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Most hobby gardeners use tap water to water their plants in the home because they have no rainwater available. Depending on the place of residence, however, the degree of hardness of the water can be very different. In general, it is very easy to find out the hardness of your own drinking water. Many water utilities publish their values on the Internet or provide personal information. If the degree of hardness in drinking water reaches values above 21° dH, it should no longer be used for the water supply of the plants, without having prepared it in advance.
Hardness range / calcium carbonate per liter / hardness
1 / <1.5 mmol / 0 - 8.4° dH / soft
2 / 1.5 - 2.5 mmol / 8.4 - 14° dH / medium
3 / 2.5 -3.8 mmol / 14-21° dH / hard
4 /> 3.8 mmol / over 21° dH / very hard
Tip: With the aid of test sticks from the garden retailer, aquarist's retailer or the pharmacy, you can precisely determine the degree of hardness of your tap water and act as needed.
The right substrateThe best protection against a rise in the pH value is the regular replacement of potting soil in the pot. Fresh potting soil usually has a slightly acidic pH and is able to buffer a large part of the water hardness. An annual repotting into fresh substrate protects the plant for the next time from deficiency symptoms when it is poured with tap water.
Descaling irrigation waterIf the tap water is very calcareous, there are various ways to descale the water. Some methods are based on removing the calcium (and magnesium) from the water so that lime is no longer precipitated. Another possibility is to add acid in different forms to the irrigation water in order to lower the pH. At pH values below 7, lime no longer precipitates as the carbonate is removed from the water.
1. Lowering the calcium and magnesium concentration
If less salts are contained in the irrigation water, the water softens and less lime can precipitate.
One effective way to decalcify irrigation water is to mix normal tap water with desalinated water. This method is a pure dilution method, all salts are retained in the water, only the concentration is lowered so that less or no lime precipitates.
- Hard water dilution (grade 3): two parts tap water + one part desalted water
- Dilution with very hard water (grade 4): one part of tap water + two parts of demineralized water
- Desalinated water can be purchased commercially, it is available under different names
- battery water
- deionized water
- demineralised water (demineralised water)
- distilled water
- demineralised water
Lime contained in the tap water precipitates as a solid when the water is allowed to stand in a jar (watering can) for some time. The whole thing works faster and more effectively when the water is heated.
- Let tap water stand for a long time (at least one day) in a sunny spot
- Fill hot tap water (from the tap) and leave for a day
- Heat water in a saucepan (over 60 degrees) and leave it for one day
- Filter the water through a coffee filter before pouring
This method will retain the nutrients important to the plant. Calcium and magnesium levels will not change. Only the carbonate, which is largely responsible for the formation of solids, is removed from the water. Some of these methods require a bit of technical understanding and exact procedures, so they are not necessarily suitable for any hobby gardener. It can quickly lead to overdoses. Acidic water is at least as bad for the plants as very calcareous water.
Peat is naturally acidic and can lower the pH to some extent. The advantage of this method is that it can not lead to overdoses, so the process is very safe. However, the use of peat is not necessarily environmentally conscious and also relatively expensive.
- About 1 g of peat in one liter of water lowers the water hardness by about 1° dH
- the water does not have to be completely softened
- About 100 to 200 grams of peat per 10 liters of water are sufficient
- Peat in a cotton sack or old stocking fill
- to tie up
- put in water for at least 24 hours
B) vinegar or other acids
Caution is advised when dosing pure acids.Overdosing quickly turns the water too acidic. Vinegar should therefore either be dosed carefully or even better: the pH value is controlled by means of test sticks or a pH meter (pH meter). PH meters are usually expensive and therefore not necessarily a worthwhile investment for hobby gardeners.
- Initially, the pH hardly changes when vinegar is added
- then there is a sudden drop in pH to about 4
- this is completely normal and does not cause any problems
- An overdose (below pH 4) must be avoided at all costs
- Alternative without pH measurement: add about 1 teaspoon of salad vinegar to 6 liters of water
- lowers the pH by about 0.5, which already has a significant effect on the lime
Fallen leaves of coniferous trees such as fir or spruce reduce the pH in the soil. Conifer compost is also good. When using conifer compost not only the irrigation water is decalcified, but also enriched with nutrients for the plants, so less fertilizer must be.
- about 300 g of spruce or fir compost per 10 liters of water
- fill in bag or old stocking and close with a thread
- If necessary, complain with a stone and leave for 24 hours
Wood pieces or bark mulch of coniferous trees are slightly acidic and thus lower the pH of tap water. A relatively safe method to decalcify the irrigation water, as it is difficult to overdose.
- about 500 g of wood per 10 liters of water
- in cotton sack or old stocking fill and seal
- leave for 24 - 48 hours
For descaling irrigation water, very hard water can be mixed with desalinated water. Alternatively, peat, coniferous compost or old coffee filters can be placed in tap water for about a day. These substances release a small amount of acid, which lowers the pH in the irrigation water.