How to Plant & Grow Clasping-Leaf Pondweed (Potamogeton perfoliatus)


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Clasping-leaf pondweed in a canal
As pictured above, the leaves of clasping-leaf pondweed hug or ‘clasp’ the stems, as they have no stalks. Christian Fischer, CC BY-SA 3.0, via Wikimedia Commons

Potamogeton perfoliatus is a perennial plant with much value to the aquatic community. Commonly known as clasping-leaf pondweed, redhead grass, or perfoliate pondweed, this modest species maintains a fully submerged habit and can contribute significantly to a waterbody’s structural diversity.

It belongs to the Potamogetonaceae family, which includes more than 100 species of pondweeds. Many of these plants are important in the field of aquatic ecology due to their uses as food or as habitats for freshwater life. Of the six genera under this family, Potamogeton is the largest and has an almost cosmopolitan distribution. Clasping-leaf pondweed originated from Europe but can now be found on all continents, with the exceptions of Antarctica and South America.

With round stems that can grow to a generous length of 3 meters (9.8 feet), this species produces translucent, oval-shaped leaves. The base of each leaf hugs or “clasps” the stem, as they have no stalks. Occurring alternately, and on opposite sides of the shoot, the leaves range in color from yellow-green to olive or brown. Flowers are produced each summer, but these are rather inconspicuous. At the end of each growth season, these develop into clusters of tiny disc-like fruits which sink and release seeds upon maturity.

Facts, Benefits & Uses of Clasping-Leaf Pondweed

Clasping-leaf pondweed is remarkably similar to another pondweed species, P. richardsonii, with which it can hybridize. To distinguish P. perfoliatus from its almost identical cousin, peer closely at the veins and edges of the leaves. The former has smaller leaves (1 – 5 cm long) that possess just 7 – 15 visible veins. On the other hand, P. richardsonii has larger wavy-edged leaves (3 – 12 cm long) that are marked by 13 – 21 veins. Moreover, these don’t clasp the stem fully, reaching up to just three-quarters of its circumference. Both species are found in freshwater and brackish communities of lakes, ponds, streams, and rivers.

Unfortunately, clasping-leaf pondweed communities are in decline. This species is now listed as vulnerable or endangered in the wild, particularly in the US and Europe. There are restoration efforts to help protect and conserve its populations, which are valued for the multiple environmental services that they provide. For one, their spreading rhizomes help stabilize sediments, effectively reducing shoreline erosion. The leafy shoots provide protection and shelter to many freshwater fish and invertebrates. Additionally, the entire plant is a nutritious food source for insect larvae, waterfowl, fish, and crustaceans.

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Clasping-Leaf Pondweed Fact Sheet:
PLANT TYPE
Aquatic perennial
HARDINESS ZONES
USDA 3 – 10
LIGHT REQUIREMENTS
Full sun to partial shade
BLOOM COLOR
Green
BLOOM PERIOD
July to October
MAXIMUM GROWTH
3 meters (9.8 feet)
PLANTING DEPTH
6 – 9 inches (15 – 23 cm) of water
WATER QUALITY
Moderately acidic to alkaline

 


Clasping-Leaf Pondweed Growth, Hardiness & Climate

Clasping-leaf pondweed underwater
Clasping-leaf pondweed prefers reasonably clear, alkaline water. Natural Resources Wales, CC BY-SA 4.0, via Wikimedia Commons

This species can withstand a wide range of conditions, but will grow best in calm water or in a slowly-moving current. Its roots and rhizomes spread quickly in firm, muddy soil. Though wild populations are in decline, this species can grow quite rapidly in captivity; it will even require regular pruning in the absence of any plant competitors or grazers. Apart from ample light exposure, it does not have heavy requirements and will thrive on standard nutrient concentrations in your aquarium or pond. When nutrient concentrations are too high, algae and phytoplankton may shadow the leaves and prevent them from photosynthesizing efficiently.

Though it is generally not sensitive to water chemistry, clasping-leaf pondweed prefers reasonably clear, alkaline water. Water depth may influence the color intensity of its leaves, with the plant generally being darker in shallow water and paler in deep water.


