Hydrilla verticillata Care Guide
Hydrilla verticillata is a vigorous oxygenator with whorled serrated leaves; it is invasive and legally restricted in many regions.
Compiled by Aquairi from published sources · Published · Updated
Overview
Hydrilla verticillata is a submerged stem plant in the family Hydrocharitaceae and the only species in the genus Hydrilla. It bears whorled, serrated leaves and is among the fastest-growing aquatic plants, reproducing by stem fragments, turions and tubers.
Taxonomy
- Family: Hydrocharitaceae
- Genus: Hydrilla (monotypic)
- Scientific name: Hydrilla verticillata
- Common synonyms: Hydrilla, waterthyme
Habitat
The species is native to the cool and warm waters of the Old World across Asia, Africa and Australia, with a scattered natural distribution. Stems reach up to 2 m, with leaves 5-20 mm long and 0.7-2 mm broad arranged in whorls of two to eight. It can grow to the surface and form dense mats.
Aquarium requirements
- Placement: background
- Temperature: 16-30 °C (61-86 °F)
- pH: 6-8
- GH: 4-18 °dGH
- Lighting: low to high
- CO2: not required (responds to 5-40 mg/L)
- Maximum height: about 80 cm
Growth and care
Hydrilla is rated very easy and grows extremely fast, in field conditions up to about 2.5 cm per day. It tolerates a wide light range and is an efficient oxygenator and nutrient remover. Frequent trimming, roughly every ten days, is needed to keep it under control. The plant cannot grow emersed.
Propagation
It propagates readily from cuttings and fragments, and in nature also from turions (overwintering buds) and tubers, which is part of why it is so persistent.
Notes on invasiveness
Introduced to the United States via the aquarium trade in the mid-20th century, Hydrilla is now widespread and is regarded as one of the most serious aquatic weeds in Florida and much of the US. It is allelopathic toward some hornworts. Import, sale and possession are restricted in many regions.
Propagating Hydrilla verticillata (Waterthyme)
Overview
Hydrilla verticillata (waterthyme) is a submerged aquatic plant with stems up to 2 m long bearing leaves in whorls of two to eight. The leaves are 5–20 mm long with serrations or small spines along the margins and a midrib that often appears reddish when fresh; air spaces in the tissue provide buoyancy. It is an extremely vigorous oxygenator that can grow up to an inch a day.
Propagation Method
Hydrilla reproduces primarily by vegetative means rather than flowering, and it does so through an unusually wide arsenal: stem fragmentation, rhizomes and stolons, overwintering turions, and subterranean tubers that can stay dormant for several years. This redundancy is exactly why eradication is so difficult and why containment must be absolute.
Step-by-Step
- Stem fragments: any node-bearing piece will root and grow — this is the fastest and most common spread vector.
- Turions: small overwintering buds form in the leaf axils and detach to start new plants.
- Tubers: starchy underground tubers form on stolons and can sprout after years of dormancy, so disturbing the substrate spreads them.
- Stolons: horizontal runners creep through the substrate and send up new shoots.
- For any controlled multiplication, isolate the parent plant and account for every fragment, turion and tuber it can shed.
- Treat all removed material as hazardous: bag it, seal it, and dispose of it in household waste — never compost or rinse it away.
Conditions for Healthy Growth
Hydrilla is native to the cool and warm waters of Asia, Africa and Australia and tolerates a wide range — roughly 16 to 30 °C, pH 6–8 and moderate hardness. It thrives under medium lighting, needs no added CO2, and notably tolerates low light and even some salinity, letting it grow in deeper, shadier water than most competitors. That adaptability is the core of its invasive success.
Trimming & Maintenance
Given growth of up to an inch a day, expect frequent trimming — roughly every week. Top the stems before they mat at the surface, but understand that cutting alone spreads it, since fragments root readily. Net out every clipping the instant you cut, inspect the substrate for tubers, and never share, sell or gift trimmings.
Common Challenges
The overriding challenge is legal and ecological, not horticultural: in the US it is a Federal Noxious Weed that is illegal to possess or transport, and many other regions restrict it. Practically, its multiple propagule types — fragments, turions, tubers and stolons — make it almost impossible to fully remove once established, and its herbicide-resistant biotypes show how hard it is to control even at landscape scale. The only safe posture for a hobbyist is rigorous containment and lawful disposal.