Table of contents
- water hardness
- PH value
- Determine degree of hardness
- The right substrate
- decalcify the irrigation water
- 1. Decrease in calcium and magnesium concentration
- 2. lower pH
- Conclusion
Limescale that precipitates out leads to unsightly deposits in the potting soil, but these are not harmful to the plant. It is much more important for the well-being of the plants that the pH value in the substrate rises if it is continuously poured with very calcareous water. The optimal pH value for the irrigation water is around 6. Deficiency symptoms such as yellow leaves (leaf chlorosis) can occur at higher pH values. In the garden soil, this phenomenon is rarely encountered, since the acidic rainwater (pH about 5.6) counteracts an increase in the pH value.
water hardness
Drinking water that flows from our pipes does not only consist of pure water. Numerous other substances are dissolved in it, which differ in type and concentration depending on the origin of the water. The term water hardness is used to quantify some of these substances with a value. Above all, the content of calcium and magnesium salts in the water contributes to water hardness. So the higher the amount of calcium or magnesium, the harder the water. Together with the carbon dioxide in the air, both form poorly soluble compounds known as carbonates. These not only settle and form an annoying coating, but also influence the pH value in the water.
PH value
Very calcareous water also increases the pH value in the substrate over the long term, so that dissolved minerals such as iron, copper, manganese and zinc, which are essential for good plant growth, are no longer absorbed can. Optimal irrigation water has a slightly acidic pH value (like rainwater).
Determine degree of hardness
| hardness range | Calcium carbonate per liter | degree of hardness |
| 1 / < 1.5 mmol | 0 – 8.4 °dH | soft |
| 2 / 1.5 – 2.5 mmol | 8.4 – 14 °dH | middle |
| 3 / 2.5 -3.8 mmol | 14 – 21 °dH | hard |
| 4 / > 3.8 mmol | over 21°dH | very hard |
Tip:
With the help of test sticks from garden shops, aquarium shops or pharmacies, you can precisely determine the degree of hardness of your tap water and act if necessary.
The right substrate
The best protection against an increase in pH is to regularly change the potting soil in the pot. Fresh potting soil usually has a slightly acidic pH value and is able to buffer a large part of the water hardness. An annual repotting in fresh substrate protects the plant from deficiency symptoms in the near future when watering with tap water.
decalcify the irrigation water
If the tap water is very calcareous, there are various ways to decalcify the water. Some methods rely on the calcium (and magnesium) being removed from the water so that no more limescale forms. Another option is to add acid in different forms to the irrigation water to lower the pH. At pH values below 7, limescale no longer precipitates because the carbonate is removed from the water.
1. Decrease in calcium and magnesium concentration
If there are fewer salts in the irrigation water, the water becomes softer and less limescale can form.
A) Dilute
An effective way to decalcify the irrigation water is to mix normal tap water with deionized water. This process is purely a dilution process, all salts in the water are retained, only the concentration is reduced to such an extent that less or no more lime is precipitated.
- Hard water dilution (degree of hardness 3): two parts tap water + one part deionized water
- Dilution for very hard water (degree of hardness 4): one part tap water + two parts deionized water
- desalinated water can be bought in stores, it comes under different names
- battery water
- deionized water
- fully desalinated water (DI water)
- distilled water
- demineralised water
Tip:
As a rule, all ultrapure water can be used to dilute tap water for watering flowers. Exception: ironing water. It often contains fragrances.
B) heating
Limescale contained in tap water precipitates out as a solid if the water is left to stand in a container (watering can) for some time. The whole thing works faster and more effectively if the water is heated.
- Leave tap water in a sunny place for a long time (at least one day).
- fill hot tap water (from the tap) and leave for a day
- Heat water in a saucepan (over 60 degrees) and leave for a day
- Filter the water through a coffee filter before pouring
2. lower pH
With this method, the nutrients important for the plant are retained. Calcium and magnesium levels do not change. Only the carbonate, which is largely responsible for the formation of the solids, is removed from the water. Some of these methods require a bit of technical understanding and precise procedures, so they are not necessarily suitable for every hobby gardener. Overdoses can quickly occur. Too acidic water is at least as bad for the plants as very hard water.
A) peat
Peat is naturally acidic and can lower pH to some extent. The advantage of this method is that overdoses cannot occur, so the procedure is very safe. However, the use of peat is not necessarily environmentally friendly and is also relatively expensive.
- about 1 g of peat in a liter of water lowers the water hardness by about 1 °dH
- the water does not have to be completely softened
- about 100 to 200 g of peat per 10 liters of water is enough
- Put peat in a cotton bag or old stocking
- to tie up
- soak in water for at least 24 hours
Tip:
Coffee grounds are cheaper and more environmentally friendly than peat. This also contains small amounts of acid, which are released into the irrigation water when soaked.
B) Vinegar or other acids
Care should be taken when dosing pure acids. In the event of an overdose, the water quickly becomes too acidic. Vinegar should therefore either be dosed carefully or, even better: the pH value is checked using test sticks or a pH measuring device (pH meter). Measuring devices for the pH value 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 around 4
- this is perfectly normal and will not cause any problems
- an overdose (below pH 4) must be avoided at all costs
- Alternative without pH value 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
C) pine needles
Fallen leaves from coniferous trees such as fir or spruce lower the pH value in the soil. Conifer compost is also suitable. When using conifer compost, not only is the irrigation water descaled, it is also enriched with nutrients for the plants, so that less fertilizer is needed.
- about 300 g spruce or fir compost per 10 liters of water
- fill in a bag or old stocking and close with a thread
- If necessary, weigh down with a stone and leave to act for 24 hours
D) Pieces of wood or bark mulch
Pieces of wood or bark mulch from conifers are slightly acidic and thus lower the pH value of tap water. A relatively safe method of decalcifying the irrigation water, as it is difficult to overdose.
- about 500 g of wood per 10 liters of water
- fill into a cotton bag or old stocking and close
- leave on for 24 – 48 hours
Conclusion
Very hard water can be mixed with desalinated water to descale irrigation water. Alternatively, peat, conifer compost or old coffee filters can be placed in tap water for about a day. These substances give off a small amount of acid, which lowers the pH of the irrigation water.
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