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:
- 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
- blood and bone
- tea leaves
- coffee grounds
- 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.