How to Plant & Grow Float Grass (Glyceria fluitans)


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A single float grass plant
Float grass has a notably sweet taste due to its high carbohydrate composition. Stefan.lefnaer, CC BY-SA 4.0, via Wikimedia Commons

Glyceria fluitans is a grain-producing plant that is more commonly referred to as float grass, water manna grass, or floating sweet grass. It is classified under Poaceae, a flowering plant family that includes some of the world’s most notable grasses, such as bamboo, lawn grass, and several cereal crops. 

Glyceria is just one of 800 genera under this large family and includes several species of sweet-grass found in temperate regions worldwide. An economically important source of tradeable grain in the 1900s, G. fluitans is a Eurasian species that is now present all over the world.

Characterized by long narrow leaves, this aquatic grass is pale green in color and rough to the touch. Its thick stem grows to approximately half a meter in length, with leaves that tend to fold downwards and float on the surface of the water, forming a loose flat mass. It can grow partly submerged in water and has two types of leaves: aerial leaves which have hydrophobic cuticles on both sides, and floating leaves, which have hydrophobic cuticles on only the adaxial side.   

Facts, Benefits & Uses of Float Grass

As float grass thrives in a variety of wet habitats such as lakes, ponds, streams, rivers, and along the margins of wetland systems, it has the physical properties for maximum flood tolerance. It is a great addition to a pond or bog garden and is relatively hardy in terms of its requirements for growth. Fluitans, which is Latin for “floating,” is a species epithet indicative of this plant’s typical appearance – with 3-10 mm wide leaves that are typically folded along the keel and peacefully floating on the surface of standing water.

The seeds of G. fluitans are produced by small flower heads that are distinguished by open panicles. Each panicle has around 20-30 spikelets that contain the seeds, more appropriately called “caryopses” of the plant. The caryopses of float grass have a high carbohydrate composition (approximately 75%), giving them a notably sweet taste. It’s no wonder why the grains of this species were regarded as a form of manna.

Float grass was a highly appraised crop that was once accepted as a tribute with which peasants paid landowners in Eastern Europe. Later, it was introduced to America and other parts of the world as a pasture species, and via contamination with other grass seeds.

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Float Grass Fact Sheet:
PLANT TYPE
Perennial
HARDINESS ZONES
USDA 4 – 8; UK Zone 5
LIGHT REQUIREMENTS
Full sun
BLOOM COLOR
Green
BLOOM PERIOD
May – August
MAXIMUM GROWTH
0.5 m
PLANTING DEPTH
3 – 5 cm
WATER QUALITY
pH 4 – 9

Float Grass Growth, Hardiness & Climate

Float grass in a pond
Float grass can grow in standing or moving water. James Lindsey at Ecology of Commanster, CC BY-SA 2.5, via Wikimedia Commons

G. fluitans has an affinity for wet soils and is able to grow in standing or moving water. It can withstand a wide range of pH levels and can reputedly survive in very acidic or very alkaline soil conditions. Its green fronds require exposure to full sun, but are able to photosynthesize efficiently in shallow water. Though it is known to dislike shade, it is a remarkably hardy plant that can successfully grow in a wide range of environments, as long as its creeping rootstock is kept wet or moist. This hardiness is likely a major reason why this plant has thrived in so many countries outside of Europe and Asia, and may in consequence compete with endemic grasses outside of its native jurisdiction. 


How to Plant Float Grass

Float grass by a wet path in the woods
When planting float grass, sandy, loamy, or clay soil can be used. Stefan.lefnaer, CC BY-SA 4.0, via Wikimedia Commons

Float grass can be planted with the use of seeds or via division. To plant seeds, prepare loosened, moist soil in a pot that sits in approximately 3-5 cm of water. You may use sandy, loamy, or clay soil. Place seeds either directly on top of the soil surface or just underneath a few millimeters of soil. Under favorable conditions, float grass seeds should germinate within 3 weeks. Let seedlings grow until they are large enough to handle, and then transfer them to individual pots. Bear in mind that the soil should be kept moist throughout this entire stage, as this species has difficulty tolerating dry conditions. Once seedlings are mature enough to withstand outdoor elements, you may outplant them into your pond or garden, preferably during the early summer months.

Propagation of float grass via division of the mature plant is much simpler. Divide the plant into large clumps, and separate the small clumps for propagation in pots. Take the large clumps and plant them in a few inches of soil where you intend for them to be permanently situated. As a precaution against flooding or strong winds, smaller clumps should be allowed to develop more roots in their own individual pots, in a cold frame or greenhouse if possible. Upon the arrival of spring, you may outplant them into their permanent positions.


How to Care For Float Grass

Float grass in water with a number of other plants
As float grass is a hardy plant, caring for it is quite straightforward.Panek, CC BY 3.0, via Wikimedia Commons

Caring for G. fluitans is fairly straightforward; it is quite a hardy grass after all. Just ensure that your plant receives full sun throughout the day and that the soil remains moist or wet. Aside from thriving in a wide range of soil pH levels, it is fairly tolerant of high nutrient levels, physical damage (such as grazing by animals), and cold temperatures. Regularly check for pests or diseases, and remove any weeds or dead leaves around the plant.


How to Winter Float Grass

Float grass is frost tolerate plant and can be left outdoors over winter. Christian Fischer, CC BY-SA 3.0, via Wikimedia Commons

Float grass is not a frost-tender plant. It can withstand winter conditions and may be left outdoors for the duration of the season. However, if your pond or garden is located further north of this species’ native region, you may transfer your pond plants to an indoor or protected setting in preparation for a harsh winter. If doing so, place your plant in a container with water, and let it sit in a corner of your greenhouse that receives ample sun. As this species is a perennial, it should survive through seasonal changes and thrive in your garden for years to come. 


Is Float Grass Invasive or Toxic?

Float grass is reported as invasive in 6 countries, including the US, Australia, and Mexico. Its spread, however, is largely mitigated with the use of manual techniques or herbicide. As this plant relies on wind as a vector for pollination, and has both male and female organs, it has the tendency to rapidly reproduce on its own. Fragments of its stem and seeds also tend to spread via water flow, livestock movement, soil erosion, and contamination of boats and diggers. None of its parts contain harmful toxins, but do take care when cultivating this species so that it does not spread uncontrollably beyond your garden.


Is Float Grass Edible? Will Fish Eat it?

The most edible part of float grass is its seeds. Though harvesting the grains is time-consuming due to their minute size, there is much history surrounding the consumption of G. fluitans, particularly in Poland, Germany, and Hungary. The seeds were eaten as gruel or pounded into flour for use in breads, soups, dumplings, and more. There is even prehistoric evidence of the seeds being consumed by humans during the Paleolithic and Mesolithic periods.

Fish with pharyngeal teeth, such as grass carp, have been shown to readily consume G. fluitans as their chewing mechanism is compatible with the leaf toughness and leaf availability of float grass, meaning that single leaves are easily extracted from the main plant. It is likely that the seeds themselves are also consumed by fish because of their nutritional value.


Where to Buy Float Grass & Seeds? (UK & US)

Glyceria fluitans seeds may not be readily available online, as they are flagged as an invasive species in some areas. Mature plants that are ready for division may be found in your local aquascaping or pond supplies store. It may also be available in plant nurseries. Do bear in mind that this plant can spread rapidly, even in conditions of neglect. It is advisable to purchase this plant only if it is naturally present in your area.  

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