Whether you love a modern, minimalist aesthetic or a wild, naturalistic garden style, ornamental grasses are a fabulous, dynamic addition to many types of gardens. I'm personally so fond of them they're practically a given in my garden designs. However, with so many shapes, sizes and cultivars now available from garden centers, it can be a bit overwhelming to choose the right type for your space or know how best to pair them. Here's a quick rundown of things to consider when choosing and placing your grasses and tips for successful design.
When it comes to grasses, there are numerous options at varying heights from low mounding pompoms like Carex "The Beatles" to shin-grazing Nassella tennuissima (aka Stipa tennuissima) to towering Molinia "Bergfreund." Be mindful of the height details typically shown on the tag of each plant before purchasing – especially in spring before their seed heads have emerged giving them their fullest height.
Taller grass species will look best in the middle to back portions of a border while shorter options will do best towards the front. Try placing medium-height perennials or small shrubs in front of extra-tall grass varieties to help create balance and dimension.
Warm Season vs. Cool Season Grasses
Most ornamental grasses can be divided into two categories: warm season and cool season. In a nutshell, cool season grasses emerge early in spring while soil and air temperatures are still quite chilly (typically March) and warm season grasses break dormancy later on (usually May) once warm weather truly arrives. This can be an important distinction to make as the warm season varieties ( such as Pennisetum "Hameln" or Schizachyrium scoparium) will need until late spring to hit their stride and show much presence in the garden. That is not to say that they shouldn't be included in a planting design. Since late summer-into-fall is the peak season for their height and seed head displays one can strategically plant spring and early-summer blooming plantings in front of any warm season varieties to ensure fullness in the garden throughout the season. In smaller garden areas, or for containers, I find it's usually best to use cool season varieties (such as Festuca glauca or Calamagrostis "Karl Foerster") since there isn't much space for companion plantings.
One of the things I love most about ornamental grasses are the many nuances of color within the green family they display. Some lean more chartreuse and vibrant yellow (such as Hakonechloa macra "Aureola" or Carex "Everillo") while others gravitate towards silvery blue (such as Helictotrichon sempervirens). Little bluestem (Schizachyrium scoparium) has a rainbow-like effect up close, and interesting stripes and variegations can be seen in grasses such as Miscanthus “Zebrinus” or Carex "Evergold." Ornamental grasses are a lovely way to continue a garden's color theme by echoing the tones of other plants, or to add bright, textural punctuations throughout a bed.
Last but not least, it's very important to be mindful of spacing when planting ornamental grasses. Just as there are a myriad of heights in grass varieties, so are there variations in volume and spread. Some remain narrow and upright like Calamagrostis "Karl Foerster" while Miscanthus "Morning Light" or Muhlenbergia capillaris have ample spreads of 3' or more as well as a more fountain-like habit. Be sure to give companion plants plenty of space so they aren't shaded out or obscured by the grasses.