Making clay soil gardening easierMany people who struggle with clay soil gardening wish they could just dig the whole lot up and replace it with "good soil". In fact, with a bit of love and kindness, clay soils have the potential to be the most productive and rewarding for any gardener. So where do you start and what can you expect once you get things right? Let’s consider the worst-case scenario: A heavy clay that drains poorly, becomes sticky and horrible when wet, but then sets like concrete when dry. You spend your whole life waiting for it to be at just the right moisture content to be worked up properly, but it only ever seems to be either a sticky, soggy mess; or dry and rock-hard. Could you imagine this same soil being soft and friable; easy to work at almost any time of year; well-drained and well-behaved – a delight to garden with? What a pleasure your clay soil gardening would become if that were true. Well the transition from one to the other is not so hard to achieve and it won’t break either your back or the bank. Its important to start the process of clay soil gardening with a good soil test – in fact is absolutely essential. Not only will this tell you what is wrong, but also exactly what to do about it. Lets see what this tells us by using a real example. The important thing to look at is the "Exchangeable Cation Balance". That is, the proportions of exchangeable Calcium, Magnesium, Sodium, Potassium and Hydrogen relative to the Cation Exchange Capacity. In our example (see the Table below), the proportions of Sodium and Magnesium are very high:
A soil test lacking this sort of detail, however, would likely recommend only a 'standard' application of Gypsum, but this may insufficient to properly improve the soil. The reason is that most Gypsum recommendations are based only on the Sodium percentage and, as we see in this case, both Sodium and Magnesium are very high. In fact, the amount of Gypsum required should be based on how much Calcium is needed to replace the excess Sodium and Magnesium. Gypsum is "Calcium Sulphate" (CaSO₄). This exchanges Calcium with either Sodium or Magnesium. The resulting Sodium Sulphate and Magnesium Sulphate can then be washed out of the root zone by irrigation or heavy rainfall. The net effect, then, is that the percentages of Magnesium and Sodium go down, while the Calcium percentage goes up. One potential problem, however, lies in the condition of the sub-soil. If this presents an impermeable barrier to the downward drainage of water, a "perched" water table will develop. This will cause salts to accumulate in the root zone due to upward movement of water by capillary action. - making the situation worse. When attempting to improve soils of this type, it is always important to check the condition of the sub-soil first and there are two parts to this - the sub-surface soil (below the depth sampled for soil testing, but still within the root zone; and the sub-soil proper, below the roots.
The difference this method of improvement has on clay soil gardening with hard, heavy soils is dramatic. It will no longer set hard and water will move through it much more freely. Plant roots will gain easier access and so can more easily get the nutrients they need, so productivity increases. Biological activity will also improve and soon the soil will be alive with worms. All in all, clay soil gardening becomes a joy. Further Reading
Using Lime and Gypsum.
A reliable 5 step process for soil improvement.
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