Is deionised water safe for plants?

Deionised water, also known as demineralised water, has had its mineral ions removed, leaving only hydrogen and hydroxide ions. It is commonly used in laboratories and for industrial processes, but is it safe to use for watering plants? The answer is not straightforward.

The pros

One of the advantages of using deionised water for plants is that it does not contain any minerals or salts that could accumulate in the soil and harm the plant. This can be especially beneficial for plants that are sensitive to high levels of certain minerals, such as bromeliads, orchids, and cacti.

Another advantage is that deionised water has a neutral pH, which means it does not add any acidity or alkalinity to the soil. This can be useful for gardeners who are trying to adjust the pH level of their soil to suit specific plants.

Deionised water is also free from impurities like chlorine, which can be harmful to plants in high concentrations. This makes it a safer option for plants that are delicate or prone to damage from chemical exposure.

The cons

While deionised water may seem like a good option for plants, there are some disadvantages to consider. Firstly, deionised water lacks the essential minerals that are necessary for plant growth and development. Plants need a range of minerals, including calcium, magnesium, and potassium, to survive and produce healthy leaves, stems, and flowers. Without these minerals, plants may become stunted or discoloured.

Furthermore, deionised water can be expensive to produce and purchase, especially for those with large gardens or a lot of plants to care for. It may also be difficult to find or access, depending on where you live.

Finally, using deionised water exclusively for watering plants can reduce the diversity of microorganisms in the soil. Soil microorganisms play an important role in plant growth and health by breaking down organic matter, releasing nutrients, and protecting plants from disease.

The verdict

So, is deionised water safe for plants? The answer is that it depends. While deionised water can be beneficial for plants that are sensitive to certain minerals or that require a specific pH level, it is not recommended as the sole source of water for most plants. It is important to remember the essential role that minerals and microorganisms play in plant growth and to ensure that your plants are receiving a balanced and varied diet.

One solution is to use deionised water in conjunction with other sources of water, such as rainwater or tap water. Rainwater is naturally low in minerals and has a neutral pH, making it a good alternative for plants that need a break from mineral-rich water. Tap water is a good source of minerals but may contain high levels of chlorine or other chemicals, so it is important to let it sit for a few hours or overnight to allow the chlorine to dissipate before using it to water plants.

In summary, while deionised water can be a useful tool for plant care, it should be used in moderation and in combination with other water sources to ensure a balanced and healthy growing environment for your plants.