- My water hyacinths and other aquatic plants die in winter. Why is that?
Aquatic plants can be grouped into several hardiness zones: hardy, semi tropical, and tropical plants. Hardy plants are those that can withstand some colder temperatures. A water garden can contain floating plants, marginal plants or bog plants. Aquatic plants include lotus, sweet flag, cat tail, pitcher plant, canna lily, hardy water lily, tiger lily, pickerelweed, marsh marigold, cardinal flower, Japanese iris, corkscrew rush, broadleaf arrowhead and blue flag iris are plants that are hardy in our area.
However the extreme cold snaps from the last several winters have killed many of our cherished perennials, shrubs and trees. The common water hyacinth (Eichornia crassipes) are suitable for zones 8 through 11 and in our climate can be grown as annuals due to recent freezing in winter.
Originally native to Brazil it has become an invasive there and in tropical areas of Africa and China as it displaces native plant species. The European Union placed the common water hyacinth on an invasive species list in 2016. The anchored water hyacinth (Eichornia azurea) is similarly invasive. If these are kept out of natural water areas and confined to a private garden, they don’t cause native plants to be displaced.
The common water hyacinth is a floating leaf plant which grows densely on the water surface. Roots can grow up to 16” long. The fleshy bright green leaves float on the surface by stalks filled with air. The protruding flowers are a light violet colour and form when there is plenty of sunlight in summer. In warmer climates a capsule fruit appears from the flowers after being pollinated but our climate is not warm enough. It is frost sensitive so in our climate it is grown as an annual. The water must be warm enough and still rather than a stream. Placement in a mini pond or vat allows the water to warm up quickly. The season for growing it is May to Oct. Place the floating plants 2 to 3 per square yard. As the plants develop it may be necessary to thin them by fishing out a few or separating a few offshoots.
Overwintering the water hyacinth requires bright light (grow light) during the day for 12 hours and a temperature of 16 C. You can place them in a flat shaped bowl with a water depth of 8”. Avoid temperature fluctuations and supply with aquatic fertilizer. Remove the plants in winter so that the decomposing material doesn’t add debris to the growing area. The plants are not prone to disease or bothered by pests.
Sources
https://www.mygarden.com/plants/common-water-hyacinth Common Water Hyacinths by Karen Heimberger-Preisler Jan.5, 2021.
https://housing.com/news/everything-about-water-hyacinth/ housing.com. Housing News Desk. Water Hyacinth: Facts, benefits, grow and care tips.
https://fviss.ca/invasive-plant/water-hyacinth
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