Gardeners who intend to sow and reap this spring should now be attending to the type of soil they have inherited, whether clay or sandy based. Sandy soils are quick to warm up in spring allowing for earlier planting. But without the addition of organic matter, added nutrients and moisture are quickly leached away making steady growth difficult.
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Naturally clay soil is hard to cultivate. Slow to warm up, it is difficult to get water into the ground and just as difficult to get it to drain away. Clay is sticky when wet and bricklike in a hot summer. Yet once amended with compost and coarse river sand, clay loam is one of the richest and most productive of all mediums, retaining both nutrients and moisture.
Australian soils are old and naturally acid in the main, becoming more so in time with the regular addition of fertiliser. Lawns which are regularly fed are one area of the garden that will benefit from a spring or autumn dressing of lime to counteract the acidifying effect of sulphate of ammonia.
Lime is not a mineral that should be applied automatically on the basis that it is keeping the soil ‘sweet’. Too much lime can do more harm than good and the effects of a single application can last two or three years. Use a testing kit (available from most nurseries) to assess your soil pH from time to time.
The majority of plants will only thrive when the pH of the soil is adjusted to their needs. Camellias, azaleas and daphne, for example, perform poorly in limey soils alongside newly built brick walls. Lime lovers, on the other hand, include many alpine plants and some vegetables like peas and beans. Soils that have been well nurtured with compost and manures tend to vary little, from around neutral to slightly acid (6.5-7 pH), and will support most other ornamentals and crops.
The value of well-made compost as a soil additive cannot be overstressed. Every scrap of plant waste, shredded prunings, lawn clippings, autumn foliage, tea leaves, coffee grounds and vacuum dust, should be layered green and brown (or wet and dry), interspersed with thin layers of soil, within a lidded bin or a fenced off sunny site.
Composted plant material and animal manures can be considered the original slow release fertiliser, conserving moisture by retarding evaporation, providing nutrients and raising the soil temperature.
The difference between a natural (organic) or chemical (inorganic) plant food is not always fully understood, yet the effect on the soil is totally different. Inorganic fertilisers give an immediate chemical boost to plant growth without any long-term effect on the soil. The organic content of any soil, however, continues to offer lasting benefits, providing levels are maintained.
