How to Plant & Grow Variegated Sweet Flag (Acorus calamus)

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Variegated sweet flag leaves by a pond
Variegated sweet flag has striking leaves with a sword-like appearance, and can grow up to 5 feet tall! Krzysztof Ziarnek, Kenraiz, CC BY-SA 4.0, via Wikimedia Commons

Acorus calamus is a semi-aquatic flowering plant. It is commonly referred to by many other names, such as sweet flag, grass myrtle, muskrat root, and pine sedge. This herb belongs to the Acoraceae family, which is unique in having a sole genus, Acorus. There are just two taxonomically accepted species under this genus, A. calamus and A. gramineus (Japanese sweet flag). It is likely that the Western varieties have a cultivated origin, as they are genetically sterile. Native to the temperate regions of South Asia and Europe, sweet flag is now naturalized in many parts of the world and is widely cultivated.

One of the most popular cultivars of this species is Acorus calamus ‘Variegatus’ or variegated sweet flag. This plant has striking green leaves that gracefully arch and can grow to a length of 5 feet (152 cm)! Each leaf is marked with a cream-colored longitudinally-oriented stripe. The leaves are narrow and tapered towards their ends, making them have a sword-like appearance. Interestingly, these can display a light tinge of pink when exposed to cold weather conditions. Flowers are also produced, but are inconspicuous compared to the striking foliage. Though rare, these can develop into small red berries when conditions are optimal.

Facts, Benefits & Uses of Variegated Sweet Flag

Acorus calamus is a perfect grass-like plant for your water feature’s marginal or edge sections. Its roots and leaves are well-adjusted to sitting in shallow water or consistently wet soil as it is normally found in wetlands. It tends to occur along the edges of ponds, marshes, rivers, and lakes that experience fluctuating water levels throughout the year, making it somewhat tolerant of seasonal flooding. Though it is not considered an aggressive grower, this species has the potential to be competitive with other wetland plants.

A. calamus is not just popular for its ornamental uses – it also has many practical benefits. The dense foliage may serve as a habitat or form of protection for young amphibians and insects. It serves as the host plant for some tiny beetles (e.g., Plateumaris shoemakeri, Donacia caerulia) which feed on its sweet-tasting foliage. 

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Variegated Sweet Flag Fact Sheet:
Aquatic perennial
USDA 4 – 11; UK Zone 3
Full sun to partial shade
May to July
1 meter (3 feet)
Up to 9 inches (22 cm) in water
pH 5.5 – 7.5


Variegated Sweet Flag Growth, Hardiness & Climate

Variegated sweet flag in the ground
Variegated sweet flag is less likely to produce flowers if planted outside of a water feature. Krzysztof Ziarnek, Kenraiz, CC BY-SA 4.0, via Wikimedia Commons

A. calamus spreads quite slowly in comparison to other grass-like plants. Over time, a single plant can spread to a width of one meter and can serve as effective ground cover. Though this species can withstand partial shade or dappled sunlight, it will thrive best under full sun exposure. If summers in your area are particularly hot, the leaves would benefit from some shade. This would also help prevent the soil from drying out completely.

A marginal position with a few inches of slow-moving or standing water is best for cultivating sweet flag. It is less likely to produce flowers if reared outside of a water feature, though the tendency to flower or fruit can vary depending on the source of your variety (e.g. those with Asian ancestry are more likely to produce fruit, though sparingly). Rhizomes allow colonies of the plant to quickly become established in moist or wet soil. Hardy to USDA zones 4 – 11, it can withstand winter temperatures that dip to -25˚C.

How to Plant Variegated Sweet Flag

Acorus calamus 'Variegatus' in a pot
Once variegated sweet flag is mature enough, it should be planted in its own pot so that it has enough room for its roots to spread. Yercaud-elango, CC BY-SA 4.0, via Wikimedia Commons

The most effective way to plant and propagate A. calamus is with the use of its rhizomes. Store-bought seeds may also be used, although cold storage may be required prior to sowing them onto moist soil.

If you intend to propagate your plant via rhizome division, make sure to harvest the rhizomes in early spring, just before any new growths have formed. You may also opt to do so in late fall, when any new growths have grown large or firm enough. Don’t divide your plant unless it is at least 2 – 4 years of age as the root systems have to be large enough to increase chances of survival. Plant the small divisions in pots with consistently moist soil. Sandy, loamy, or clay soil should be suitable for use as long as the particles are prevented from drying out completely.

