Signs of healthy soil include plenty of underground animal and plant activity, such as earthworms and fungi. Soil that is rich in organic matter tends to be darker and crumbles off of the roots of plants you pull up. A healthy, spread-out root system is also a sign of good soil.

The time needed to form a soil depends on the latitude: in environments characterized by a mild climate, it takes 200-400 years to form 1 cm of soil. in wet tropical areas soil formation is faster, as it takes 200 years. in order to accumulate enough substances to make a soil fertile it takes 3000 years.

Soil forms continuously, but slowly, from the gradual breakdown of rocks through weathering. Weathering can be a physical, chemical or biological process: physical weathering—breakdown of rocks from the result of a mechanical action.

It can take 1000 years or more. Soil is formed from the weathering of rocks and minerals. The surface rocks break down into smaller pieces through a process of weathering and is then mixed with moss and organic matter. Over time this creates a thin layer of soil.

Most soils have three major horizons — the surface horizon (A), the subsoil (B), and the substratum (C). Some soils have an organic horizon (O) on the surface, but this horizon can also be buried.

The crumble: Is your soil crumbly like a good coffee cake or dry, hard and cracked? The soil should be crumbly. If it’s dry and cracked, water will run off and not absorb into the soil like it should. Also, not enough water will make it to the root system and allow the roots to grow down in all that hard soil.

Dry soil can be easily improved by adding organic matter, such as well-rotted manure or garden compost. This will improve the soil structure and will help to retain moisture.

Sprinkle 1 1/2 pounds of 5-10-10 fertilizer over every 50 square feet of soil. Turn the fertilizer into the top 6 inches of soil so plant roots can easily absorb the nutrients after you replant. Alternatively, apply a suitable fertilizer at the correct rate for the specific plants you grow.

With thoughtful handling, you can reuse potting soil in next year’s containers, or use it to solve other gardening problems. Old potting soil need not be bone dry when you store it, but too much moisture can create cushy conditions for unwanted moldy microbes. Dry soil weighs less, too.

You need to dump out the compost, add new nutrients and fluff back up. Ideally you then cut the old compost with some new stuff, 50:50, and add a good handful of slow-release fertiliser, mix it well and then place back into the pot, ready for it to be planted up.

What to Do With Old, Spent Compost

1. Make new compost. Use it to make new potting soil or compost (directions below).
2. Use it as mulch. Use it as a mulch on top of your flower or vegetable beds.
3. Use it to level your garden.
4. As a bottom layer.
5. As a top layer.
6. To grow carrots.
7. As bedding.

Using “Dead” Compost Compost that is not moldy can be energized by the addition of some fertilizer. Use a time release formula and mix in gritty material if it is heavy and clumpy. You may have to manually break down any larger chunks.

Multi-purpose compost

Compost is a soil conditioner and adds organic matter back into your soil. Garden mix is for general use in your garden, for planting trees and shrubs. Potting mix is for growing plants in containers, pots and hanging baskets. Seed raising mix is for growing plants from seed.