What Plants Filter Water? (11 Plants That Clean Water)

Whether you’ve got a pond, a cement driveway, or rivers of water running off your lawn, water pollution from fertilizer, pesticides, motor oil, and tires is a huge problem. But plants are here to help. They can filter pond water to stop algae blooms, or slow and filter runoff from your driveway or lawn before it hits the storm drain.

All plants can help filter water, but the best plants have fibrous roots or rhizomes that hold on to soil, dense growth, and an upright growth that slows water flow. The ability to withstand fluctuating water levels is also key. For ponds, look at both shoreline and aquatic plants.

But remember, just because a plant is on a list of the best plants to filter water, doesn’t mean it’s right for you and your yard. You need to select the right plant for your climate, zone, and how much water the spot is likely to get. Aquatic plants and shoreline plants like cattails are great for ponds, while Blue Flag Irises are great for those boggy places that never fully dry and Purple Coneflower is best for rain gardens that get occasional flooding.

When possible, go with native plants as they often have many of the same qualities for filtration, but without the risk of becoming invasive.

Also, just because water has been filtered by plants, doesn’t mean that it’s safe for human consumption, or even for use on vegetable crops. Always test water.

Ready? Let’s begin.

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What Plants Filter Water?

#1 Blue Flag Iris (Iris versicolor)

Blue Flag Iris is an extremely attractive iris with deep blue blooms and grass-like foliage that grows even when sitting in water for days, even when other rain garden plants struggle. Its fibrous roots hold soil in place, preventing erosion and reducing runoff. Like most plants, it’ll filter out excess fertilizer and other pollutants from the water. Best yet, Blue Flag Iris attracts hummingbirds!

However, try not to touch the seeds or sap with your skin, as it can irritate the skin.

#2 California Brome (Bromus carinatus)

California Brome is a cool-season perennial bunchgrass native to California and the Pacific Northwest that reproduces using spikelets. It is adapted to a variety of soils, from dry to poorly drained, from acidic to alkaline, from bottomlands to ridgetops.

Its quick-growing fibrous roots make it useful for erosion control. As it’s also great at absorbing heavy metal, potassium, and phosphorus, it’s used for restoring spent oil shales, coal mine spoils, heavy metal mine tailings, and roadsides.

#3 Cattail (Scientific name)

Cattails are one of the most common plants in marshes and ponds, providing habitat, cover, and shelter for birds, fish, insects, and other wildlife. Their long stems and long, tapered leaves slow the water down to trap sediment, and they’re very effective at removing pollutants from the water, especially phosphorus.

However, they are very invasive, and can quickly take over a pond or swale, spreading both through fluffy seed heads (the thick brown part) and rhizomatic roots. They grow tall, blocking the view to the water (if that’s a concern for you).

Large stands can be too good at slowing down water flow, especially for bioswales that are designed for water to flow through. They can require a lot of maintenance. So have a maintenance and control plan in use before you plant these.

#4 Cool-Season Turfgrasses

You may not even need to plant something fancy – common cool-season turfgrasses will slow water flow and remove fertilizer pollution either on slopes or in drier rain gardens. For example, bluegrass can uptake 200 pounds of nutrients per acre and tall fescue can uptake 135 pounds of nutrients.

Allow the grass to grow longer than you would normally so they grow their roots deeper to hold soil in place and take up more nutrients. You can mow the grass low during the dry season.

You can also use their annual cousins, like Annual Bluegrass. They grow much faster than perennials, and so can uptake a lot of nutrients.

#5 Clover (Trifolium spp.)

Clover helps water filtration by preventing soil erosion, so the soil can slow the water runoff before it reaches water. Overseeding or replacing your lawn with clover can also help lower or eliminate nitrogen requirements (since clover fixes atmospheric nitrogen in the soil) so you don’t need to use as much fertilizer.

Clover grows low to the ground, and produces small blossoms in a variety of colors, depending on the particular variety. Dutch White Clover is one popular species, and Micro Clover has smaller leaves and produces fewer flowers when mowed, as it has been bred as a lawn alternative.

#6 Hardy Water Lilies (Nymphaea spp.)

Hardy water lilies are floating plants, meaning they’re rooted at the bottom while the vegetation floats upon the water. They have large blooms similar to a lotus that come in a variety of colors.

Use hardy water lilies in ponds to absorb heavy metals and to control algae blooms by shading out and absorbing excess nitrogen and phosphorus from fertilizer runoff. They also oxygenate the water, which is necessary for a healthy ecosystem, and especially if you like to keep fish.

They’re native to many parts of North America, making them a great alternative to tropical water lilies, which can’t survive any cold weather.

They need full sun (at least 6 hours a day). Keep them from completely covering the water or they may deprive the water of oxygen. While they’re great for ponds, they’re not suitable for aquariums.

#7 Hornwort (Ceratophyllum demersum)

Also known as coontail, hornwort is a submerged, free-floating plant with feathery leaves that resemble a raccoon’s tail. You’ve probably seen plastic versions adorning many fish tanks.

It grows fast and is very easy to care for. Like moss, it doesn’t grow roots, but absorbs nutrients through its stems and leaves. It absorbs nitrate and phosphate from the water, which keeps the water cleaner and algae from growing, making it a great addition for a fish tank. (You will still need to clean your tank, just less often.)

