Brazilian waterweed

Brazilian waterweed key facts

Growing Difficulty

Beginner-friendly

Lifespan

Perennial; constantly renews itself from fragments

Size

Stems 40–100 cm or more long, 2–4 cm wide

Temperature

20〜24℃

Watering

Grows without CO2 or fertiliser; absorbs nutrients from the water

Lighting

Survives weak light, but stronger light gives denser stems. In poor light it turns pale and spindly.

CO2 & Fertilizer

No CO2 needed. It grows without fertiliser and absorbs surplus nutrients, helping to curb algae.

Water Temperature & Quality

Optimum 20–24°C, tolerating 4–30°C. Hardness and pH matter little; it actually prefers cool, hard water.

Substrate & Attachment

Grows planted or simply floating.

Trimming & Propagation

Grows very fast; cut and replant stems. Fragments root easily.

Cautions

Listed as a Priority Control Alien Species. Never dump it in rivers or ponds, prevent overflow from outdoor containers, and dry even small fragments before binning them.

About Brazilian waterweed

Anacharis (Brazilian waterweed) is a hardy, beginner-friendly aquatic plant that thrives in cold or cloudy water and regrows from stem cuttings, growing 40–100+ cm with whorled leaves.

7 things to know before growing Brazilian waterweed

1. 1Light & Placement

   Anacharis prefers bright conditions but should be kept out of direct sunlight — indirect light near a window or an aquarium light works well. Without enough light, stems tend to stretch and grow leggy, so aim for several hours of brightness each day.

2. 2Water Temperature

   This plant tolerates cold water well and rarely dies back even as temperatures drop. Sustained high heat through summer can damage the leaves, though, so keep it in a well-ventilated spot and avoid extreme warmth.

3. 3No Substrate Needed

   Anacharis grows happily just floating in water without being planted in substrate. If you want it rooted, lightly tuck the stem base into the substrate or weight it down with a plant anchor to keep it from drifting.

4. 4Propagation and Responsible Disposal

   Simply cut a stem to any length and place it in water — roots will form at the cut end and grow into a new plant. Note, however, that Anacharis (Egeria densa) is listed as a "priority control" invasive species on Japan's Ministry of the Environment list of alien species harmful to ecosystems, and it has naturalized in rivers and lakes across the country. Use extra plants within your aquarium, and dry out leftover plants and trimmings before throwing them away with household waste. Never dump it into rivers or ponds, and if you grow it in an outdoor container, make sure rainwater can't make it overflow and wash plants out.

5. 5Regular Trimming

   Growth is vigorous, so stems will quickly lengthen if left unchecked — trim periodically to keep the size in check. Trimmed sections can be reused as new cuttings, so nothing goes to waste.

6. 6Water Quality

   Because it tolerates dirty water and absorbs nutrients as it grows, Anacharis can help keep tank water more stable. Just watch the density, since overgrowth can block water flow.

7. 7Choosing a Plant

   Look for firm stems with deep green, evenly whorled leaves at each node. Avoid stems with discolored cut ends or leaves that look translucent or mushy.

Frequently asked questions about Brazilian waterweed

Q.Can it grow without being planted in soil?

A.Yes, Anacharis grows well simply floating in water without any substrate. If you'd like it anchored, lightly tuck the stem base into the substrate or secure it with a weight.

Q.Will it survive through winter?

A.It tolerates cold water well, making it relatively easy to keep through cooler months. That said, sudden temperature swings can stress the plant, so if it's kept outdoors, avoid conditions cold enough for the water to freeze over.

Q.What should I do if the stems get too long?

A.Simply trim the stems with scissors to whatever length you like. The cut sections will root and grow into new plants just by sitting in water, so trimmings can be reused to propagate more.

Q.Can it be kept together with goldfish or tropical fish?

A.Long known as a classic "goldfish weed," Anacharis has traditionally been kept alongside goldfish and tropical fish. It offers hiding spots for fish, and its hardiness means it recovers easily even if nibbled on.

Q.Is this okay for someone growing aquatic plants for the first time?

A.Anacharis is considered a beginner-friendly aquatic plant that doesn't require special equipment to grow well. Since it keeps renewing itself from cuttings, it's forgiving to experiment with even if something goes wrong at first.

Handy Growing Tools for Brazilian waterweed

Learn more about Brazilian waterweed in the encyclopedia

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