Testing Dosages Given by The Industry
To demonstrate how important the EC level is we have tested 5 popular types of fertilizer. Only the fertilizer for flowering was selected because during this phase growers fertilize the most (after the motto: more fertilizer = more yield). Yet during this part of the life cycle plants become increasingly sensitive to excess mineral salts.
Before we look at the results it is important to understand one thing: generally one should never fertilize more than 0.8 EC on soil. You can fertilize up to 1.0 EC if you have to quickly reverse deficiencies in adult outdoor plants. For indoor we recommend 0.65-0.7 EC for all Mandala strains that need to be fertilized.
The first important step is to find out what the EC of your tapwater is. In this example we are using a 50-50 mix of reverse osmosis water and normal tapwater to get 0.43 EC. Obviously, if you have a value over 0.8 in your tapwater you have to lower the EC level through filtration. For small gardens it's sufficient to use a Britt Filter if you do not have the money to buy a household reverse osmosis filter (approx. 100$/Euro). The Britt filter can reduce the EC level by 0.15-0.20. Another alternative would be to buy 5L/1 gallon bottles of non-carbonated mineral water when you fertilize. Good mineral water has approx. 0.25 EC.
Here are the test results on our water with EC 0,43 for 5 popular products (measured on Hanna Dist 3 meter).
General Hydroponics
One Part Bloom (N-P-K: 2-4-7)
Recommended min. dosage (Hydro): 8ml/1L or 1.5 EC
Recommended dosage on soil: "less" (?!)
Recommended frequency on soil: every second watering
2ml/1L = 1.30 EC
4ml/1L = 2.00 EC
0,5ml/1L= 0.70 EC
The amazing thing about these instructions is the inaccuracy of the amount to fertilize on soil. What does "less" mean? If we were to use the common rule and mix 50% of the recommended dosage we still get an EC of 2.0! That would lead to immediate symptoms of overfertilization. Even at 25% of the dosage we are still in the danger zone. With 0,5ml/L or 6% of the recommended dosage we finally have a safe solution! This example shows how important it is to have an EC meter at hand.
Canna
Terra Flores (N-P-K: 10-9-19)
Recommended dosage: 5ml/1L
Recommended frequency: 1-3 x weekly
5ml/1L = 1.83 EC
2ml/1L = 1.05 EC
1ml/1L = 0.76 EC
Out of interest we tested the dosage of 5ml/L. If you were to give your plants this dosage they would not be very happy about it. Surprisingly, the manufacturer recommends this high salt level for soil cultivation a level that is not even used in most hydroponic cultivation! The ratio of nitrogen and potassium is quite dangerous in this fertilizer. Both minerals are present in high amounts but flowering cannabis plants cannot store excess N and K as easily as phosphorous and magnesium. At 20% of the recommended dosage we can water with a safe nutrient solution.
Ionic
Bloom (N-P-K: unknown)
Recommended min. dosage (Hydro): 7ml/1L
Recommended dosage for soil: 1,0 ml
Recommended frequency: no info
3,5ml/1L = 1.62 EC
1 ml/1L = 0.81 EC
At least the manufacturer offers an EC value for soil cultivation. But, again, if you don't have an EC meter and mix 50% of the dosage the plants are overfertilized. At 15% we found the correct dosage. The downside is that the N-P-K values are not disclosed on the label which is below standard.
AlgoFlash
Flower (N-P-K: 4-6-7)
Recommended dosage: 4ml/1L
Recommended frequency: every second watering
2ml/1L = 1.38 EC
1ml/1L = 1.00 EC
0,5ml/1L = 0.75 EC
This concentrated fertilizer is a good choice for cannabis cultivation but it is also dangerously potent. Even half the dosage is still too strong and it has to be diluted to 12,5% before we get the ideal value of 0.75 EC. If you have a higher EC level in your tapwater you can water with only 10% and get good results.
All recommended feeding frequencies on soil for the fertilizers in our test are incredibly high. This is a general trend among manufacturers. Growers who follow the advice on the bottle or "feeding chart" automatically cause damage to their plants - even if these are not immediately visible for an inexperienced or untrained grower.