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Fertilizing Wisely

Fertilizing belongs to one of the most important gardening duties. Yet many cannabis cultivators do not know when the right time is to fertilize, how much to use, or how often. This is in part also caused by the lack of information supplied by the companies selling the fertilizer. To further complicate matters the recommended dosages are often quite confusing and tempt customers to use large amounts of fertilizer! If cultivators lack experience or, despite a good amount of gardening knowledge, they cannot find the cause of certain plant symptoms, it is very likely that they are constantly overfertilizing the plants.
To put an end to this negative trend, and because our strains grow perfectly well with only small amounts of fertilizer, we would like to share important tips from our many years of cultivation experience. By following these guidelines fertilizing your plants can become a secure routine and not a matter of life and death for your plants.

Lets start with the small print on the bottles. What many do not know: the recommended EC value is based on osmosis water with an EC of 0,0!

Ionic recommends an EC of 2,0 for flowering in hydroponics. From this value the cultivators must deduct the EC of their tapwater in order to calculate the actual recommended dosage. Let's say your water has an EC of 0,6. Then we calculate 2,0 – 0,6 = 1,4 EC. The recommended maximum dosage is therefore 1,4 EC.

Canna and other Dutch companies generally recommend even higher values. So the necessity of being aware of this formula is quite apparent. Although one really must ask how the plants should survive long term on values of 2,0 – 2,2 EC, most customers actually use such strong dosages in their grow because they are unaware of this essential information. The result is not only a waste of fertilizer in hydroponic set-ups. Plant care also becomes much more complicated and problematic. Regular flushings with water are necessary at such high EC levels. On the one hand the plants grow very fast (they stretch, get leafy, etc.), and on the other hand they develop complex symptoms of over- and underfertilization from the high salt content in the substrate. In the end massive overdoses of nutrients lead to a high risk of mold in the flowering phase, reduced levels of resistance against pests, lower yields, and possibly pose a health risk from radioactive traces in the cannabis (from phosphate).


For the cultivation on soil there is a common rule among cultivators to use 50% of the recommended dosages. Growers follow this rule without actually knowing what salt concentration they are feeding their plants with. For soil cultivation an EC meter is the most important tool to find out what the proper dosage is. This is why everyone who values their plants should not save on this rather moderate investment of 50,- Euros!

To demonstrate how important the EC value 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) and during this part of the life cycle plants become increasingly sensitive to excess 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.
That's why 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 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 value through filtration. For small gardens it´s sufficient to use a Britt Filter if you do not have the money to buy a household osmosis filter (approx. 150,- Euros). The Britt filter can reduce the EC value by 0,15-0,20. Another alternative would be to buy 5L bottles of mineral water when you fertilize. Good mineral water has approx. 0,25 EC.

Here are the test results on our water with 0,43 EC (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" (?!)
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.

Terra Flores
(N-P-K: 10-9-19)

Recommended dosage: 5ml/1L
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 hydro grows! 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.

(N-P-K: unknown)

Recommended min. dosage (Hydro): 7ml/1L
Recommended dosage for soil: 1,0 ml
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 .


(N-P-K: 4-6-7)

Recommended dosage: 4ml/1L
Frequency: every second watering

2ml/1L = 1,38 EC
1ml/1L = 1,00 EC
0,5ml/1L = 0,75 EC

This concentrated and excellent 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.

Feeding frequency on soil

Apart from the actual salt concentration of the nutrient solution the frequency and amount you water is an important aspect. Generally, cannabis plants prefer small but regular feedings. "Small" means in our case a moderate level of 0,6-0,8 EC. You can compare fertilizing to real mealtimes. People also get a stomach ache when they overeat. It's much healthier to eat small meals regularly. In the same way cannabis appreciates getting small portions of nutrients that can be "digested". So watering high dosages of fertilizer is like force feeding. But plants aren't pigs that have to be fattened.
With a nutrient solution of 0,6-0,8 EC you can't do much wrong unless you make a mistake with the feeding frequency. That's why it´s important to wait 7-10 days after fertilizing and observe the plants. How are they taking up the nutrients? Do they need a bit more or are they looking healthy enough? A slight deficiency can be easily leveled out (and does not impair flowering) but overfertilization causes irreparable damage. As you learn to observe the plants you will develop an intuitive understanding and can read small signs of nutrient deficiency that signal the best time to apply a mild nutrient solution.