A tray set-up with shallow water (about 3 cm) would work best for seed germination. Place this in a cold frame or greenhouse to ensure that the seedlings are protected from the elements. Once they are large enough, they should individually be transplanted into their own pots or be replanted so that each has enough space for its spreading roots. Mature plants (from seed or rhizome division) may be outplanted in spring or summer. You can either establish mature Acorus directly in soil along your pond edge or in pots placed in your pond’s margins. Pots can be moved further into your pond as the leaves lengthen.

How to Care for Variegated Sweet Flag

Variegated sweet flag in a botanical garden
You can cut the leaves of variegated sweet flag with clean gardening shears if they start to look untidy. Krzysztof Ziarnek, Kenraiz, CC BY-SA 4.0, via Wikimedia Commons

Variegated sweet flag is tolerant of many conditions as long as its soil is kept wet or moist. If you have colonies of this plant in your pond’s margins or edges, make sure that summer water levels don’t drop drastically enough to reduce the moisture content of the soil. Those located along the edge may need supplemental watering sessions during the hottest days of the year.

To ensure that your plant is able to produce a profusion of healthy leaves, you may provide it with a slow-release fertilizer. Make sure to use one that won’t introduce toxins or excessively high nutrient levels to your pond. It is likely that pond water itself will also be beneficial and will encourage flowering. Even a rapidly growing sweet flag colony will rarely require pruning, but you may cut the leaves with some clean gardening shears if they begin to look untidy. Every 3 – 4 years, repot or divide your Acorus colonies to prevent the roots from becoming too crowded.

How to Winter Variegated Sweet Flag

If located outside of USDA hardiness zones 4 – 11, you may need to bring your plant indoors for winter. The foliage of Acorus calamus are not hardy to frosty conditions and will naturally die back. The rootstock and rhizomes enter a resting phase and should be protected with a layer of mulch if left outdoors. Pots that are brought indoors can be treated as houseplants over the winter and should be placed in an area with heating (or with indoor temperatures above 0˚C). The rootball of the plant should still be kept fairly moist throughout this time. Once the final frosts have thawed, you can move your potted sweet flag outdoors or remove the mulch covering those that were left outside through winter.

Is Variegated Sweet Flag Invasive or Toxic?

In spite of its vegetative means of spreading, variegated sweet flag is not an aggressive grower. It is generally not known for being invasive, even in areas where conditions are optimized for its growth. The cultivars of A. calamus tend to spread even more slowly, making them ideal ground cover plants that won’t require much maintenance.

At high doses or when consumed in large quantities, A. calamus may cause some undesirable reactions. There are still safety concerns associated with the consumption of the plant, despite studies on its edibility and medicinal benefits. While small doses of its roots can be highly effective against a wide variety of disorders, large doses may cause nausea and irritate the digestive tract. Infusions that include sweet flag roots can even cause abortion. Ingestion of large portions of the roots may bring about undesirable hallucinogenic effects.

Is Variegated Sweet Flag Edible? Will Fish & Animals Eat it?

In spite of this species’ toxic potential, its roots are generally regarded as edible. It’s said that they taste simultaneously sweet and spicy and they are likened to ginger. The roots are even candied by parboiling and then covering them in sugar syrup. A small amount of this treat may aid in settling a chaotic stomach! Calamus roots, which were exploited in India, reportedly have both calming and stimulating effects. This fusion of contrasting effects is associated with the plant’s potential for inducing a grounding energy – one that both vitalizes and clears the mind.

One would wonder if these fascinating benefits are extended to animals that dare to consume sweet flag roots. The leaves are more commonly feasted upon by a variety of insects, most especially beetles. Fish may occasionally nibble on any young exposed roots but it is unlikely that they’ll consume amounts that are large enough to hurt them. In fact, supplementing fish feeds with a small concentration of sweet flag oil (1%) has been shown to positively affect the growth performance of common carp.

Where to Buy Variegated Sweet Flag & Seeds? (UK & US)

Acorus calamus ‘Variegatus’ can be purchased from plant nurseries and aquascaping shops in most temperate zones. Online pond supplies stores and garden shops are likely to carry potted sweet flag in a variety of sizes. If unable to locate this specific cultivar in your area, you may also be interested in Acorus gramineus, which has similarly variegated cultivars.


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Angeline L
About the author

Angeline L

I'm a passionate researcher and scuba diver with a keen interest in garden plants, marine life, and freshwater ecology. I think there’s nothing better than a day spent writing in nature. I have an academic and professional background in sustainable aquaculture, so I advocate for the responsible production of commercial fish, macroinvertebrates, and aquatic plants.

Read more about Pond Informer.

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