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Testing soil for drainage

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Many plants require soil that drains readily and easily. Many plants cannot cope with water-sodden roots but need to be in soil that drains well, to allow airflow around the roots.

If you're not sure how well any area of soil will drain, you can do simple tests on the soil before attempting to place plants in it. Once you have the results, you can determine the appropriate planting next.

Testing the soil[edit]

Fast soil drainage test[edit]

This method can be done in up to an hour, after the initial wetting and draining of the hole.

Dig a hole to around 30cm (1 foot) deep and 15cm (6 inches) wide.

Fill the hole with water, then let it drain.

Put a waterproof (plastic) ruler into the hole. Ensure that it is sitting firmly in place, so that it won’t fall over when water is added again shortly.

Fill with water again. Begin measuring after a minute, making note of it. Start timing from that measurement, and write down the water level after each minute.

Assess the drainage capacity as follows, using your timing and measurement notes:

  • If the water drains out within 0 to 10 minutes, the soil is fast draining.
  • If the water drains out within 11 to 60 minutes, then the soil is well-draining. This is the ideal soil for most plants.
  • If the water drains out any time after 60 minutes, then it is slow draining. In this case, it may be heavily clay-based.

See fixes below, if needed.

24-hour soil drainage test[edit]

This method takes 24 hours but allows you to test different areas of a garden or field for poorly draining soil. While less exact than the previous method, it does have the benefit of showing you areas that don’t drain without you having to wait around.

Select the area of the garden, yard or field where you wish to test the soil. Dig several holes in the soil in separate places, as this will allow you to test different parts of the garden or field. The depth of the hole should be about 50cm (1 3/4 feet) deep.

Fill each hole with water. Leave it to drain out (provided it is going to do so, but you’ll find that out shortly).

Check after 24 hours. If you can still observe water in the hole after this time, it is poorly draining soil. The higher the level of water in the holes, the less drainage the soil has.

See fixes below, if needed.

Fixing soil that drains poorly[edit]

There are different ways to deal with poorly draining soil. These include:

  • Amend the soil. For example, add well-rotted compost and/or sand to amend a clay soil.
  • Find a different place to grow the plants.
  • Where a different location isn't possible, consider using raised beds. These can be filled with better soil on top of the poor soil. You will need to water the raised bed more often though, as being higher and with easily draining soil, it'll dry out faster than non-raised areas. Also, be sure that it is raised high enough for the roots of the plants you intend to grow in it.