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What to fill up the bottom of a deep container with?

Hi all,
I did a quick search here but didn't find an answer.

We've some 50 cm wide containers that hold around 60 litres.  If we were to put some bedding plants in, some bulbs or other not deep going plants what could or should be used to fill the container base?

It seems obvious that some holes should be made in the container for drainage, as well as some broken crockery placed over the holes.  But it seems like a huge waste filling it with compost when only maybe 30 cm at most is going to be actually used by the plants.  Also, it'd get a bit heavy(ish).

I've read online that old plastic bottles, polystyrene blocks and styrofoam peanuts and other non-degradable waterproof and light weight items could be used.  If using small items like those packing peanuts, they should be put into a bag first, to prevent roots growing into through them.  I also read that some of that weed prevention membrane/landscape fabric can be used as a barrier between 'filler' items and compost on the top.

Has anyone any experience doing this?
Are there things that work better, or particular practices that just don't work?



  • MontysGalMontysGal Posts: 70
    I use chunks of broken polystyrene from white-goods packaging. I’ve always put the compost straight on top without putting a layer of anything in be honest it never occurred to me to do so, but I’ve not had any problems. 
  • K67K67 Posts: 2,507
    There was a thread quite recently and I think it covered most of the things you mentioned.
    I use those flimsy square plant pots  and landscape fabric on top although a plant can grow roots through it. The fabric just stops the compost settling down between whatever you have in the base. 
  • WibbleWibble Posts: 89
    I have chunks of polystyrene in mine. I cut up a builder’s bag I’d had soil delivered in as membrane between the polystyrene and soil (not strictly necessary). I got the polystyrene by asking on a local Facebook page if anybody had any from packaging- saved it going to landfill.
  • Check out your cupboards, old jumpers are great!
  • LoxleyLoxley Posts: 5,234
    The upturned pots and membrane idea is probably the most efficient, free pots are easy to come by if you don't have any yourself
  • KeenOnGreenKeenOnGreen Posts: 1,790
    We found that plastic bottles eventually leaked oxygen and became squashed by the soil above them.   Polystyrene works best for us, however I would recommend putting a membrane on top of it, as otherwise there is a risk of polystyrene granules ending up in your soil.  
  • GravelEaterGravelEater Posts: 119
    K67 said:
    Thanks for the link.  Clearly I didn't use the right search terms else I would have posted there.  Good job!

    Thanks to everyone for the suggestions and comments.  Interesting.

    I'm thinking I may try a cheat way, with something like geraniums (pelargoniums), and just plant them into smaller containers, which I'll stand on top of bricks inside the larger container.  So not a solid compost surface, but the foliage of such plants should kind of spread and cover over the gaps between the smaller containers.
    Not the quickest dismantling job, but it'd make it all light weight individually.  Should make for an easier time to ditch and replant annuals in future.
  • AthelasAthelas Posts: 750
    @GravelEater, I’ve done something similar with hollow concrete blocks. If you can find a smaller plastic pot of the right size, the outer edge can overlap and fit over the deeper container. Just make sure to test you can still take the inner pot out, for example to repot or replant, when it’s filled with compost and plants. It shouldn’t be a problem for a relatively small/shallow pot. As an added bonus, the inner pot can have a lot more drainage holes than large decorative pots which often just have one stingy hole at the bottom.
  • borismrdjaborismrdja Posts: 35
    edited April 2021

    this is how i did it

    its a kind of self-watering pot  
    upturned nursery pots and/or polystyrene chunks around with cinder block(with holes facing up) in the middle.

    i didn't cover the cinder block with bubblewrap but filled the holes with compost to serve as a wick to draw water up from the bottom of the pot. 

    (important: drainage holes are about 10cm from the bottom of the container so there is a reservoir of water at the bottom but the roots cant get in it and rot... my pot is plastic so water at the bottom wont rot it but if you are using wood or other perishable material avoid water reservoirs ) 

    in my case reason for using bubble wrap is that i had it and it doubles as insulation (my pots are exposed to both extreme heat and cold on the rooftop terrace)  
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