Calamagrostis ‘Karl Foerster’ may not win the prize as my favourite grass, but it certainly wins the prize for being the grass with the most distinct form, and, therefore, possibly the most useful of all ornamental grasses.
Its form is its greatest asset, and is unique in the world of perennials. As the slender arching purple-stained flowers ripen to golden seed heads, they stand bolt upright. And I mean really bolt upright, so that the superfine stems stand, for their entire length, in perfect parallel lines by which you could set a spirit level. Only at the very top of their flower heads do they occasionally, and only slightly, flare out. It lives in perfect defiance of that stupid saying ‘nature abhors a straight line’ (as do mountain ash trunks, or cooling lines in volcanic rock etc etc – don’t get me started).
And legible lines are incredibly emphatic and reassuring in amongst the too-often amorphous mass of a perennial planting.
Its foliage is, alas, without any distinction. It’s a grass that could easily be weeded out of a young planting, being mistaken for an invasive interloper from a nearby paddock. But once it’s in flower, it’s another matter. While only grown for its seed heads, the flowers, seen through the lens of a bonus, are exactly that. They’re tiny, and held apart like a cloud of minuscule purple gnats. At this stage, if it’s rained upon, it’ll arch over until its 1.8 – 2.1m stems are touching the ground – annoying if you have to brush past it, but otherwise not an issue, for an arching stem will always eventually fulfil its created purpose of exaggerated verticality.
As Calamagrostis ‘Karl Foerster’ flowers before Christmas, and therefore before it gets too dry in mediterranean-type climates, it performance is never compromised by a dry summer in the way a Miscanthus, which flowers in late sumner, often is. Indeed, it seems totally impervious to drought. Once the flowers have ripened, they’ll stand to attention throughout the hottest, driest summer, even if the foliage dries right out.
The variegated form, Calamagrostis ‘Overdam’ seems to be slightly shorter than ‘Karl Foerster’, so may be able to be used in slightly shorter planting. The variegation is quite good and clean, but isn’t very effective, given that the leaves are so narrow that the striping is only evident very close up. Furthermore, as you always want the flowers hovering up above surrounding planting, it’s likely the foliage will be blocked from view anyway.
What I’d love is a dwarfish form of this species, to perhaps 1m, which I could use to get the some effect of vertical lines in lower planting. In deliberately starved conditions in Germany, I’ve seen Calamagrostis ‘Karl Foerster’ limited to 1.2m. But given the choice of a smaller form, I wouldn’t swap it for what we have. The height is fabulously dramatic, and as a major contributor to my perennial plantings, I can’t ever imagine being without it.
Some Melbourne gardeners find that it never puts on enough flowers to justify its space in the garden. My plants (in Woodend – long cold winters) flower with outrageous density. In discussion with many growers, we’d wondered if there’s a requirement of a decent dormancy from a cold winter for good flowering, but others in Melbourne say that it performs brilliantly for them. What’s your experience?