Spiked Water-Milfoil Facts & Care Guide (Myriophyllum spicatum)


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Flower from a spiked water-milfoil plant poking out of the water
Spiked water-milfoil’s flowers are largely inconspicuous and carry both male and female parts. Leslie J. Mehrhoff, University of Connecticut, Bugwood.org, CC BY 3.0, via Wikimedia Commons

Myriophyllum spicatum is a submerged aquatic plant that is commonly known as Eurasian watermilfoil or spiked water-milfoil. It is a perennial herb that belongs to the Haloragaceae family, which includes a wide diversity of species found in habitats ranging from freshwater lakes to the most arid deserts.

Unlike most of its cousins that are native to the southern hemisphere, M. spicatum has a remarkably widespread distribution. It is now dispersed through Asia, Europe, Africa, Australia, and North America. In the US, it is notorious for being an aggressive grower that must be controlled to prevent its invasion of lakes, canals, and waterways.

This somewhat troublesome species is quite attractive and beneficial when its spread is restricted. It possesses elongated stems with whorls of fine, herring bone-like leaves. Air canals in the stems allow the plant to maintain an upright position in the water column. This ensures that its flowers, which are generally wind-pollinated, break through the surface of the water. Borne on leaf axils, these small flowers are largely inconspicuous, are dark orange to light yellow in color, and carry both male and female parts. At maturity, a single spiked water-milfoil shoot can reach a length of 3 meters (9.8 feet)!

Facts, Benefits & Uses of Spiked Water-Milfoil

Owing to this species’ many forms of propagation, spiked water-milfoil can form extensive mats in streams, rivers, and lakes that do not have well-established communities of native plants. As each plant fragment is capable of generating more individuals, this species can grow to be a nightmare if left unchecked.

Myriophyllum spicatum, along with other watermilfoil species (e.g. M. sibiricum and M. heterophyllum), is an invasive plant that has sorely impacted many freshwater ecosystems, resulting in socio-economic consequences for the fishing and boating industries of some major North American regions.

Though the structure of spiked water-milfoil can provide safe habitats for juvenile fish, it can be extremely obstructive towards larger fish species. Crowded milfoil communities attempt to fill up all available spaces in the water column. Consequently, light is blocked out, oxygen levels are markedly reduced, and an entire waterbody can be deprived of light/oxygen-dependent food sources. This can, unfortunately, result in irreversible ecosystem collapses.

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Spiked Water-Milfoil Fact Sheet:
PLANT TYPE
Herbaceous aquatic perennial
HARDINESS ZONES
USDA 5 – 9
LIGHT REQUIREMENTS
Full sun
BLOOM COLOR
Yellow, orange
BLOOM PERIOD
June to July
MAXIMUM GROWTH
3 meters (10 feet)
PLANTING DEPTH
2 inches (in soil), 1 meter (in water)
WATER QUALITY
pH 5 – 11

 


Spiked Water-Milfoil Growth, Hardiness & Climate

Spiked water-milfoil plants underwater
Spiked water-milfoil can be found in water depths of up to 10 feet! Ryan Hodnett, CC BY-SA 4.0, via Wikimedia Commons

Spiked water-milfoil can grow just about everywhere! This extremely hardy plant can be found in water depths of up to 10 feet, particularly in low-energy areas that allow its shoots to peacefully creep towards the water’s surface. It can withstand a wide variety of conditions, but will grow quite rapidly in clear water that receives full sunlight. It also prefers high calcium and nutrient-rich conditions. Like other invasive milfoils, this species thrives best in low-salinity environments, but has been observed to grow in brackish environments as well.

This species multiplies more rapidly via fragmentation than seed dispersal. In spite of this, spiked water-milfoil puts a lot of energy into flower production. Perhaps these compounded methods of regeneration are vital; genetic recombination and fragment dispersal allow the genes of this weed to roam far and wide, and to withstand increasingly extreme conditions. This species has even been shown to tolerate waters that are polluted with heavy metals.


How to Plant Spiked Water-Milfoil

Spiked water-milfoil seeds
Spiked water-milfoil seeds are best sown in spring, onto pots of soil submerged in a few inches of water. Steve Hurst @ USDA-NRCS PLANTS Database / Public domain

Spiked water-milfoil can easily be grown via seed, vegetative fragments, or root cuttings. Fragments and cuttings can become established quite rapidly when planted at least 2 inches deep into loamy soil. This can be done directly on pond bottom sediment. A depth of at least 12 – 30 inches over the plant’s base is recommended. Moreover, provide a space of at least 1.5 square feet of soil for each plant. Do keep in mind that using baskets would perhaps be a wise choice to prevent this plant from rapidly spreading.

