The Inverted Life Cycle
Curly-leaf pondweed has one of the most unusual life cycle patterns of any aquatic plant in North America — it grows and thrives in conditions (cold water) that limit or eliminate most other aquatic weeds, and it declines when conditions are optimal for most aquatic plants (warm summer water). This inverted phenology compared to native warm-season submerged plants is the key to its ecological success and its management challenge. By occupying the spring growing window before native plants establish, it gains competitive dominance in the littoral zone, and by dying before summer, it releases its stored nutrients at exactly the moment when summer algae are ready to bloom.
Life Cycle Phases
Turion Germination: Late Summer to Fall
The curly-leaf pondweed life cycle begins in late summer and fall, when turions (the spiny, compact overwintering structures produced the previous spring) germinate in the sediment. Germination is triggered by declining water temperatures below approximately 20°C, typically in August–October depending on latitude. Turions germinate while temperatures are still warm enough for initial growth but declining — initiating a new generation before winter. In mild years or southern locations, turion germination may begin earlier. Initial growth produces a small rosette of leaves close to the sediment surface.
Winter Growth
Curly-leaf pondweed grows actively through winter — even under ice in northern lakes — at water temperatures as low as 1–4°C (33–39°F). While other aquatic plants are completely dormant or leafless, curly-leaf pondweed continues to elongate and develop. This winter growth is slow compared to summer growth but represents a fundamental competitive advantage: curly-leaf pondweed is accumulating biomass and depleting nutrients in the shallow sediment while native plants are completely inactive. By late winter (February–March), curly-leaf pondweed plants may be 20–50 cm tall in shallow bays that will open from ice before deeper portions of the lake.
Spring Surge
The most critical and ecologically impactful phase of the curly-leaf pondweed life cycle is the spring growth surge (March–May in most of the northern U.S.). As water warms from 5° to 15°C, curly-leaf pondweed growth rate accelerates dramatically. Stems elongate rapidly, reaching the surface of shallow water (1–3 meters depth) in April and May and forming dense canopies that block light. By late April or May, dense curly-leaf pondweed stands have occupied large areas of the littoral zone in infested lakes, often before ice has melted from deeper portions and certainly before native warm-season submersed plants have begun significant growth. This spring canopy dominance is the competitive advantage that allows curly-leaf pondweed to suppress native plants in many northern lakes.
Turion Production
Simultaneously with the spring growth surge, curly-leaf pondweed produces turions in the leaf axils and at stem tips (April–June). Each plant produces numerous turions — some research suggests up to several hundred turions per plant in favorable conditions. Turions drop to the sediment as plants begin to senesce and carry the population's genetic material through the summer dormancy period and into the next growing season.
Senescence and Die-off
As water temperatures rise above 20–22°C (approximately 68–72°F) in early summer, curly-leaf pondweed enters senescence. Stems yellow, weaken, and fragment. By June–July in most northern states, the above-ground biomass has largely decomposed or settled to the bottom. This natural die-off is simultaneous with the release of nutrients from decomposing biomass — a phosphorus and nitrogen pulse that enters the water column at the beginning of the peak summer growing season, potentially fueling algal blooms.
Ecological Effects of the Life Cycle
Competition with Native Plants
The spring canopy formed by curly-leaf pondweed reduces light available to native submerged plants that are just beginning to grow in late April–May. Species like wild celery (Vallisneria americana), muskgrass (Chara spp.), and native pondweeds that depend on spring light for growth establishment can be severely suppressed in heavy curly-leaf pondweed infestations. Multi-year competitive exclusion can gradually reduce native plant diversity in heavily infested lakes.
Summer Nutrient Pulse and Algae
The decomposition of curly-leaf pondweed biomass in June–July releases phosphorus stored in plant tissue into the water column. Studies in Minnesota lakes have documented measurable increases in epilimnetic total phosphorus concentrations during and immediately after curly-leaf pondweed die-off events. This nutrient pulse can trigger or intensify cyanobacterial (blue-green algae) blooms that persist through the summer. Management programs that effectively control curly-leaf pondweed in spring have in several studies documented subsequent reductions in summer algal bloom intensity — confirming the nutrient-release link. For management guidance, see curly-leaf pondweed control methods.
References
- Catling, P.M. & Dobson, G. (1985). Biology of Potamogeton crispus in Ontario. Canadian Journal of Botany 63:2108–2116.
- Bolduan, B.R., et al. (1994). Curly-leaf pondweed phosphorus release. Journal of the Minnesota Academy of Science 59:3–8.