Acorus
( ACK - or - us )
At-A-Glance InformationAcorus, also known as Sweet Flag or Calamus, is a genus of perennial plants that needs ample water and light shade in the hottest climates but can take full sun elsewhere. These plants are native to North America, Asia, and Europe. They can grow with their roots in either water or soil, and look like clumps or tufts of grass. Plants are handsome when used in borders, at edges of pools, in shallow water, or in containers that are kept wet, and are commonly planted in groups. They also do well as foundation plants, in rock gardens, as edgings or groundcovers, and can even do well in containers. Take care when planting these grasses in the landscape, as there is some evidence that roots and other plant parts may cause toxic reactions in pets.
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Acorus Species and Varietals
The genus Acorus is the type genus member of the plant family Acoraceae, and includes just three species, though there is a good deal of debate concerning the classification of the species in the genus. The common name 'Sweetgrass' refers to the sweet scent of leaves when they are crushed. The best growing zones for Acorus vary by species; for more information, see the descriptions below. To find your zone, click here: Zone Map.
Acorus calamus (Common Sweet Flag, Sway, Muskrat Root) Grows best in zones 2-10 and 14-24. Leaves form in an upright clump about 2 feet wide. Foliage is sweetly fragrant when bruised or crushed, and plants will die back in winter but return in springtime. 'Variegatus' is a popular variety that has white-bordered leaves. Grows from rhizome. |
Acorus gramineus (Japanese Sweet Flag, Grassy-Leaved Sweet Flag, Slender Sweet Flag)
Grows best in zones 3b-10 and 14-24; native to Japan, China, Korea, India, Thailand, Myanmar and the Philippines. Develops fans of semi-evergreen leaves rising from the ends of rhizomes. The specific epithet gramineus means grass in Latin. Varieties are listed and described below.
Grows best in zones 3b-10 and 14-24; native to Japan, China, Korea, India, Thailand, Myanmar and the Philippines. Develops fans of semi-evergreen leaves rising from the ends of rhizomes. The specific epithet gramineus means grass in Latin. Varieties are listed and described below.
Caring for Acorus
Plant Acorus in full sun to partial shade. The more sun these plants get, the lower the temperature needs to be; keep these plants out of direct sun during the warmest hours of the day to avoid heat and sun stress issues from developing. Plants typically should be spaced between 8 and 12 inches apart; these plants spread by rhizomes, so they will eventually fill in gaps in planting space. Plants prefer being installed near streams, bogs, or ponds, in woodlands, in rock gardens, or near foundations. Acorus grows well in many soil conditions, including boggy sites, and are perfect for rain gardens. Ensure that soil is well-draining but water-retentive. Acorus plants prefer soil to have a pH of between 5.5 and 6.5. Apply a thick layer of mulch around the base of new plantings to increase soil moisture retention, suppress weed growth, and maintain soil temperatures. Fertilization is not necessary for these plants; as long as local soils are rich in nutrients and a layer of compost is applied under mulch each year in springtime, these plants will grow well without any additional fertilizing. Prune off dead, damaged, diseased, or scorched leaves as necessary to improve the appearance of the plant. Every few years, check the growing area where Acorus is planted, and determine whether they need to be divided. After some time, Acorus will develop a bit of a central 'bald spot', and this is when they should be divided and replanted for both aesthetics and plant health.
Propagation
Acorus plants spread via underground rhizomatous roots, and the best way to propagate them is by dividing these roots after a few years' time. This process is necessary even if the goal is not to propagate the plants; dividing Acorus will ensure the health of plants as well. This type of propagation is relatively simple; you will need a clean shovel, mulch, fresh soil (any kind will do, though it does need to be well-draining), compost, and pots (these are only necessary if you will be saving divided plants for transporting elsewhere). Division is best done in spring or fall (after the plant has entered dormancy and been cut to the ground, but before it has begun its new spring growth), and needs to be done every four to five years regardless of whether you have the goal of propagating the plants for best performance. To propagate by division, follow these steps:
- Gather your materials. Using a shovel, dig up your existing plant. Start from the outside and work your way in to avoid damaging the rhizome roots. Once you have worked it up out of the ground, lay it out.
- Start to tease apart the roots with your gloved fingers. Once the roots are untangled, separate your plant into segments, ensuring that each one has at least one thick section.
- Prepare your pot(s) or new planting site(s) with amended, well-draining soil. You can either bring in new soil or simply amend your existing soil with compost to complete this task. Then, plant your divided tubers about an inch under the soil surface and water thoroughly.
- Apply a thick layer of mulch over the new planting to protect it from cold weather as it acclimates to its new home. Then, enjoy watching it sprout.
Problems and Pests
Acorus plants are generally pest and disease resistant, though they can infrequently have issues with the following:
- Slugs and Snails
- Aphids
- Mealybugs
- Scorching
Gallery
The little foliage tufts provided by Acorus contrast well in this bed against Japanese Blood Grass.
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Here, Acorus is planted amongst blue sedge and other low-growing plants.
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Use Sweet Flag in between stepping stones to soften hard edges.
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Acorus naturally grows near bodies of water, and appreciates wet feet.
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Some leaf margins on Acorus plants are wavy.
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This tropical walkway is edged with beds filled with Acorus, Calathea, Cordyline, and Bird's Nest Ferns.
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Videos
Learn about these grassy landscape plants.
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All about Acorus, or Sweet Flag, plants.
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Resources
The New Sunset Western Garden Book: The Ultimate Gardening Guide (2012) - Page 133, Acorus
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