According to Mr Google ponds are “nothing more than shallow holes where water collects. Yet, if left alone, ponds will fill in with dirt and debris until they become land” This is succession and was exactly what was happening to our 30 year-old pond despite my best efforts to remove the more vigorous water plants.
Houttunynia cordata ‘Chameleon’ has pretty red, yellow and green leaves and, 30 years ago, when I constructed the pond and adjacent bog, I had made the mistake of introducing just one small specimen of this alien invader into my bog garden. The rhizomes have crept relentlessly strangling many other choice plants. It had to go, but Houttuynia rhizomes resist weedkiller and are brittle and easily break. Even the tiniest fragments are viable so to eradicate it, all traces must be removed. This is easier said than done, particularly when the rhizomes, which have a characteristic orangey smell, are tangled up with the roots of other plants. The umbrella plant, Darmera peltata, has also spread but much more slowly than the Houttuynia and the large rhizomes can at least be removed, although it takes forceful digging with a spade (or even an axe) to cut through the thick woody layers of rhizomes. Digging up the entire bog and margins of the pond seemed to be the only option to get rid of these unwanted invaders.
3. Liner leak
In our efforts to disentangle Darmera from a very fine specimen of Bowles’ golden sedge, Carex elata Aurea, it became clear that after 30 years the sedge had managed to penetrate the liner in several places. Our claggy soil was partially controlling the leak but the holes explained why we were endlessly having to top up the pond. This was the final straw. It looked as if we either had to accept that we were going to lose the pond (and the habitat) altogether, or we had to bite the bullet and redo the wet area.
Rescuing plants and wildlife
Decision made, we embarked on the project this month and thank goodness the weather was kind to us. The first few days were spent removing plants I wanted to keep and planting them temporarily in Mr B’s vegetable patch (no garlic sown yet this year). The old paddling pool was inflated and used for the sludge from the bottom of the pond, associated wildlife, and many of the pond plants (I suspect the pool will never be the same colour again). I also acquired a couple of buckets for storing pond plants such as bog bean. Alarmingly, bits of Houttuynia seem to have come with the hostas and are popping up in the veg patch. I just hope that I remove them all and that Mr B does not found he has acquired a problem.
Digging out the pond
We had to get a mini-digger into the back garden but the path at the side of the house was too narrow. The digger came through the bottom fence (courtesy of a kind neighbourly farmer), through the “window” in our hedge, across Mr B’s grass-and under our wooden garden arch, (we had to dislodge the top) to the pond.
A large skip was placed in the farmer’s field on the other side of our ha-ha and boards arranged so we could barrow up the slope of the ha-ha and tip the contents into the skip. The remaining water was scooped out by hand and digging commenced. After a long day the old liner was finally exposed.
During all this activity, a Southern Hawker dragonfly was investigating progress and seemed to be laying eggs on the sensitive fern at the edge of the muddy hole. Fragments of Houttuynia were still present in the bog area and the pond-edge so I doubt we have got rid of it. It should definitely be sold with a clear warning. On the second day we finished digging and removed the old liner revealing a layer of sand and the true extent of the pond and bog we had created all those years ago.
Good bye digger and skip!
Remaking the pond
A new layer of sand was added and raked, then levels checked. Sand was covered with a protective matting to ensure the new butyl liner is not going to be punctured by sharp stones. We laid the butyl both in the pond and across the base of what would become adjacent bog.
Another layer of protective matting was laid on top of the butyl as recommended by the wildlife expert, Chris Baines. As Chris suggests in his wildlife gardening book, we also added a layer of loam and some gravel so wildlife would have a home. The gently sloping sides ensure wildlife can easily get in and out and in the centre, the pond is about 3 feet deep. This is exactly how we constructed the pond last time so I hope it proves equally successful. A hose pipe that connects to water butts draining the roof runs under the grass and into the pond so that we can use rainwater to top up the pond. A line of breeze blocks separate the bog from the pond and prevent all the claggy loam in the bog from falling into the pond.
Water was trickled gently into the pond over some scraps of butyl so that the soil was not dislodged and the contents of the padding pool returned (including at least a dozen dragonfly larvae).
Job done! All that remains is to put back the plants (I hope without Houttuynia).