Fertilising Smart Guide

Fertilising belongs to one of the most important gardening duties - especially outdoor and, of course, in hydroponics too. Yet many cannabis cultivators do not know when the right time is to fertilise, how much to use, or how often. This is in part also caused by the lack of information supplied by the companies selling the fertiliser. To further complicate matters the recommended dosages are often quite confusing and tempt customers to use large amounts of fertiliser! 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 over-fertilising the plants.

To put an end to this negative trend, and because our strains grow perfectly well with only small amounts of fertiliser, 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*.
* * Mandala Seeds shall not be responsible for the use of any information herein presented and you must make your own decision as to its suitability and completeness for your use. We are not responsible for the use of a product mentioned and any effects or consequences it may have on your cultivation.

Extra notice: this guide has been updated and expanded August-September, 2010. We have made an effort to present the old and new information in easy to understand and straightforward steps & guidelines. We hope that it benefits you in your cultivation & studies on cannabis and the Mandala strains in particular.


What's Special About Mandala Genetics

To start with we would like to introduce you to some of the special features of Mandala strains. This is particularly important information for growers who are accustomed to growing commercial strains that are mainly standard inbred genetics. 

Nutrient efficiency vs nutrient sensitivity

Mandala Seeds is the first seed bank to introduce the concept of "nutrient efficiency" and breed with this goal in mind. Nutrient efficient plants have the ability to assimilate and fertilisation nutrients quickly, efficiently, and naturally. This enables amazing stress-free cultivation if you are not going to interfere with this natural potential. The vigour and robustness of our strains ensures that mistakes can be forgiven. Mandala plants can bounce back quickly if there is a period of deficiency or drought. Over-fertilisation also does not kill them as quickly as with weaker genetics.  

For indoor cultivation Mandala plants can grow and flower in soil from start to finish without extra fertilizing. How this can be done is explained in detail in our SOIL GUIDE

Nutrient sensitive plants are common in genetics weakened by what is know as "inbreeding depression": repeated self-breeding and inbreeding. They are also common among strains created by poor breeding and seed production practises such as random crosses and pollination, inferior parent selection, low quality control, etc. In addition, long-term hydroponic generations gradually become genetically conditioned to grow under synthetic feeding and start to loose certain abilities in self-sufficiency. Unfortunately, a substantial amount of mainstream strains fall under these categories. Nutrient sensitive plants do not have the natural ability for fast and vigorous growth and require long vegetative growth periods for their development, root development is slow or insufficient, they do not grow abundantly in soil without extra feedings, and so on. Many nutrient sensitive plants do not perform satisfactorily unless they are grown hydroponically and may require high nutrient levels. On the other hand, such strains/plants tend to be finicky. They may constantly alternate between showing deficiencies and symptoms of over-fertilisation, or both at the same time.

Energy-saving genetics

This is another typical Mandala concept: energy-saving genetics mean that you save time, money, and energy on growing.

How this should be applied in your cultivation methods

Successful gardening cannot be bought in a bottle. Mainly ignore what the multi-billion dollar agrochemical industry is trying to sell to you. They don't even test their products scientifically on large-scale marijuana plantations. Focus on the essentials because that is all your plants need.

Keep it simple. Mastering simplicity is the foundation of gardening. It makes you learn from your plants. Once you have achieved this you can proceed to more complicated cultivation methods.

Your plants know how to grow! They have been doing it since thousand of years. The less you interfere in natural development the better the results. Learn how to assist your plants with basic, but essential, gardening tasks. 

Learn how to grow you Mandala plants indoor in soil with no extra fertiliser or only minimal feedings to top-up nutrients. This is the easy plant care that they were created for! Read our guides for expert tips on how this can be achieved in easy steps.

Manage your hydroponic cultivation with low to medium range EC levels (i.e. approx. EC 1.0 mS/cm based on a starting EC of 0.4-0.5 mS/cm). You will be surprised how healthy and big your crop is. Overfeeding is a chronic problem in cannabis gardens that leads to prematurely shortened flowering times, lower yields, poor calyx-leaf ratio, bud mold, pest susceptibility, inferior aroma/taste, and increased pollution from fertiliser run-off.

