Blanket and duck weed again, and other matters

Last year’s big effort to clear blanket weed by physically removing it has paid off, so far. It has been surfacing again in clumps this spring but not nearly as much, so an hour’s work in waders was enough to clear it. Every bit that comes out removes nutrient from the pond, because – looking on the bright side – you could regard blanketweed growth and removal as a way of sucking up excess nitrates and phosphates and putting the pond in better balance.

There is still plenty of it close to the bottom but I suspect that the combined effect of the clouds of daphnaea and the three grass carp – all algae eaters – may be keeping it under control.

Since this is the breeding season for many creatures we pulled the weed out in small clumps and then laid it by the water’s edge so they could escape. We seem to have large numbers of common newts, more than we have seen before, and we made sure they didn’t get trapped. They obviously like it here.

Only very small quantities of duckweed so far. Spoke to a gardener in the neighbouring village of Mellis about his duckweed problem on a pond with perhaps a third more area than ours. He has hauled out tons of it over the years, he says, using similar method to mine, but it covers the surface again within days and even stays there through the winter, so he has given up for the moment and is concentrating on his lovely garden. The whole pond is an unsightly green.

Why is it so intractable? My guess is that it is  partly because the pond has not been cleaned for a long time so it has a couple of feet of mud on the bottom which makes working in it difficult. That also discourages repeat cleanings, which are needed if the exercise is to be effective in any given year. Duckweed survives by sinking to the bottom and lying in a dormant state over winter so old mud may be riddled with the stuff, just waiting to surface if there is any light to prompt it, which would be the case after partial cleaning. Furthermore, the excess nutrients that stimulated the duckweed in the first place stay in the pond and continue to accumulate as the leaves rot, if they are not thoroughly removed. As with blanket weed, disposing of duckweed gets the nitrates and phosphates they have fed on out of the pond.

With a thoroughly contaminated pond perhaps cleaning is the only way to conquer the menace, and of course that’s not something to be undertaken lightly.

Otherwise, our pond revetments have been stable over the winter and no replacement stakes or timbers are needed. Having used softwood instead of oak stakes to hold up the timber boarding for cost reasons, we are expecting to have to replace them every five to seven years but so far there are no signs of deterioration after nearly four years. The softwood boarding, which was double treated under pressure, was claimed by the supplier to be good for 15 years under water.  By then the banks should be well and truly consolidated.


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