home permaculture basics about me permaculture links	2. Soils and your first garden New Zealand is generally considered to have fertile soils. However, all soils tend to have deficiencies either because minerals were absent in the original soil parent material or because minerals have been leached out of the soil over time. Examples of soil deficiencies are ‘bush sickness’ on the pumice soils of the Central North Island, where the soil grew wonderful grass but the cattle died due to a cobalt deficiency, and the magnesium deficiency of the volcanic ash soils of the Bay of Plenty. Fortunately these nutrient limitations are easily rectified. More difficult to rectify are limitations due to soil texture and structure. Textural limitations range from the heavy clay soils of Northland, where soil particles have been broken down over a long period of time to form clay particles which clump together very strongly due to electrostatic forces, to the barely modified sands of many coastal areas which are formed on old sand dunes. The application of gypsum (calcium sulphate) can help lighten the heavy clay soils, which should then have compost and perhaps sand added. The addition of compost can also help sandy soils by increasing the water holding capacity. Soil structure varies widely also. Structure is the stability of the soil and is due to the presence of organic material which binds the soil particles together. The ideal structure is one which is firm but open, allowing soil particles to form clumps which increase the water retention, while also allowing excessive water to drain freely. Too strong a structure (e.g. clay) will impede plant roots and will either become waterlogged (if low-lying) or remain too dry. Too weak a structure (e.g. sand) will be unable to hold plant roots in strong winds due to lack of cohesion, will blow away and will not hold sufficient water for plant growth between periods of rain. The best soil for growing plants is a friable loam. This consists of a variety of particle sizes (from clay to sand) which pack together to form micropores which increase the water holding capacity. It is of a moderately strong structure, strong enough to stick together in clumps, yet not so strong that it impedes root growth. A useful field test for the three main components of soil is to take a small sample of the soil, wet it, then rub it between finger and thumb. Silt, medium sized particles, is felt as a smooth feeling, clay is sticky and sand is gritty. If there is some stickiness, e.g. when you lift your thumb off your finger small peaks of soil form, there is clay present; if it feels smooth there is silt present; and if you can feel a few particles of grit then there is sand present. Soil structure can take a long time to develop, can be easily destroyed, and has a huge impact on water and nutrient retention, and hence on plant growth. Worms are nature’s soil builders. The mucilage that worms secrete from their bodies (to help them slide through the soil) provides the ‘glue’ to hold soil particles together to form a robust structure. However, this can easily be destroyed by over-cultivation and by growing maize or corn crops in the same place for several years. The following suggestions will help you develop good soil structure and retain this structure once it is developed: • Minimise soil surface disturbance and cultivation. • Maintain an organic mulch layer on top of exposed soil. • Introduce and encourage worms by keeping a mulch layer on the surface and by maintaining surface soil dampness (note soil worms are a different species from compost worms). • Rotate crops. Soils form in layers called horizons. • A horizon - the black layer near the top of the soil generally referred to as topsoil. • B horizon - the layer below the A horizon where soil formation is most active • C horizon - the layer below B where the soil looks more like the parent material underneath than soil • Parent material from which the soil is being formed. In natural soils, e.g. in forests, or in well designed and maintained gardens, there will be an O horizon on top of the A horizon consisting of actively decaying organic material. This is very valuable as it retains soil moisture, provides a habitat for worms and other beneficial invertebrates, rots to produce soil nutrients and prevents dry soil blowing away or being washed away by rain. In some places layers may be missing or jumbled up. This is particularly prevalent in new subdivisions, where they strip off the topsoil and sell most of it, then remove the B and often the C horizons and use them as fill, then bulldoze the parent material to form a ‘desirable’ contour, then replace about 100mm of A horizon back on top of whatever is there. They then typically plant grass and sell the sections quickly before it has time to die. And people wonder why their gardens don’t grow! When developing a garden it is well to remember that nature is the original gardener and placed soil in layers for a purpose. If your garden copies nature’s garden, then it will be most productive, require least maintenance and will allow a natural ecosystem to thrive, all of which coincide with the aims and ethics of permaculture. Nature does not use a spade, nor should you. Digging a garden is simply destroying the carefully developed structure and layering that has taken nature many years to produce. Leave your spade in the shed when gardening. To start your garden you will need the following: • Old newspapers or advertising material (the best use for advertising I know) but not the glossy coloured material - some of the inks may be toxic (so worms won’t like that) and the paper tends to repel water. Recycle the glossy stuff. • A supply of compost, preferably well rotted but even fresh material from a brush chipper will suffice. • A supply of water. • Organic fertilisers (e.g. sheep pellets, blood and bone, dolomite), essential if using fresh material because the bugs which break down that material will take nitrogen from wherever they can, creating an initial nitrogen deficiency you get it back once the material has rotted. To make your garden: (Example is making small plots for pumpkins) 1. Spread newspaper at least 4 pages thick over the area where you want your garden. 2. Water the newspaper well (on a windy day it helps to have someone laying the paper and someone else watering). 3. Spread at least 50mm of compost or organic material on the wet paper. 4. Spread a mixture of organic fertiliser on the compost or organic material. 5. Spread at least another 50mm of compost or organic material on top of the fertiliser. 6. Plant your plants. Examples of newly established gardens: Strawberries and tomatoes in a 4 month old garden (the mesh over the strawberries allows us to eat them before the birds eat them). Potatoes in a 6 week old garden. Beetroot and lettuce in a 2 week old refurbished garden (the old garden was full of oxalis - it will be interesting to see how much of this comes through into the new garden.) Courgette in a 2 week old plot (as described for pumpkins above). Notes: • It is important that the plants you grow in this area for the first year are not root crops (e.g. carrots, parsnips) because the fresh organic material will cause deformed roots. The exception is potatoes, which can be planted in this new garden straight away. • Over time the newspaper will rot, providing more organic compost, and worms will establish in this area. • This method is also useful for renovating a neglected garden, simply remove any large weeds or clumps of grass and rake it more or less level first. • If you have invasive grass species like kikuyu, it is best to remove that first as its runners can persist and reappear. • As the soil structure in this garden is totally undeveloped, it will need frequent watering in dry conditions.
Custom permaculture designs to suit your needs Alan Willoughby MSc, PDC * PO Box 296, Tauranga, New Zealand * Tel (07) 544 3087 * willoughbys@xtra.co.nz © 2006-9 Permaculture Designz Site designed by Dreamscape