Dear Chief Secretary to the Treasury,
I'm afraid to tell you there's no money left.
Signed, Liam Byrne

(Outgoing Labour Chief Secretary to the Treasury. May 2010)

Saturday, 27 March 2010

Beating the green blanket

Blanketweed**, the bête noire of garden ponds - or should that be the bête verte?

Ghastly stuff, that can choke oxygenators and because it takes up so much space means there's less room for fish. Removing it manually can mean hours of trying to twiddle it round a garden cane, a bit like making candy floss, only to find it's magically glued itself to a bamboo leaf joint and refuses to let go.

But, there's something that'll deal with it - barley straw.

It works too, even if the pond doesn't have a pump. Just throw in some bags or 'logs' of the stuff and let them work their magic. It takes about four weeks for them to start working, and they should stay active for about four to six months, depending on the amount of straw used.

Apparently as the barley straw decomposes it releases chemicals or enzymes which inhibit algal growth. Robyn Rhudy has an easy, but detailed, explanation and links to a scientific paper. Both make interesting reading and should tell you everything you need to know, both are very readable, so there's no need to be worried about too much technical stuff or incomprehensible scientific jargon.

If you don't fancy the idea of seeing lumps of barley straw in amongst the plants in your, now crystal clear, pond there's a liquid alternative - barley straw extract. All the blurb about it claims it will work almost instantly, instead of having to wait a few weeks for the bacteria and bugs to get to work on the straw, because the stuff is an extract of the decomposing/fermenting straw. If you use this it'll possibly mean two or three doses throughout the growing season.

There are barley straw pads and pellets too, all are meant to work equally well. There are some that contain lavender stalks, but these should only ever be used along with a pump/filter that moves the water around, because concentrations of lavender can kill insects, even in water.

We Rigbys have only tried using little (about 8" diameter) barley straw bags we were able to get from our local pet shop. Each one cost us just over £1 and is, essentially, a loose ball of straw inside a plastic net. We did think about making our own, but as our pond only needed four we decided that getting, and storing, a whole bale of straw wasn't worth the effort - and most of it would either end up on the compost heap or be used as a playground for mice.

Last year we dropped the bags into the bottom of the pond, weighed down with a large holey stone, but it would seem that keeping them nearer the surface might be more effective - because the warmer surface water keeps the bacteria and other micro-organisms happier. We don't plan to 'experiment' as such, there's no point, we just want to keep the blanketweed away so we'll tuck some bags of straw in behind the baskets sitting on the marginal shelf and see what happens.

Decaying barley straw isn't toxic, even though the EU tried to prohibit its' use. Here's an extract of a comment from Dr. Nick Everall from here (he wrote the paper linked earlier). He does seem to know what he's talking about.
The chemical aspect of straw control is universally accepted as a lignin derived breakdown process and thus banning straw at the levels it is applied would be like banning leaves falling into watercourses in the Autumn
All sources seem to say we can't overdose the pond and kill off everything (including the new fish we've bought for the local heron) so we reckon the more bags the, err, clearer the water.

As an aside, it would be nice if Spring would arrive in Rigby Town. It's the first year we haven't had big daffodils out for March 1st, and they still aren't showing their faces - the ground is too cold, because it's too wet. Only one or two celandines so far too, even though there are crocuses, which is unusual because our celandines are usually welcoming us in through the gate in February.

A bit of botany.

Blanketweed is Spirogyra spp. A filamentous alga that lives in freshwater habitats and was once studied as sixth formers following the A-level Botany syllabus - an exam that probably doesn't exist any more. It's named from the spiral arrangement of the chloroplasts. It doesn't like moving water very much, but will happily choke a small, nutrient rich, pond. There are some rather good microscopy pictures on this Dutch site, which even show the wretched stuff mating.

And the paper written by Dr Nick Everall is titled "Control of Algae with Straw.". Go on, read it, you know you want to.

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