EC Meter
Essential Knowledge About Nutrient Dosage
How We Fertilise During Growth (Soil)
How We Fertilise During Flowering (Soil)
Hydroponics and EC
Product Recommendations
Products With Uncertain Benefits
Purchasing Guidelines
Avoiding Misdiagnosis/Symptoms of Overfertilization
Common Mistakes


EC meter

If you ever need to fertilise it is essential to mix the correct dosage using an EC meter.

Do NOT blindly follow instructions printed on the fertiliser product or a conventional "feeding schedule" from the manufacturer.

The word “EC” stands for electrical conductivity. Pure distilled water conducts no electrical current. But once you add mineral salts to it this changes. Tap water, rainwater and well water will also contain traces of minerals and this will show on an EC meter. The first step is to always measure the EC of your water source so that you know how pure it is or if it is contaminated with a lot of minerals. If the EC is over 0.6 mS/cm you should consider using cleaner water. Read our WATER & PH Guide for more info.

Nutrient salt concentrations are measured by their ability to conduct electricity through a solution. If you do not know how concentrated the nutrient solution is that you intend to give to your plants you are gambling in a life and death situation. One fatal mistake can seriously damage or kill your plants. Therefore you must know three things before you even consider fertilising:

1. What the EC is of the water (this is called the “starting EC”).

2. What EC your plants can easily tolerate.

3. What the EC is when you add a measured amount of fertiliser to it and if this is within the range of tolerance (this is called the EC of the “nutrient solution”).

Buying an EC meter

We recommend that you buy an inexpensive EC meter such as the 45$/Euro model from Milwaukee or Hanna. This is perfectly sufficient and rarely breaks down. You need to calibrate your EC meter every once in a while. For this you need calibration fluid (grow shop) and a simple thermostat (pharmacy).

Read our Quick Start Guide for advice on the complete essential gardening kit.


What to watch out for

There are various other scales or measurement systems used to measure the EC. These are called CF (conductivity factor), ppm (parts per million), and TDS (total dissolved solids). North American growers tend to use ppm and European growers use EC.

The problem with these other measurement systems is that they are all based on the EC but the manufacturers then use their own system of conversion to convert the EC to ppm, TDS or CF. These conversions are not as accurate as when you simply measure the nutrient salts with an EC meter in the first place! This means that each tester/meter will give you a different reading. You cannot tell what the EC is when you use a TDS or ppm meter. You cannot even compare readings between a TDS or ppm meter from different manufacturers!

Other systems make it very difficult to provide advice and for growers to compare information on their fertilizing methods and dosages. That’s why we always recommend to purchase an EC meter and avoid this confusion. You can then easily follow our advice on fertilizing and you always get accurate readings.

EC meters are available in two versions: milliSiemens (mS/cm) and microSiemens (µS/cm). All readings used in our guides are in millisiemens (mS/cm). Here is a conversion table for calculating the value in millisiemens. The conversion is quite simple: 1mS/cm = 1000 µS/cm. 

If you already have an expensive ppm or CF meter that you want to keep using, there may be a conversion table available online for some popular meters.


Essential Knowledge About Nutrient Dosage

Let's start with the small print on the bottles which your would generally use as orientation for mixing your nutrient solution. 

What many do not know: the recommended EC value is always based on reverse osmosis water with an EC of 0.0 mS/cm!

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 levels of 2.0 – 2.2 mS/cm, most customers actually use such strong dosages in their gardens because they are unaware of this essential information. The result is not only a waste of fertiliser in hydroponic systems. Plant care also becomes much more complicated and problematic. Regular flushing with water or weak nutrient solution are necessary at such high EC levels in hydroponics. 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 under-fertilisation from the high salt content in the substrate.

For the cultivation in 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 45$/Euro!

High overdose of nutrients lead to:


Testing Dosages Given by The Industry

To demonstrate how important the EC level is we have tested 5 popular types of fertiliser. Only the fertiliser for flowering was selected because during this phase growers fertilise the most (after the motto: more fertiliser = 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 fertilise more than 0.8 mS/cm on soil. You can fertilise up to 1.2 mS/cm if you have to quickly reverse deficiencies in adult outdoor plants. It is better to fertilise with a medium range and repeat the treatment after a week or so, rather than starting with a heroic dosage that can be difficult for the plants to cope with all at once. For indoor we recommend 0.65-0.7 mS/cm for all Mandala strains that need to be fertilised. 

