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Measurement and cannabis plants

pH meter soil

Measurement is knowledge

Some growers like to dish out to their female plant a whole array of supplies, wanting to fatten up their little ‘chickens’. But whereas it is also possible to go too far and actually make a chicken into an over-stuffed battery hen, is it also possible to overfeed a plant?

For the answer to the question of how to go about feeding, we have to take a closer look at the differences between how plant and animals (and humans) are fed. What is and isn’t in the nutrition, and what function and influence does it have on the plants?


To start with: plant nutrient consists of minerals and salts, so the EC in other words. These are the Plant nutrientssum total of what the plant takes up via its roots, dissolved in water. Salts are the compound created by binding a metal and a non-metal. Dissolved in water this connection breaks and the salt splits into ions. These are tiny particles that can be directly taken up by plants.

Our own food and that of animals contains carbon compounds, which are larger compounds that cannot be taken up via plant roots. They contain the carbohydrate fuel and thus the energy (via respiration) that is needed for making the large building blocks (made by the cell) used by animals and man.

Plant nutrient contains no fuel and therefore is not responsible for the energy supply of the plant. That’s what the light is for. Conclusion: you can fatten up a chicken by giving it all the food it can eat, but not a plant. What’s more, battery chickens are not of very high quality.

If we want to grow a fatter plant, then we not only have to feed her more we also have to make sure more photosynthesis can take place. To achieve the latter we need more light and CO2 to create the right conditions. In short, many of us know the meaning of the old saying ‘a chain is only as strong as the weakest link’, meaning here that the weakest factor in your grow determines how well the whole process proceeds.

Extra nutrients

We can extend our folk wisdom metaphor and say that the chain will not get any stronger by just making one link stronger.  

All extra nutrients that the plant cannot use up will eventually end up in the soil as residues that will build up as the grow progresses – with many very detrimental effects! The EC value of your soil can be raised too high. This means that when there is a high salt concentration around the plant’s roots these are sucked dry, so to speak, and have to work at their very hardest to maintain a reasonable water status in the plant.

Excess salts are not taken up by the plant unless the plant cannot avoid doing so (there are certain poisonous salts that the plant absorbs 'by accident', and these are often ‘dumped’ or in some other way made harmless – but this all costs the plant energy).

PhotosyntheseRemember that the plant has to take up a lot of water anyway to be able to move the salts around to where they are needed. Because water evaporates from the leaves, there is a sucking power created which is used to draw the absorbed salts up into the leaves.

Water is also necessary for photosynthesis (CO2 + H2O = sugar), but 95% of the water that the plant takes up is used for transportation needs! Too high an EC works against all this. It is true that the EC in your soil can be reasonably high without it creating any major problems, but this has its limits. Flushing your soil to get rid of the excessive salts is a poor option because the soil will then be too wet, even with holes in the base of your pots!

A good example of problems caused by too high an EC is given by how just-rooted clones put into heavily fertilized soil do not progress very well due to burning. Too high an EC in the soil puts a brake on the plant’s development.

If the EC is too high in a soil and the pH is not good either then it is much harder to bring the pH back to a good level than if the EC had been more reasonable. In practice the soil becomes acidified too often among cannabis growers as a result of giving their plants too much nutrient.

Feeding plans

The producers and manufacturers of mineral nutrients for cannabis often give little or no explanation of the possible negative effects of the use of their products, and their feeding plans seem to assume that your plants will always be in tip-top condition and growing fast. When that is no longer the case you might as well throw those plans away, practice suggests.

Feeding plantAlso be aware that ‘bio-mineral nutrients’ makes them sound as if you can give plants triple the doses stated on the bottles, but that is not the case. There is basically the same amount of nutrients in them as in good old PK 13/14, and so they can push up your pH enormously if misused. So measure well folks!

In a good soil mix (10 litres per plant) with the right pH and the right quantity of water a nutrient deficiency in the second week of bloom has hardly any chance of occurring. If you see a yellowing or some such problem then the cause is most likely not a nutrient deficiency but something else.

This is how in some test gardens I’ve set up there were plants that had been given no extra nutrition and were still looking great in their 3rd week of blooming.

In short: it all revolves around the pH and EC values in the soil, and these are seldom the same as the values of your water. Measurement is knowledge, as we all know. So growing in soil is not exactly easy; it’s anything but an automatic process, if you know what I mean!

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