How we fertilize during flowering

To provide the plants with many useful nutrients we first lower the EC level of the water to about 0,45 EC. With this level we either mix a nutrient solution of 0,55 EC and water with this solution every 5 days, or we mix a solution of 0,75 EC and water that every 8-10 days. Does it work? Definitely! In the following posts you can see some examples of plants growing beautifully on this feeding schedule.

If we use our feeding schedule during a typical 70 day flowering cycle a plant receives approx. 5 fertilizations with the maximum dosage of 0,75 EC. Why only 5 times? Because in the last 2 weeks of flowering you should stop fertilizing. Let the plants use up the stored nutrients in the plant tissue and soil naturally. In the last weeks before harvest the plants are practically "dying" and absorb only small amounts of nutrients.


This product from General Hydroponics is a real "calorie bomb" with NPK: 0-6-5 and 2,5% magnesium. It's almost a complete fertilizer. In cannabis cultivation Ripen is a good choice for fertilizing extreme Sativas that quickly respond to nitrogen with unwanted stretching, leafy buds, and retarded flowering. Ripen should be applied in the last month of flowering and at least 15 days before harvest. The recommended dosage is way too high (4-5ml/L) so please check your EC levels for the correct dosage.

What you should watch out for

The quality of the soil and size of pots decides a great deal about the nutrient needs of your plants. If you use strongly pre-fertilized soil it´s possible that your plants don't require any additional feeding till harvest! A good example are organic grows that use composted material with a high mineral content (like manure, etc.). Some manufacturers sell very potent soil mixes that are almost toxic in their pure form. An example is All-Mix from Plagron which has 2,4 EC! If your pots are too small compared to plant size or maturity you will find that your plants quickly suffer from nitrogen deficiency. Another factor is light intensity. A fluorescent grow cannot be compared to a sodium vapor grow. More light means bigger plants and higher nutrient requirements.

Watering amount

Not only the EC but also the amount of nutrient solution determines salt levels in the soil. The amount you water should not exceed the normal requirements of the plant. If a grown cannabis plant in your garden uses 500ml water daily then you should water that same amount with the nutrient solution. Never fertilize on dry soil!


Outdoors the quality of the soil, plant size, and climate play an important role in nutrient uptake. It's best to fertilize when warm/sunny days are predicted so that the plants can transform the nutrients directly into growth. Due to plant size the most common deficiency is nitrogen. This deficiency is easy to detect: first the leaves lose their leaf shine and become dull, then the lower sun leaves start to yellow, these symptoms gradually move upward and affect more leaves, in advanced stages the lower leaves dry up and die and the plant has yellowed up to the shoot tips. A flowering fertilizer with a good amount of nitrogen (like AlgoFlash) should be used when nitrogen deficiency appears during or after sexing. When a deficiency is already apparent you can use a higher EC of about 0,9-1,0 to compensate the low level of nutrients quickly.
The second most common deficiency is phosphorus which is required in large amounts for root and bud growth. Phosphorous is stored generously in plant tissue so that if you have a regular feeding plan the plants will get enough phosphorous to last till harvest even when feeding stops about 2 weeks beforehand.

Things to consider

Always purchase high quality fertilizer from reputable companies such as General Hydroponics, Hesi, Bio Bizz, Canna, AlgoFlash, Compo, etc. With these fertilizer brands you will have the guarantee of a product that contains high grade minerals and nutrients that are easily absorbed by the plants. As you can see, fertilizer is not expensive when used at the proper dosage. All of the fertilizers we tested can be used without problems as long as the dosage is correct.

Some growers claim that their plants are thriving on very high EC levels and have no problems whatsoever. There are mainly two reasons for this assertion:

1. These are strains that are genetically predisposed to grow under high amounts of fertilizer (in another article we will elaborate on this)

2. The cultivator does not recognize the negative symptoms/damage from overfeeding (this occurs quite often)

We hope that these guidelines will assist cultivators in growing healthy plants and harvesting generous crops in a more plant and environment friendly way. Mandala growers will especially benefit from these tips because our strains are very efficient in nutrient uptake and grow extremely well with only minimum amounts of fertilization. In the second part, coming soon, you can read what makes Mandala strains so vigorous and easy to grow.