How to Plant Clasping-Leaf Pondweed

Inflorescences of clasping-leaf pondweed
When propagating clasping-leaf pondweed via cuttings, you should install the cuttings at a depth of at least 6 – 9 inches of freshwater. Krzysztof Ziarnek, Kenraiz, CC BY-SA 4.0, via Wikimedia Commons

Clasping-leaf pondweed can be propagated via seeds or cuttings. Its rootstocks can also be used to generate new shoots and rhizomes at a faster pace. These tend to have a higher survival rate when established, though they produce a lower yield compared to seeds. To propagate rootstocks or cuttings, plant them in a few inches of suitable substrate, such as aquatic compost or sand. Cuttings should be installed at a depth of at least 6 – 9 inches (15 – 23 cm) of freshwater, and they may need to be weighed down or secured so that submerged roots can form without disturbance. It is ideal to plant them in baskets or pots that can be moved further into your pond as the shoots increase in length.

If you intend to propagate this species via seeds, you will need to collect its mature fruits during summer. Sow the seeds onto aquatic soil or sand, making sure that they don’t become buried under more than a centimeter of substrate. You can leave them completely uncovered or with just the right amount of substrate to secure each seed’s position. Keep in mind that too much soil above each seed may prevent germination. When done properly in a set-up with standing shallow water, seeds should begin to germinate in just 10 days. When seedlings are mature enough, they can be out-planted in the summer.

To increase germination rates or if you intend to save the seeds for the following growth period, you can cold store them for 6 – 9 months in slightly saline water, at a temperature of about 40˚F (4˚C). Transfer them to a warm freshwater setup as soon as the next growth period begins.


How to Care For Clasping-Leaf Pondweed

Submerged clasping-leaf pondweed
Clasping-leaf pondweed is fairly easy to maintain and does not require any additional fertilizer. Christian Fischer, CC BY-SA 3.0, via Wikimedia Commons

If you intend to grow this species in your pond, you may need to provide it with some form of protection from herbivorous fish. This is optional for older/mature plants, but is a must for newly transplanted cuttings or juvenile plants. A mesh barrier that will not impede the flow of water should suffice. Once roots are well-established and the shoots are robust enough to withstand occasional grazing, the barrier can be removed.

Clasping-leaf pondweed is generally easy to maintain when it is grown in clear, clean water. It will not require additional fertilizer as it can thrive on low nutrient levels or those typically found in ornamental fish ponds. Simply make sure your pondweed community receives enough sunlight, and regularly prune overgrown or decaying shoots.


How to Winter Clasping-Leaf Pondweed

Clasping-leaf pondweed will not require any special overwintering needs. Its shoots will naturally die back once temperatures begin to drop and its rootstocks may grow dormant in particularly cold conditions. To prevent decaying shoots from accumulating in your pond, you may opt to cut down or “mow” your pondweed communities before winter. Baskets or pots can then be moved further into your pond so that the roots can remain submerged under a few feet of water throughout winter. These can be moved to shallower areas in spring so that new shoots can gain more access to sunlight.


Is Clasping-Leaf Pondweed Invasive or Toxic?

Clasping-leaf pondweed is generally non-invasive in the wild, although fragments are easily dispersed and introduced to other waterways by boats and nets. It can spread rapidly in enclosed aquariums and ponds, especially when no other aquatic plants are present. For this reason, it can sometimes be considered a “weed” that may require mechanical control to prevent uncontrollable spread. In New Zealand, where P. perfoliatus is sold as an ornamental plant, it is considered a high-risk species (based on their Aquatic Weed Risk Assessment Model).

Luckily, the spread of this non-toxic species can easily be controlled in ornamental ponds. If you have a thriving community of pond fish and aquatic plants, it is highly unlikely that this plant will overgrow its assigned space. To be on the safe side, however, you can always prevent its roots from spreading out by restricting their growth to within pots.


Is Clasping-Leaf Pondweed Edible? Will Fish & Animals Eat it?

Like many other common pondweeds, clasping-leaf pondweed is safe to consume but does not necessarily have economic value as a food source. It is more vital for fish, crustaceans, and macroinvertebrates, which can eliminate entire communities of this plant when other sources of nutrition are sparse. Moreover, the stems, rootstocks, and particularly the fruits and seeds, are a prime source of food for waterfowl.  Ducks, geese, mallards, and swans are known for favoring the fleshy parts of this plant.


Where to Buy Clasping-Leaf Pondweed & Seeds? (UK & US)

Potamogeton perfoliatus can be purchased from aquarium stores and aquatic plant nurseries in areas where this species has been naturalized. Online plant portals may also carry bare-root individuals or cuttings that you can plant directly into your pond. Keep in mind that this plant can look remarkably similar to other pondweeds, so do make sure to check for the appropriate scientific name.

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