Karl foerster feather reed grass


Im trying to creat a big clump of Karl Foerster feather reed grass in my garden bed, right in front of an old overgrown globe arborvitae, and besides a smooth hydrangea bush which will mature to about 5 by 5 feet.
I have 5 feather reed plants in total, and the space for them is about 5-6 feet irregular shaped. How should I space and arrange the grasses so that they look like one big clump instead of a few individual ones with gaps in between? I currently put 4 there in a drifted way but wonder if it would get too crowded.
I have other perennials in front of the grasses so I don’t want the clump to be too big, but big enough to be about the same size as the hydrangea and cover a good portion of the giant globe cedar. I feel maybe 3 is enough but I’m not sure. They are not in their mature size yet so it’s hard to see how big they will grow. Also, how do I arrange them to creat an oval or horizontal tear-drop shaped clump instead of a round or straight line?


It would have been helpful to have a photo of the garden area.  From your description, I believe that the globe cedar is likely around 1.5 x 1.5 metres (5 x 5 feet), the same size as the hydrangea bush will be when it’s mature.

Karl Foerster Feather Reed Grass (Calamagrostis acutiflora) generally grow to a height of 1.2–1.8 metres (4-6 feet), with a spread of 0.6–0.9 metres (2-3 feet).  So the final height of the grass will be about the same as the hydrangea.  I’m not sure, though, how much of the globe cedar the grass will “cover”.

Can you obtain one more plant?  This might give you the best chance of ending up with a single teardrop-shaped clump.  For example, I’d suggest planting the grass in a roughly teardrop-shaped pattern, 3 plants deep in one spot (the rounded end of the teardrop), then next to that, 2 plants, and finally the last plant at the “top” (pointed end of the teardrop).  Plant each clump around 0.5 metres (1.5 feet) from its neighbour – just a little closer than the usual mature “spread” of each plant.  This way, the clumps will grow towards each other and should not crowd one another out – this should also minimize the gap between the plants.  You can prune the plants into the shape you want for them.   Once the plants are in place and have been growing for awhile, you should be able to determine if the shape of the clump is what you were looking for.  At that time, you can move the plants and/or purchase additional ones to “correct” the look.  If you prefer an oval, trace an oval shape on the ground and space the plants accordingly – you likely would need at least 6 plants for this shape, too.

Most on-line photos of this grass show it growing in discrete clumps, with a clear distinction between individual plants.  However, some show large clumps made up of several plants that manage to look like a single plant. For example, the Missouri Botanical Garden Calamagrostis × acutiflora‘Karl Foerster’ has a great photo of a few plants arranged in a single row – although we can see that there are individual clumps, the overall effect is that the plants are close enough together (but not overcrowded) such that they look like a single plant.  Consider “googling” the grass to look for photos that might give you some ideas.

All the best with your garden design!


May 30 2022