Reed Mannagrass is in the Poaceae family, which includes true grasses and bamboos, and the mannagrass (Glyceria) genus. Its common names include great mannagrass, reed mannagrass, reed sweetgrass, and greater sweetgrass. This species thrives in open, wet habitats such as marshes and riverbanks. It is a perennial species, meaning its roots become established and it generally has a long lifespan. It originates in north temperate zones of Europe (including the UK) and Western Asia, and is considered a highly invasive plant outside of this range, particularly in North America.
Glyceria maxima is a tall grass with a stately, upright appearance. During the growing season it takes on an overall vivid green color. Younger individuals sometimes take on an attractive reddish appearance, especially along the sheaths and stems. The sheaths also have a distinctive cross-hatched pattern that help to identify this plant. The leaf blades are long (up to 60 cm), narrow, and abruptly pointed. The inflorescence (flower) is often considered the most attractive part of the plant and appear as large (up to 45 cm) branched panicles, which is considered an archetypical grass form similar to that of wheat or rice.
The drooping and swaying inflorescence, which is usually slightly yellow, matures into a seed cluster that bends slightly under the weight of the seeds. The seed cluster is usually green with tinges of purple until the seeds mature, at which time it dries and becomes golden. The root stem is extremely fibrous and dense and plants send out numerous rhizomes laterally. Healthy plants can form dense mats of vegetation.
There are also specially cultivated variations on the market, bred for attractive patterns. The most common is Glyceria maxima var. variegata, which has green and cream-white stripes.
Facts, Benefits & Uses of Reed Mannagrass
In its native range, wildlife is dependent on it for habitat use. It can provide important shelter for nesting birds as well as fish and amphibians. It seeds are a source of food for waterfowl and water voles. However, the stems and roots can contain naturally occurring cyanide in small amounts, which is thought to discourage large grazing mammals such as deer, who tend to avoid it.
It is also important for a variety of invertebrates for both food and protection, including wetland snails and dragonflies. In very few remaining areas of the UK, it provides crucial habitat to the brightly colored Zircon reed beetle, which is considered a Priority Species under the UK Post-2010 Biodiversity Framework. Like many other wetland grasses, it provides important ecosystem functions in water quality via soaking up excess nutrients and preventing erosion
Unlike most grasses, whose seeds are spread by wind dispersal, reed mannagrass seeds are spread by animals and flowing water. Seeds may lie dormant and remain viable for many years before germinating, which may help with dispersal.
Its status in the IUCN red list is currently least concern.
Reed Mannagrass Growth, Hardiness & Climate
In the first 2 years of its lifespan, a single reed mannagrass plant may produce up to 100 shoots and may establish very quickly under good conditions thanks to both seed dispersal and aggressive rhizomatous roots. At maximum height, it can grow up to 2.5 m tall in the wild. The variegated type, most frequently used in aquatic gardening, is smaller and grows up to 1 m tall.
Individual plants are believed to have an average lifespan of 3-10 years; however, it can be difficult to tell its age because of its rapid growth rate and ability to spread via rhizomes. Approximately 50% of the biomass will be concentrated in the root system, meaning half of the plant is not even visible. It has a competitive advantage because it begins growth early in the spring and has a long blooming period, producing florets and seeds through the summer and autumn.
This grass prefers slow moving, fresh water and full sun. It can tolerate partial shade, but does not thrive in full shade. It is naturally found growing in cooler, temperate climates.
How to Plant Reed Mannagrass In Ponds
G. maxima should be planted in a loose substrate and along shallow banks. It should be planted up to 25 cm below water level. Rocks and gravel are not ideal for substrate. It requires damp, nutrient-rich soil for successful growth and does not tolerate a dry environment, even for a short period of the year. It also does not tolerate alkaline soils well. Established colonies might actually push the water pH lower, so consider this if growing in an aquaculture setting. As long as the roots do not dry out, it can survive most other conditions and is considered quite hardy. The roots can extend to depths of up to 1 m. If provided enough space, it will expand to form floating mats attached to the shore.
How to Care For Reed Mannagrass
Reed mannagrass is often sold and planted as an ornamental plant for its attractiveness. It is very easy to care for and requires little maintenance. Given its success at proliferation, if you are caring for it in a small pond you may want to be proactive by cutting it back in the autumn so that it does not dominate your habitat and crowd out your other plants.
How to Winter Reed Mannagrass
G. maxima is rather hardy and tolerant of seasonal changes, including frost. Given that it already prefers cooler temperatures, you shouldn’t need to change anything for this species seasonally other than some pruning to control spread. Its growth rate does slow to dormancy in colder conditions, but growth will resume again in the spring.
Is Reed Mannagrass Toxic, Poisonous or Invasive?
G. maxima grows so aggressively that it has the ability to form monocultures and reduce other species’ diversity even in its native range. It is considered an invasive species and a conservation concern in other regions of the world, such as North American and Australian wetlands. If it spreads enough beyond its periphery, it can slow water flow, cause local flooding, and change environments to anaerobic conditions.
As stated above, it can contain small amounts of cyanide as an effort to deter large grazers, and can be toxic to native mammals and livestock. This plant is aggressively targeted for removal in Australia for this reason.
Removal can be extremely challenging in invasive conditions because the plant can regenerate from rhizomes left in the soil or from dormant seeds up to several years after a removal attempt.
Is Reed Mannagrass Edible? Will Fish Eat it?
Fish do not seem to feed on the tough vegetation or root systems, although some species may feed on the fallen seeds. Fish may use submerged plants for protection or as a nursery for eggs and fry. It is becoming popular with koi ponds because it is quite tolerant of the waste created by koi.
Where to Buy Reed Mannagrass & Seeds? (UK & US)
Seeds and root cuttings are available by mail order in its native range. Some nurseries may also offer juvenile plants. Planting G. maxima outside of its native range is strongly discouraged, and in some locations, such as Australia, its sale is banned.
Hello
I want to plant reeds in a pond.
This pond is about 1 acre and i want reeds that will help clean soiled water.
What do you recomend and can i plant these in October