PLANT OF THE WEEK #8: Calamagrostis 'Karl Foerster'

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?

Discussion

  1. KF is all of these things. I’ve always found it pretty reliable. Well, that is, unless the client has dogs. Dogs love to chow down on this plant like I don’t know what. Even dogs that haven’t shown any proclivity for eating plants in a garden make a beeline for it the second it comes on site.

    It’s bizarre, frustrating and intriguing all in the same measure. If a client has dogs I can’t use it.

    1. Oh … location…. north east vic… Mansfield way

    2. Hi James. I have two dogs and neither have ever shown any interest in the KF. Mine by the way only reach 1m – maybe because they are in a heavy soil.

    3. This is fascinating. What on earth is it about it that would attract a dog? Must find out if my clients have had any trouble

  2. I agree with every thing you have said about Karl Foerster – it’s a truely beautiful plant in every way. Mine rarely get over the 1m mark but they are pretty shaded so perhaps that’s the way to ‘miniaturise’ them.

    1. Root competition would do it too, no doubt

  3. It does quite ok for me in Melbourne. It does like a wet and cold winter. And doesn’t like being dug around in the root zone. Mine flowers , although it flowers more profusely in the country though.

    1. Where in the country do you mean, Wei?

  4. This plant is a giver. I’ve got it growing in half a dozen different gardens mainly to enjoy but also to sus out how it delivers with some very different soil profiles…. such as shaley crud with no water to delicious, sensual realms of loam and some good inbetweeners …. all gardens that it’s growing in experience prolonged frosts and long winters…(so interesting re the cold thing you mentioned) .. blazing hot brutal summers… awesome Springs and Autumns…. the plants growing in shaley crud have no irrigation with the others having little to moderate amounts of water…. all with a decent amount of mulch…. sings in all these scenarios but differently…… Great dancer in the wind wether blowing the trampoline across the paddock or being delicately caressed… makes me smile… catches the light like the two elements are in love with each other… makes me go all gushy….to know what will come from such a common looking clump makes it exciting… good in squeeze…. tall, commanding, contrasting and graceful in good soil… same in the crud but just leaner and smaller…. skeletons left behind after Autumn keep the song going stronger… there’s plenty in this plant that fills the soul and has a habit of grabbing your attention while joining the dots… sitting up front or in the back stage…. but not my favourite! Ha oh and divides up easy as pie… cheers

    1. Oh … location…. north east vic… Mansfield way

    2. ‘Commanding’ is a great word for it. And so good to hear of comparative responses in different soil profiles. Clearly a winner in all. Not many plants could boast of that

  5. Is KF a fire hazard? Would you worry about patch of KF in your garden if you are concerned about summer fires, or does it keep enough green that it’s safe?

    1. Hi Ed, Mine stay green through summer but I do give them a little water over summer. This year of course they have looked wonderful – enjoying the unusual late summer rain. I am about 300km east of Melbourne in a rain shadow so usually pretty dry.

    2. I think mine would burn, Ed, but by mid summer there’s simply no biomass. It’d burn quicker than a piece of newspaper

  6. We have KF growing on the edge of a bank in heavy clay and strong winds in the Adelaide Hills. This is its first year and hasn’t skipped a beat. Watered in it at planting time in October and hasn’t been watered since except for the occasional testing of the fire system.
    Sadly the local kangaroos decided last weekend that it was a delicious snack. We could see them from our bedroom window. Sent my husband outside to scare them off. He clapped his hands, shouted a bit, banged a stormwater pipe on the ground, but they weren’t budging. They just stared back nonchalantly chewing on the flowers. There were enormous so didn’t want to get too close. Turns out they HATE sprinklers so when I turned on the fire system, they hopped away and haven’t been back. Fingers crossed!!

    1. I love this story. How weird that animals which must constantly be standing around in rain are deterred by a sprinter. Now that you’ve mentioned it, I’ve noticed some grazing be kangas here and there, but it always seems to be of the green foliage, and mostly on plants that haven’t flowered (if I’ve divided them up to small to do so)

  7. The first year I planted them 2 years ago here in my Dandenongs Ranges garden they too were nibbled at by something (no idea what but we do have wallabies your rarely see and deer also rarely seen). I planted Nepeta in front of the border and the problem was solved! I love this grass, here it isn’t growing as tall or wide (as Michael’s do) but I love using it as an accent plant in my perennial border.

  8. Thought I would give this plant a go – didn’t understand why it was so slow until I saw the dog eating it – yes she really likes it. Add cage for KF on to-do list! I hope when it gets a bit of size she will leave it alone.

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