Improving Sandy Soil

Adelaide’s beachside suburbs are a great place to live and garden – a relatively frost-free Mediterranean climate that supports a broad range of fruits, vegetables, herbs, natives and exotic ornamentals.

However, there is a downside to living on what was once a series of sand dunes – without its native ecosystem to keep it in balance, the soil gets pretty unhappy. Gardeners often find that plants dry out very quickly, don’t thrive and eventually succumb to neglect because it all seems too hard to persist with. If you don’t want to switch to a Zen garden of raked sand and gravel, read on.

The main problems with the soil tend to be:

  1. Lack of soil structure due to the sandy texture – water and nutrients are easily leached out
  2. Water-repellence (water beads on the soil surfaceand runs off rather than being absorbed and retained)
  3. Alkaline pH
  4. Salinity (for beachfront properties)

Here are a few tips for gardening near the coast:

  • If you receive salt spray off the sea, plant a buffer zone of tough, salt-tolerant plants to shield your garden – and position more delicate plants on the sheltered side of the house.
  • Test the soil’s pH. Add sulphur if required to correct alkaline pH (follow directions on packet from hardware or garden centre) – re-test pH every 6 months
  • Add clay to improve water retention (e.g. a bucket of clay soil from friends, or some potters’ clay from craft supplies or bentonite clay from a garden centre – add water to make a slurry and then mix into soil). This is worth doing BEFORE you add fertilisers, so that they don’t just wash away through the soil and into waterways where they do more harm than good.
  • Add well-rotted manures and compost twice a year to improve soil structure and water retention.
  • Do not allow the soil to completely dry out – it needs to stay slightly moist to overcome water repellence.
  • Use mulch over the soil to help retain moisture. If using drip irrigation, install this on the soil surface, under the mulch. Composted pine needles or pine bark are a good choice of mulch to help neutralise alkaline soil.
  • Before planting vegetables, you could grow a green manure crop (e.g. grains and legumes) and dig them back into the soil before they set seed. This will enrich the soil in preparation for vegetable growing and will also give you a good indication of how much watering is required in that area. This is better than leaving an area of soil bare and untended, as it would deteriorate.
  • Choose coastal plants and those that can tolerate a degree of alkalinity. Avoid those that require acidic soil (e.g. blueberries, azaleas, camellias) – or plant them in containers with special potting mix, instead of in the soil.
  • Use raised garden beds with imported soil if you prefer – but test a soil sample first!

If you have space, you might want to consider a 3-bay composting system to keep your garden supplied with home-made compost year-round. Plenty of materials are freely available for hot composting – lawn clippings, stable manure, food scraps and garden prunings for a start.

It does take time and effort and a lot of organic matter, but sandy soils can be improved until they are teeming with life and far more productive. Don’t give up after the first season or two – keep building up the soil over a few years for best results.

This entry was posted in permaculture design, planning, sand, soil. Bookmark the permalink.