Water with tap water: Can plants tolerate calcareous water?

Often you can’t avoid having to water your garden, balcony or even houseplants with tap water – rainwater is not always available. We take a look at why even tap water containing lime is not as bad as its reputation suggests.

The water supply of plants

Plants absorb the water they need through their roots. It is sucked into the cells of the roots, so to speak, by a negative pressure. From there, it is transported further up through the stems and stalks. This works because water is constantly evaporating through the leaves. The water from below then flows in. This illustration is very simplified, but it shows how the plant manages to make water flow from the bottom to the top.
A little theory: Why do plants need water?

The short answer: To supply nutrients and to perform photosynthesis. There are all kinds of important substances dissolved in the water that the plant needs. They enter the cells with the water. Photosynthesis takes place in the leaves, at the end of which the plant has produced sugar with the help of light and CO2.

Rainwater or tap water for plants?

Rainwater represents the natural water supply for plants. In the natural cycle, it falls to the ground and some of it percolates into the soil where there are groundwater supplies. Another part evaporates, either through the plants or the soil. Simply put, evaporated water rises back up into the air and new rain clouds are formed.

Ideally, plants are watered with rainwater. To do this, it is collected in rain barrels or cisterns, for example. But if you don’t have the possibility to collect rainwater in a barrel or your plants are covered, you have to rely on water from the tap. But even a rain barrel is empty faster than you think in a dry summer. So most of us won’t have the benefit of being able to water exclusively with free rainwater and will have to water our plants with tap water.

This can be problematic because tap water contains lime. But where does the lime actually come from? When rainwater seeps into the ground, it has to pass through very different layers of soil, depending on the region. In regions where the soil contains particularly high levels of limestone, calcium and magnesium dissolve in the process and remain in the water. The higher the proportion of these minerals, the harder the water.

This is why tap water is very soft in some regions of Europe and very hard in other places.

Can plants tolerate calciferous water?

There are some plants that do not tolerate lime so well. These include, for example, blueberries, which need a slightly acidic soil. But don’t worry, tap water can only cause damage if it is really, really rich in lime. From a value of about 10°dH, it should be decalcified for watering lime-sensitive plants. From values of 15°dH and upwards, this also makes sense for other plants.

In the vast majority of cases, however, it is completely safe to water with tap water. So you don’t have to worry about too much lime in the water. Some plants even like slightly calcareous water, for example citrus plants.

Overview: Plants and calciferous water

These plants do not like lime and react sensitively when the pH value of the soil increases due to hard water:

  • Vegetables: cucumbers, pumpkins, watermelons, radishes, rhubarb.
  • Herbs: peppermint, parsley
  • Fruits: blueberries, blackberries, currants
  • Flowering plants such as hydrangeas, rhododendrons.

These plants like lime and a slightly alkaline soil:

  • Vegetables: cabbage, carrots and other turnips, onions and leeks, potatoes
  • Herbs: oregano, lavender, sage or chives
  • Fruits: raspberries, strawberries, gooseberries, grapes, fruit trees like apples, pears, cherries, plums, peaches & co.
  • Flowering plants: roses, geraniums, fuchsias, butterfly bushes