If you keep fish and houseplants, there's a good chance the two best things in your living room can co-exist right next to each other! The best houseplants to grow on top of an aquarium do two jobs at once. They get a constant supply of water and nutrients, and in return they strip nitrates out of the tank, acting as a living filter for your fish.
Not every houseplant can live like this, though. Here's which ones thrive with their roots in a fish tank, why they work, and how to transition them without fouling your water.
Why grow houseplants on top of a fish tank?
It's one of the oldest tricks in the fishkeeping hobby, and it works because of a happy overlap in biology. The waste your fish produce breaks down into ammonia, then nitrite, then nitrate. Nitrate is exactly what plant roots are looking for.
Fast-growing houseplants absorb nitrates far quicker than most true aquatic plants, because they have unlimited access to CO2 in the air. A pothos with its roots in the tank can make a measurable difference to your test readings within weeks.
It also happens to be a free water and food for the plant! No watering schedule or fertiliser is needed. The plant sits in a nutrient solution that tops itself up every time you feed your fish. It's hydroponics with fish doing the dosing.
The air directly above an aquarium is naturally humid, which tropical aroids love. No gadgets needed; the tank does the work that a pebble tray or humidifier would normally do.
And for the fish, trailing roots create shade and hiding places. Shy fish, fry and shrimp will use a root curtain the way they'd use dense planting.
The best houseplants to grow on top of an aquarium
The plants below can grow happily with their roots permanently submerged in water, provided their foliage remains above the surface. Always keep the leaves dry, as submerged foliage will quickly rot, cloud the water and reduce water quality. With the right setup, these plants can thrive in vases, aquariums and other water-based displays with minimal maintenance.
Epipremnum
The undisputed champion. Pothos is a hemiepiphyte, meaning in the wild it starts life on the forest floor and climbs into the canopy, rooting as it goes, so its roots are built to handle everything from soaked to barely moist. In a tank, it grows dense white water roots within a couple of weeks and hoovers up nitrate faster than almost anything else you can buy.
Any variety works. Classic golden pothos is the fastest, but brings silvery blue, lance-shaped leaves that look far more interesting trailing along the back of a tank.
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Heart-leaf Philodendron and other vining Philodendron
Like pothos, vining are hemiepiphytes with roots that adapt readily to water. Philodendron hederaceum (the heart-leaf philodendron) is the classic choice: quick, forgiving, and happy in the lower light levels most aquariums sit in. Cuttings root directly in tank water, so you don't even need to buy a plant specifically for the job if you already own one.
Syngonium (Arrowhead Plant)
Syngonium comes from genuinely swampy habitats, so wet feet are its natural state. It roots quickly in water, grows fast enough to make a real dent in nitrates, and the arrow-shaped foliage comes in everything from soft pink to crisp white variegation. 
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Monstera
Yes, really. Monstera aerial roots are designed to drink from wet leaf litter and rainwater running down tree bark, and they adapt well to permanent submersion. A is the neatest fit for most setups, with silvery juvenile leaves and a manageable size. A Monstera deliciosa cutting will also root happily in a tank, though give it a plan for where it goes once it gets big, because it will.
Spathiphyllum (Peace lily)
The peace lily is one of the few plants on this list that can grow as a whole plant, roots fully in water, for the long term. Wash the roots clean, sit the crown safely above the waterline in a net pot or floating ring, and it will flower away on fish waste alone. A compact cultivar like adds white-splashed foliage to the top of the tank without swamping it.
Spider Plant Plantlets
When your spider plant produces pups, remove them and add them to the top of the tank. They're pre-packaged aquarium plants as they are soil-free, with root nubs ready to go. Rest them in the filter outflow or a floating support and they'll root within days. They're slower nitrate processors than the aroids above, but they cost nothing if you already have a parent plant!
Aglaonema (Chinese evergreen)
This is a really underrated option. Aglaonema stems root happily in water, tolerate low light better than almost anything else on this list, and bring genuine colour to the top of a tank, with cultivars in red, pink and cream. Treat it like the peace lily: roots in, crown above the waterline, and it will sit there contentedly for months.
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Our top tips to safely transition houseplants to an aquarium
This is where most people go wrong, and it's almost always due to the soil.
Remove every trace of soil before the roots go anywhere near the tank. Soil clouds the water, feeds algae, and can carry fertilisers straight into your fish's home. Slide the plant out of its pot, crumble away as much compost as you can, then rinse the roots under a lukewarm tap until the water runs completely clear. Be thorough. A few stubborn crumbs left in the root ball will find their way into your tank.
Cuttings work brilliantly, and skip the messy stage entirely. For pothos, philodendron, syngonium and monstera, you can bypass soil altogether: take a cutting with a node or two, and place it straight in the tank. It roots directly into aquarium water, so there's no transition shock and no washing. This is honestly the easiest way to start.
Expect a short sulk from soil-grown plants. Roots grown in soil are structurally different from water roots. A transplanted plant often drops a leaf or two while it grows a fresh set of water roots over two to four weeks. Cuttings skip this, which is another point in their favour.
Keep leaves and crowns above the waterline. Roots in, foliage out. Any leaf sitting in the water will rot, and a rotting leaf in a closed system is a pollution event.
Watch out for pesticide residues. Commercially grown houseplants are sometimes treated with systemic insecticides that are lethal to shrimp and harmful to fish. Buy from a nursery you trust, rinse thoroughly, and if you keep invertebrates, consider growing a fresh cutting in a jar of water for a few weeks first as a quarantine step.
Give them somewhere to sit. A hang-on-back filter chamber is the classic spot. Otherwise, use suction-cup holders, a net pot wedged in the hood cutout, or simply drape vines along the back rim with roots trailing in.
Choose fish-friendly placements. Goldfish and larger cichlids will graze on tender roots. If your fish are nibblers, keep the roots inside the filter where they can't reach.
Plants to avoid growing on top of an aquarium
Skip anything that hates wet feet. Succulents, cacti and Snake Plants will rot at the base. Avoid Dieffenbachia, whose sap is best kept out of a closed system with livestock. And be cautious with slow growers generally; a plant that barely grows barely filters.
Will the plants sitting on top of an aquarium hurt the fish?
The plants on this list are safe with their roots in the tank. Aroids like pothos and philodendron do contain calcium oxalate in their tissues, but this stays in the plant; it isn't released into the water. The only risks are the ones covered above: soil residue, submerged rotting foliage, and pesticide-treated plants.
If you've struggled to keep houseplants alive, this might be the most reliable way to grow one, and our are the natural place to start.
And if a cutting eventually earns a promotion to a pot of its own, our will ease it back into life on land!
Unsure whether a particular plant will cope with tank life? Get in touch with us today and we'll happily advise you.