The first important step is to find out what the EC of your tap water is. In this example we are using a 50-50 mix of reverse osmosis water and normal tap water to get 0.43 mS/cm. Obviously, if you have a value over 0.8 in your tap water 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 mS/cm. Another alternative would be to buy 5L/1 gallon bottles of non-carbonated mineral water when you fertilise. Good mineral water has approx. 0.25 mS/cm.

Here are the test results on our water with EC 0,43 mS/cm for 5 popular products (measured on Hanna Dist 3 meter). All values are in milliSiemens (mS/cm).

General Hydroponics
One Part Bloom (N-P-K: 2-4-7)

Recommended min. dosage (Hydro): 8ml/1L or EC 1.5 mS/cm
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 fertilise 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 mS/cm! 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
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 fertiliser. 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.

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 over-fertilised. 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.

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 fertiliser 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 mS/cm. If you have a higher EC level in your tap water you can water with only 10% and get good results.

All recommended feeding frequencies on soil for the fertilisers 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.

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 moderate but regular feedings if and when they require extra fertilisation. "Moderate" means in our case a level of 0.6 mS/cm (indoor) to 1.0 mS/cm (outdoor). 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 fertiliser is like force feeding. But plants aren't pigs that have to be fattened.

With a nutrient solution of 0.6-1.0 mS/cm you can't do much wrong unless you make a mistake with the feeding frequency or amount of nutrient solution. 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 levelled out with one mild feeding (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.

Regular feedings such as once every 10-15 days are rarely required indoor unless you are growing in poor soil quality or using a small container size. It is a major mistake to assume that Mandala plants automatically need regular feedings indoor on soil. Read our SOIL GUIDE and you can learn how to grow a great crop in soil without any extra fertilizing.

How we fertilise during growth

To provide the plants with many useful nutrients we first lower the EC level of the water to about 0.45 mS/cm. With this level we either mix a nutrient solution of 0.65 mS/cm for indoor, or 0.8-1.0 mS/cm for greenhouse/outdoor.


All Mandala strains are grown in 5L/1.2 gallon containers with high quality soil that is enriched with worm manure or compost. During the typical 4 week vegetative cycle they receive no extra fertiliser.

If individual plants show the need for a mild feeding they are given 1x a nutrient solution with NPK 5-6-7 or 4-8-6 and 0.65 EC a few days before switching to 12/12. Nitrogen is used up fastest by Mandala strains due to their quick and vigorous growth. Nevertheless a complete NPK fertiliser is essential because there are also other nutrients which may need replenishing. They will also play a role in facilitating the assimilation and use of other nutrients in the plants.

Individual plants may need nutrients to be topped-up after 4 weeks, because it will take another 7-12 days before the females have all shown sex and can be repotted into bigger containers and fresh soil. For this purpose a flowering fertiliser with sufficient nitrogen is chosen. Fertiliser with a high % of nitrogen is not conducive to supporting flowering and can also influence a higher ratio of male plants during sexing.

Large plants such as mother plants eventually require feedings every 2-3 weeks, for example, because there is a limit to container size. We use an organic fertiliser such as CANNA Terra Vega for this purpose. This is a very concentrated fertiliser that lasts a long time because only small dosages are needed. CANNA Terra Vega is assimilated quickly by plants and helps in levelling out a deficiency (such as nitrogen) quickly. Read our SOIL GUIDE for advice on growing mother plants organically in containers.


All Mandala strains are grown in high quality soil that is enriched with worm manure or compost. After 5+ weeks a mild feeding is given to all container plants with NPK 5-6-7 or 4-8-6 and an EC of 0.8-1.0 mS/cm. Plants grown in the ground usually do not require extra fertiliser for a long period because we use high quality soil mixes.


How we fertilise during flowering

To provide the plants with many useful nutrients we first lower the EC level of the water to about 0,45 mS/cm. With this level we either mix a nutrient solution of 0.65 mS/cm for indoor, or 0.8-1.0 mS/cm for greenhouse/outdoor.


