An introduction to blanket weed: What is it and how can you remove it?

Find out how to build a low maintenance pond.


Blanket weed is a type of algae that is commonly found in garden ponds. Alga is an extensive species, with thousands of species living in different water ecosystems and environments. Spirogyra (sometimes called blanket weed or water silk) is one genus of alga species that exists.

Blanket weed is widely found in freshwater systems, such as ponds. Commonly found in Spring and Summer during the warmer weather, blanket weed can be identified due to its bright green, fine, hair-like texture. These often form together into cotton-wool-like clumps in the water.

There are two types of blanket weed; one grows suspended in water while the other grows submerged in the water. Floating blanket weed floats on the water's surface, creating a blanket that covers the pond. Suspended blanket weed grows from the base or sides of the pond.


Dense algae, such as blanket weed, can be a problem for your pond. Not only does it cover the pond surface and block sunlight, but it can heavily reduce the oxygen available. If blanket weed is about, your pond’s ecosystem will be suffering.

Pond temperatures are naturally lower in Spring, meaning most of your pond life is relatively inactive. During this time, algae is the only significant contributing factor to a pond’s ecosystem. With a lack of competition for vital food sources, algae can grow freely.

Not only is a thick layer of blanket weed incredibly unsightly, but it can affect your pond life, too. Both fish and aquatic plants will be deprived of essential sunlight and oxygen. That’s because algae consume much oxygen to grow, leaving very little for the rest of your pond life.

Low oxygen levels during the summer can significantly affect your pond’s ecosystem. Fierce competition for oxygen can result in aquatic plants dying and fish suffering from hypoxia. In extreme circumstances, hypoxia can cause the fish to die.

The severe consequences of pond algae make it an unwelcome guest in anyone’s pond. As soon as it starts to appear, you need to act to prevent harm to your pond’s ecosystem. But before we cover how to remove and prevent it, let’s cover what causes blanket weed.


Blanket weed results from a culmination of three factors. Each of these factors contributes towards the growth of the blanket. The first of these is sunlight. Blanket weed produces and grows through photosynthesis, just like your garden plants. Sunlight is needed to provide the energy for growth.

A high water pH level is another contributing factor for blanket weed growth. pH is a measurement of the acidity of water. The greater the acidity, the lower the pH value. The greater the alkalinity, the higher the pH value. A pH above 8.5 is high enough to support blanket weed growth.

The other contributing factor for blanket weed is mineral content. Pond water with a high mineral content provides a rich source of nutrients to kick-start a growth spurt. The spores in water will lash up the nutrients to grow rapidly (provided the other two conditions are present).

Many different things contribute to high nutrient content in the water. Fallen leaves, fish faeces, acidic rainwater, organic matter, and fertilisers build up your pondwater’s mineral content. Gradually, the nutrient content increases, providing more food for blanket weed to grow.

How to prevent blanket weed

If you want to try and prevent blanket weed growth, there are some things you can do based on the above three factors. Firstly are the spores. Spores already exist in the water, which are blown by the wind. This is unavoidable and cannot be prevented as you cannot see them.

Next is the sunlight. While you cannot stop the sun from shining, there are other ways you can limit the sunlight on your pond. Consider adding some shade around your pond using trees or tall aquatic plants. This will limit the sunlight reaching the pond, which causes algae growth.

The pH level can also be controlled. Ideally, you want to keep yours at a neutral seven pH level. Keeping your pond at this healthy level limits algae growth and supports a healthy pond ecosystem. Adding natural solutions, such as white vinegar, may also be necessary to reduce pH levels.

Make sure to make the change gradual to avoid upsetting pond life. You should also be careful not to get any on your fish or aquatic plants. While vinegar may be nice on fish and chips, your pond fish won’t like it very much!

You can also do several things to prevent high mineral and nutrient build-up. Firstly, remove any fallen leaves and dead organic matter as soon as possible. Secondly, regularly change your pond water. Finally, use rainwater to top up your pond over tap water.

These preventative measures can help prevent or limit pond algae growth. However, if your pond has fallen victim to a large algae bloom, these steps will be futile until you remove the existing algae. Here are some tips for removing blanket weed and keeping it away for good.

How can you remove blanket weed?

If your pond has succumbed to a spout of blanket weed, you may be tempted to grab a net and scoop it out. Disturbing the algae releases spores into the water, amplifying the problem later on. Scooping out the blanket weed only acts as a temporary solution.

Before attempting to scoop out the blanket weed from your pond, you must kill it. Killing the weed first prevents the spores from being released into the water. Using a suitable pond weed remover should suffice. Ensure to follow the instructions for maximum results.

Once the pond weed remover solution has worked on the blanket weed, you can safely scoop it out using a net. Again, this is only a temporary solution, as blanket weed will likely return sooner or later. Instead, a permanent solution is needed to prevent growth in the first place.


A blanket weed controller is a permanent solution to prevent future outbreaks of blanket weed. A blanket weed controller works by distributing the balance of calcium forms in the water needed for simple cell structure growth, such as blanket weed growth.

The device is fitted between the pump and filter and emits a low-frequency magnetic field that disturbs the balance needed for algae metabolism. This signal results in a sudden and rapid growth spurt that causes the algae to die naturally.

No additional chemicals or treatments are added to the water, which can affect existing pond life. The emitted signal is also harmless to fish and plants and does not disturb their natural ecosystem. The device is safe to use and can installed as a quick DIY job. No plumbing is required for installation.

A blanket weed controller can provide these additional benefits:

• - Low-cost solution that only uses 3 watts of power (the same as an alarm clock).
• - Helps maintain a healthy ecosystem and appearance of your pond.
• - Can easily be fitted around existing piping.
• - A permanent solution to preventing blanket weed.
• - Easy installation with no moving parts or maintenance required.
• - Prevents algae blockages in pipes, pumps, and filters.
• - After fitting and switching the device on, you can leave it to work its magic.

Check out these blanket weed controller FAQs.

With the problems that blanket weed can cause, finding an effective solution to help sustain a healthy and balanced ecosystem can be difficult. A blanket weed controller is a permanent and easy solution for preventing blanket weed growth that your pond will love!