What not to dig

classicgardenpond

If you look around the web at advice on making wildlife ponds you might think something like this was ideal, with different water depths and ‘shallow’ shelves for planting. Although it looks quite neat and tidy, ponds like this are too steep-sided and too deep to create the best wildlife habitat. The shape always reminds me of one of those giant open-cast mines.

Most people giving advice on how deep to dig a wildlife pond make their ponds too deep. I heard someone on the telly the other day say the depth they were aiming for was up to a child’s waist.

So I measured Katy’s 7 year old waist – 70 cm from the ground. Roughly twice as deep as the deepest area of my pond, twice as deep as it needs to be.

Ponds like this won’t be lifeless, especially if you are scrupulous about clean water. Practically any shape of hole in the ground will be a good wildlife habitat if you can keep the pollutants out. But natural ponds this size are rarely so deep or steep sided.

Digging down deep also makes it impossible to create the very gently shelving shallows where most wildlife lives.

A better shape which overcomes these problems is shown in the photo sequence for my new pond. Though we’re still learning: I expect people will improve on my designs.

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2 Responses to “What not to dig”

  1. Tristan Hatton-Ellis Says:

    Jeremy, I don’t agree with your post in this case. Here’s why not: although you can dig your hole this shape and size, it doesn’t follow that your pond has to be. The shape the liner takes is only the starting point; I think much the best thing to do then is backfill with some low-nutrient material such as sand (maybe with a little aquatic compost thrown in). The backfill material can then be used to create the shallow water that so many animals and plants crave, plus it will protect the liner from UV light from the sun.

    As for deep areas, well here I agree that the stuff about freezing solid is quite unlikely, even here in Wales. I expect this advice has come from the specifications required to keep fish. But personally I like to grow plants that prefer deeper water like lilies and pondweeds, and it’s nice to retain some open water. In this case, deeper water in the centre is a boon.

  2. Jeremy Biggs Says:

    Hi Tristan

    I think I might be misunderstanding your comment – so apologies if that’s the case – because I wasn’t suggesting the pond should be the profile shown in the picture – the opposite really.

    But you’re right, if you dug the pond like this, you could change the shape afterwards by adding a clean and inert substrate like play sand. Though I’d steer clear of aquatic compost for the time being as I’m not convinced it doesn’t add unwanted nutrients – but that’s just a feeling at present as we haven’t tested it thorougly ourselves yet. My only other thought is: if you’ve got a liner in already, there might be problems with the material slipping of the slopes and into the bottom.

    But you make a good point about deep water: if it’s unpolluted and you can keep it that way, it’s a good habitat for the aquatics that like…well….deeper water.

    In practice, though, I’ve hardly seen any ponds where the deep areas are in good enough condition (i.e. unpolluted enough) to support the more sensitive plants that you mention. It would be wonderful if there were more ponds like this!

    The other problem I see with deep areas in small ponds is that you end up with very few shallow areas because you need steep (or vertical) steps to get the depth. And then it become a trade off between deep or shallow – and as so many things like shallows I naturally go for those first.

    But of course – this doesn’t work for the plants you mentions that like deeper water.

    To get deep water and good shallows combined you need quite a large area – often more than people can fit in in realively small modern gardens.

    But I think all this points to the fact that we’re still in the early stages of knowing how to design really good wildlife ponds in gardens. We’ve got some of the basics but there’s still a huge amount to learn.

    Jeremy

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