I ended the last article in July making reference to the concept of raised garden systems for smaller house lots. Obviously the idea is applicable to all size blocks. It is a method that can be employed to increase productivity where space is a premium or the existing soil type is not suitable to in ground vegetable gardening.
The materials used to construct these raised beds can vary from timber sleepers placed on edge to the corrugated metal types that you can purchase in various sizes. I recommend that whatever these beds are made of make sure that they are at least 500m to 600m deep. This depth will allow you to grow root crops like beetroot and carrots. This depth will also keep the soil cooler which will aid in moisture retention and enable you to turn the soil after each harvest when it will be appropriate to add more compost and humus to help reinvigorate the soils.
Generally these beds are constructed with no bases, so they need to be deep enough to allow for drainage. The drainage material can simply be gravel or course sand covered by perforated weed moulting material to prevent the soil from clogging the drainage area. I prefer to have at least some drainage in the base to help prevent water logging of the soil during rainy periods. (It’s easier to rescue plants if the soil is dry as apposed to the possibility of root rot).
With the timber bed method it will be wise to line the interior with Builders plastic or cut sheets of corfu to help prevent the timber from rotting and to separate the timber from contact with the soil just in case the timber has been treated with preservatives that may contain toxins. To keep this liner in place use a suitable sized zinc washer held in place using zinc flat head brads.
To get the maximum productivity from the beds employ a quality soil blend that is suitable for vegetables. At least a good garden soil blend. Incorporate plenty of humus and manure and some suitable organic fertiliser such as blood and bone. I suggest you add some moisture retentive granules at this stage due to the fact that some commercial soil blends are difficult to wet evenly, and will in fact repel water. (Hydrophobic soil).
To maintain good soil health with active microbes and nutrition use only organic based fertilizers and I suggest you start a compost bin as the material will really improve the soil over time. Do not use potting soils for these raised beds as they are mostly composed of composted bark (especially the cheap ones) and this will very quickly deplete and shrink. You can easily construct a framework made of polytubes over the raised beds and cover with insect exclusion nets or bird netting.
An alternative to constructed on ground beds is the pod type raised garden like the popular ‘Vegepod’ system. These pods can be raised on stands that suit the size or you can elevate them using concrete blocks and timber to support them.
These ‘pods’ are in fact large deep pots complete with a water well system that has drain point and as opposed to on ground systems employ quality potting soil as the growing medium. They come complete with an insect proof hood that is easily detached and also comes with micro sprays that connect to the hose. You can also purchase a clear poly hood that slips over the insect net making the pod a mini hot house for the cooler months.
Jon (Plantman) Lovett