Trying to control blanket weed & algae in my pond

Trying to control blanket weed and algae in my pond

Over the past year, I’ve watched in despair as algae has wrapped its ever extending arms around my pond; I feel like algae is threatening to suffocate my pond at any moment.   The other ponds I’ve created in the past have never really suffered with algae to the same extent that my current pond has.  The smaller pond that we built in our garden some years ago (this pond was installed in exact the same spot where my current pond stands – it was my current pond’s predecessor) experienced an algae bloom in late spring, each year, but it was far less noticeable than the algae is in my current pond, now.

My pond, as pictured on the 7th June 2020, with Leucanthemum vulgare in bloom on the right hand side of the picture and Verbena bonariensis coming into bloom on the left hand side of the picture.

My current pond was created just over a year ago.  When this pond was filled with water for the first time, the aquatic plants I had ready to plant were all very young specimens, so until the plants developed, my pond was really just a vessel of open water with only one or two minuscule leaves on the surface of the water.

Sunlight promotes algae growth and within a few days of installation, the pond water had turned deepest green, it was full of algae.  Happily, the water became clearer almost immediately after my Oase pond kit was installed.  I’m absolutely certain that the Oase products I’m using are still helping to reduce the algae; however, I’m sorry to say that my pond is now almost choked with algae.  Algae seems to bubble up around Ranunculus aquatilis and other aquatic plants that grow over the surface of the water, threatening to submerge and drown my plants, as it strangles my pond with its suffocating green scum.

Methods I’ve tried to control algae in my pond

I took this photograph of the Oase filter and pump on the 21st April 2019, just before the equipment from Oase was added to the pond.

Oase pond kit

Oase kindly sent me some pond equipment to try out.  Since April 2019, I’ve been trialling the following products, in my pond:

After these Oase products were installed in my pond, the effect they had was transformative!  My pond changed from a pond with vivid green water – to a pond with clearer water – it was remarkable!  I dread to think what my pond would look like without the use of these products, but I am sorry to say that my pond water isn’t free from algae after using this equipment (and other products) over the past year.

I took this photograph on the 21st April 2019; as you can see, my newly created pond is green with algae and topped with a liberal dusting of pine needles!
I took this photograph on the 12th May 2019. The Oase AquaSkim 20 is in position in the pond where this equipment is collecting up leaves and pine needles from the pond water.

Manually removing the algae by hand

Blanket weed is quite amazing; it forms long hair-like structures and develops rapidly in sunny locations.

Earlier in the year, the algae was either gently scooped up with a net or wound around a stick and then left at the side of the pond, to allow any creatures that had been accidentally caught up in the algae to find their way back into the water.  However, in springtime and summertime I leave the algae alone – so as to avoid disturbing newts, dragonflies and damselflies who lay their eggs in the water at this time of year.  The last time any algae was manually removed was on the 22nd March 2020, when a single scoop of algae was lifted out of the water.

Fishing out algae from the pond, as pictured on the 22nd March 2020.

Barley Straw

This pack of Barley straw was added to my pond on the 10th April 2019.

Usually, I use packs of barley straw to help control algae in my ponds, but this year, (for the first time) I’m yet to purchase a pack of barley straw.  This omission wasn’t intentional, I was waiting for an aquatic plant to come into stock before placing my order with a specialist aquatic plant nursery, (to save the same delivery driver having to make an extra journey to my home during the COVID-19 pandemic).  I’m still waiting for the plant to come into stock, so I’ve yet to place an order; instead I’ve been trying out other algae controls.

Barley straw pictured in my pond on the 18th April 2019.

Barley Bio Control

Last year, I purchased Barley Bio Control to control the algae in my pond.  However, as I was still experiencing problems with algae after I’d been using Barley Bio Control for over six months, I became open to trying other methods; so I ceased using Barley Bio Control and tried an alternative product.

This week, (on the 7th June 2020), I decided to try this product again, so I added an initial dose of Barley Bio Control to the pond water.  When I added the Barley Bio Control, I had already added my weekly dose of Nualgi to the pond water, earlier in the week.


A lovely reader contacted me to say how well Nualgi was controlling the algae in her beautiful pond.  I’d not heard of Nualgi before, but on hearing that Nualgi was natural and safe for wildlife, I decided to give Nualgi a try.

I purchased my bottle of Nualgi online.  On the 8th March 2020, I started using Nualgi in my pond for the first time, following the instructions on the pack.  Early in the morning, once a week, the exact quantity of Nualgi has been added to my pond, precisely as directed on the pack.  Sadly, I’ve yet to notice any discernible improvement.  Since I’ve been using Nualgi, the algae in my pond has continued to grow.  Naturally, it’s hard to gauge these things – had I not used Nualgi I might have been dealing with twice or three times as much algae, as I’m faced with currently – this is true of all the products I’ve trialled.

Water Daphnia

I then decided to buy a quantity of Water Daphnia (also known as Water Fleas, or by their scientific name of Daphnia pulex) as these creatures feed on certain types of algae.  I wasn’t sure how many Water Daphnia were in each pack, but I took the plunge and purchased ten packs!  I added the Water Daphnia to my pond when they arrived, on the 7th April 2020.  Perhaps I didn’t add enough Water Daphnia, or perhaps the algae in my pond isn’t the right sort of algae for them – but since I added the Water Daphnia – I’ve not noticed any reduction in the algae in my pond.

