3rd May 2023 -

Blanket weeds are a blight for many gardeners, covering ponds with unsightly green growth and harming the health of pond life. It’s therefore important to target these stringy green algae as soon as they appear, whether in a garden pond, or a larger public one. There are a series of blanket weed treatments available in the UK, helping to restore a pond to pristine condition. But it’s ultimately more important to treat the root cause of algae growth in a pond.

Why UK Gardeners Hate Blanket Weeds in Their Ponds

Blanket weeds, sometimes known as water silk or string algae, can be a common occurrence in UK ponds, caused by complex factors such as an excess of nutrients in the water, bad water circulation, water temperature, or excessively high pH levels. Blanket weeds can quickly come to cover large areas of the surface and the water below, leading to serious visual and health issues for a pond:

  • Unnatractive: The green, soggy, and overwhelming appearance of blanket weeds can be seriously off-putting, making a pond look unhealthy and messy. This can undermine an otherwise spotless garden and is one of the key factors for many gardeners looking to remove it.
  • Danger to pond fish: As blanket weeds are dense and stringy, they can cause animals to become trapped, whether that’s fish within the pond or insects around it.
  • Harms other pond plants: Like weeds within a garden, algae on a pond will take nutrients and sunlight from any plants you have growing, threatening their health over time.
  • Lower oxygen levels in a pond: Blanket weeds can consume huge amounts of oxygen from a pond, which will cause further issues to plants and fish in and around them. A good level of oxygen is vital for plants and marine life.

Landscapers and gardeners will therefore be looking to clear all blanket weeds from their ponds as soon as possible, to ensure the health and aesthetic beauty of their outdoor space. Thankfully, there are many blanket weed treatments available.

man in pond

What Are the Best Blanket Weed Treatments?

When looking to treat the blanket weeds within a pond, you’ll have a few options available, with both manual methods and treatment products available:

  • Manual removal: As blanket weed is a string alga, it can be removed manually, using a long stick or a specific weed remover to twist and pull all weeds from the surface of your pond. However, this is a temporary solution to a serious problem, and the weeds will regrow unless you also opt for a specific treatment.
  • Barley straw: A traditional method to stop algae growth on a pond is to submerge barley straw within a mesh bag. You’ll need to have about 50g of straw per m2 of pond surface and can also add lavender to boost efficiency. You should submerge the straw in spring, and only remove it once the colour has changed to black, which will take about half a year.
  • Modern treatments: Many companies now sell treatments for pond algae including blanket weeds, which will work to kill the algae within the pond. When selecting one of these treatments, you should pay careful attention to ensure it is safe for use within your pond, and closely follow instructions when applying it. While this is far more effective than manual removal, it again doesn’t treat the root causes of blanket weed.

Important Additional Steps

To fully treat blanket weed within a pond you’ll need to alter the conditions that caused it to grow in the first place. As the main cause of algae growth is excess nutrient content, you should work to lower the levels in your pond, and avoid contributing to them:

  • Avoid adding soil to your pond
  • Avoid fertilisers within your garden running into your pond
  • Use a net to avoid leaves entering your pond water
  • Top up pond levels with rainwater
  • Install a pond filter 

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