Everyone is aware that rainwater is the best thing for houseplants. It is rather acid, which is something most plants like. It is also soft and reasonably pure. Most plant lovers will probably have their own ingenious methods of catching the falling raindrops. Unfortunately tap water can be far from ideal for plants. If often contains a high content of magnesium salts, chlorine and a high salt content, as well as a generous portion of lime, which causes hard water.
For true lime-loving plants such as Aspidistra, Campunula isophylla and Hoya varieties, this is hardly a disadvantage. But most of houseplants dislike lime, which we continue to add to the compost with every libation of water. Consequently, an agglutination of mineral salts gradually builds up in the compost.
The correct acid level (pH) is disturbed and progressively declines (the current proprietary composts have a pH value of 5.5). We should use every means to prevent the effect of calcification in our house plants. When we see this as a chalky white crust on the outside of porous clay pot. It is sometimes too late. White chalk blotches on leaves (a result of spraying and sponging) or a hard.
White crust on the soil surface are equally ominous warnings. All clear evidence that the water department has been adding too much lime and magnesium to it’s water supply. Consequently, the degree of hardness of such water is much too high (more than 12 degrees). You can find out the degree of the hardness of your water supply by contacting your local board.
Special water-softeners can be purchased from hardware stores and large supermarkets or tap water can be boiled to soften it temporarily. For acid-loving plants put a ball of peat fiber in a muslin bag and leave it hanging in a bucket of water overnight; the humic acids of the peat will restrain the particles of lime.
You can also buy reasonably inexpensive water-filters that screw onto a tap. These supply as much distilled water as you want, but for ease of use it is advisable to have an extra tap installed. If you decide to purchase one of the chemical water softeners, make sure the information on the packets expressly states that the product is suitable for houseplants.
The well-known domestic products that produce ‘soft’ water for rinsing clothes and those that deter chalk from forming in the washing machine are certainly not suitable.
Authors: A. C. Muller-Idzerda, Elisabeth de Lestrieux, Jonneke Krans