Growing Ornamental Grasses

Ornamental grasses are something you can add to your garden that can be used in lots of different places. This article goes through everything you need to know about growing them.

Grass is something you'd normally think about for your lawn, but ornamental grasses are quite different. They come in a wide range of heights, shapes, colours and foliage. Some plants that aren't technically grasses/Poaceae are often referred to as ornamental grasses because they behave the same way.

When to plant ornamental grasses

The time of the year for planting grasses is similar to many perennials, where spring is a good time to plant them so they have time to settle before the colder weather in autumn. If you miss this, you can also plant them in mid-autumn but they may have a harder job settling.

Most will need things like watering during dry periods for the first few years, but each will favour certain conditions, so when you plant them, you should see what soil, light and water is best suited. Once they've been there for a while, they're fairly hardy so you don't need to worry too much and they're fairly resistant to disease/pests.

A grass will do most of its growing and have denser foliage/seeds at its top during particular seasons/temperatures, so this will affect how the grass looks throughout the year. You might use a selection of grasses in a garden suited for both hotter and colder temperatures.

Grasses suited for hotter seasons will come out in late spring and grow through the summer with foliage/seeds at their tops lasting to autumn. Some will then stop growing, thin out and lose their foliage/seeds as it gets colder, some may continue to grow throughout colder weather but with a thinner and dryer appearance.

Grasses suited for colder seasons will come out earlier in spring and grow throughout spring, with foliage/seeds at their tops in early summer. As it gets hotter in the summer they thin out, lose their seeds/foliage and stop growing. They then come back when the heat has gone by in Autumn. Many evergreen grasses are suited for these colder seasons.

Varieties of ornamental grasses

Many ornamental grasses are non-invasive, where you can plant them anywhere in your garden and you'd get a bunch that would form a particular shape. But you can also get some that are quite invasive, and will spread across your garden aggressively.

Make sure you know which type you're planting, and if planting an invasive one you use some sort of container to prevent it spreading; keeping in mind the top should be at/above the top of the soil and roots may grow through any holes in the container.

There are a few general shapes common for most ornamental grasses. They might grow vertically upwards and not take up much space on the ground. They might grow upwards and then curve/bend outwards or spread outwards gradually and take up more space on the ground. Or they might just grow in all different directions. Grasses that grow outwards may have a more informal look and require more maintenance than more formal looking vertical grasses.

They can come in a range of colours, the density of their foliage can vary a lot, and they might look very different at different times of the year or have a similar look all year round. They might have seeds for example at certain parts of the year. The height of ornamental grasses can also vary a lot depending on their variety from less than a foot to as high as 11 or 12 feet.

Where to plant ornamental grasses

As ornamental grasses can vary a lot in a be difficult to work out where to put them in the garden. We'll give some examples of where you might use them.

Large grasses

Larger grasses can be useful for things like filling large spaces, or for example to separate different areas of a garden instead of a hedge, where certain grasses can have dense foliage and may be cheaper than comparable shrubs. Larger grasses may be more affected by wind than smaller ones as they're taller, so may be best in less windy areas.

Miscanthus grass is a grass that grows very tall and curves towards the top, so it could be used to fill/add some height to an area or to separate different garden areas.

Medium grasses

Medium-sized grasses can be useful to fill spaces such as beds, where they can work well alongside perennials for example. You can use a combination of grasses in groups, maybe vertical thin ones alongside wider denser ones to add variety/depth.

Switchgrass is a grass that grows quite vertically with foliage that isn't too dense, so could be used to fill a small space or frame something behind it. Vertical grasses can have a fairly formal look if you want to display one by itself in a container.

Fountain grass is a grass that grows fairly vertically but curves sideways towards the top. It has denser foliage than more vertical grasses and takes up more space on the ground, so can be used to fill slightly larger spaces. Curved grasses can have a more informal look than vertical ones.

Blue oat grass is a grass that grows in all different directions with parts growing vertically, so it can get fairly tall.

Small grasses

Smaller grasses can be useful to add variety to things like rock gardens, make up the edges of beds/paths and fill smaller spaces, where they can give definition throughout the year.

Japanese forest grass is a grass that grows in all different directions.

Sedge (also called carex) is an example of a plant that isn't technically a grass but behaves a lot like a small-sized grass, where it grows fairly vertically but curves sideways quite a bit.

Cutting back ornamental grasses

If you need to cut back a grass to avoid it getting too large, try to do this around the end of winter/start of spring. Be careful not to cut yourself on any tools you use or on the grass itself, it can be quite sharp.

Grasses suited for warmer seasons can grow quite fast through the summer, so you can cut them back quite far to fairly near the bottom. Grasses suited for colder seasons grow slower so you need to be more careful. If you cut them back too far, they can die or take several years to recover. Try not to cut off more than around a half.