Check your soil condition

With funding and support from the Ministry for the Environment, Ministry of Agriculture and Forestry and various regional councils, Graham Shepherd, a soil scientist at Landcare Research, developed a practical way to check soil conditions.

Called Visual Soil Assessment, it was originally developed for farmers and soil conservators. But the basic principles are the same for any soil - so with permission we've adapted the technique for the home garden.

The test we describe below is designed for parts of the garden that have not been cultivated or cropped for several years (such as lawn), so it's ideal for checking out soil condition before breaking in new ground.

Allow around 15 minutes for the test. For best results the soil should be moist, neither soaking wet nor bone dry.

You'll need:

• A spade
• A plastic basin
• A flat piece of wood (such as ply or particle board) to place in the bottom of the basin
• A large plastic bag (around 500 x 700mm)
• This report and a pen.

The drop shatter test

Dig out a 20cm cube of soil with the spade. (Most spades are 18-20cm wide.) Many soils will come out as a single lump, especially if slightly moist. If yours doesn't cling together at all, dig out enough to have the equivalent of a 20cm cube.

Drop the soil from a height of one metre (about waist height) onto the wood in the bottom of the basin so it shatters into pieces. Drop large clods again once or twice. Don't drop any piece more than three times. If it breaks into small pieces with the first or second drop, move on to the next stage. If roots are holding the soil together, pull it apart along any large cracks. Avoid crushing any pieces smaller than they break into naturally.

Spread the plastic bag flat on the ground beside the basin and transfer the soil onto it. Grade the fragments as you go so the largest clods are at one end and the finest at the other.

Soil structure and consistence

Compare your sample with the photos below and put the appropriate score on the Your soil score column of the score card .

Soil porosity

Now take a slice of soil from the side of the hole created by taking your original 20cm cube, break it in half and look at the exposed soil. Alternatively, take large clods from your plastic bag.

Compare what you see to the photos below. Mark the score on your card.

Soil colour

Examine the colour of a handful or slice of your soil. Using the photos below as a guide, record the score.

Soil mottles

Look at the side of the hole or at the largest clods on your plastic bag and compare them to the photos below and record the score.

Earthworms

Sort through the soil on the plastic bag and count the number of earthworms you can find in five minutes. Make sure to look carefully through the soil that was closest to the surface.

Fewer than 10 earthworms scores 0, 10-20 scores 1, more than 20 scores 2.

Record the score on your card.

What now?

Use the soil score card to calculate your total score. This will give you a good indication of the quality of your soil.

Then see Improving your soil for advice on how to improve and maintain your soil quality.