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I have a 8m x 3m bed in my garden which has a mix of well-established shrubs (Weigela, ornamental cherry, smoke bush, roses), ground cover (ivy and honeysuckle), and red valerian, lemon balm and lungwort.

I recently dug up a snowberry to replace it with a hydrangea, and found that the bed is actually about 20cm of gravel with two layers of weed membrane under it. It has obviously been there a long time as enough leaf litter and detritus has built up to turn the gravel into poor soil, into which the valerian and the other smaller plants are rooting. The weed membrane is largely intact and is blocking the roots from spreading into the soil below.

I'd like to clear some of the ivy and try planting some other plants in there. My aim is to slowly move towards permaculture/forest gardening ideas, growing more edible plants.

But all the roots tangled up in it mean removing the gravel and membrane is extremely difficult (apart from the intrinsic difficulty of shifting large volumes of gravel!) The soil under the membrane is well-compacted clay with apparently little organic matter.

Any ideas how to deal with this situation? I had thought of putting a fork down through the membrane to open up some holes and then just planting in the gravel, but it would be pretty poor soil. Should I focus on improving the gravel and leaving the membrane alone?

  • I'm confused - is the membrane both on top of and beneath the 20 cm of gravel? and do you actually mean 20cm, 8 inches, of gravel? Presumably, then, the larger shrubs you mention are rooted into the soil beneath the membrane/s? Actually, a photo of the area would be useful – Bamboo Apr 10 at 13:35
  • I'll do a photo when I can. From the top, it's: plants; gravel (and roots); 2 layers of membrane; clay. The large shrubs are planted through holes in the membrane, yes. – aucuparia Apr 10 at 14:13
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20cm of gravel is an unusually high amount - the layer is more often less than half that. Presumably the double membrane beneath is perhaps because it's the thinnest membrane so they doubled up.

If you want to start planting other stuff in there, you might as well accept that the only way you're going to do that successfully is to remove the gravel, take out the double layer of membrane, then dig over the clay with a fork, inspecting it as you do because its possible they removed topsoil if the layer of gravel is really that deep, leaving behind mostly subsoil. You can usually tell if its subsoil (depending what part of the UK you're in) because it looks different - for instance, in the London area, it's often orange/yellow in colour. When you've decided if it needs topsoil, put that in but also add plenty of organic material, such as composted manure or any kind of soil conditioning compost (but not potting compost). If you're not in the middle of a big city, you may be able to find leaf mould or spent mushroom compost from local suppliers, both of which are sources of organic material. If you decide it doesn't need topsoil because the soil is just heavy clay, you could even add back in a little of the gravel to help lighten the clay, working it in with as much organic material as you can get hold of. Unless there's a slope or drop in soil level from where the large shrubs are growing, then its likely the soil beneath is just clay topsoil, and although that's difficult to work, it does hold onto nutrients quite well, so it's not all bad.

After that, if you can, let the area settle for a week or so prior to planting. Note that the plants you describe (such as valerian) which have rooted themselves into the gravel are plants which will grow on poor thin soil quite happily - you will need to remove those and anything else that's small (meaning not a large shrub) at the same time, to allow as much free access to the soil beneath as possible. If you want to keep one or two, stick them in pots for the time being and add them back in later, when the soil preparation is complete.

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