How I assembled the soil for my raised beds

raised vegetable garden beds

Weeds and leaves heaped in the garden bed form the first layer

When it comes to actually filling the raised garden beds, sometimes the ideal gives way to other pressures.    Ideally I would build the raised bed frame then fill it with varied layers of nitrogen rich and carbon rich.  Sprinkle on activators such as blood and bone and add trace elements through rock dusts.  I would let it sit for several months and encourage the chooks to turn it mixing it more and adding a little extra chicken manure.

Because of the circumstances of my move I found myself building garden bed when we were already half way through spring.  I needed to build some beds fast, and get some veggies in if I was to have anything growing this summer.  I also had little spare cash after the expense of moving, so buying material in was mostly out of the question.

Adding layers of nitrogen and carbon materials

raised vegetable garden beds

The bed is half full before I line the walls with plastic.

I gathered what I had available, used straw, grass clipping, weeds, dried leaves, some rich top soil which also contained lots of tree bark (not ideal), kitchen scraps.  I layered and mixed it as well as possible, watering it as I went.  I did buy a coir block and added that to one of the beds.  It did take me some time to gather all this, I started collecting and layering the material before I had even built the frames, and the first bed got a considerable amount of rain during the process.

When a raised vegetable garden bed is made out of treated or unknown timber it is important to line it with plastic.  Otherwise the poison used to treat the timber will leach into the soil and be pick up by your vegetables.  But this can be a fiddly business, especially if there is any wind about.  I find it useful to have some material already in the bed to hold the plastic in place as I line the walls of the bed.

Adding a plastic lining for the walls.

raised vegetable garden beds

Plastic prevents chemicals used to treat timber from leaching into the soil.

Initially, whilst still constructing the walls I had heaped material in the centre. When I was ready to line the frame I spread it out and added straw, until it was about half way up the walls.  I pushed the straw back just far enough to line the walls with plastic, where possible I wrapped the plastic around the top piece of wood or anchored it behind a post.  In this way I was able to hold the plastic in place with one hand and push the straw back onto it with the other.  After that I added a layer of nitrogen rich grass clippings.

One handy trick if you wish to plant into a bed that is not ready is to make a hole, fill it with compost and plant your seedlings into that.  Similarly a layer of compost on the top to plant your seeds into works well.  It takes several weeks for the seeds to germinate and the roots to grow beyond the compost, by which stage the soil components have broken down further.  But I hadn’t been here long enough to have any compost.

Purchased vegetable garden soil as the top layer is my compromise.

There was only one option left if I was going to get anything growing this season.  I had to buy in some top soil.  Now I know that purchased “soil” is inferior quality, but vegetable soil is generally better than the top soil that they sell, which is usually full of household garbage.   One cubic meter of soil doesn’t go very far in raised garden beds, but if its only 20cm deep it should cover 5 square meters.

raised vegetable garden beds

Tuck the plastic in so that it doesn't become a home for slugs and snails. It looks much better too.

I bought some “vegetable garden soil” which turned out to be a mixture of cow manure, sand, composted bark and who knows what else.  The cow manure should help things along a bit.  As I moved it I discovered not only does it contain lumps of bark, but lots of stones as well.  I filled the top of the beds with this purchased soil.

The final touch was to hide the plastic that was showing at the top edges, not only is it unattractive, it will harbour slugs and snails which would come out at night and eat my precious seedlings.  My raised beds were complete.

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Garden soil for raised vegetable beds

raised vegetable garden beds

Dried leaves and weeds are good composting materials

When it comes to filling the garden bed many people immediately think about buying soil and having it trucked in, but the truth is that it is the inferior option.  The main reason that raised garden beds can grow so more vegetables in the space than in-ground beds is that they are filled with compost rather than soil.

The principle of no-dig gardens is to fill the raised bed with layers of material then leave them for three months to breakdown into  a rich growing medium for the vegetables.  There are a couple of main differences to making compost, the first is that the material is not normally turned, to compensate for this layers of material are quite thin to allow the necessary interaction between the ingredients. The second difference is that the material is often not deep enough to reach the temperatures required for true compost.

 Ingredients for the growing medium

The main categories of materials used in this soil creation process are usually referred to as ‘carbon’, ‘nitrogen’, ‘minerals’ and ‘water’.  By carbon we mean plant materials which contain a high percentage of carbon in their structure, similarly ‘nitrogen’ refers to plant materials that are rich in nitrogen.  Minerals are derived from rocks and are present in small quantities, the most important being lime which is used to regulate the pH level of the bed.  The correct amount of water is needed for the microbes to work their magic on the mixture and turn it into our growing medium.

Carbon materials are brown

Brown plant materials are generally high in carbon, but be aware that many of them take far too long to decompose to be used in the vegetable garden.  Anything that is closely related to wood should be shredded, combined with some very high nitrogen products and composted for at least a year.  Good materials for your no-dig garden bed include the following:

  • straw
  • autumn leaves
  • newspaper (soak and use in small quantities)
  • dry grass clippings
  • wood ash
  • brown hay
  • peanut shells
  • peat moss  (soak and use in small quantities)
  • dried weeds
  • shredded corn cobs
  • sugar cane mulch

Nitrogen materials are soft and brightly coloured

Fresh plant materials are generally high in nitrogen, they are often green but other colours are common too, occasionally they are even brown.  As these materials dry out the nitrogen is often lost with the moisture.  There is a wider variety of materials high in nitrogen available and using a wide variety will increase your success.

  • green leaves
  • green grass clippings
  • fresh weeds
  • kitchen scraps
  • manures
  • blood and bone
  • hair
  • feathers
  • tea leaves
  • coffee grounds
  • seaweed
  • fish meal

 Minerals and other ingredients for compost

These materials are added in small quantities and do not contribute to the bulk of the garden bed, they add trace elements.  Generally these are not materials that you will have around the house and garden, and if your budget or source does not stretch to these additives don’t let that hold you up. They can be added as top dressing when you have them available.

The most common mineral materials are these

  • gypsum (increase calcium, breaks up clay)
  • dolomite ( increase alkalinity, calcium and magnesium)
  • rock dust (add iron, boron, chlorine, cobalt, copper manganese, copper, zinc and molybdenum)
  • potash (increase potassium)
  • sulphur (increase acidity)
  • Epsom salts ( increase magnesium)
  • egg shells (calcium)


Most people fail to add enough water to their garden bed and this can hold up decomposition of the material for months.  You should be able to squeeze a few drops of water out of a handful compost materials with your fist.  Whilst good soaking rain is the best means of watering your garden bed, adding water to each layer as you apply it will help get the process started.

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