Fertilizing during the vegetative period

Quick tips:

1. Use good size pots with quality soil instead of small pots & bad soil and fertilizing a lot to compensate for the lack of nutrients. If you give the plant enough natural nutrients in the soil then you don't need to fertilize for the first 25-30 days of growth.

2. Never fertilize seedling or plants that are only 10-14 days old if you grow on soil!

3. Do not stretch commercial soil with a lot of perlite/vermiculite/hydroton/coco coir etc. This only reduces the amount of available nutrients. Don't fill the bottom of the pots with stones/clay pellets. The roots grow down and need a substrate that holds water at the bottom. Good potting soil like Compo Sana Universal already contains enough additives for a balanced air-to-soil ratio and roots get plenty of oxygen. If you are growing outdoors in very compact soil then you should add 20-25% perlite for a better air-to-soil ratio.

4. The same rules on EC levels during flowering apply here as well. Do not water with more than EC 0,8.
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Mandala plants on our feeding schedule...

In the first 3 weeks of growth they grow in 4L pots on commercial potting soil, no additives, and get plain water.

The preflowering stage. These Satori ladies have had their second dose of nutrients at EC 0,6-0,7. They are still in the 4L pots but are being transplanted now into 10-20L (2,5-5,5 gallons) pots.



The Tri Guy
ICMag Supporter
Or you could start off with a decent compost and forget the food altogether.
Halfway through flowering and two more feedings. All leaves are a vibrant green and no signs of deficiencies or overfeeding.

Group of Mandala plants


GMT said:
Or you could start off with a decent compost and forget the food altogether.

With an excellent soil quality you can certainly do that. We once had the opportunity to get rich composted soil (humus) from a gardener who tended an old cemetary with huge old trees and many other green areas. The soil had a wonderful creamy black texture with a fragrant smell and yielded a bumper crop. Unfortunately, most growers have a difficult time getting hold of decent compost - especially if they live in the city or in a country where this is not available for sale. Which is why I recommend to compensate this by adding worm manure to the soil mix as this is easier to get hold of.
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Using fertilizer sparsely does not influence resin production or yield negatively as these photos show. On the contrary, the plant is not under stress from salt build-up and remains healthy to develop it's full potential.

A new indica strain we are developing

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The last two images show a new strain for which we are using a specially selected Sadhu male (J7). This resiny male has intense and pleasant aromatic properties among other positive attributes. I will post more info in autumn when we expect to have seeds for this mystery girl available. :wink:


Active member
hi mike

great thread

so sadhu is the male and the female is? looks interessting!
staying tuned for more pics ;)



Rubbing my glands together
Excellent info Mike. You guys are a class act who are concerned with getting the most from your genetics. Thanks

Dr. D

Well-known member
excellent thread man..i am just in the process of doin this with bio-bizz whre i have had major probs in flower bfore due to lock up..since i got a cf meter i kno wot the cf is and noticed that following there schedule would result in major over feeding where u are adding three products at 4ml per litre at the end of flower :yoinks: and i noticed bio-bizz have just upped the top dose on a few of there products to 5ml per litre....wot cf do u recommend in hydro and coco??? thanks for the info this is very interesting...peace
Dr. D said:
wot cf do u recommend in hydro and coco???

A low one for starters. Depends very much on your system with hydro too 'cos there are many different set-ups available. We don't go over EC 1,5 in Aquafarm/Water Farm for mother plants for example. Nutrient solution is topped off daily and changed completely every 3-4 days. Flowering plants in this system tend to do fine on EC 1,2-1,3.

We are fortunate in receiving much feedback from a very experienced coco grower. He hand waters his plants, which is quite distinct from drip-feeding. His starting EC of 0,3 is a 50-50 mix of osmosis water and tap water. Rooted clones and seedlings get 0,6. This is eventually raised to 0,8-1,0. Depending on the strain he either continues with 1,0 throughout the plants life cycle, or raises the EC periodically up to 1,3. As soon as plants show nute sensitivity he flushes the pots with clean water and let's them dry for a day or two before feeding with a lower dosage. Mandala strains grow well with EC 1-1,1 using his grow technique on coco (an example is the featured Satori grow).

