What to Add to RO Water for Plants? Find Out Here!

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Just like us, houseplants need vitamins and minerals in order to thrive. But they are not getting them from tucking into a healthy serving of fruit and vegetables, they are getting them from the soil they grow in and the water source they are exposed to.

This poses an issue when using RO water, as it has been completely stripped of its mineral content.

Thankfully for your plant babies, it is possible to add nutrients to RO water or your plant soil to counter this.

What to add to RO water for plants? Find out below!

Key Takeaways

  • Various things can be added to your RO water or soil of your plants to increase its mineral content.
  • Your remineralization medium should be chosen with your specific plants in mind, but an NPK fertilizer is an excellent base to start with.
  • Aside from nitrogen, phosphorus, and potassium, your plant might also require magnesium, calcium, and sulfur. Important trace elements may include iron, manganese, zinc, molybdenum, and boron.
  • Organic components such as eggshells and coffee grounds can also be added for an extra boost.

What to Add to RO Water for Plants?

Before we get into details, this was written with houseplants in mind, not larger-scale crop growing.

That said, you can add various things to your RO water to remineralize it and help your plants flourish. What you select will be based on what is best for the type of plant you are trying to grow.

  • For example, MSU fertilizer has a nutrient balance that is fantastic for orchids and well-suited to other house plants.
  • Ferns and tropicals can be sensitive to certain fertilizers, so these should be remineralized with a gentle and slow-release nitrogen, phosphorus, and potassium fertilizer (NPK).

All plants need these three nutrients to thrive, just in varying doses.

If you have multiple kinds of plants, look for the ratios in an NPK fertilizer. NPK fertilizer can be used as a base, and then if your plant needs more nitrogen, for example, you can add it from a different source. NPK fertilizer will come with a number to show its ratios. A 4-4-4 NPK has 4% nitrogen, 4% phosphorus, and 4% potassium.

watering plants

Some plants prefer a granular fertilizer, and others prefer a liquid added to the RO water. Granular fertilizers are applied to the soil, and their nutrients are released every time the plant is watered, whereas liquid blends are diluted in the water and applied weekly.

There are also some natural options for boosting nutrients in the soil and water of your houseplants, such as banana peels for potassium, coffee ground for nitrogen, and eggshells for increased pH and calcium.

Adding sugar or salt to your plants is a risk, as sugar can attract bugs and promote mold growth, and salt can kill your plants in doses that are too high.

Reverse Osmosis Removes Minerals

Reverse osmosis removes almost all minerals from your water. They include:

  • Sodium
  • Calcium
  • Magnesium
  • Potassium
  • Iron
  • Manganese
  • Copper
  • Zinc
  • Cadmium
  • Barium
  • Chromium
  • Chloride
  • Bicarbonate
  • Nitrate
  • Phosphate
  • Chromate
  • Sulfate
  • Boron
  • Selenium

Nitrogen, phosphorus, potassium, calcium, and magnesium are some essential things that all plants need for growth, plus various plants will have different requirements for other minerals too.

All in all, most common plants need about 20 minerals for basic growth. As such, when choosing your remineralization agent, be sure to look for one that has as many of the essential nutrients your particular houseplant species needs and the ratios at which you should apply them.

What Is RO Water and How Does Reverse Osmosis Water Purification Work?

RO water is basically water in one of its most pure forms. Free from almost all contaminants, it is close to 100% H2O. Reverse osmosis purification requires your water to run through an RO system, which has several stages of filtration, including

  1. One or more sediment pre-filters
  2. One or more carbon pre-filters
  3. A reverse osmosis membrane
  4. A carbon-based post-filter
  5. Remineralization post filter (with some models or as an added extra)

Your household water moves through these filters, eventually arriving in a storage tank and ready for you to use.

Also, there are different types of RO systems, such as portable countertop units that attach to your tap or under sink units that require a little more installation.

Do Plants Like Reverse Osmosis Water?


Chlorine has been added to our water supplies for years. This has been an amazing advancement in public health, as it kills waterborne pathogens that cause disease.

But some of our more sensitive plants don’t love it. Dracaena, Cordyline, and Calathea are examples of this. They all are chlorine sensitive.

Water pH

Houseplants do best with water with a pH of around 6.0. RO water is usually pH 6.5, dropping down to 5.5 sometimes, particularly if you let it sit for too long before use.

5.5 isn’t considered too much of an issue, as the soil will usually buffer it anyway. Just note that too high or low water pH can lead to issues such as stunted growth, necrosis, leaf death, and brown spots.

pH scale

Advantages and Disadvantages of Using Reverse Osmosis Water for Plants

  • Removes most harmful contaminants.
  • Protects you from contaminants – If you are growing edible plants, RO water will prevent those plants from uptaking stuff like lead and arsenic, which can be toxic when ingested.
  • Improves plant growth.
  • Complete control of water quality – RO water provides a neutral base for remineralizing.
  • Removes beneficial minerals essential for proper plant growth.
  • Acidic water could affect the pH of the plant soil.
  • Setup costs and maintenance are higher.

If you have any questions about what to add to RO water for plants please don’t hesitate to leave a comment below!

About the Author Gene Fitzgerald

Gene Fitzgerald is one of the founders of BOS and currently head of content creation. She has 8+ years of experience as a water treatment specialist under her belt making her our senior scientist. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
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