These are the packs of Water Daphnia I added to my pond on the 7th April 2020.

I’ve not solved the algae problem in my pond yet, but I’m still actively searching for a solution – one that isn’t harmful to plants or wildlife.  I’m currently considering trying a specially developed ultra-violet light.  Meanwhile, here are some tips to help you avoid problems with algae in your own pond……..

My pond, as pictured on the 7th June 2020, with Leucanthemum vulgare in bloom on the right hand side of the picture and algae covering the much of the surface of the pond.

Tips for avoiding problems with algae when you’re setting up a pond

Choosing the best position for your pond

Sunlight promotes algae growth.  My pond is in a very bright position, it enjoys full sunshine.  If you position your pond in a similarly sunny position, you’ll be far more likely to have problems with algae.  Choosing a partially shaded position for your pond will reduce the temperature of your pond and limit the intensity of light that your pond is exposed to, which will go some way to help to diminish algae’s ability to reproduce, thereby reducing the algae in your pond.

Algae would struggle to gain such a stronghold in the cooler, darker waters of a shaded pond.  However, many aquatic plants thrive in full sunshine or partial shade.  Sunny ponds attract a wide range wildlife, as insects gravitate towards the warmth and the light, so partially shaded or sunny ponds are usually more preferable.

Falling leaves

When choosing a position for your pond, avoid siting your pond near trees and shrubs, whose roots may puncture your pond liner. Deciduous trees shed their leaves in autumn and winter. Take care to collect up any fallen leaves that fall into your pond.

Avoid siting ponds close to trees; as tree roots can damage and puncture pond liners.  Take care to prevent the leaves from nearby deciduous trees and shrubs (plants that shed their leaves in autumn) falling or being blown into your pond.  Many gardeners net their ponds, but you could also use a pond skimmer – I have an Oase AquaSkim 20 in my pond – it’s absolutely brilliant!  The skimmer is in constant operation, collecting up fallen leaves and any debris from the surface of the water; it’s very effective, picking up tiny pine needles, as well as larger leaves, and plant material.

My Oase Aquaskim 20 creates continual movement in the water, which will help to prevent the entire surface of my pond freezing over in wintertime.  This will allow birds and other wildlife more reliable access to the water in the pond, throughout the winter months.

Please note: I do not recommend using the Oase AquaSkim 20 for use in wildlife ponds – please see this update for more information.

Pond depth

Shallow water heats up more rapidly than deeper water.  Heat and light fuel algae growth, making shallow ponds more prone to problems with algae.  My pond is deeper in the centre, where it extends to around 75cm (2.5ft) deep.  The sides of the pond are shallow; all around my pond there’s a gradual slope into the water and areas for marginal plants, which require shallower water.

Many aquatic plants require a certain depth of water to thrive.  It’s worth checking out the specifics for any aquatic plants you’re considering purchasing, so you’re aware of their preferred position, ideal water depth, and you’re absolutely certain you can accommodate each plant, before you make a purchase.  It’s also important to consider these requirements when you’re purchasing aquatic planters for your pond plants – you don’t want to buy a planter for one of your marginal plants that will stand proud above the surface of the water.

A deeper area of water that extends down to around 60cm (2ft) deep, will be beneficial to plants, wildlife, the health of your pond, and its resilience to algae.

This drawing shows a cross section of my wildlife pond.


If the area around your pond has steep, sloping sides that allows rainwater to wash fragments of soil, compost, and nutrients into your pond water, then you’ll be helping to fuel the algae growth in your pond.  Sculpt the landscape around your pond in such a way (avoid deep inclines and instead create a level or very gradual, shallow slope down to your pond) so as to avoid this problem.  Plant ground cover plants and taller plants around your pond, to hold onto the soil and help prevent nutrients and debris being washed into the water when it rains.


After my pond was constructed, I filled it up with tap water, as my water butt was totally empty at the time.  Tap water is known for causing rapid algae blooms in new ponds – so use rain water instead, if you can.  This year, I would have liked to have topped up my pond with rainwater, but we’ve enjoyed a particularly dry and sunny spring, which has meant there hasn’t been sufficient rain to allow me do this; instead, I’ve had to continue topping up my pond with tap water.

NB. Avoid the temptation to take water from another pond, as you can spread pests and diseases (as well as algae and invasive plants) to other ponds by doing this.

Aquatic plants

Some aquatic plants, like waterlilies, have large leaves that float on the surface of the water, shielding the water from sunlight.  Make sure you have included a sufficient quantity of leafy plants with floating leaves to shade the surface of your pond.  I prefer ponds with very little open water, as I love to see as many plants as possible, so I tend to cover at least three quarters of the surface of the water with plants, if not more.  If you’re creating a pond, aim to cover at least half of the pond’s surface area with plants.  Remember that many aquatic plants are in leaf during the main summer growing season, but not many aquatic plants provide leaf cover during winter and early spring.  Although algae grows at a reduced rate during the cooler months of the year, when there are fewer hours of sunlight; algae may still be increasing its hold in your pond during the winter and early spring.

