If you've decided to grow using hydroponics then there is some important information regarding nutrients that needs to be clear before starting. Those who come from a soil growing background may have already learnt the ins and outs of a cannabis plant's feeding requirements, however, the nutrient application is different in a hydroponic setup. This article explains how nutrients work in a hydro system so you can make sure your plants get the right dose and leave you with humungous yields.
Nutrient Requirements of a Cannabis Plant
In order for a cannabis plant to thrive, it needs a variety of macronutrients and micronutrients. The difference between these is simply the amount needed by the plant. Macronutrients make up the larger part of the diet, whereas micronutrients are only consumed in very small quantities.
Nutrients for hydroponics consist primarily of macronutrients, specifically nitrogen, phosphorous, and potassium (NPK). These 3 nutrients are essential throughout the whole of a cannabis plant's life, but are dosed at different levels depending on the stage of growth. Being the most important nutrients, N, P and K are clearly labelled on the front of almost all hydroponics nutrient bottles.
A cannabis plant in vegetation needs high levels of N and K and low amounts of P. Once in flowering, the feeding is adjusted to give less N and larger quantities of P and K. Phosphorous, for instance, is vital for cell development and helps to transfer energy and nutrients to different parts of the plant.
Carbon, hydrogen, and oxygen are also macronutrients but these are provided to the plant externally through the environment.
Key secondary macronutrients for healthy cannabis plants:
- Magnesium
- Calcium
- Sulphur
Bottled nutrients also tend to contain a number of micronutrients in small traces, which should also be listed somewhere on the label. Although in tiny amount, these are fundamental for proper growth, and without them a cannabis plant can seriously suffer.
Essential micronutrients include:
- Iron
- Zinc
- Chlorine
- Boron
- Manganese
- Molybdenum
- Copper
The main thing to watch out for when feeding hydroponic cannabis using fertilizers is the strength. Most of time hydroponic nutrients are heavily concentrated and the recommended dosages are often unnecessarily high. Diluting with water at a quarter or half strength tends to be sufficient to start with.
Soil vs Hydroponic Nutrients
When we compare with hydroponics, there is quite a big difference in how soil plants use nutrients. Soil contains thousands of living microorganisms which digest organic matter into food. This is how soil delivers the required macronutrients and micronutrients, and in a much slower manner.
In a hydroponic setup, there is no substrate to hold the nutrients before they are absorbed by the roots so they need to be broken down into smaller compounds. The nutrients are often chelated, which means they can be more easily absorbed by the plant. The solution comes into direct contact with the roots and nutrients are more readily available, therefore the plant responds faster.
A cannabis plant grown in a hydroponic system generally needs feeding much earlier on because the plant does not have any nutrients already available like it does in a soil setting. Normally, a high quality bagged soil contains enough for a cannabis plant to survive for 2-3 weeks. Hydroponic nutrients can work in a soil grow, but not the other way. However, it is best to choose nutrients specifically designed for the set up you use.
The advantage of using hydroponic nutrients over soil nutrients is that although they are mostly synthetically made, they do not usually include organic matter, which can bring a whole set of annoying problems to the table when it comes to keeping your grow fungus and pest-free. Use them if you want, just be aware of the potential risks.
Monitoring the nutrient levels in soil is particularly difficult without proper testing. An analysis of the soil is possible but most growers stick with trial and error until they find a balance that works. Remember, practice is the best way to learn about growing, so keep at it!
Salt build up and pH imbalance in soil is harder to deal with and takes longer to overcome. In hydroponics, the nutrient solution can be replaced with a fresh dose, which the plant can start using straight away.
Soil also tends to provide many of the micronutrients needed by the plants. Hydroponic nutrients have these added or are available as separate nutrients to be added during the cycle.
The Importance of pH and EC
PH and EC are two factors which determine how efficiently a cannabis plant is able to absorb nutrients. No matter which nutrients you use, if the pH is off around the roots the plant cannot use them. The chemical structure of nutrient molecules adjust depending on the pH, making them more or less difficult to take up.
The recommended pH levels for a hydroponic system is between 5.5 - 6.5, with 5.8 being the optimum level for most nutrients to be taken up effectively. However, it helps to have some fluctuation to make sure we allow the whole spectrum of nutrients to be taken up by the plant. Check your nutrients as the manufacturer may have included a feeding schedule indicating the best pH and EC for their products.
The following chart illustrates how the essential macronutrients are absorbed at different pH ranges. Also see our full chart further down the page.
| Nutrient |
Optimum pH |
| Nitrogen |
5.5 - 6.5 |
| Phosphorous |
5.4 - 6.1 |
| Potassium |
5.5 - 6.5 |
| Magnesium |
5.8 - 6.5 |
| Calcium |
6.0 - 6.5 |
| Sulphur |
5.5 - 6.5 |
It can also be helpful to check the EC (electrical conductivity) or TDS (total dissolved solids) of the feeding solution to make sure you're not overfeeding or underfeeding your plants. An EC/TDS meter allows you to monitor the concentration of nutrients in a water solution, meaning you can see whether the plant is using nutrients at the same rate you are feeding it. When the EC is too high, nutrient lock-outs tend to occur.
