Plantwatch: How ornamental plants can help clean up waterways

Ornamental flowering plants are more than attractive, they can also help to clean up water pollution. Fertilisers and manure on farms are loaded with phosphorus, nitrogen and other nutrients that get washed away by rain and flushed into waterways. Algae can then feed on the nutrients and grow so rapidly that they starve the water of oxygen, killing off fish and contaminating entire ecosystems.

To clean up this pollution, scientists in Miami experimented with using flowering plants floating on waterways, inspired by ancient Aztec floating farms in Mexico. Selections of ornamental plants were grown on inexpensive mats and floated on polluted canals. After a 12-week trial period, large African marigold plants proved the most successful at cleaning the water, extracting 52% more phosphorus and 36% more nitrogen than natural cycling of nutrients removed from untreated water. Trials are now under way using other ornamental plants.

It is worth noting that while filtering out pollution, the marigolds grew high-quality large blooms on long stems, as good as any from commercial flower farms. The hope is to harvest the marigolds to be sold as cut flowers, helping to finance water pollution cleanup operations.