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The irrigation water is one of the most important elements for plants, regardless of whether they are kept in the garden, in a bucket on the balcony or as a houseplant in a decorative pot. Depending on the species, the plants need a different pH value in order to thrive. The hardness of the water and the high lime content in Central Europe pose a problem for many, especially tropical, plants, which can lead to deficiency symptoms and diseases such as chlorosis.

Why descale?

Does your cabbage feel at home in the limestone soils of southern Germany? Do you have no problem watering numerous types of vegetables with hard water? Not all plants prefer alkaline and calcareous soils, let alone hard irrigation water. Plants such as rhododendrons, hydrangeas, azaleas, various types of bamboo or primroses want neutral to slightly acidic soil so that they can easily absorb the added nutrients. Hard tap water has some disadvantages that have a negative effect on the growth of plants and can even lead to diseases:

  • Nutrients are flushed out
  • The pH value of the substrate is increased over time
  • white deposits are formed on the substrate and plants
  • numerous deficiency symptoms such as chlorosis occur

The more often you give hard water, the worse it is for the plant. The lack of nutrients is simply too high, which the plants cannot withstand in the long run. You should therefore definitely check how hard the irrigation water is in your region and decalcify accordingly or lower the pH value.

measure water hardness

Before using any of the descaling solutions below, you should measure the hardness of your water. This allows you to check exactly what degree of hardness it is and act accordingly. The typical water hardness levels are:

  • soft (1): below 1.5 mmol, 0 to 8.4 °dH
  • medium (2): 1.5 to 2.5 mmol, 8.4 to 14 °dH
  • hard (3): 2.5 to 3.8 mmol, 14 to 21 °dH
  • very hard (4): from 3.8 mmol, from 21°dH

The irrigation water must be medium to soft. Values above 3.8 mmol should be avoided, but are often found in many regions of Germany. The units of measurement relate to the carbonate hardness and, depending on the test medium, either mmol (millimoles per liter) or °dH (German degrees of hardness) are used. However, the use of mmol is recommended for test kits from abroad. The carbonate hardness refers to the dissolution of substances with carbonic acid that make the irrigation water harder:

  • magnesium
  • calcium
  • sulfates
  • chlorides
  • nitrates
  • more salts

With the exception of magnesium and calcium, the other salts cannot be dissolved by decalcification, but only by lowering the pH value. You can find out water hardness and pH values from the following sources:

  • Contact water supplier
  • Water hardness test strips (5 - 7 euros)
  • Water hardness test kits (about 15 euros)
  • pH test strips (7 - 10 euros)
  • electronic pH meter (50 - 150 euros)

tip: A quick check for hard tap water is to use a clear glass and fill it with fresh, cold tap water. If the tap water is whitishly cloudy, it is lime, which makes the water hard.


Irrigation water can be decalcified easily using two methods. These ensure that the salts are dissolved in the irrigation water, which makes it softer and therefore ideal for watering all kinds of plants such as orchids. These methods do not lower the pH of the water, which is important to note. If you only need low-lime water, but not directly soft water, these methods are recommended:

1. Desalting

When desalinating, you mix H2O from the tap with demineralized water, which causes it to be descaled. This is offered under various terms, for example battery water, which is H2O that is free of dissolved salts. With a water hardness of 3, mix 1 part demineralized water with 2 parts tap water, with a water hardness of 4, mix 2 parts demineralized water with 1 part tap water. You can now use this for casting.

2. Heating

If you heat the irrigation water, the limescale is dissolved and it can be used. You can either use a kettle or a saucepan for this. After heating, you have to leave the tap water for a day until it is decalcified.

3. Filtering

You can easily use water filters to decalcify the water. Simply run the tap water through a water filter and you can water, as the water is deionized.

Tip: You can use any form of water that is completely pure for desalination, except for ironing water. Although this has the same properties, it is often mixed with perfume, which has a negative effect on the plants.

lower pH

Not only the measures for descaling can be used to soften your irrigation water. Once you know how hard your tap water is, you can easily use a few tools to bring it to a pH of 4.0 to 6.0. 6.0 is the ideal value for most ornamental plants and many trees, but a value of 4.0 is fine as sometimes lowering the value can be a bit imprecise. Apply any of the following methods on:

1. Bark mulch

With bark mulch you do not run the risk of reducing the value of the water to the point where it is too acidic. This must come from coniferous trees, as they have acidic properties. Alternatively, you can just use softwood if you don't have bark mulch available. You need 500 g of bark mulch for a quantity of 10 l of liquid, so that the value drops. Fill the bark mulch into a cotton sack and leave it in the watering can for 24 to 48 hours. Over this period, the value of the water drops so much that it becomes soft.

2. Pine needles

Pine needles are just as effective as bark mulch. Fir and spruce are particularly suitable for this, but you can also choose compost based on conifers, as they have the same properties. For 10 l you need 300 g of pine needles, which must act in the same way as the bark mulch for 24 hours. However, be sure to close the sack with a rubber band and weigh it down with a stone, as the needles like to float up.

3. Vinegar

Vinegar is a method that can quickly go wrong. As this is an acid, the pH value can drop to 4.0 within a short period of time. On average, one teaspoon of white wine vinegar reduces the value of six liters of irrigation water by 0.5. However, with this method you should always measure the pH value to be on the safe side. Don't be surprised if the value drops significantly even after small amounts of vinegar, that's normal.

4. Peat

Peat is a classic when it comes to lowering the pH value in the substrate. However, you can also use the sediment for the irrigation water. It is especially good if you are afraid of acidifying the water. This is not possible with the material. If you want to use the fabric, proceed as follows:

  • use between 100 and 200 g of peat for 10 l of irrigation water
  • works with hard water
  • fill in bags or stockings
  • close
  • leave on for at least 24 hours

You need as much of the sediment as one gram lowers the value by 1°dH. However, keep in mind that this method is not really environmentally friendly and inexpensive. Therefore, the other methods are more recommended.

An advantage of lowering the pH value is the preservation of the important nutrients that are completely lost during decalcification. Above all, the content of calcium and magnesium is not reduced, which has a positive effect on the growth of the plants. The only substance flushed out by these agents is carbonate. In addition, lowering the pH value has a significantly better effect on the plants than decalcification, since limescale is no longer released to the plants from a pH value of less than 7.0.

Bark mulch in the garden

tip: An environmentally conscious yet inexpensive way to give the water a boost allow neutral value is coffee powder. Brew a coffee and use the dried coffee grounds in the same amount as the peat fraction.

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