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Filling up raised bed


I have a small backyard surrounded by fence on all 3 sides and covered in flagstones.

I was thinking of removing flagstones from an area to make room for a raised bed. So the raised bed would be 1330mm (W) x 1330mm (L) with height of 300mm

I already have some store bought topsoil, compost and some homemade compost to fill it up.

I would appreciate advise on few things please

  • what should be the ratio of topsoil and compost? 
  • Also do I need to mix horticultural grit as well. And what should be the ratio that I need to add with topsoil and compost
  • And presumably I should mix them all together and fill up the raised bed. 

I mostly plan on growing mainly leafy greens like Kale, Swiss chard, mustard in the raised bed. And possibly some sprouting broccoli and green beans in the future. 

As you can tell from the questions I’m asking that I’m new to raised beds and having searched the internet one gets different views. So thought best to post it here for getting good advise from experienced gardeners.  

Many thanks in advance




  • Pete.8Pete.8 Posts: 11,286
    I have some raised beds. 
    I used similar ingredients to yours and they work well.
    I used a bit too much topsoil to compost so the result is quite heavy.
    I used about 80% topsoil and 20% farmyard manure.
    The first season it was good, but as the manure broke down it's almost all topsoil again, so I'm topping it up each year with home made compost and bought in farmyard manure to open it up.
    If I were doing it again, I think I'd use something like -
    50-60% topsoil 30% organic matter and 10-20% horticultural grit
    Whatever you use it will settle over the first couple of years, so you can top it up with more compost.

    Multi purpose compost for seeds, baskets and the like is not of much use as it breaks down quickly.

    Billericay - Essex

    Knowledge is knowing that a tomato is a fruit.
    Wisdom is not putting it in a fruit salad.
  • @Pete.8 thanks for your advise. Since I would removing few flags and any debris underneath I was thinking would it be also good to layer with some shredded paper/cardboard first and then top soil, compost(store bought and homemade) and grit mixture where ratio is 40:40:20

  • Pete.8Pete.8 Posts: 11,286
    That sounds fine jay
    Best of luck!

    Billericay - Essex

    Knowledge is knowing that a tomato is a fruit.
    Wisdom is not putting it in a fruit salad.
  • I would definitely add at least 25% of well-rotted manure to the mix if you are growing veg.  The bagged stuff from GCs is ideal as it's easy to handle.  As Pete mentioned, whatever you use will rot down and the soil level will fall over the year.  I top mine up with the aforementioned each autumn and again when planting out in spring, if necessary.  There is no need for extra feed if you do that. 
    A trowel in the hand is worth a thousand lost under a bush.
  • @BobTheGardener, Sorry but since I’m new to this what is bagged GCs manure? 

  • GC =garden centre  , they sell bagged manure. 
    AB Still learning

  • Thanks 🙏   :)
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