The Mandala female plants are repotted into larger containers after sexing. The container size is adjusted to the size of the plants and their expected flowering time. Read our SOIL GUIDE for info on recommended container size.

Short flowering indicas and small strains usually receive only 1 mild feeding during flowering, more often if an individual plant shows a mild deficiency.

Longer flowering sativas and sativa-indicas are given 1x a nutrient solution with NPK 5-6-7 or 4-8-6 and EC 0.65 mS/cm after 3-4 weeks of repotting. At this stage they are usually at 45+ days of flowering. This is when significant waves of new bud development occur. Some nutrients have now been depleted to a certain level in the container and a liquid feeding can give the plants a boost. Another mild feeding is useful at 55+ days for long flowering plants that finish after 70 days (such as the late phenotype of Satori and Krystalica). At 2-3 weeks before harvest the plants still have the energy to assimilate and utilise new nutrients. 

As flowering reaches the final phase and the plant is nearing the end of it's life cycle a biochemical change occurs and cannabis plants switch to using up the nutrients stored in the plant tissue/leaves rather than absorbing soil nutrients. This is also accompanied with a minimised uptake of water. It is not recommended to fertilise anymore during this phase. Fertilising at this late stage can cause premature wilting of pistils, bud mold, isolated male flowers in the buds and late seeding, and unpleasant aroma/taste in the harvested buds.


Container plants receive mild feedings with a liquid flowering fertiliser and EC 0.8-1.0 mS/cm.


The number of feedings depends on:

In a long season (for example April to October) container plants definately require regular moderate feedings every 10+ days, unless you plan to repot in super-size containers of 150 Liters/40 gallons or more for flowering. To make plant care much simpler and less costly we recommend late planting. You can germinate seeds as late as mid June and save 2-3 months on plant care! Your plants will still grow to a good size and yield well.

Plants in the ground are fertilised according to individual requirements. Strains or plants that are shorter, more early, or very nutrient efficient can flower until harvest with few feedings because we use high quality soil. Observation is the key to smart fertilising!

Greenhouse and outdoor plants are sometimes fertilised with a moderate dosage of granular time-release fertiliser. This is particularly effective and necessary if you have guerilla plantations. We have included some tips on using time-release fertiliser below.

In the last 2 weeks of flowering we stop fertilising and 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.

What you should watch out for

Soil and containers

The quality of the soil and size of containers decides a great deal about the nutrient needs of your plants. If you use strongly pre-fertilised 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 an EC of 2.4 mS/cm! If your containers 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 vapour grow. More light means bigger plants and higher nutrient requirements. Read our SOIL GUIDE for advice on soil quality and container size.

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 an adult cannabis plant in your garden uses 500 ml water daily then you should water that same amount or less with the nutrient solution. Never fertilise on dry soil!


Outdoor the quality of the soil, plant size, and climate play an important role in nutrient uptake. It's best to fertilise 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 fertiliser with an adequate amount of nitrogen 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 mS/cm 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 an intelligent feeding plan the plants will get enough phosphorous to last till harvest even when feeding stops about 2-3 weeks beforehand.


Hydroponics and EC

With a low to medium range strength (i.e. EC 1.0-1.6 mS/cm) you should be in the safe zone and can then optimize this if necessary. This recommendation is based on a starting EC of 0.4-0.5 mS/cm of your water. Adjust accordingly if your water has a very different EC and consider purifying your water if the EC is high. During flowering most Mandala strains can be grown with approx. EC 1.0-1.2 mS/cm and don't require heroic dosages. 

A safe EC for your hydroponic set-up has to be determined by you through practice and observation. There is no standard guideline because of the many variable factors that influence nutrient uptake and demand! If you are just starting out with a hydroponic system, using a different substrate & nutrient line as an established grower, or planting various new strains - consider the initial cultivation as a trial. There is always a learning curve before everything runs smoothly. This is no different for the pro's!

