Implementing a water reservoir in an ordinary garden bed


Marina Bistrin, an avid gardener and also the facilitator of the Watsonia Home Gardening Group at Watsonia Neighbourhood House. Here she discusses their recent implementation of a water reservoir.

My son and I have put in a water reservoir into one of the Watsonia Neighbourhood House garden beds. As the watering roster people are often away on summer holidays when the veggies are at their best and most prolific, it will hopefully keep enough moisture in the bed for them to thrive (the veggies, that is, rather than the roster people!).

We implemented the water reservoir by:

  1. Digging out the fantastic friable soil, which was around 30cm deep, down to the level of subsoil/clay. There, below the root zone of most plants, we dug a 15cm deep x 15cm wide trench down into the clay underneath longways down the whole bed, and then widened out the sides a bit, so it was a bit like a mini bath-tub.
  2. We then laid down double black plastic in that area but did not go right to the edges of the bed, so there is contact between the subsoil and garden soil as before, but with a central water well.
  3. We then added some water absorbent material, including waste paper towelling, shredded paper, coffee husks, blood and bone (to provide nitrogen to help the micro-life there break down the cellulose in the paper).
  4. We then put in some compost that we had made, poured over a clay slurry, and topped it up with the soil that was there in the first place.

There is now lots of nutrition in the bed plus a trench that holds water like a wicking bed but lets excess water out over the sides if it gets too wet.

In summer, we will put in an offcut of wide plastic pipe into the middle of the bed, such that water can be put directly into it without disturb the soil or plants growing there. The dug-out clay can be used for adding to compost as it is meant to increase the nutrient holding capacity for compost, and the spare soil can be reserved for the next garden bed to be installed.

Note that not all clay is the same. For example, the clay at my home much stickier and more water absorbent than the clay at Watsonia Neighbourhood House. From what I have read, clay or clay-loam is an essential element for making nutritent-rich compost.

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