All About Compost

When planting a new garden or giving an existing one a well earned boost, the incorporation of compost can be the difference between a very successful garden and one that performs poorly. Compost is the easiest and simplest way to improve your soil and grow happy healthy plants. Put simply, if you look after the soil then the soil in turn will look after your plants. What is compost? Compost is the end product of the decomposition of organic materials, either of plant or animal origin.

Healthy Soil, Healthy Plants

Why is Compost Important?

Many of our backyard soils in New Zealand have minimal top soil and it is usually seriously depleted of organic matter like compost. The soil type is also often heavy clay or in some instances (volcanic or coastal sandy areas) a fine, overly free draining soil.

The benefit of compost is that it improves soil structure, provides important nutrients and food for vital soil micro organisms and helps plants develop strong healthy root systems.

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How Compost Improves Soil

Not only does compost create a healthy environment for your plants' root systems, but it also acts like a sponge that holds water in the soil for longer without compromising air spaces. Soils low in organic matter can suffer two issues. Either the water doesn’t even make it into the soil and runs straight off, or the water runs quickly through. Organic matter like compost helps distribute water evenly. Essentially it improves the soil structure by opening up clay soils and binding together sandy soils.

Heavy Clay Soils
This type of soil is typically very wet in winter and bakes hard and dry in summer. Adding generous quantities of compost prevents it from being too wet or dry by enabling better drainage.

Fine Soils
With very fine free-draining volcanic or coastal soils, water enters and drains away quickly. This also means it cannot store nutrients that plants need to thrive. Compost improves the soil's water-holding capacity and ability to retain nutrients.

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When to Apply Compost

There is no rule, compost can be added to the soil at any time of the year. 

In the veggie garden it is normal practice to dig in (mix well with existing soil), compost to a depth of 10-12 cm prior to planting. 

When planting new trees and shrubs; mix compost with existing soil at the time of planting. Be especially generous where soils are particularly heavy.

With existing trees and shrubs, compost can be applied around the plants at any time during the growing season.

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How Much Compost to Use

It is almost impossible to use too much compost. Amazingly, compost appears to almost disappear in your garden, therefore repeat applications are recommended during the growing seasons, especially in new gardens. Compost is versatile and can also be used as mulch throughout the garden. Apply it to a depth of 5cm.

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Garden Tip

Modern potting mixes are especially free-draining which is an important factor when growing in containers. When it comes to container planting, compost should not be used as a potting mix. It has significant water holding capabilities and physical properties which makes it unsuitable as a potting mix.  

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