The optimal EC depends on many factors such as:

As you can see there are many factors that play a role in nutrient uptake and nutrient demand!
Be prepared to adjust the EC once any of the above factors change significantly. For example, nutrient demand changes if temperature fluctuates and an EC that is perfect in the summer may need to be modified during winter months.

You will be surprised how little fertiliser is required to grow our high performance strains. Mandala plants are bred to utilise nutrients extremely efficiently (not to be confused with nutrient sensitivity). They are not finicky... as hydroponic cultivations maintained on high EC levels have proven. Our strains are tuned for optimal performance. Their profuse root growth, thick stems, and large leaves function as super-highways and storage houses for the uptake, assimilation, and storage of nutrients.

Remember: You can always adjust your EC upwards a bit if required...but you can't reverse damage from overfeeding!

By using an EC level that sufficiently provides for your plants without going over the top you will have a less care-intensive grow time, save $$ on fertiliser, achieve even higher yields and optimal calyx-leaf ratio, and enjoy better tasting herb.

Product Recommendations

Always purchase high quality fertiliser from reputable companies such as General Hydroponics, Hesi, Bio Bizz, Canna, AlgoFlash, Compo, Fox Farm, etc. With such fertiliser brands you will have the guarantee of a product that contains high grade minerals and nutrients that are easily absorbed by the plants. Some brands also carry a quality seal.

Fertiliser is not expensive when used at the proper dosage. All of the fertilisers we tested can be used as long as the dosage is correct. Among the many products offered there are differences in quality concerning how easily nutrients can be assimilated by the plants and also the NPK ratio. In particular the NPK ratio is, unfortunately, not optimised for cannabis plants in quite a substantial number of products. It is common that fertilisers contain too much potassium (K) for the flowering phase. This has been an issue since decades. Part of the problem is that most manufacturers do not test their products scientifically on large-scale marijuana plantations due to the legal challenges involved. At the end of the day it is not the same to compare marijuana with tomatoes, cucumbers and yucca plants (it is also unscientific to put out a product for the general public to test due to a complete lack of control over the situation and unverifiable data). Although potassium is theoretically important for flowering it is also easily overdosed because cannabis does not have such a large tolerance for this mineral as for phosphate (P). Symptoms of potassium over-fertilisation are quite common in hydroponics and, even if diagnosed correctly, you cannot reduce the potassium level unless you have an alternative fertiliser with less K. Therefore, we particularly recommend products with a balanced P-K ratio, such as in NPK 4-6-6 or 3-7-6, and so on. 

Our top product tips:

CANNA BioVega (Soil)

CANNA is one of the most serious companies on the market with decades of experience. They are also one of the few companies who actually test and develop their products scientifically on cannabis (what a surprise!). BioVega has become our prime choice in the vegetative phase such as for preserving our parent plants. It is very potent - a thick organic liquid that requires only minimal dosage. As such, great value for money. One bottle can last years if it weren't for the expiry date (always watch out for this on organic products). 

Although CANNA mentions that this product cannot be overdosed we have observed quite the opposite. An EC meter is highly recommended so that you don't overdose. Please follow the general guidelines for fertilizing on soil as outlined in this guide and also consult our SOIL GUIDE, because you may not need to fertilise at all during the growth phase. Due to the potency of this fertiliser you should be very careful not only with the dosage (EC), but also the frequency of using this product on soil. It also plays a role how much light the plants are getting. If a plant is standing in a darker corner of your indoor grow space it may react more sensitively than a plant near or under the lamp. This is because it is not receiving enough light to utilise the extra nutrients for growth. Adjust the dosage or amount you water accordingly. Do not fertilise under low-light unless you have made a major mistake and the plants are seriously undernourished. BioVega contains highly absorbable betaine nitrogen which can cause leaf burn or leaf drop if not used properly. Also make sure you are not fertilising during critical periods, such as when flowering commences, as this can cause undesirable side-effects.

The nutrient absorption is good but you should give your plants a few days to show how they have taken up the nutrients. BioVega is excellent for topping up nutrients once plants are getting root bound, for maintaining large mother plants, keeping potted plants fresh and green outdoor or in a greenhouse, etc. 

