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Marijuana (Cannabis)

Nutrients And Hydroponic Marijuana

For plants, light provides energy and nutrients are similar to what vitamins & minerals are to people. The primary nutrients in plant supplements are Nitrogen (N), Phosphorus (P), and Potassium (K) also called Potash.

In addition to nitrogen-phosphorus-potassium, marijuana plants require a lesser amount of secondary nutrients and trace quantities of other elements.

Secondary nutrients include calcium, magnesium, sulphur. Trace elements for plants, also called micronutrients, include small quantities of boron, chloride, cobalt, copper, iron, manganese, molybdenum, zinc.

Plant nutrients are measured in an N-P-K format
N is Nitrogen
P is Phosphorus
K is Potassium (Potash)

A 7-4-3 plant nutrient contains:
7% Nitrogen
4% Phosphorus
3% Potassium

A 30-15-15 plant nutrient contains:
30% Nitrogen
15% Phosphorus
15% Potassium

The percentage of the nutrient not comprised of nitrogen-phosphorus-potassium is secondary nutrients, trace elements, inert material.

An all purpose nutrient with secondary nutrients and trace elements might get you through all stages of growth. But when growing marijuana, you can adjust the nutrient level quantities during different stages of plant growth.

For seedlings, clones, vegetative growth, the plants need lots of N (nitrogen). They also need a fair amount of P (phosphorus) and K (potassium), 10-5-14, or 30-15-15, or something with a similar ratio of N-P-K, and secondary nutrients, and trace elements will work.

During flowering the plants need more P (phosphorus) and the same amount or more K (potassium) than they did for earlier growth. They still need some N (nitrogen) but not more they did prior. They also need secondary nutrients and trace elements.

If you used:
--- Something like 10-5-14 for seedling/vegetative growth, then try using 5-15-14 for flowering.
--- Something like 30-15-15 for seedling/vegetative growth, then try using 15-30-20 or 25-30-30 for flowering.

The important thing here is that when flowering compared to when the plant was in the seedling, clone, vegetative stage:
N (nitrogen) be less or the same.
P (phosphorus) be higher.
K (potassium) be higher or the same.

Preparing Nutrients
Measuring Nutrients
Nutrient Strength
Nutrient Temperature
Flushing Or Leeching
Amount Of Water
List Of Materials


In most cases, you should not run a hydroponic system on tap or well water. They can contain things that are harmful to plants. Municipal water is treated with things like chlorine and chloramine.

These are added to kill certain bacteria and microbes in order to reduce or prevent spreading diseases like cholera, dysentery, jaundice, typhoid. Unfortunately they are harmful to the plants.

City water or water from a well can contain concentrations of nutrients, minerals, heavy metals, salts, or other things that can harm marijuana plants, and the people that ingest them.

To be safe, concerned growers have a reverse osmosis water filter or they purchase reverse osmosis or distilled water at a grocery, or similar store that stocks them.

Both reverse osmosis and distilled water production methods are capable of eliminating at least 90% of any impurities. You can measure how pure the water you have is with an EC or TDS meter. The closer the reading is to 0, the purer the water.

Before adding nutrients, the water you use should be as close to 0 as possible. That way you know there is nothing but the optimal quantity of nutrient you add being supplied to the plant via the nutrient solution.

Preparing Hydroponic Nutrients

Hydroponic nutrient is available as dry powder or as a liquid. In addition, it can be purchased in single-part or multi-part nutrient formulas.

Single-Part Dry Nutrient Mixed With Water In A Glass

With a single-part dry nutrient, put some water in a glass or similar container. Measure the amount of nutrient you want, and then put it in the glass with the water.

Stir the water and nutrient together until the nutrient powder dissolves in the water. After it has dissolved, add it to the nutrient reservoir for your hydroponic system.

With multi-part dry nutrients, do the same thing as you would with a single-part nutrient, but use a separate glass for each part. If you have a 3 part dry nutrient, fill 3 glasses with water.

Multi-Part Dry Nutrient Mixed With Water In Separate Glasses

Then measure the amount of part 1 you want, and put it in a glass of water and stir together. Mix part 2 in a separate glass of water and stir, then mix part 3 in a separate glass of water and stir.

After each part has dissolved into the water it can be added to the nutrient reservoir. Most manufacturers of multi-part dry nutrient recommend mixing each part separately, rather than combining them and mixing them with water in the same glass.

With liquid nutrients, you can add them directly to the nutrient reservoir after measuring. Some manufacturers of multi-part nutrients will recommend putting a certain part of the nutrient in first.

For example, with the 3 part nutrient in the image, the manufacturer says to put the part with trace elements, also called micronutrients, in the nutrient reservoir first.

Always shake the container the liquid nutrients comes in to mix everything together, before you measure the amount you need and add it to the nutrient reservoir.

After the nutrients have been added to the nutrient reservoir, measure how strong the nutrient solution is with an EC or TDS meter. If necessary, adjust the strength of the nutrient.

