January Perennial of the Month-Sweet flag

The typical perennial shade garden usually includes plenty of hostas, ferns, and heucheras. The typical perennial shade garden also looks pretty darn bland over the winter months…in fact, some look completely barren. Winter interest is so lacking in most gardens, especially shade gardens, so when a perennial does well in the shade AND provides winter interest, it becomes a rock star, even if it doesn’t have showy blooms. One such star is sweet flag or Acorus grass. (Acorus gramineous)

The common name “sweet flag” is named for the fragrant foliage when crushed or bruised. The plant originates in the wetlands of Asia, so if you have the double-whammy of soggy soil and deep shade, Acorus is an option that tolerates those conditions and brightens them up with the fun chartreuse to yellow foliage. Acorus spreads by rhizomes into thick, impenetrable masses but is easy to dig up, remove, or divide.

Rarely growing more than 12″ high, it’s a great companion for hostas and ferns with its grassy texture. It’s extremely low maintenance with no significant pests or disease issues. It will take sun, but protection from late afternoon sun is appreciated. Dry soils are not tolerated. If Acorus dries out, brown foliage results. It makes a great bog or rain garden plant and can be submerged just below the water’s surface of a shady water feature.

The most common cultivar found at local garden centers is Acorus gramineous ‘Ogon’ with its variegated foliage. (see top photo) ‘Variegatus’ is a taller cultivar growing to 30″.

What I love about this plant;

-Great for moist, problem areas, rain gardens, and water features.

-High pest and disease resistance.

-Semi-evergreen yellow foliage brightens and provides interest year-round. ‘Semi’ evergreen means it keeps its foliage most of the winter but produces new foliage each spring.

What’s not so great;

-Acorus is not considered invasive, but it will spread steadily by rhizomes when it’s happy. It’s easily divided and controlled.

-The foliage can turn brown or develop scorch in harsh winters or too dry conditions. Acorus can be trimmed down in late winter or early spring, like liriope February Perennial of the Month-Liriope (garden-lou.com), to tidy the plant up. 

Comments or questions? Email Garden-Lou at gardenloustl@gmail.com

Words and photos by Jo Batzer

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