Nitella flexilis (Stonewort)

Nitella flexilis | Stonewort

A native submerged oxygenating stonewort for garden ponds and wildlife ponds, providing fine underwater habitat, natural cover and support for clearer pond water.

Native oxygenating stonewort for wildlife ponds, fish cover and natural pond balance

Nitella flexilis, commonly known as Stonewort or Smooth Stonewort, is a native submerged oxygenating pond plant suitable for garden ponds, wildlife ponds, natural ponds and larger planted water features. Although often sold alongside oxygenating pond plants, Nitella is technically a stonewort, a type of charophyte algae, rather than a traditional flowering aquatic plant.

This makes it a very useful choice for customers who want a more natural pond environment. Nitella flexilis grows below the water surface, forming fine green strands that create soft underwater cover. This submerged growth provides an excellent habitat for small pond creatures, aquatic insects, newts, tadpoles, fish fry and invertebrates. In wildlife ponds, this type of underwater structure is incredibly valuable because it gives small animals somewhere to hide, rest and feed.

As an oxygenating plant, Nitella flexilis supports pond balance by photosynthesising below the water surface when enough light reaches the growth. During daylight, submerged oxygenators release oxygen into the water and help take up nutrients as they grow. This can support water quality and may help reduce the nutrients available to algae as part of a wider pond planting scheme. It should not be treated as a guaranteed cure for green water or blanketweed, but it is a very useful plant for natural pond health.

Nitella flexilis is suitable for ponds of most sizes, from wildlife ponds through to larger natural ponds. It can be introduced by simply dropping the strands or bunches into the water around the pond. It does not need to be weighted or planted, although it may establish better if gently placed into aquatic soil, gravel or a soft pond substrate.

For best results, start Nitella flexilis in around 20 cm to 30 cm of water while it establishes. Once settled and growing well, it can gradually colonise deeper areas of the pond where light levels are suitable. A general planting depth guide is 30 cm to 1.5 m, although established growth may reach deeper areas in clear water.

This is a great choice for customers looking for a native, non invasive oxygenator that provides excellent underwater habitat and supports a more balanced wildlife pond.

Key benefits

• Native submerged oxygenating stonewort

• Suitable for garden ponds and wildlife ponds

• Fine green underwater strands provide excellent habitat

• Useful cover for fish fry, newts, tadpoles and invertebrates

• Supports clearer water as part of a balanced planted pond

• Helps take up nutrients as it grows

• Can be dropped straight into the pond

• No need to weight or plant in most ponds

• Can establish in shallow water and spread into deeper areas

• Suitable for most pond sizes

• Native and not invasive

• Excellent natural choice for wildlife friendly ponds

Reasons to buy Nitella flexilis

Nitella flexilis is a brilliant choice if you want a native oxygenating plant with a very natural look. Unlike more rigid or upright oxygenators, it forms soft green strands below the water, creating valuable underwater cover.

It is especially useful in wildlife ponds where habitat matters. Newts, tadpoles, small fish, pond insects and other aquatic life benefit from submerged plants because they provide shelter and a safe place to move through the water.

This stonewort is also a good option if you want an oxygenator that can be introduced easily. Bunches can be dropped into the pond without needing to be potted, weighted or planted, although planting into soil or gravel can help in some situations.

Nitella flexilis works well with other pond plants, including native marginals, waterlilies, floating plants and other oxygenators. Together, these create planting at different depths and help make the pond feel more mature and balanced.

Care instructions

Introduce Nitella flexilis into a pond with good light levels below the water surface. Submerged oxygenators need light to photosynthesise, so very dark, shaded or heavily murky water may reduce establishment.

Start the bunches in shallow water, ideally around 20 cm to 30 cm deep. This gives the plant the best chance to receive enough light while it settles into the pond.

Once established, Nitella can spread into deeper water where conditions are suitable. It may grow at greater depths in very clear water, but it is not recommended to start it too deep.

No planting is normally required. Simply drop the strands into different areas of the pond, ideally near shallow shelves, plant baskets or softer pond substrate.

If you want to encourage stronger establishment, gently tuck some strands into aquatic soil, gravel or a planting basket.

Avoid adding Nitella flexilis immediately after using pond treatments unless the treatment is clearly safe for oxygenating plants and aquatic life.

Remove excess growth if it becomes too dense, especially in smaller ponds. Take out any decaying or loose material before it breaks down in the water.

Flowering period

Nitella flexilis does not produce flowers.

It is a submerged stonewort and is grown for its fine underwater growth, oxygenating value and habitat benefits rather than flowers.

Its main value is below the water surface, where it provides shelter, texture and support for a natural pond ecosystem.

Size, spread and growing conditions

Botanical name: Nitella flexilis

Common name: Stonewort, Smooth Stonewort

Plant type: Native submerged oxygenating stonewort

Height: Usually grows as submerged strands below the water surface

Spread: Can gradually spread through suitable areas of the pond

Growth rate: Medium, depending on light, water clarity and pond conditions

Flower colour: Not applicable

Flowering period: Does not flower

Position: Full sun to partial shade, provided enough light reaches below the water

Recommended starting depth: Around 20 cm to 30 cm

General planting depth guide: 30 cm to 1.5 m

Possible established depth: May colonise deeper water in very clear ponds where light reaches the growth

Soil: Can be dropped loose, but may benefit from aquatic soil, gravel or soft pond substrate

Native status: Native to GB and Ireland

Invasive status: Native and not invasive

Best suited for: Wildlife ponds, garden ponds, natural ponds, fish ponds, planted ponds and larger water features

Wildlife value: Provides underwater shelter for fish fry, newts, tadpoles, aquatic insects and invertebrates

How many bunches will I need?

As a useful guide, allow approximately 3 bunches per square metre of pond surface area.

For example:

• 1 m² pond area: approximately 3 bunches

• 2 m² pond area: approximately 6 bunches

• 4 m² pond area: approximately 12 bunches

This is only a guide. The amount needed will depend on pond depth, water clarity, planting density, shade levels and how quickly you want the oxygenator to establish.

For new ponds, it is usually better to introduce a good mix of oxygenating plants rather than relying on just one species.

5 bunches per pack

Your plant on arrival

Nitella flexilis is usually supplied as loose or weighted bunches of submerged oxygenating growth.

The appearance can vary depending on the season and growing conditions. It may arrive as fine green strands, and the density of each bunch can vary naturally.

Place the bunches into the pond as soon as practical. Do not allow oxygenating plants to dry out.

If the bunches are supplied loose, simply place them around the pond in suitable shallow areas. If supplied weighted, they can be lowered gently into the pond.

Dispatching your pond plants

Pond plants are carefully selected, packed and dispatched to help them arrive in good condition. As living aquatic plants, Nitella flexilis can vary in colour, length and density depending on the season, weather and natural growth cycle.

Unpack your oxygenating plants promptly when they arrive. Keep them wet at all times and introduce them to the pond as soon as practical.

Do not leave Nitella flexilis exposed to sun, wind or drying conditions. If you cannot place it into the pond immediately, keep it in a container of pond water in a cool, shaded position for a short period.

For best establishment, place into shallow water first, then allow it to grow and spread naturally into suitable areas of the pond.

Explore more oxygenating pond plants or browse our complete pond plants range.