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Soil for rendered planters

Hi! First off, this is completely alien to me. So much so, that as I’ve worked through building my garden project, plants, even turf/lawn has yet to materialise…but it’s time to get started 😊

I've build 2 long L sharped rendered planters so far - I’d filled with gravel and then a good 10” of whatever random topsoil was in the garden (new build but built in a field - doesn’t feel very clay like).

I keep reading mixed views on how best to top it up. Some say use JI3 for a few inches, maybe mix/blend into that topsoil? I plan to plant hostas, alliums, maybe cordylines, so a mix, but keep them good and full all going well.

What advice do you have on topping up the soil/fertiliser please? Keen not to kill everything like I tend to do indoors ☹️


  • WilderbeastWilderbeast Posts: 1,415
    JI3 has a high soil content so I wouldn't bother. You would be better adding lots of manure, well rotted stuff. You can beg it of horse people, buy at garden/DIY centre or get it in bulk online. It will provide lots of goodness and humus to the soil which would be brilliant. It would want working into the soil and can also be applied after planting as a mulch. No doubt others will have different ideas so good luck deciding on your path forward 😜
  • LoxleyLoxley Posts: 5,423
    Yeah if you've only a two or three inches, you may as well lay composted bark / manure and then work it in to the upper layers of the soil. That will help with the soil structure and drainage. Bear in mind though, any bulky organic stuff you add to the soil will shrink and lower your soil level over time so make an allowance for settlement.
  • Thank you both, that’s helpful. I read about ‘tilling’ into soil but having to do that long in advance. Am I safe enough just mixing into the top layer as suggested and planting shortly after?
  • BobTheGardenerBobTheGardener Posts: 11,391
    Yes, especially if you use the bagged farmyard manure available from garden centres, as that is generally weed-seed free in my experience, and you can plant immediately after mixing it in.  In the long term, you would ideally put down a 2" layer (aka mulch) of well-rotted manure on the surface of the beds each autumn.  That will stop weed seeds from germinating over winter and the worms will gradually take it down into the soil for you.
    A trowel in the hand is worth a thousand lost under a bush.
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