Wednesday, 20 May 2015

Duckweed (Lemna minor) and water hawthorn (Aponogeton distachyos)

Top pool which overflows to create the waterfall into the pond 
       I was confronted with an interesting conundrum yesterday: my pond is enlivened by a waterfall which works  on the basis that water spills over from an upper pool which is fed by a pump.The puzzle was - how did tadpoles get into the top pool? The pump is switched on each day and the turbulence means that nothing lives in it on a permanent basis. Only two possibilities came to mind: a. they had climbed up the sheer rock face from the pond, or b. they had passed through the pump, shot up the pipe and been regurgitated into the top pool.

      I ruled out possibility a. by close examination of the tadpoles in question and could determine no sign of climbing boots. In any case, there were no feet to put them on. The more I thought about it, the more unlikely that option seemed. Also, imagine the conversation;

"'Ey, pass the belay device, Tad"

"Oops, sorry Tad - forgot to bring it - let's have an alga butty", say six voices. And this brings another difficulty regarding working in teams - they all have the same name. Derived from middle English, 'tad' means 'toad' and 'pol' is 'head' and goes some way to explaining Mrs Thatcher's poll tax, although I'm damned if I know why parrots are always called Polly. The comment about alga raises further questions: read any advice about what to feed pet tadpoles on and top of the list is boiled lettuce. Boiled lettuce????? Where the hell does a tadpole get lettuce, let alone a boiled one? And who found out that they like it? Somewhere there must be a bloke who's devoted his career to tadpoles, trying different menus and maybe conducting psychological studies. Tadpoles in normal circumstances eat plant material, small insects and even each other if times get hard. Drop a bit of Spam in the pond and they'll demonstrate their lack of discernment by descending on it in hoards.

That left option b. and the difficulty here was the fact that there is a filter on the pump to stop it getting clogged with weed and other detritus. I can only think that tadpole body structure at an early age is so flexible that they can be squeezed through the workings of the pump without being damaged. Admittedly some of them did look a bit punch-drunk but apart from that seemed unmarked. Maybe they sported other injuries like black eyes but it's hard to make out a black eye on a tadpole.

      As I watched, they departed in the water rushing over the edge back into the pond. They seemed to be taking turns at doing it, bringing to mind the water chute at one of those woodland holiday resorts we once took our kids to. When I moved closer and held my breath I swear I heard them shouting wheeeee! as they went over the edge.
Waterfall with water hawthorn
      A tadpole reentering my pond via the waterfall will quickly come across a floating patch of water hawthorn, also called water hyacinth (Aponogeton distachyos). This is a South African semi-evergreen, rhizomatous, pond plant which adapts well to the English climate. The white flowers, resembling yacht sails, appear in spring and autumn during the cooler weather and accordingly it is a good companion for the water lilies which  flower in the heat of the summer. It has an attractive scent which, as this can best be appreciated by putting your nose close to the water, is probably best enjoyed by the recuperating tadpoles.
Water hawthorn (Aponogeton distachyos)
      Providing company for the water hawthorn is the ubiquitous duckweed (Lemna minor). This consists of tiny leaves with a single floating root. Two plants will bud off the parent and the effect is a quickly spreading carpet over the surface of the pond. It doesn't like the cold, so in winter it forms organisms called 'turions' which sink to the bottom and remain dormant until spring. Then it restarts growth and pops up again ready, like a Nazi u-boat, to see what devastation it can cause.
Duckweed (Lemna minor)
      Duckweed can be a problem, because in carpeting a pond it cuts out light to oxygenating plants lower down, leading to their death. The resulting de-oxygenation of the water has a knock-on detrimental effect on fish and other water life, so regular skimming of the plant is desirable. Birds (especially ducks) and fish eat the stuff and apparently it is sometimes grown as a commercial crop to provide feed. I find it a useful regular addition to the compost heap. The turmoil caused by the waterfall restricts spread to some extent, but skimming is still necessary. A difficulty in doing this at tadpole time lies in the fact that the taddies like to feed off the bottoms of the plants, so you always get a net full of the little wrigglers and separating them is a bit of a nightmare.

      Successfully getting completely rid of duckweed is an unlikely scenario, due to the potential of each single plant to so quickly replicate. Its sudden appearance in your pond can be explained either by the fact that the sticky roots have adhered to birds feet and plumage or, in some cases, the introduction of new oxygenating plants which have the odd bit of duckweed attached. Either way, compromise and learn to live with the little floater. The tadpoles like it.

      For information about frogbit, a plant with apparent relevance to the tadpolian nature of this blog, go to Frogbit.


1 comment:

  1. Hi John - Such a pleasure and delight to read your latest instalment. Your garden must be really something. When I read your blog it makes me wish I had a garden again. Hope it will not be too long before you pop up on my reading list again. Take care.