Making A Bad Soil Good

A learning resource from ACS Distance Education
Do you have a hard, clayey material in your backyard, with which you expect to grow a fecund garden? Or perhaps a sandy soil with no nutrients to offer your much loved plants? Well do not despair, there are ways to improve soils.

What Makes Good Soil?
It all depends on the plants growing within the soil and what has occurred to that soil over the seasons.
For some types of hardy plants, a good soil might be one with minimal friability, and nutrition. For water loving plants, a good soil might be one with minimal drainage.
For most plants though, a good soil drains freely, is fertile (contains plenty of nutrients), holds moisture (doesn’t dry out too quickly after watering and isn't water repellent) and is loose, friable and easy to dig.

How to Treat Soil over Winter
If you live in an area where the soil stays wet and heavy for most of winter, you help to improve it. For example:
  • Don’t dig very wet soil and don’t walk over it or compact it with vehicles or heavy machinery.
  • Drench the soil with a hose-on clay breaker (if your soil is sodic clay).
  • Add layers of loose matter to the surface. This will protect the soil from erosion (from heavy rain) and compaction. It won’t break down as fast as in warm weather but it will gradually rot and improve the soil.
  • When the soil dries out, a drainage system could be installed to minimise the problem next winter.

How to Improve your Soil
All soils used for growing plants will benefit from additional organic matter, but the different particle sizes of the different soil types require different solutions.

Clay Soil
Clay soils tend to be have a high plant nutrient content, but they are both difficult to water and easily waterlogged. Some clay soils can be improved by cultivating the soil and adding gypsum (clay breaker) for example sodic clays; on non-sodic clays gypsum has little benefit.

Sandy Soil
Sandy soils usually have excellent drainage and low nutrient levels. They are also susceptible to wind and rain erosion. They can be improved with lots of organic matter.

Rocky Soil
Rocky soils can’t be cultivated and are usually very low in plant nutrients. In this situation the cheapest option may be to build garden beds on top of the existing soil. This can be done by importing soil to the site or by using the No Dig gardening method. Simply build up the soil by laying down layers of organic material such as compost, newspapers and lawn clippings; mx lawn clippings with a coraser material such as straw though as otherwise it can create an inpentrable barrier on top of the soil and then water won't penetrate.

Improving Soil Fertility
Plants need nutrients to grow and any soil can lose its supply of nutrients over time if you don’t replenish them.
The best way to do this is to keep adding compost, manure, or a good mulch – every year, if not more often. As these materials decompose, they release nutrients, maintaining a high level of soil fertility. Mulches such as raw sawdust and fresh wood chips can create nitrogen drawn down from the soil if they touch or are incorporated into the soil - so try to use mulches that are composted, lucerne hay or pea straw will also add rather than take away ntirogen.

Fertilisers should be used as well, to supplement or top up the plant's nutrient requirements. Don’t depend totally on fertiliser though - it just isn’t enough in most cases. Inorganic fertilisers can also cause environmental damage when used over long periods.

Compacted Soils
Because clay soils are made up of very small particles, they can be easily compressed together by the weight of vehicles or pedestrians. This results in soil that either repels water, or once wet, is unable to dry out. It is also low in the oxygen needed by plant roots.

Aerate compacted soils by digging them over and mixing in loose material such as compost and washed coarse sand.

Soils to Build On
Soil needs to be solid if it is to support a wall, building, steps, paving or any other structure. You might need erosion control, rolling, compacting, grading, etc, if you are going to construct a path, driveway, wall, building or any other structure.
When planning to add a structure to your garden, make sure you are doing it on stable ground, or else stabilise the ground before building. If you plan to invest a lot of time or money in building something, you should seek advice from an engineer or landscape professional before commencing.

How to Stabilise Soil
Shallow fill (e.g. 10-30cm) may be settled by watering thoroughly and compacting with a machine (eg. vibrating plate or roller – these can be hired). If possible, leave it for six months before constructing anything on the surface.

Deep fill can take years to settle, even with compacting treatments. If building in under three years, you may need stronger, reinforced foundations to prevent structural damage.

Slopes and Erosion
Erosion can be a problem, particularly on steep slopes. Soil can be stabilised by creating retaining walls, terracing, installing drainage or grading the soil.

So, if you are willing to do a bit of background homework and possibly a bit of hard labour in the backyard, there is hope for your soil, no matter how bad it seems!

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