Blanket weed is a type of algae, scientifically called filamentous algae. It’s also commonly known as string algae or silk weed. Pond owners often struggle to identify blanket weed because it occurs in different forms.
Typically, it appears either floating on top of or submerged within pond water as clumps of thick green, hair-like strands. These dense clumps have no leaves or stems but will attach themselves to pond walls.
Ornamental ponds with high sunlight exposure and organic nutrients create the perfect environment for it to thrive.
Blanket Weed is similar to Duck Weed – see our Duck Weed Guide for more details.
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Not sure if you have blanket weed?
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Here at Envii, we know it can be difficult to keep your pond clean and blanket weed free – but you do need to keep an eye on your pond throughout the year. Here are 5 problems that can be caused by blanket weed in your pond.
1. Bad Aesthetics
Blanket weed ruins the appearance of a pond.
2. Chemical Imbalance
Not only does it make ponds unappealing, it’s often a sign of chemical imbalance in the pond. (Yes, even if the water looks clear!)
3. Lower Pond Oxygen Levels
It consumes large amounts of oxygen from pond water. This creates a harmful environment because aquatic plants and fish are forced to compete with it for oxygen. Especially in summer, when pond oxygen levels are low.
4. Deprives Pond Plants
Floating blanket weed deprives submerged oxygenating pond plants of sunlight. Preventing their process of photosynthesis and further reducing pond oxygen levels.
5. Harmful to Fish
Fish can get tangled in submerged string algae. When unable to escape, fish can potentially suffocate and die.
It has three main causes: 1 – excessive sunlight, 2 – a high pH and 3 – excess nutrients.
Nutrients in pond water, caused by the build-up of organic matter, act as a food source for the blanket weed. While sunlight stimulates growth through the process of photosynthesis. Blanket weed, like other forms of algae, thrives in ponds that have a higher pH, typically anything above 8.5. These three factors are also the likely reason for any recurring problem.
Here are some simple tips to help you prevent blanket weed from returning in the future:
1. Fill your pond with aquatic plants that will absorb excess nutrients in the pond.
2. Keep an appropriate stock of fish to suit the size of your pond.
3. If and where possible, provide your pond with shade.
4. Check your water quality regularly with a test kit to make sure your pH, KH and GH levels are balanced.