The pH value of a medium is very important, but also one of the most commonly misunderstood factors.
A plant transports elements through water. It is therefore essential that the elements are available for optimal absorption, which depends on the pH value of the medium.
For example, if the pH in the root zone is too high, elements like phosphorus, manganese, and boron are absorbed much less efficiently.
This leads to long-term deficiencies of these elements and can cause leaf burn due to excess in the medium. With each watering, these elements are added again without being absorbed, causing accumulation.
If the pH is too low, optimal absorption of all elements is also not possible, leading to similar deficiencies and "leaf burn" symptoms.
The best pH for almost any medium ranges between 5.0 and 6.2.
This does not apply to coco as a medium.
In coco, if the pH is below 5.4, the fibers retain copper and do not release it to the plant roots.
Measuring pH
pH should be measured in the medium itself, not in the container or drainage water.
In hydroponic or NFT systems, pH is best measured by extracting a small amount of water from the medium with a syringe and testing it.
For soil or coco media, use a specialized (electronic) soil pH meter. If you don’t have one, take a moist sample about half an hour after watering, squeeze it slightly in your hand, and insert the pH meter. This releases enough moisture for an accurate reading.
pH depends on the buffering capacity of the medium and water (bicarbonate content). If the buffer is completely full or empty, pH can change rapidly up or down.
Many issues with low pH can be easily corrected by adding new buffering elements to the medium.
When soil or coco is properly treated with quality fertilizer and a good buffer, the medium can last for years.