We hate blanket weed. It makes a green blanket (of course) on the surface, and creates slimy bubbles around itself. Light is obscured for the creatures and plants below and given half a chance it takes over a whole pond.
There are all sorts of remedies for it, including ridiculously expensive chemical treatments and the simple, old fashioned use of bales of barley straw, which are sold at extortionate prices in garden centres but can be found cheaply for sale in the countryside, if you look. But barley straw has to be left floating for months to rot, and is unsightly, so we’ve stuck to a simple old-fashioned method, which is to haul it out and put it on the compost heap – or rather, with a pond the size of ours, make a compost heap with it.
We ignore the advice we read that breaking it up makes it spread faster, because that just doesn’t happen. What we do is wait until the surface bloom appear in large quantities in the spring and then remove it all, piling it around the pond for a day or two so creatures can escape and then wheelbarrowing it to the compost heap.
We have experimented with several ways of getting it out. The most effective is to get into the pond, grab a chunk of it with your hands, and spin it round slowly, keeping it under water: it will draw in strands from all around until you have a lump the size of a football and you can throw it on the bank. If you don’t like handling it, then use a stick to twirl it. The main thing is to do it gently to avoid breaking the strands. But in an infested pond it is possible to extract a large amount in an hour or two.
If you don’t feel like using waders, a really wide rake can extract a lot of blanket weed. We have a 48 tooth nylon grass rake by Spear and Jackson, which is £23 on the web and advertised as self cleaning. We took off the handle it came with and replaced it with a 12 foot pole cut from a hedgerow, so it reaches right out into the pond. It is also useful for raking out fallen leaves in the autumn.
The blanket weed doesn’t disappear. We find, however, that after removing the first surface bloom in the spring it doesn’t grow back to the surface, and remains through the summer as a bottom-growing algae. Our theory is that once it is trimmed, daphnaea and other creatures that feed on algae take over and keep it under control. Removal is best done as soon as the bloom appears on the surface, while frogs are mating, and before their spawn floats into view.