How to measure and adjust water pH for your plants?
When caring for plants, it is essential to understand the importance of the pH of the water you use.
Why? Because pH directly influences the ability of plants to absorb nutrients . In this article, we will see when and how to measure the pH of a watering solution, and especially how to adjust it to optimize the health of your plants.
Figure 1. Diagram of nutrient assimilability by plants as a function of pH (Mérelle, 1998).
As shown in this graph (Mérelle, 1998) the quality of nutrient absorption depends on the pH of the water or soil. Thus this graph illustrates the assimilability of nutrients by plants as a function of the pH of the soil or water
The horizontal axis (pH) : Represents the pH scale, from 4.5 (acidic) to 8.0 (alkaline).
The vertical axis (nutrients) : Indicates the main elements essential for plant growth: Nitrates (NO₃) which are used by plants to assimilate Nitrogen, Potassium, Calcium, Phosphates, Iron, Magnesium, Sulfur, Manganese, Molybdenum, Zinc, Copper, and Boron.
The thickness of each band shows how available a nutrient is to plants at a given pH; the thicker the band, the more the element is well assimilated by plants, and conversely, the thinner the band, the less or not at all the element is assimilated.
Most essential nutrients, such as nitrate, potassium or phosphorus, are well available in this slightly acidic pH range, from 5.5 to 6.5.
If the pH is too acidic, some elements like aluminum (not listed as a nutrient but present in the graph) become toxic at very low levels. And calcium, magnesium, and molybdenum are less available. Finally, if the pH is above 7, elements like iron, manganese, zinc, and copper become much less available, often leading to deficiencies.
To optimize the growth of tropical plants, it is important to maintain a pH between 5.5 and 6.5 , as this is where most nutrients are available. If the pH deviates from this range, some essential nutrients become inaccessible, even if they are present in the substrate or water.
When to measure the pH of water for your plants?
The first question to ask is: should you measure the pH before or after adding fertilizers to the water? The answer is simple: always after .
Fertilizers, whether liquid or powder, often change the pH of the water. Therefore, measuring the pH before adding the fertilizer will not reflect the actual value your plants will receive. Wait until the fertilizer is thoroughly mixed into the water, then measure the pH of the final solution.
💡 Practical tip : Use room temperature water to mix your fertilizers and avoid variations that could distort the measurements.
How to measure the pH of water?
To measure pH, you will need an accurate pH tester, preferably an electronic one. Personally, I use the HM Digital - pH 200 Tester .
Here are the steps to follow:
Prepare your solution : Mix your water with the fertilizers according to the recommended doses.
Dip the tester : Turn on your device, immerse it in the solution and wait a few seconds for the value to stabilize.
Read the result : Note the value displayed. It will tell you if the pH is in the ideal range for your plants.
How to adjust the pH of water?
If the measured pH is not in the optimal range for your plants, i.e. between 5.5 and 6.5 , it needs to be adjusted. Here's how to do it:
1. If the pH is too high (above 6.5)
Use a product called pH Down (often based on phosphoric or citric acid). Here are the steps:
- Add a few drops or a small amount of pH Down to your solution.
- Mix well.
- Measure the pH again.
- Repeat if necessary until desired pH is reached.
2. If the pH is too low (below 5.5)
In this case, use a product called pH Up (often based on potassium carbonate). Proceed in the same way:
- Add the product in small doses.
- Mix well
- Re-measure the pH.
💡 Caution : Always add adjustment products gradually. Changing them too abruptly can stress your plants.
Why is this important?
An improper pH prevents your plants from absorbing certain nutrients, even if they are present in the solution. For example:
- pH too low : Calcium, magnesium and molybdenum become less accessible, and toxic elements such as aluminum can appear.
- pH too high : Nutrients such as iron, zinc, copper and manganese become unavailable, causing deficiencies.
Maintaining an optimal pH between 5.5 and 6.5 ensures that your plants receive the full benefit of nutrients, promoting healthy, vigorous growth.
Conclusion
Measuring and adjusting the pH of the water you use to water your tropical plants is an essential step for their health. With a pH tester and the right products, you can easily ensure that your plants are getting everything they need.
Do you have any questions or tips on the subject? Share them in the comments! And if this article was useful to you, don't hesitate to share it with other plant lovers. 🌿