with a rake.

The plant is also very tolerant of environmental salt, pollution, and urban environments—making it adaptable for use in all types of landscaping. However, it does not prefer very hot or humid summer seasons, since it is a cool season grass.

Pests and disease are generally not a problem for blue oat grass plants, though they can develop rust in overly humid conditions. Additionally, if you fail to space these plants far enough from each other (at least three feet is recommended), they may suffer from a lack of air flow and be subject to tar spot.

Plant a single blue oat grass plant for variety in your garden, or a whole row as a landscape border, beautiful accent to your sidewalk or driveway, or as part of a xeriscaping plan. 

Light

Blue oat grass thrives with full sun conditions. It’s capable of growing in areas with part sun and part shade, but it may become leggy under these conditions. Ideally, look for a location that receives at least six hours of direct sunlight per day for this plant.

Soil

Ensure that you plant blue oat grass in well-draining soil. Too much retained water leads to rotting of the roots or crown. For this reason, heavy clay-like soils are not ideal.

Blue oat grass does best with an alkaline to neutral pH level in soil; a pH of 6.5 to 7.5 is considered best. These plants are also tolerant of environmental salt in the soil and are not adversely affected. 

Water

Generally speaking, you won’t need to water blue oat grass often or much once established. This plant typically thrives just on the rainfall it receives. Keep in mind that the soil moisture should be average to dry at all times, so don’t overwater these plants or you could cause rotting of the root or crown.

Blue oat grass is considered drought-tolerant, though it should be noted that periods of drought can induce a semi-dormant state in the plant. 

Temperature and Humidity

Blue oat grass prefers a dry and cool climate. The distinctive blue hue that this plant is known for is most prominent in dry climates. In cool weather, these plants are semi-evergreen and retain their blue-green foliage through the majority of the winter—if conditions are not too harsh. In hot weather climates, summer temperatures may become too warm for the preference of blue oat grass, and the plant may not flower as expected. 

Fertilizer

Hardy and healthy, blue oat grass doesn’t generally need supplemental fertilizer. When deciding whether or not your plant needs fertilizer, consider the health and color of the plant’s foliage.

If you determine that the plant is faring poorly in the soil conditions, you could opt for an organic fertilizer that will be easily utilized by the plant—like compost, leaf mold, etc. If you decide to go with a conventional fertilizer, a 10-10-10 formula is typically recommended for ornamental grasses. Anything with too much nitrogen can cause the plant to overproduce foliage and underproduce flowers, leading to a leggy, poorly flowering specimen.

Propagating Blue Oat Grass

Blue oat grass can be propagated by seed or division, but it should be noted that many gardeners find this plant to have a low rate of seed germination. The most popular way to propagate an ornamental grass like this one is by division; usually this is done every three or four years in the spring before the growing season commences.

To propagate blue oat grass, do the following:

  1. Dig around the perimeter of the plant using a shovel or spade. Take the time to dig deep enough that you free the entire root ball, remembering that ornamental grasses can have a substantial root system.
  2. Using the shovel or spade, cut the plant from the crown into two or three pieces of roughly equal size. Depending on how dense the root ball is, it might take lots of muscle, a sharp tool, or a chainsaw to complete the task.
  3. Replace one section of the divided plant back into the original hole. The additional pieces can be planted in a new garden location or in a container. 

Varieties of Blue Oat Grass

  • Helictotrichon sempervirens ‘Saphirsprudel’: This variety is very similar in appearance to conventional blue oat grass. However, this cultivar has been developed to have a significantly more pronounced blue hue to its foliage, with slightly thicker grass shoots, and an increased tolerance for heat and humidity. 
Helictotrichon sempervirens sapphire blue oat grass
'Sapphire' cultivar of blue oat grass. skymoon13 / Getty Images

Toxicity of Blue Oat Grass

For pet owners and animal-lovers, you’ll be happy to know that blue oat grass is not toxic. It’s also non-toxic to humans, though not considered an edible plant. Despite the fact that this plant is not poisonous, it has proven to be relatively deer-resistant, making it a good chance if these animals frequently are looking to graze your garden.

Pruning

Blue oat grass is famously low maintenance, but it’s beneficial to occasionally clear dead growth from each plant. You can easily pull out dead, brown stalks of grass by hand or use a garden rake to comb through the clump and remove old growth.

When the plant goes into dormancy each winter, you can trim foliage down—leaving several inches above the crown of the plant. However, in some climates with mild winters, blue oat grass retains its characteristic blue-green color throughout the winter season. In such cases, it’s not necessary to cut back any growth and you can enjoy the foliage of the plant throughout the season. 

Being Grown in Containers

Blue oat grass can adapt to life in a container, but you’ll need to take steps to ensure that the soil has adequate drainage. In addition, some plants grown in containers lack the necessary nutrients for sustained healthy growth of foliage in flowers. While blue oat grass plants in the ground rarely need fertilizer, you may need to supplement soil nutrients when this plant is located in a container.