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My fiancée and I bought our first house last December and the previous owners did a fantastic job with the garden. Beautiful plants, shrubs etc, and a small pond (estimate about 2m x 1m and 2m deep). Up until a few weeks ago the water was fairly clear with a few lilies. I noticed we had frogs (I counted 8) and they produced frog spawn which has since given birth to lots of tadpoles, although I haven't seen them.

The problem now is that we've suddenly hit summer and duckweed has blanketed the pond. I would like to manage the duckweed as I know it's hard to get rid of completely, but I'm not sure if I'll be harming the tadpoles and frogs if I remove it as they might like it?

I have absolutely no idea, its the first time I've had a garden with grass let alone an ecosystem! So any advice would be really appreciated.

  • An interesting observation is that if you do a google image search for duckweed, you will notice that half the images has a happy-looking frog in it. – pipe Jun 8 '16 at 4:15
  • A prized feature of many Japanese gardens is a still pond solidly covered in duckweed - a more astonishing sight that a golf green in a desert. – Jim Young Jun 8 '16 at 4:32
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Congratulations on your new neighbours. I have frogs in my pond for some of the year. They have no problems with duckweed or plants. They do like:

  • areas of water that do not move, perfect for duckweed!
  • shallow areas where they can sit and pretend to be invisible
  • lots of bugs

Frogs and fish do not go well together. Fish will eat frog eggs. Pesticides, herbicides and chlorinated water are not advised for a frog habitat.

You can leave the duckweed as it takes up nitrates in the water. Harder to control is stringy algae. Nothing eats it and it will cover the surface of the pond and shade out everything else.

I tried UV lights and algaecides but the most effective and least intrusive method was a copper anode moderated through an electrical current. Expensive but effective. You might find this to be a problem later in the summer. See here for comments on large scale use or here for a retail product that I use for algae control.

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  • Nice answer kevinsky...I have to add that that tiny pond needs a way to drain and to be infused with freshly oxygenated water. Lillies are best to shade and hide the fauna safely in water. He is so very right about the algae...it will suck the oxygen out of the water and make it a toxic place for your frogs...is there a drain of some sort? A little leak so that it is necesssary to add fresh water? If at all possible don't use tap water with chlorine, fluorine and all kinds of crap involved. Hopefully you have well water. Can't be stagnant for healthy frog/fishes... – stormy Jun 7 '16 at 22:41
  • @stormy Right you are, any pond, even a small one, needs some kind of circulation. A pump and filter chamber are common. I did assume that they were there. – kevinsky Jun 7 '16 at 22:43
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    Yeah but that is for someone like you sweetheart...I always assume they know little about gardening especially how everything is connected. Even knowing an awful lot about botany won't prepare anyone for the multitude of different departments to consider when trying to manipulate the natural environment. If they think TMI,well fine, that should at least make them feel better about what they do know. I've run across homeowner made ponds and NONE nada, had any circulation. Full of chlorine...sicky tap water!! No life, except for algae tough stuff! Easy to fix harder to educate for maint. – stormy Jun 7 '16 at 22:53
  • What algae? The OP is not reporting such a problem. – Graham Chiu Jun 8 '16 at 0:50
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    And no one has suggested barley straw yet? I have full sun on my aquaponics setup and no algae problems, probably because all the nutrients are taken up by the tree growing in the radial filter, and weeds that I grow! – Graham Chiu Jun 8 '16 at 0:58
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Duckweed is just annoying if you have fish because then it reduces your surface visibility so that you can't see them. But otherwise there's no down sides.

If you use a net to remove the duck weed and put it in the compost, or feed the chickens, you may find that the increased light levels might stimulate algae growth if there's a lot of nitrates etc in the water.

If the tadpoles need oxygen, they can come to the surface. Or, you could just install a cheap solar fountain to help aerate the water.

If you do get algae problems, one way around this is to heavily plant around the pond edges so that the plants take up all the nutrients.

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I have a very small purpose built frog pond as they were living in my ground lever bird bath. It is in a semi shaded spot and I find the duckweed can get quite thick which i believe keeps the water temperature down which in turn slows the tadpoles development right down. So i carefully skim some of the weed off the top with a small net, checking each lot by hand for any tadpoles. then placing the but weed beside the pond so any crawlers csn go back to the water. Just enough to thin the layer of weed. It grows back very quickly so is a never ending job. But I quite like it and frogs seem happy.

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