Dr. D

Well-known member
Thanks Mike this is very interesting i grow on coco, soil(chem and organic) and hydro i currently have a Dankouver in a bubbler and am just finishing a crop in coco they dont like alot of feed iv been giving them max 15 cf and they ok...the one
in the bubbler is 09cf and it is booming

like this wen i put it in about 14 days ago then this one is from a few days ago
thanks for ur info Mike but there is one thing i noticed u havent mentioned and that is ph...peace


An Indica from Mandala?! I'm gonna' be all over that!

So... lemme get this straight: Since I use a pretty "hot" organic soil [Fox Farm Ocean Forest/Perlite], I don't have to fert at all? Been using FF OF for a while now in conjunction with all sorts of nutes. Best ones I've found so far are the Pure Blend and Pure Blend Pro formulas for soil. I use Original PB for veg and the new Pure Blend Pro for soil during flower in small, but regular feedings... increasing the meal size as we go on, then flush for about a week with regular ol' water.

In theory, I don't have to do all that feeding and adding micronutrients [from Liquid Karma]??? Is Ocean Forest good 'til harvest or is the 30 day use-up accurate? In *most* personal experiences, I've noticed nothing but lush green, gorgeous plants from Ocean Forest and minimal feedings. I've never done a straight-up run with it, though. I've always fed, just 'cuz I've always heard feeding is vital.


P.s. Your Kalichakras [more indica pheno] are doing freakin' FABULOUS. They love to be cloned and grow very fast... holy crap.

big bud

this is some strange stuff i'm reading here !

i have a couple of coco grow's under my belt but 1.3 at the end ??

i start with 1.3 for my rooted clones !

i understand that much plants are getting allot of nutes especially when you go up to 2 or higher with you're ec, but at the end of the 7th week of bloom i to am on 2.0 with my feedings, week 8 gets just water with enzyme and ph'd with citric accid.

i work on coco slabs and flush them 1 or 2 times during the grow and 1 time in the beginning when i re-use them.

i'm gonne give this link to a friend of mine who also knows alot about feeding and stuff, curious on whet he has to say, he grows on rockwool tho.

the reason i'm so interested is because my next clones will proabably be satori or kalichacra, the more i read here the mor i can't wait to grow them, been reading for a day or 3 here now :)

think i wil go for the satori for a coco slab sog.

will let you know how it turns out !

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big bud said:
the reason i'm so interested is because my next clones will proabably be satori or kalichacra, the more i read here the mor i can't wait to grow them, been reading for a day or 3 here now :)

think i wil go for the satori for a coco slab sog.

will let you know how it turns out !


High! :wave:

Thanks for sharing your thoughts on this subject. Well, as I said in the article - there are strains that grow well on high nute levels. But it is very important to differentiate between hydro and soil!
Strains growing on high nutes do so mainly because they are carrying this information from the way they are grown by the breeders. But, it doesn't mean that they would not do just as well with lower levels of feeding. In fact, I have not come across a single strain that does not grow and flower nicely under our recommended dosages.

As far as Mandala strains are concerned - we have the great opportunity to work with a very experienced coco test-grower who has tested all our varieties. According to his keen observations, photos, and meticulous notes every Mandala strain so far performed perfectly well with the low EC levels I am talking about.
Now, obviously, you have to adapt your feeding levels to the grow conditions. If you work with CO2 enhancement, 1000W sodium vapour lamps, or grow particularly large plants (for clones, etc.) - then EC levels have to be adjusted accordingly.

I find it's important to focus growers attention on the importance of EC levels particularly for soil gardens, because this is most often ignored by growers since they trust the dosages recommended by fertilizer manufacturers.

You can check our website gallery for photos on Satori grown on coco. All the pics with the red/blue batik type background belong to coco grows.
AND...just in at Seedbay/Seed Boutique: our brand new stock of fresh seeds of SATORI. :woohoo:

Look forward to hearing from you again.
Mike :bandit: