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Algae & Blanket Weed 
in your Pond

Algae & Blanket Weed:
Blanket Weed is a form of filamentous algae and in common with other pond algae occurs when there is an imbalance in the pond ecosystem.  This may occur in early Spring as the temperature of your pond water starts to rise and before the other plants in the pond have re-established after the Winter.  It will usually clear up within a few weeks.  Or it may occur with a newly constructed pond before a natural balance has been established.

Algae will always occur naturally in ponds, but excessive growth can be detrimental.  The following factors will all affect the amount of algae present:

  • the weather, 

  • amount of sunlight penetrating the water, 

  • temperature of the water, 

  • concentration of oxygen in the water, 

  • amount of nutrients present 

  • the number and variety of plants present

A balance is needed between each of these factors to keep the amount of algae in check.

Pond Balance:
For a healthy pond you will need a balance of different pond plants (marginal, floating and submerged including oxygenators) and scavengers (snails and tadpoles).  Increasing the number of pond plants will increase competition for nutrients.  Adding plants and floating plants will increase surface shade and decrease the amount of sunlight available for the algae.  Oxygenating plants will increase the oxygen levels in your pond and reduce the carbon dioxide levels – algae needs carbon dioxide to survive.  The increased oxygen levels will also be beneficial for other pond organisms and snails; snails and tadpoles will actually eat the algae and help keep the balance.  Your pond should have at least one gently sloping side to encourage frogs etc to breed in the pond.  Ensure that you don’t increase the amount of nutrients introduced into your pond: ie avoid using tap water to fill the pond; prevent run-off from lawns or garden borders into the pond (particularly if fertilizers have been used); only use good quality aquatic compost in your planting baskets. 

If algae persists, then you need to improve the balance of your pond.  There are pond additives on the market, but I wouldn’t recommend them as they will not help to correct the basic imbalance in the long term.  

Natural Control:
Once you have taken steps to improve the balance of your pond, you can help by removing as much of the blanket weed as possible by twirling it around a stick.  Leave the blanket weed at the side of the pond for a while so that any small pond creatures living in it can return to the pond.  Barley straw can also be used to inhibit the growth of algae while the pond finds a natural balance – see our Pond Pads which are made from barley straw and release natural compounds which inhibit the growth of algae in the pond water for about six months giving the pond a chance to establish a balance.




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