Gardens come to life in spring with an injection of colour on the tips of trees, grass, beds, and borders. But not all shades of green are welcome, as many pond owners will know.

Gardeners with ponds have been urged to take simple steps to prevent the water from turning green. Sharing insights from Koi, Pond, and gardening experts Alec and Val Scaresbrook, Gardening Masterclass said: “Spring should be upon us in April, with the whole garden waking up, including waterlife. So it’s time to prepare your plants and pumps and take a stand against predators.”

The experts warned: “If your pond is going to turn green at all, it’s likely to be around now because of the increased light levels that enable algae to make use of nutrients in the water.”

Pond algae can manifest in various forms, from murky, green water to visible growths on the surface or edges of the pond.

It can also look like green scum, dense strands, or even resemble pea soup. Some types of algae, like filamentous algae, can resemble moss or pond scum, forming long, green, wavy mats.

If your pond has small amounts of filamentous algae, this is usually not a problem. However, excessive algae growth can be unsightly and even lower the oxygen levels in the pond water.

Water plant growth uses surplus nutrients and shades out light, so without competition from other plants, algae in the water can “multiply rapidly”, said Gardening Masterclass.

For this reason, creating a barrier of beneficial plants around your pond can work wonders to stop the water from turning green.

A native British plant known as starwort is particularly effective as it remains active all winter. Starwort is a type of “bunched oxygenator”, which plays a crucial role in keeping ponds healthy and thriving.

Starwort isn’t like most plants. It is usually sold as a bunch of cuttings that can be dropped into the pond or placed into pots and submerged in 18 inches of water.

As the name suggests, once established, the plant grows star-shaped leaves that float like a mat on the pond’s surface.

Plants For Ponds explained: “They release oxygen into the water through photosynthesis, which is essential for fish, amphibians, and other pond life to survive. By absorbing excess nutrients like nitrates, they help prevent algae growth, keeping the water clearer.”

Clear water isn’t just more aesthetic for a garden pond. It means more sunlight can reach the plants, boosting oxygen production and creating the perfect environment for pond life.

Koi love pond plants and will often nibble on oxygenators like starwort. If you have Koi fish or other Carp varieties, it is recommended that you protect plants with barriers to prevent them from being eaten.