Most feeding schedules give measurements in PPM (part per million), which is the total amount of dissolved solids (TDS) in the solution. If it's too high you can simply add more water or if it's too low you may need to up the dosage so the plant always has the nutrients it needs available.
As always, the optimum pH and EC can be different depending on the particular strains you are growing, so it can be a worthwhile idea to experiment to see what your plants like best.
Tip: Consider the temperature of the water in your reservoir. For proper nutrient absorption, keep the nutrient solution at approximately 21-22°C.
How Cannabis Plants Use Nutrients In Hydroponics
The roots in a hydro setup come into direct contact with the nutrient solution. The small size of the compounds dissolved in liquid fertilizer means the nutrients are small enough to be quickly taken up. As a cannabis plant uses the nutrients, the concentration of the minerals in the solution fluctuates, which changes the pH and EC. Regular adjustments need to be made so the roots are working at their most efficient and nutrients are not being left out.
When cannabis plants do not receive the right amounts of certain nutrients, deficiencies, lockouts and pH imbalances occur. Discolouration and deformation of the leaves becomes apparent as the plant loses vigor. Remember, a plant can have all the nutrients it needs readily available, but if the pH or EC is out the proper range, it won't be able to uptake them correctly.
Seedling
A young seedling does not have a well developed root system to make use of nutrients. Most of its energy it gathers through its leaves, primarily through light, as well as via the air and moisture present in the atmosphere. This is why it is important to keep them in warm, humid conditions.
The seed contains enough nutrients to give a little cannabis plant a push in its early stages but that supply soon runs out, even more so in a hydroponic system. Some growers will start feeding as soon as there are 2-3 sets of leaves, but the solution should be very well diluted (at eighth or quarter strength).
Root stimulators can be mixed with water and given by hand until the roots have grown into the hydroponic system. These supplements aren't entirely necessary but can encourage the roots to be as healthy as possible. Root stimulating products tend to contain beneficial rhizobacteria, which help to keep them protected, while also aiding their ability to grow.
Tip: Avoid watering directly at the base of the stem. Water in a circle around the edge of the root zone to encourage growth.
Vegetative
The vegetative cycle starts once a cannabis plant has developed its first set of 5 finger leaves. Depending on the grow medium you use, or the strain you are growing, light feeding generally begins at around 2-3 weeks from seed.
Although we do not recommend it, you can experiment with higher doses but just be careful not to overdo it. Even though giving your cannabis plants a boost by feeding early can be beneficial, there are risks involved. A safer alternative would be to try introducing your seedlings to a light feed as they enter their vegetative phase and give a stronger solution with each or every other feed. Some growers wait until their plants show signs of needing food before giving their plants anything.
It is advised to start giving fertilizer at a very low strength and work your way up with each feeding. Keep in mind that it is easier to up the dose than correct problems caused by overfertilizing. You also ease your plants into the routine rather than potentially shocking them with a heavy feed right from the start.
During this time, a cannabis plant needs a lot of nitrogen. This macronutrient is essential for plant development and is required through most of the cycle, although most growers do not include it in the last weeks of flowering, as too much nitrogen can cause seeds to grow and make the plant taste overly 'green'. Nitrogen is more important for growth, for the development of chlorophyll and for photosynthesis.
Recommended NPK: 3:1:1
Flowering
Hydroponic nutrients often come in separate bottles that make it easy to make the switch between vegetation and flowering. These liquid nutrients tend to be labelled as 'grow' and 'bloom', with the main difference being the NPK ratio. Depending on which line of nutrients you go with, take the time to study the whole range as it is likely most of them are included in the schedule recommended by the manufacturer.
That is not to say that you have to purchase all of your nutrients from the same brand, but this way you know the products are compatible which means there is less room for error. However, there are many supplements available for hydroponics that work just fine alongside the basic nutrients.
Once your cannabis plants reach flowering, the NPK ratio of your feeding solution needs to be adjusted. Plants will need more P and K, and less N. You can use the following NPK ratios as an example of how to adjust the ratios as flowering progresses:
- Early Bloom: 2:1:2
- Mid Bloom: 1:1:2
- Late Bloom: 0:1:2
Some growers often include a potassium and phosphorous (PK 13-14) supplement after around 5 or 6 weeks of flowering on top of their regular feed to help with flower development. Then, lower doses of nutrients can be given in the last weeks or two of flowering as the plants mature.
