advice for nursery and greenhouse growers

Growing Cool-season Grasses

If you understand cool-season grasses, you can manage them better.

Cool-season plants photosynthesize most efficiently when soil and air temperatures are mild and the soil is relatively moist. Under these conditions, they’re able to devote resources to abundant growth. In most temperate climates, this happens in spring and fall. For an overview of the differences between warm- and cool-season grasses, consult this chart.

Note that all species in the genus Carex are cool-season growers. But as sedges, we treat them a little differently. This section is about grasses (in Poaceae) that are cool-season plants.

What’s Great about Cool-Season Grasses?

Cool-season grasses offer unique advantages that can boost sales and brighten landscapes. Their foliage and blooms are peaking when warm-season plants are just getting started, so they offer a jumpstart on early spring sales. Then in fall, a second flush of growth looks great when warm-season plants are heading toward dormancy. They can make great fall and winter container plants, which also stretches sales into the off-season.

Cultural Requirements for Cools in Containers

As in a natural setting, cool-season grasses need more moisture during spring and fall when they are actively growing, and they do best with drier soil conditions when not actively growing. Festuca glauca cvs., Arrenatherum elatius ssp. bulbosum ‘Variegatum’, Helictotrichon sempervirens ‘Sapphire’, Leymus arenarius ‘Blue Dune’, and Calamagrostis x acutiflora cvs., such as ‘Karl Foerster’, are all sensitive to moisture and will suffer if over watered. In colder climates, it’s especially important to provide winter protection for these moisture sensitive plants and make sure they don’t stay wet.

Transplanting Cools

Transplanting should be done when the plant is actively growing. With cool-season grasses, this means a window from fall into spring. Our window at Hoffman Nursery is from September through April. Many cool-season species go partially or completely dormant in hot summers and should be transplanted during the fall-to-spring time frame only (e.g., Festuca glauca ‘Elijah Blue’, Arrenatherum elatius ssp. bulbosum ‘Variegatum’, Helictotrichon sempervirens ‘Sapphire’),

Some species are less heat sensitive and don’t go fully dormant (e.g., Calamagrostis x acutiflora cvs., Leymus arenarius ‘Blue Dune’). They have a wider transplant window. You’ll need to adjust based on conditions in your region and microclimate.

The more control you have over your growing environment (exhaust fans, shading, etc.), the more you can stretch the transplanting window. Avoid stressing the plant as it approaches its partial or full summer dormancy. It needs all the reserves it can muster to make it through the tough season.

Cool-Season Trouble Spots

Cool-season grasses, like most ornamental grasses, tend to have few pest problems. Even so, there are a few scenarios you’ll want to keep an eye on. Cool-season grasses put on lush, new growth just when aphids are most active. It’s important to scout regularly during these times and use Integrated Pest Management (IPM) methods to keep populations down. Aphid damage will stress the plants and make them more vulnerable to other problems.

Rust is the most likely candidate for disease problems on cool-season grasses. It’s not typically a big problem but should be addressed as soon as it’s detected. The cultural environment plays a critical role in prevention. Don’t over water the plants, control aphids, and make sure you have good air circulation. Fortunately, we don’t see much rust on the blue-foliaged, cool-season grasses. If rust occurs, you’re most likely to see it on Calamagrostis x acutiflora cvs, Arrenatherum elatius ssp. bulbosum ‘Variegatum’, and Deschampsia.

Planning for Cool Season - An Example

Although cool-season grasses vary in their growth habits and requirements, there are some general guidelines to help you get the timing down.

Festuca glauca ‘Elijah Blue’ (Blue Sheep’s Fescue) is a typical cool-season grass, so we’ll use it as an example. It is a fast grower during its active periods and will continue to grow through winter. In our unheated, poly cold frames, Blue Fescue will put on top growth even during the coldest months of January and February. In colder climates, minimally heated cold frames may be necessary to maintain growth during deep cold. Of course, you may need to adjust based on your region and growing conditions.

Spring Sales—Bring in Blue Fescue liners in January or February and pot them up for early spring sales. They’ll be filled out in 10 weeks or so with bright foliage and thick root masses. Depending on your region, you can time them to flower with peak demand. Growers in colder climates may need to adjust this timing or start them in marginally heated cold frames to have them ready faster. Several of the cool-season grasses we offer will work well with this timing, including Deschampsia cespitosa, Deschampsia flexuosa, and Arrenatherum elatius ssp. bulbosum ‘Variegatum’.

Fall & Winter Sales—Bring in Blue Fescue liners in October or November for a quick turnaround. They’ll boost late fall and winter sales. Their lush, bright foliage stands out in mixed containers. In mild climates, cool-season grasses are suited to fall landscape planting, and liner sizes are cost-effective for big jobs. You can also take extra liners, pot them up into gallons or larger, and overwinter in a cold frame. They’ll continue to grow throughout the winter and will be knockouts in the spring.