A clear plastic tub sat on my kitchen windowsill all January, lit by a small grow light I clamped to the frame. Inside floated a scoop of red root floater and frogbit. I pulled both from the woods-edge pond before the first hard freeze. They stayed green while the pond outside locked under ice. I check that tub most mornings while the coffee brews.
So which floaters take the cold? The winter hardy floating plants that live through it outside are hornwort, frogbit, and some duckweed. These go dormant and come back in spring. Tender tropical floaters die at the first frost. Red root floater and water hyacinth fall in this group. They only make it through winter if you bring them inside.
The split comes down to where each plant evolved. Hornwort sinks to your pond bottom as the water cools and waits out the cold as a dense clump. Frogbit drops small winter buds called turions that settle into the mud, then float back up once your water warms. Some duckweed does the same. A fraction of the colony sinks to survive while the surface layer you see dies off.
Tropical species have no such backup plan. Water hyacinth and red root floater turn to mush the moment ice forms on their leaves. They want water above 50°F (10°C) to stay healthy, which no outdoor pond holds through a northern winter. I learned this with my first batch of red root floater. A single overnight frost wiped out a whole surface I had spent the summer growing. The next morning it was a brown slick.
Here is the part to plan for. Even cold hardy aquatic plants barely grow in winter. Clemson Extension data from 2024 shows that plant growth and nutrient removal both fall sharply in cold months. So your hardy floaters will not clean your water or spread the way they do in summer. Expect a long pause, not active growth, and adjust your filtering to match.
Your first step is to match plant choice to your hardiness zone. If you live in zone 6 or colder, lean on hornwort and frogbit for the outdoor pond and treat tropical floaters as summer-only color. In zone 8 and warmer, many tender floaters skate through a mild winter outside with little fuss.
For any tender plant you want to carry over, the trick is overwintering floaters indoors. Scoop a small handful into a clear tub of pond water and set it on a bright windowsill. Add a cheap clip-on grow light if your window faces north or the days run short. That little bit of warmth and light is the whole reason my windowsill tub stayed green while the pond froze.
Keep the indoor tub topped off and skip the fertilizer until spring. Plants barely sip nutrients in low light, and extra feeding just fuels algae. Watch the water level too, since a warm room evaporates a tub fast. I top mine off with dechlorinated water about once a week. A loose cover helps slow that loss without blocking the light.
Come April or May, you scoop the survivors back into the warming pond and they take off again. Wait until your nights hold above 50°F (10°C) before you move tender floaters out. A late cold snap can undo all your winter care in one night. One saved handful reseeds a whole season, so you never have to buy these plants twice.
Read the full article: Floating Plants: Benefits, Care and Risks
