How to overwinter brazilian waterweed

Brazilian Waterweed is hardy to roughly USDA zone 5 — winter lows around -29°C. That means it can stay outside all winter in most temperate gardens. Brazilian Waterweed is properly hardy and overwinters outside without fuss. Tidy away anything dead or diseased, apply a mulch over the crown to steady soil temperatures, and otherwise leave it alone — many hardy plants actually need a cold period to flower and grow well the following year. Save hard pruning for the right season rather than doing it in autumn.

Tidy and mulch in late autumn; leave the plant undisturbed until spring.

No winter watering needed in open ground. Containers only need water in long dry, frost-free spells.

Cutting brazilian waterweed hard back in autumn "to tidy up". That removes the growth that shelters the crown, and on some plants removes next season's flower buds entirely.