If you intend to cultivate this species via seed, you may have to use a set-up in a cold frame or greenhouse. Seeds are best sown in spring, onto pots of soil that are submerged in a few inches of water. Once the seedlings are of manageable size, you can transfer them into individual pots and outplant them the following spring.


How to Care For Spiked Water-Milfoil

Spiked water-milfoil plants in a body of water
Spiked water-milfoil is generally low-maintenance, but you should try to plant it in an area with full sunlight to make the most of its oxygen-producing capacities. Stefan.lefnaer, CC BY-SA 4.0, via Wikimedia Commons

Spiked water-milfoil is generally a low-maintenance plant. Situate your plant in an area that receives full sunlight so that its oxygen-producing capacities are fully exploited. As it is tolerant of a wide range of water parameters, you need not worry about fluctuations affecting its growth. Simply make sure to maintain its spread by routinely pruning shoots. Excessive growth should be prevented to ensure that this species doesn’t overgrow your pond. You may also choose to snip flowers before they develop into seeds. This prevents them from spreading via wind pollination.


How to Winter Spiked Water-Milfoil

Spiked water-milfoil is a winter-hardy plant that normally survives through freezing temperatures in the wild, even in ponds and lakes that ice over. Exposed plant parts will likely die back during the coldest months, especially if your area experiences strong frosts. The root system of this plant should survive outdoors, especially if it is submerged under a few feet of water.

If your spiked water-milfoil plants are in aquatic baskets or pots, you can trim down their foliage and move the plants to the deeper areas of your pond. When temperatures begin to rise the following spring, they can be moved back to shallower positions where they may receive more intense sunlight.


Is Spiked Water-Milfoil Invasive or Toxic?

Spiked water-milfoil is a highly invasive plant in temperate freshwater bodies. Introduced to the US as an ornamental plant in the 1940s, it has spread to major water systems across the continent. As this plant self-propagates via fragmentation, virtually all moving bodies that it comes into contact with become vectors for its dispersal. Fragments can attach to boats and ships and re-establish themselves elsewhere. Natural vectors, such as waterfowl, can also carry fragments that become attached to their plumage.

In some areas of the US, spiked water-milfoil has become an incredibly difficult plant to control. Some lakes are filled shore-to-shore with dense milfoil mats, making transport, fishing, and recreation almost impossible. Ambitious control efforts, costing thousands of dollars, have been adopted as a means to reduce the spread or create barriers for growth. The detrimental impact is undeniable, and management as a means to prevent hazards is an absolute must. This plant is even associated with flooding risks and irrigation interference!

Though spiked water-milfoil is non-toxic, it must be grown with caution to minimize its spread. If your pond is located close to other sources of water, you must take extra care to prevent any fragments or seeds from reaching shared canals or waterways.


Is Spiked Water-Milfoil Edible? Will Fish Eat it?

Thankfully, this rapidly spreading plant is safe to eat and even has medicinal properties! The nutrient-rich roots of spiked water-milfoil can be consumed raw or cooked. A delicacy to some Native American tribes, these are said to be sweet and crunchy. However, much caution must be taken prior to consuming this plant. It is sometimes found in polluted environments that may carry harmful bacteria, such as E.coli.

Leaves of spiked water-milfoil are not commonly regarded as palatable, though they are occasionally consumed by fish. Grass carp (Ctenopharyngodon idella) were once used to control the growth of milfoil shoots. Unfortunately, they had the tendency to avoid milfoil when other native plants were available. Evidently, the leaves of this plant are not regarded as a primary nutrient source, even by herbivorous fish.


Where to Buy Spiked Water-Milfoil & Seeds? (UK & US)

Myriophyllum spicatum can be purchased from aquarium stores and aquatic plant nurseries in areas where it has been naturalized. Online plant portals may also carry bare-root individuals that you can plant directly into your pond. This species looks remarkably like other milfoil plants, so do make sure to check for the appropriate scientific name.

If located in a region where spiked water-milfoil is considered invasive, it would be best to stay away from this plant. There are many submerged aquatic alternatives that can provide your pond with various benefits, minus the need for strict growth management. Bear in mind that a single fragment of watermilfoil can multiply into millions of new plants each year!

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