BioVega is one of the few products on the cannabis market that is certified organic (OMRI) and has several European organic accreditations. The OMRI Listed® seal assures the suitability of a product for certified organic production. More info on the CANNA bio products can be found here: http://bio.canna-uk.com/bio/indexphp.php

Special note: although we have also tested CANNA BioFlores it did not convince us as much as BioVega. There are alternatives (see below).


GENERAL HYDROPONICS FloraNova Bloom (Soil/Hydroponics)

This is what we have been waiting for since a looong time! Finally, a well-balanced NPK ratio of 4-8-7 that is perfectly suited for cannabis during all stages of flowering, and also for topping up nutrients before or during sexing in soil. We tested the new product outdoor and found it to be an excellent fertiliser which is "soft" on the plants. Nutrient uptake is very easy and effective and holds up to the optimum nutrient absorption as advertised by GH.

The price-quality ratio is equally impressive. This fertiliser is highly concentrated and only a small dosage is needed for soil cultivation. We used just one bottlecap per 6-7 Liters of water to feed potted plants and plants in the ground. This potency makes it an attractive choice for cost-intensive hydroponic cultivation too. Certainly the NPK ratio of FloraNova Bloom is a clear improvement to the 3-part Flora Series from GH. FloraNova Bloom is based on mineral and organic sources but looks and smells like a rich organic fertiliser. The bottle needs to be shaken well to mix the contents properly before each use.


CANNA AquaVega & AquaFlores (Hydroponics)

A good choice for the European hydroponic market.

CANNA Coco (Hydroponics)

Probably the best selection of products for growing in coco coir.



Extended-time release fertiliser

Extended-time release fertiliser is an option for greenhouse/outdoor cultivation. It can be particularly practical if your cultivation area is located further away from your residence and you do not have the possibility to tend to the plants regularly. Cultivation in the ground with poor soil quality also benefits from this type of feeding. Whenever possible you should at least dig a hole for young plants and fill that up with quality potting soil/compost.

There are organic and mineral based products in powder or granular form.

When using extended-time release fertiliser you should follow some guidelines:


Products with Uncertain Benefits

We specifically warn against the incautious use of bud boosters on Mandala strains and cannabis plants in general. Root growth activators can also do more harm than good on some plants. Due to the inborn vigorous root growth of Mandala strains such products are unnecessary in the first place. The products listed below should be used with extreme caution, as they may simply be a waste of money and some can even damage your crop. It is not uncommon that growers report undesired effects such as leaf discoloration, bud mold, or an unsavoury taste when using some of the products listed below. Many products are never tested scientifically on significantly large marijuana plantations under controlled conditions. Some biological products contain no active ingredients due to expiry dates of the manufactured stock or poor quality. There are many pitfalls in the industry and you should always exercise prudence when buying a product. Do not test it on all your plants at the same time and do not treat perfectly healthy plants. All our advice on measuring EC levels, providing basic & essential plant care, not interfering with natural development & using common sense, leaving healthy plants do their own thing, applies to this subject. 

Purchasing Guidelines

There are so many different products available worldwide that it is impossible to offer an overview or test them individually. That's why we are offering some simple guidelines. They give you more clarity to decide which product can be a suitable choice for cultivating your cannabis plants. These tips are not a bible or the last word on this subject. Treat it as a check list that can help you make more sense out of the differences between products offered. You should read through this fertilizing guide beforehand so that you understand some of the points below.

Finding a suitable product can be a process of trial and error. Ideally you should always test a new product on a sufficient number of plants to determine it's efficacy, quality, and method of use. A control group growing under the same circumstances gives you more assurance about the results or any particular observations you may take note of.

Avoiding Misdiagnosis

A regular occurrence in cannabis cultivation is that pH related symptoms are confused with deficiencies. The pH of your water or nutrient solution must always be adjusted to the correct value. Please read our WATER & PH GUIDE for more details.

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 fertiliser (hydroponic generations, etc.)
2. The cultivator does not recognise the negative symptoms/damage from overfeeding (this occurs quite often)

Even if your plants look nice and green for some time, as you continue to fertilise with high EC levels eventually you will run into one or more of the following symptoms of over-fertilisation.


Symptoms of Over-fertilisation

Examples of some of the above mentioned symptoms.



















Common Mistakes