Siergras 'Karl Foerster'

Calamagrostis × acutiflora 'Karl Foerster'

Engels: Feather Reed Grass

ornamental grassPoaceae

Siergras 'Karl Foerster' (Calamagrostis × acutiflora 'Karl Foerster') is a ornamental grass from the Poaceae family that grows up to 170cm tall. This plant thrives in full sun to partial shade and requires low maintenance. Blooms in autumn and summer with beige flowers and attracts birds.

Hoogte

120–170 cm

Breedte

50–70 cm

Zonligging

full sun, partial shade

Waterbehoefte

moderate

Grondsoort

loam, clay soil, sandy soil

Onderhoud

low maintenance

Bloeitijd

autumn, summer

Bloemkleuren

beige

Ecologische waarde

Trekt vogels aan

Verzorgingskalender

Taak	Jan	Feb	Mrt	Apr	Mei	Jun	Jul	Aug	Sep	Okt	Nov	Dec
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Care tips

Planting

Feather reed grass thrives in full sun but tolerates partial shade, though flowering may be less prolific in shadier spots. It adapts to a wide range of soil types—loam, clay, or sandy—making it one of the more forgiving ornamental grasses. The key is reasonable drainage; while it copes with heavier clay better than many grasses, it won't tolerate waterlogged ground. Plant container-grown specimens in March, April, September, or October. Spring planting gives the grass a full growing season to establish, while autumn planting works well if the soil isn't too wet or cold. Dig a hole roughly twice the width of the root ball and the same depth. Break up any compacted soil at the base and sides of the hole to encourage roots to spread. If your soil is very heavy clay, work in some grit or coarse sand to improve drainage. On sandy soils, incorporate garden compost or well-rotted manure to boost moisture retention. Position the plant so the crown sits at the same level it was in the pot—planting too deep can lead to rot. Space plants 60 cm apart; 'Karl Foerster' will reach 50–70 cm wide, and adequate spacing ensures good air circulation and allows each clump to develop its upright, architectural form. Backfill with the excavated soil, firm gently with your heel, and water thoroughly to settle the roots. Apply a 5 cm layer of mulch around the base, keeping it clear of the crown itself, to suppress weeds and conserve moisture while the grass establishes.

Pruning

Feather reed grass requires very little pruning, but an annual cut-back is essential to keep it looking tidy and to make way for fresh growth. The best time to prune is March, just before new shoots emerge in spring. Many gardeners leave the dried foliage and seed heads standing over winter—they provide structure, movement, and interest in the dormant garden, and the bleached stems look striking after frost or snow. In early to mid-March, cut the entire clump down to about 10–15 cm above ground level. Use sharp bypass secateurs for smaller clumps or a pair of hedging shears for larger, established plants. Some gardeners find it easier to gather the stems together with string or a bungee cord before cutting, which makes clearing up simpler. The old foliage can be composted if it's disease-free, or left as mulch around other plants. Avoid cutting back in autumn. The dead foliage protects the crown from winter wet and cold, and many beneficial insects overwinter in the hollow stems. If you find the dried grass unsightly or it has collapsed in wet weather, you can tidy it lightly, but a full cut-back should wait until spring. 'Karl Foerster' is a sterile cultivar, so it won't self-seed, and there's no need to deadhead for tidiness or to prevent spread. Simply enjoy the feathery beige plumes through summer and autumn, then cut everything back once in March.

Maintenance

Feather reed grass is low-maintenance once established. Water regularly during the first growing season to help roots settle in, especially in dry spells. After that, it has moderate water needs and tolerates short periods of drought, though growth and flowering are better with consistent moisture during summer. In very dry summers, water deeply every couple of weeks rather than little and often. Avoid overwatering; this grass dislikes sitting in wet soil, particularly in winter. Feed once a year in April with a balanced general-purpose fertiliser or a slow-release granular feed scattered around the base of the clump. A light dressing of garden compost or well-rotted manure in spring also works well. Avoid high-nitrogen feeds, which can cause lush, floppy growth that's prone to flopping. 'Karl Foerster' is naturally upright and self-supporting, but overfed plants may lose this tidy habit. This grass is fully hardy to zone 4a, so overwintering in temperate Europe is straightforward. Leave the foliage standing until March; it needs no protection. Mulch lightly around the base in autumn if you wish, but keep mulch away from the crown to prevent rot. Pests and diseases are rare. Occasionally, rust (orange or brown pustules on leaves) can appear in humid conditions, but it's seldom serious—remove affected foliage and ensure good air circulation. Slugs and snails generally ignore the tough foliage. Clumps remain vigorous for years without division, though you can lift and divide in spring if they become congested or you want more plants.