Hippuris vulgaris, more commonly known as mare’s tail or bottle brush, is an aquatic plant known for its oxygenating capabilities. Native to temperate zones across the northern hemisphere, it belongs to the family of plantains, Plantaginaceae. This family consists largely of flowering shrubs, rooted aquatic plants, and bright green herbs which have been studied for hundreds of years for their medicinal properties! Mare’s tail is one of three species in the Hippuris genus and is commonly mistaken for an unrelated plant with a similar name, horsetail (genus Equisetum).
H. vulgaris’ common names hint at its striking appearance. Similar to industrial bottle brushes or pipe cleaners made for scrubbing vials and test tubes, this plant seems like the inspiration for some modern cleaning brushes! Arising from rhizomes that are typically rooted underwater, mare’s tail produces stems with regions that vary in appearance, depending on their exposure to water.
The majority of this plant’s leaves occur on emersed stem segments, or those which extend to heights above the water’s surface. These leaves reach lengths of 0.5 – 2.5 cm (0.2 – 1 inch) long, and gradually decrease in length towards the top end of the stem. Submersed stems produce whorls of leaves that are longer and more delicate. As its flowers are quite unnoticeable, this plant’s appeal lies with its whorled blue-green foliage.
Facts, Benefits & Uses of Mare’s Tail
With singular, unbranching stems that grow to lengths of 60 cm (23.5 inches), mare’s tail is often found in non-acidic shallow water environments such as ponds, ditches, and mudflats. Its appearance and growth preferences make it an ideal candidate as a pond margin plant, around which juvenile fish can play and seek refuge.
Interestingly, this species is known for being a methane emitter. It acts as a conduit of sorts, as its roots can proliferate downwards into anoxic layers of soil and transport trapped gases into the atmosphere. Though not generally known, this ability is actually quite common in the plant world. Trees are capable of emitting vast amounts of methane.
Mare’s Tail Growth, Hardiness & Climate
Mare’s tail is a remarkably hardy plant and is generally resistant to diseases and pests. Given the right conditions, it can develop a colony that spreads to a width of 0.5 m (20 inches) after just 2 years of cultivation. As an oxygenating plant, its leaves can aid in pond water aeration as they give off tiny bubbles during the daytime. Though this species favors stagnant water, it can tolerate mild water currents and cold temperatures. This makes it a great option for ponds located in northern temperate zones.
This plant thrives best under full sun exposure and when partially submerged. It has a tolerance for most soil types, but prefers neutral to alkaline conditions. Ideally, it should be grown along pond edges, as it is normally found along lake or river shorelines in the wild. Bear in mind that mare’s tail produces roots that can grow deep into the anoxic layers of soil. This means that it can secure the soil along the perimeter of your pond. If left unchecked, it may also rapidly overgrow your pond bottom.
How to Plant Mare’s Tail
Mare’s tail is considered a beginner plant and is fairly easy to cultivate. Though it produces tiny nutlets with seeds, it is normally grown via divisions. These can be planted into their permanent positions during spring or summer. If you are able to acquire seedlings, which may be referred to as plug plants at your local plant nursery, you will have to pot these as soon as possible. This plant can also be propagated via stem cuttings. Two plants per square foot of soil should suffice.
The best potting medium for mare’s tail is aquatic soil. Fill a fine-mesh basket halfway with soil, and situate your plant in the center. Take care to not disturb the roots as you fill in the remainder of the basket. Gently pat down and create a mound of soil around the crown of the plant. Make some space towards the top of the basket and fill this part with washed pea gravel to weigh down the soil. Once the plant is secure, the basket can be submerged into the pond. The soil should fully absorb water so that seepage is prevented. Depending on the height of your stems, the plant should be situated at a depth that permits a section of its stem to emerge above the water. Do bear in mind that the stems will continue to grow upward, so the divisions need not be too tall.
How to Care For Mare’s Tail
Given adequate sunlight exposure and proper submersion, mare’s tail will require little to no maintenance. Under intense sun, this plant’s foliage can adopt a warm, reddish color. Though this plant can grow in waters as deep as 100 cm (40 inches), it is advisable to maintain a water depth of up to 15 cm (6 inches) for maximal growth and light exposure. As this plant prefers alkaline conditions, you may opt to regularly check the pH of your pond water and soil. Though this species is fairly resistant to pests and diseases, scan the foliage every now and then for decaying leaves.
Do remember that this plant has a spreading rootstock from which new stems may arise. With proper care, you can regularly retrieve divisions from mature plants without compromising their growth. Keep in mind, however, that this plant has the tendency to spread and may overgrow small ponds if propagated extensively.
How to Winter Mare’s Tail
Mare’s tail is a cold-hardy plant and does not require special overwintering conditions. As it is native to temperate zones, it is equipped with a temperature tolerance that will allow it to survive winter elements! Its stems and leaves will simply dry out and grow brown throughout the autumn and winter months. To prepare for the possibility of your pond freezing over, trim the exposed stem and ensure that your water level is deep enough to facilitate warmer pond bottom conditions. As long as its submerged roots are not exposed to frost, new shoots will appear again in spring.
Is Mare’s Tail Invasive or Toxic?
Mare’s tail can be mildly invasive in warmer zones and can be a nightmare to get rid of. To prevent this plant from overgrowing your pond or garden, its roots must be restricted to soil that is bound by fine mesh or strong pots. Its foliage can also form a dense carpet and create undesirable conditions for less vigorous plants.
Unfortunately, this plant is often confused with other invasive weeds that can wreak more havoc in a pond or garden. One such plant is Conyza canadensis, which is also referred to as mare’s tail but has no relation to the non-toxic Hippuris vulgaris. Unlike H. vulgaris, it is normally found in pastures, is highly invasive, and can cause skin irritation. Additionally, it is not at all related to horsetail, Equisetum hyemale and E. arvense, which can be invasive and challenging to control.
Where to Buy Mare’s Tail & Seeds? (UK & US)
Hippuris vulgaris can be purchased as plant plugs (that have to be repotted right away) or in fine-mesh baskets that can be placed directly into your pond. If you’re located within their native range, they should be available at your local aquascaping shop or plant nursery, and can be purchased from online plant portals as well. When buying mare’s tail, pay close attention to the scientific name. Don’t forget that there are other species that have the same common name, and can turn out to be invasive in your garden.