Tip: Cal-Mag is a handy supplement that is worth having on the shelf during flowering, as plants may not be getting enough with just their standard nutrients.
Best Nutrients in Hydroponics
There are plenty of high quality hydroponic nutrients on the market but choosing the right products comes down to your experience, goals, and budget. You'll find the ideal solution by experimenting to see what works for the strains you are growing.
Wicked_Stix from GrowDiaries using GHE nutrients with hydroponics.
Be wary of nutrients that have overly chemical ingredients. A fertilizer may contain the correct nutrients for your plants but be made of some pretty unnatural elements. To save you some hassle, we've outlined some of the preferred nutrients for growing in hydroponics.
Fertilizers
General Hydroponics Flora -
The General Hydroponics Flora range is widely used and has shown particularly good results for hydro growing. The brand offers quality nutrients in a highly soluble form. The Flora series comes in 3 different bottles; one for vegetation (FloraGro), one for flowering (FloraBloom) and another which contains all the necessary micronutrients needed for healthy growth (FloraMicro).
Fox Farm -
There are very positive reviews about Fox Farm's set of nutrients, which also comes as a pack of three. Big Bloom, Grow Big and Tiger Bloom make up the series. Big Bloom is designed for the whole grow cycle as it focuses on maintaining root health and efficiency. Grow Big is used for vegetation and Tiger Bloom provides the required nutrients for massive bud production during flowering.
Advanced Nutrients -
Advanced Nutrients have been around for years and rightly so. Their products are very well respected amongst growers for the spectacular results they deliver. Similar to the Flora series, the base of these nutrients comes in 3 parts specifically created for hydro systems (Grow, Micro, Bloom). What's special about this range is the pH Perfect Technology, which helps to keep the pH of the nutrient solution stable.
On that note, regularly check your pH anyway, as nutrients that claim to regulate pH often do not do it as well as if you were to just do it manually.
There are many other products worth looking into, but these brands should give you a starting point on which you can build from. As you get more experienced you'll feel more comfortable experimenting with additional nutrients to further fine tune your grow practice.
Hydroponics Feeding Tips
Chelated Nutrients - Chelates act as layers that surround nutrient molecules, allowing them to be more easily absorbed by the roots. Some of the heavier minerals dissolved in liquid nutrients may not be used correctly without the addition of chelates. These are available in both chemical and organic forms but are generally considered higher quality nutrients that improve the functionality of a hydroponic system.
Flushing - If you accidentally overfeed your cannabis plants, flushing can help to 'reset' the system. If you notice signs of nutrient burn, you may want to cut back on the feeding and replace the reservoir with water for a day before add a fresh nutrient solution. Some growers flush their hydroponic system with pH corrected water once every week or two to avoid salt build up, but it may not be necessary unless you have been feeding heavily and the plants are still very green (probably too much nitrogen during bloom).
If you choose to flush at the end of flowering in a hydroponics system only do so for 3-7 days before harvest to prevent cutting the food source off too early, which may affect yields.
Circulate and replenish reservoir - It helps to give your cannabis plants a fresh nutrient solution at least once per week to avoid deficiencies or salts building up in the system. Add airstones to your reservoir to keep the solution well oxygenated and mixed.
Conclusion
Once a grower finds a product that works for them, they tend to stick with it in order to learn it really well. To ensure the highest quality bud, we suggest you get to know your products as best you can so you can dominate the nutrient schedule. We ecourage you to experiment, but make sure you keep an eye on the plants to see whether adding or removing an ingredient makes a positive difference.
External References
Impact of N, P, K, and Humic Acid Supplementation on the Chemical Profile of Medical Cannabis (Cannabis sativa L). Frontiers in Plant Science. - Nirit, Bernstein & Gorelick, Jonathan & Zerahia, Roei & Koch, Sraya. (2019).
Comparing hydroponic and aquaponic rootzones on the growth of two drug- type Cannabis sativa L. cultivars during the flowering stage. Industrial Crops and Products. - Yep, Brandon & Gale, Nigel & Zheng, Youbin. (2020).
Hydroponics Cultivation Cannabis sativa L. Plants. Planta Medica - PLANTA MED. - Chandra, Suman & Lata, Hemant & Khan, Imtaz & Elsohly, Mahmoud. (2010).
Liquid organic fertilizer production for growing vegetables under hydroponic condition. International Journal of Recycling of Organic Waste in Agriculture. - Phibunwatthanawong, Thanaporn & Riddech, Nuntavun. (2019).
Effect of Irrigation and Fertilization Levels on Mineral Composition of Cannabis sativa L. Leaves. Notulae Botanicae Horti Agrobotanici Cluj-Napoca. - Wogiatzi, Eleni & Gougoulias, Nikolaos & Giannoulis, Kyriakos & Kamvoukou, Christina-Anna. (2019).
This article was updated October 2020.
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