We've got this small concrete pond that we wish to fill in to make a flower bed.

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The pond is 60cm deep at one end and 30cm at the other.

It currently has two 1cm holes in the bottom of it, which has been enough to keep it from filling with rain water over the winter.

My approximate plan is to fill it with whatever rubble or gravel I can get my hands on, and then the top 15cm with soil.

But my concern is drainage. Even if I drill more holes in the bottom, won't soil eventually wash down and fill up those holes? What can I do to make sure it doesn't start filling with water?

  • Is this adjacent to a building? I would be concerned about water getting into the foundation of that building.
    – Boba Fit
    Commented May 23, 2023 at 12:32
  • A few taps with a crowbar to crack the bottom will do. Commented May 23, 2023 at 12:43
  • 1
    A whole 15 cm/6" of soil? not exactly nice to your future flowers...
    – Ecnerwal
    Commented May 23, 2023 at 15:38
  • What mostly will block drainage is organic debris. I suggest cracking or breaking the whole bottom. Commented May 24, 2023 at 0:50

2 Answers 2


Either crack the bottom as Polypipe Wrangler suggests, or drill more holes in it. Put in a centimeter or three of loose drainage rock, then geotextile fabric big enough to cover the bottom and reach up all 4 sides (fold, don't cut, the corners) then fill as you like.

The geotextile fabric should hold the fines in. Cracks or plenty of holes will let the water out.

Trim the top of the geotextile fabric neatly after you fill the bed with soil (or vast quantities of rubble and not much soil as you plan - in which case use some more geotextile on top of the rubble layer.)


I think you need to open more drains before filling in. You want your garden to drain at least 1 inch per hour once it is filled in. I can't see that much soil draining through 6 sq. cm.

Break up the bottom until you see soil, and then fill it in. The drainage in the area will still be impeded by the walls, but it should be adequate.

As an aside, 15cm of soil isn't very much for most garden plants. You may want to research what kinds of plants you want there before you decide how much soil to backfill with.

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