Attack of the Duckweed

One of the reasons we fell in love with Parsons Brake Farm is the beautiful lake overlooked by the garden. Not only is the lake a good size for a fountain and fish, it even has an island with mature Ash trees in the middle!

Sadly, like the rest of the farm, the lake and its banks had been neglected for years and when the heatwave of 2018 hit it turned very quickly to a rather sickly shade of green. Drawing nutrients from a centuries worth of mulch on the lake bed, duckweed took over every inch of water in a matter of weeks. In small quantities duckweed is not a problem as many aquatic birds feed on it, but when an infestation gets severe it chokes all other plants in the lake and becomes a threat to any marine life as the water is stripped of oxygen.

We looked through many ways of treating it. Scraping it proved futile due to the sheer volume of weed. Chemicals were the easy option, but we didn’t want to use anything that may leech into the local ecosystem. Using a percolation system to get more oxygen into the water would help stop it spreading but it was clear that more drastic action was needed.

As the summer heatwave continued the water level in the lake dropped by about a third so we decided to make the most of the opportunity and go all out to clear the mulch from the bottom of the lake, cutting off the duckweeds food supply. Doing this would also mean we could tend to the banks and work on the wider renovations all in one go. Once we got the all clear from our Ecologist that there were no protected species relying on the water we set to work by draining the lake into the slurry pit on the other side of the farm.

We knew it was going to be a big job, but it is fair to say the scale of the task surprised us all!

We were going to need a bigger digger. A much bigger digger.

As the water receded the volume of mulch to be shifted became clear.

Even our trusty Sitemaster couldn’t cope as it bogged down when we got near. Time to bring in the big guns.

A tracked excavator and dumper were the right tools for the job. Even with this heavy machinery the clearing of the lake bed took a week. I couldn’t guess at how many tonnes we moved, and you don’t want to know about the smell!

While the lake was empty we also took the opportunity to give some much needed TLC to the tress on our island. They were stripped of dead and damaged branches and crowned to open up the view of the surrounding farm land. This would ensure the trees would stay healthy and make them less likely to be damaged by strong winds.

Now cleared and duckweed free the lake is now refilling from rain water and as soon as it is deep enough we are planning to install a percolation system to keep the water fresh and oxygenated. The pond will again become a haven for local wildlife and migratory birds, we may even stock a few fish in it too.

After all that hard work, there was only one thing for it: