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When is rainwater just too much?

If like us, you also get a huge amount of rain at this time of year, you may also wonder if this is too much for the plants. When using irrigation through the taps we often make the mistake of overwatering plants.

If for instance you water your plants with 30 centimetres of water, through sprinklers or hoses or even drip irrigation, your plants would not look as good or as healthy as when the same amount of water is received through rain.

What is so special about rainwater?

The most important reason why rainwater is better is due to chemistry. Tap water contains chlorine which is a necessary disinfectant, whereas fluoride is then added to prevent cavities.

Nearly all plants are susceptible to chlorine toxicity which is usually expressed in burnt leaf margins.  Indoor plants, pines and even fruit trees will show symptoms ranging from burnt, discoloured or spotted leaves which are due to fluoride toxicity.

Calcium and magnesium is what makes tap water hard, and this is often remedied with the addition of sodium, acting as a water softener. You may have noticed white sediment on the leaves of your plants after using irrigation water. This is calcium and magnesium sediment, and just like sodium, is toxic to plant tissue.

Sodium that reaches the ground is damaging to the soil structure. In a productive garden soil, particles clump together in beneficial aggregates whilst sodium disperses these aggregates and creates cracks on the soil surface.

If you are not yet catching rainwater for your plants then you should truly consider this. Plants do look better after rain as air consists of 78 percent nitrogen. This element in its nitrate and ammonium forms comes down in the rain, and is immediately taken in through the roots and leaves of the plants. Nitrogen is an element that makes plants green.

With continuous days of rain it is understandable to think that the plants are being dangerously waterlogged as a result of excessive rain. Well, rainwater contains more oxygen than tap water. When overwatering your garden with tap water, waterlogging may bring about anaerobic soil conditions which could lead to root rot. Because rainwater is highly oxygenated it brings about a much higher margin of safety when soil is saturated after a downpour.

Carbon dioxide is another element brought down by rain. When carbon dioxide combines with other minerals in the atmosphere, the rainwater generates an acidic pH. This acidic rainwater helps to release micronutrients such as zinc, manganese, copper and iron when it is released into the soil, and it is all essential to plant growth.

The benefits of rainwater are endless as it also leaches salt down to beyond the root zone. Salts are carried in irrigation water which accumulate throughout the soil profile and inhibit plant growth. With heavy rains these salts are flushed through the soil creating an explosive growth in plants.

Unlike irrigation, rain falls uniformly in the garden. This means that all soil is leached and even the furthest corner of the plant’s root zone will be bathed and cleansed of salt. Rainwater covers every particle of the plant thus washing off mineral deposits, pollutants and dust that covers the leaves.

The splendour of new growth on plants after a downpour of rain is such a spectacular sight as the process of photosynthesis is encouraged. Plants turn water and carbon dioxide into carbohydrates which they then consume as a life-sustaining energy food.

Catching excess rainwater may seem like just another expense, the benefits to your garden are certainly endless. When you have such a high rainfall like we have, collecting rainwater can certainly go a long way. Start off small and catch the rain from the roof through rain gutters into containers.

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