It didn’t take long. Scrape the gravel to clear the surface. Out with the knife to cut the shape into the geotextile. Spade the soil, then the clay, into a heap at the back. About 2’6″ deep at one end, shallow, shaped edges. Excavate a small channel under the back frame of the polytunnel to connect with the rain-water filled depression in the gravel outside. Then fill with water and leave for a couple of hours to see how much leakage took place. Almost none. About an hour and a half’s work.
Why? Surely a polytunnel is for growing food, not wasting space with garden ponds?
Well, it fulfils a number of functions. Firstly it helps maintain humidity in the enclosed environment. Secondly, and more importantly, it will provide a habitat for a number of beneficial species, notably frogs! Thirdly, we can plant a number of wetland flowers in the ‘rockery’ around the side that will hopefully attract beneficial insects. Fourthly, it provides a drainage system for the rainwater that collects in the depression outside. This means we don’t have to refill the pond so often, since we aren’t usually short of rain here!
We transferred water from our outdoor pond, which contained a large amount of frogspawn and other microbial and insect pondlife, in order to give it a good start.
After a few days the frogspawn hatched, about 3-4 days earlier than the outside pond, which was still experiencing the prolonged cold weather.
After a few weeks the jelly had all been eaten and the tadpoles spend much of their time resting around the edge.
Most seem to have survived so far. There is other activity in the pond, including some plant life and lesser water boatmen, as well, of course, as the algae the tadpoles are feeding off.
Hopefully in a few weeks time we will have a few resident frogs to feed on the slugs and other unwanted insects!