However, it’s also messy, with the stems breaking off, and it grows so prolifically that it’s not great for aquascaping. Most of your maintenance is going to be keeping it from taking over your tank. It also needs medium to high light to grow, so it’s not great in darker corners.

#8 Moss (Bryophyta)

Unlike most other plants on this list, moss doesn’t have roots. Instead, moss absorbs water and nutrients throughout its entire body, which allows it to bind large amounts of heavy metals like lead and arsenic inside its cells. In fact, one study at Stockholm University in Sweden found that Warnstofia fluitans (an aquatic moss) could drop arsenic levels in water by 82% in an hour.

Moss is becoming popular as an alternative lawn in wetter climates, as once established, it’s very low maintenance and does well even in compacted, nutrient-poor, shady soil. There’s over 12,000 unique species of moss, allowing at least one moss to grow in just about every situation possible.

However, you need to keep it weeded and clear of debris (like fallen leaves), and it’s too delicate for more than very light foot traffic.

To grow, skip the moss milkshake and find a reputable moss nursery. They propagate moss in sod-form (similar to turfgrass), and often rescue moss from sites about to be demolished (not from the wild). They can also help you find the right moss for your situation and teach you how to take care of it.

Don’t remove moss from public areas, nature preserves, and the wild. It’s often against the law, and moss grows so slowly that the area may never recover.

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#9 Purple Coneflower (Echinacea purpurea)

Purple Coneflowers produce large, purple flowers that bloom throughout the summer and into fall. Their fibrous roots prevent soil erosion and they help slow down water. They grow well in areas with full sun and prefer well-drained soil while being able to tolerate short periods of wet conditions.

That makes them particularly great on the drier side of a bioswale or rain garden, and in rain gardens that may only get a few uses throughout the year.

They’re easy to grow, attract beneficial predatory insects, and also have some medicinal properties.

#10 Rushes (Juncus spp.)

Rushes grow in shallow water and along water edges like in marshes and along the edges of lakes, ponds, and streams. They may look like sedges at first glance, but while sedges have edges, rushes have round, hollow stems.

Rushes are great for removing heavy metals and nutrients from the water. They produce subdued flowers that aren’t showy but still add interest. You have your pick of species, with 9 common rushes native to North America, so you can find one suited to your area.

#11 Sedge (Carex spp.)

Sedges look like grass, with their long, tapered leaves, and can be used as lawn replacements. They grow branching, fibrous roots that hold on to soil, and form dense crowns that slow runoff.

They can also remove toxic compounds from the water. Many also grow in both wet and dry conditions, which allows them to survive in rain gardens and bioswales between heavy rains.

There are thousands of different sedges, meaning that you can find the right sedge for your particular situation. Some are even native. Just a quick snapshot best for rain gardens and bioswales includes Dense Sedge (Carex densa), Slough Sedge (Carex obnupta), Saw-Beaked Sedge (Carex stipata), and Tussock Sedge (Carex stricta).

How Do Plants Filter Water?

Plants help filter water in 5 ways:

Attracting sediment to the plants. Many of the particles in the water have a negative charge, while the vegetation has a positive charge. The negative charge moves toward the positive, helping the particles settle to the soil.
Plants absorb excess nutrients (like from fertilizer or manure run-off) and heavy metals. This process is called nutrient cycling. When a heavy rain causes synthetic fertilizer with high amounts of nitrogen and phosphorus to run off the lawn, the filtering plants will uptake those nutrients out of the run-off water and use them to grow. Likewise, they may take up heavy metals like lead, cadmium, copper, and arsenic (although this process doesn’t make the water safe for human consumption).
Upright stems slow the flow of water, giving the water (and pollutants) longer to soak into the soil, rather than run off into waterways and storm drains.
Plant roots (especially fibrous roots) hold on to the soil, preventing soil erosion. Decaying plant matter also adds to the organic matter in the soil, improving its water retention and filtration. This means that more water is absorbed and filtered through the soil rather than running off into a storm drain or waterway, and while the water filters away, many particles get caught in the soil.
Shoreline and floating aquatic plants provide shade over waterways, controlling algae growth. Algae need sun to grow and reproduce. Shaded spots limit algae’s ability to get the sun it needs. But be careful with floating aquatic plants. Many are invasive, and if they cover the entire water surface, they can starve the water of the oxygen that other life forms need to survive. You’ll end up with the same problem as an algae bloom – a dead pond.

Can Plants Filter A Tank?

Yes, plants can filter fish tanks. Fish waste is essentially nitrates. Too much nitrogen buildup, and your fish will die. But do you know what plants eat? Nitrates!

In fact, some people keep fish to grow vegetables like lettuce in a system called aquaponics. The fish add nitrate to the water, which is sent to a hydroponics tank with live vegetable plants.

(You can learn more about some good plants for aquaponics here).

The plants take up the nitrates, and the water is filtered for particles and sent back to the fish tank. You get both fish and lettuce to eat.

But if keeping fish is your main love, then you can use aquatic plants like hornwort, houseplants like pothos, or even perennial plants like strawberries, to filter the nitrates for you. You will still need to clean your tanks, as the plants won’t remove the particles, but you’ll need to clean it a lot less. Plus your fish will love some aquatic plants or roots to hide behind.

Conclusion

These plants are just a start. Look for native plants that complement these and fit your unique bioswale, rain garden, or pond. The best plants are an ecosystem, one supported by a long-term maintenance plan.

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