Sure, these reliable grasses have become nearly ubiquitous in public plantings, and some might say they are being over used; but there is no denying it, this feather reed grass is very hardy.
I know from experience 'Karl Foerster' will endure harsh Zone 2 conditions with good grace. I recommend it as a specimen plant, as a contrast to other perennials or as a graceful screen.
'Karl Foerster' is a cool season grass, beginning its growth in spring as soon as the temperature rises above freezing. By early summer they are flowering and growth slows. (In contrast, warm season grasses wait for the soil to warm before they begin to grow and they flower later.)
This perennial grass is touted as 'low maintenance', but what do we really need to know to get the best effect from this vertical beauty? Here are a few tips.
Clean up ...
Early growth means it's important to get into the garden and cut down old stems before active growth begins. A thorough clean up of last season's flowering rejuvenates the plant and ensures the clumps – which are among the first plants to green up – look their best.
'Karl Foerster' is a clump-forming grass. Its roots grow in a ball, reaching deep for moisture and nutrients. It is not invasive, but over a three-to-five year period it will spread to 24 inches or more. I've used this division method:
- Plan to divide this grass in spring when growth has begin, but days are still cool.
This will minimize stress.
- Dig clump out using a transplanting spade (its flat blade slices more vertically than a conventional shovel).
- Use a serrated garden knife to cut grass in good-sized sections.
- Pot up in sandy loam any sections that will not be replanted right away.
- When replanting, space plants to allow for future growth; if plants are to be grouped, consider your preference for an open or more dense growth effect.
No gardener should miss the poetry of 'Karl Foerster' moving in the lightest summer breeze. In my garden, these tall guardians provide vertical interest and continuity between terraced beds. They serve as a pleasing backdrop for many hardy companions, including rudbeckia, tall sedums, monarda and heliopsis.
Height: 90-120 cm
Foliage: bright green
Flowering: June through July
Hardiness zone: Zone 3 with reports of up to Zone 2
Conditions: full sun, moist to wet fertile soil;
This grass will tolerate dry conditions, although regular watering, especially during the hottest periods, will result in greater height and better flowering.
Pronunciation ... Calamagrostis (kal-ah-mah-GROS-tis) actiflora (ah-KYOO-tih-flor-ah)