As well as installing plants with leaves that float on the surface of the water; to create a healthy pond, it’s important to provide enough oxygenating plants that grow as submerged plants, under the water.

Plants make such a difference to the look and feel of the pond; they have a great effect on the health of a pond and the amount of algae in a pond.  When choosing plants for your pond, select aquatic plants that remove nitrates and help to maintain clear water.  Many plants remove nitrates, including: our wonderful native Hornwort (also known by its botanical name of Ceratophyllum demersum), Bogbean, a super UK native plant (also known by its botanical name of Menyanthes trifoliata), the fabulous Marsh Marigold (also known by its botanical name of Caltha Palustris), and another of my favourite native UK plants – the beautiful Water Crowfoot (also known by its botanical name of Ranunculus aquatilis).  There are many native and non-native aquatic plants that remove nitrates, including waterlilies.

Marsh Marigold (Caltha palustris and Caltha palustris alba) and White Water-Crowfoot (Ranunculus aquatilis) flowers, in bloom on the 23rd April 2020.

If you know, you’re planning to create a pond in the future, it’s worth buying some pond plants in advance and growing them on in tubs of water.  This way you’ll have larger, more established plants, with more leaves to shade the water when you come to plant up your pond.

Do you have a shadier or sunnier side of your pond?  If so, tailor the planting to provide more surface cover, with lots of leafy plants, like waterlilies, shielding the brightest side of the water.  Plan for any areas of open water to be situated on the shadier side of your pond.

Aquatic compost

Plant your pond plants in aquatic compost or a low nutrient compost, which won’t add an excess of nutrients to your pond; as any extra nutrients will exacerbate algae growth.  Use specially developed aquatic plant fertiliser to feed your plants – I use tablets that I add to the compost in each of my aquatic planters, each spring.

When potting up your aquatic plants, use aquatic planters that are designed to be used underwater.  Rather than buying expensive pre-cut pond liners, I saved money by purchasing a roll of natural hessian material.  When I’m planting up an aquatic plant for my pond, I cut out a square of hessian, which I pop inside the pot to use as a liner; this helps to keep the aquatic compost safely inside the planter and stops it from clouding the water.

Barley straw

Packs of barley straw can be added to ponds to control algae.  This is a lovely, natural solution; the barley straw packs are simply dropped onto the water, where they float for a couple of weeks or so, before eventually sinking to the bottom of the pond.

Barley straw isn’t something you add to your pond once to fix your algae problem for all time; you’ll need to add a new pack of barley straw at least every six months.  Before placing your order, check the information from your supplier for directions on how many barley straw packs are required for the size of your pond.

See my update after emptying my pond and filling it up with rainwater

To see my pond update from spring 2022 and see my wildlife pond after it was emptied and filled up with rainwater, please click here.

To see photographs of the spring and early summer flowers in my pond, please click here.

To see all of the articles I’ve written about this pond, please click here.

For all articles that mention water features, please click here.

Other articles that may interest you………….

For tips on super plants to grow for bees and butterflies, please click here.

For information on why I recommend using peat-free compost and to find out about my Compost Trials, please click here.

For advice on how to create a successful meadow, please click here.

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One thought on “Trying to control blanket weed & algae in my pond

  1. Malcolm Storey

    June 8, 2020 at 10:54pm

    I suspect filling and topping up your pond with the liquid fertiliser that passes for tap water is the cause of your algal blooms this year.

    The best way to remove blanket weed is with a garden cane – just twist it and the algae will form a ball which you can slide off. This allows you to work round plants much better than with a net. You’ll never get rid of all of it of course.

    The only thing I’ve heard of that eats algae is ramshorn snails.

    PS: I keep getting interupted about no pinnable things!

    • Author

      Pumpkin Beth

      June 9, 2020 at 7:20am

      Hello Malcolm

      We were also twirling canes to lift the algae out (as well as using a net), but I was anxious not to do this now, in case any eggs came out with the algae and because I wanted to avoid disturbing the newts. There are a lot of snails in the pond, but I’ve not seen any Ramshorn snails, yet. I’ve my fingers crossed that some find their way to our pond! Thank you for your ideas.

      I hope this message finds you safe and well.

      Best wishes

  2. Malcolm Storey

    January 12, 2023 at 4:36pm

    We’ve largely solved the algae problem in our pond by introducing Bladderwort (Utricularia minor). It forms similar underwater green growth but it doesn’t float up to the suface and look unsightly. Of course it’s probably harmful to the Daphnia etc but that’s just ecology in action!

    • Author

      Pumpkin Beth

      January 12, 2023 at 8:17pm

      Hello Malcolm

      It’s good to hear from you. I drained a lot of water out of the pond last year and filled it up with rainwater; I’ve not had a problem with algae since then. When I filled up the pond after installation I had wanted to fill it with rainwater but I was advised by a pond expert to use tap water – I regret not following my instincts, but I’m happy with how everything is going in my pond now.

      I’m glad that your pond is going well.

      Best wishes

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