When the nutrient has been added to the reservoir and is the proper strength, you should measure the pH and adjust it so it is within optimum levels for the plant.

A single-part hydroponic nutrient has the primary nutrients, secondary nutrients, trace elements blended together. A multi-part formula keeps various nutrients separate, and lets you adjust the amount of each part you put in the reservoir.

Measuring Nutrient Solution - EC, TDS, PPM

For hydroponic growers, an EC or TDS meter will measure how strong a nutrient solution is. A larger EC or TDS meter reading indicates an increase in the concentration of nutrient in a nutrient solution, when compared to a lower reading.

EC and TDS meters measure the amount of N-P-K, secondary nutrients, trace elements, as well as any impurities that are dissolved in water. For cannabis growing applications impurities should be kept as low as possible.

If you start with reverse osmosis or distilled water the amount of impurities will be next to nothing. When measured with an EC or TDS meter, the reading will be near 0. Unless filtered, well and tap water will contain impurities.

EC stands for electrical conductivity. EC meters are a method of measuring the amount of dissolved solids in nutrient solution. More solids will conduct electricity more efficiently, resulting in a higher reading.

Depending on the meter, EC can be measured on several different scales, including:
A) µS/cm (microSiemens per centimeter)
B) cf (conductivity factor)
C) mS/cm (milliSiemens per centimeter).

The scale the different EC readings are measured on is similar to those on a volt meter that can measure millivolts (mv), volts (v), kilovolts (kv) ...

The difference is instead of letting you view readings of several different scales, some EC meters only allow you to take a reading on one or two different scales.

If you have an EC meter that reads in µS/cm you can compare your measurement with someone that had a reading in cf or mS/cm by moving the decimal place.
100 µS = 1.0 cf = 0.1 mS
200 µS = 2.0 cf = 0.2 mS
400 µS = 4.0 cf = 0.4 mS
600 µS = 6.0 cf = 0.6 mS
800 µS = 8.0 cf = 0.8 mS
1000 µS = 10.0 cf = 1 mS
1400 µS = 14.0 cf = 1.4 mS

TDS stands for total dissolved solids, TDS meters are another method of measuring the amount of dissolved solids in nutrient solution.

TDS meters display a reading in parts per million, ppm. To get a reading, they take measurements like an EC meter, then convert to ppm based on a conversion factor according to several different standards.

Different TDS standards include:
NaCl conversion (NaCl)
442 conversion (442)
KCl conversion (KCl).

NaCl conversion works out to approximately: EC in µS divided by 2. So 1000 µS is equal to about 500 ppm (NaCl).

To compare TDS meter readings with other people, you will need to know the conversion standard of both meters, if they are the same you can compare directly.

If TDS meters are calibrated to different standards, you will need find out what standard each meter is calibrated to and then find a conversion chart or formula, to convert between the two different standards.

To convert between EC and TDS (NaCl):
100 µS = 1.0 cf = 0.1 mS = 50 ppm (NaCl).
200 µS = 2.0 cf = 0.2 mS = 100 ppm (NaCl).
400 µS = 4.0 cf = 0.4 mS = 200 ppm (NaCl).
600 µS = 6.0 cf = 0.6 mS = 300 ppm (NaCl).
800 µS = 8.0 cf = 0.8 mS = 400 ppm (NaCl).
1000 µS = 10.0 cf = 1 mS = 500 ppm (NaCl).
1400 µS = 14.0 cf = 1.4 mS = 700 ppm (NaCl).

Hydroponic Nutrient Strength

Here are various ranges of nutrient strength that have worked best for the author of this guide. The amounts are low compared with some other recommendations. You can vary the amount but here are some possibilities to consider.

Starting seed/clones: 000-200 µS or 000-100 ppm (NaCl)
Rooted seed/clones: 200-600 µS or 100-300 ppm (NaCl)
Early veg: 400-800 µS or 200-400 ppm (NaCl)
Late veg: 600-1000 µS or 300-500 ppm (NaCl)
Early flowering: 800-1200 µS or 400-600 ppm (NaCl)
Late flowering: 1000-1400 µS or 500-700 ppm (NaCl)
Last 4-7 days: 000-700 µS or 000-350 ppm (NaCl)

The optimal nutrient strength gradually increases as a plant matures. There are also other factors to consider when adjusting the nutrient strength.

Aim for lower EC or TDS readings if;
the temperature is over 76°F/24°C.
the relative humidity is below 60%.
the light is under 600 watts.

Aim for higher EC or TDS readings if;
the temperature is between 70-76°F/21-24°C.
the relative humidity is at or over 60%.
the light is 600 watts or more.

Higher temperatures and lower humidity levels cause a plant to transpire and evaporate more water. If a plant processes more water, the concentration of nutrient increases. With lesser amounts of light the plant requires less nutrient.

During first 1-2 weeks, before a seed or clone has rooted, use a very mild (10% or less of the amount when flowering) nutrient solution. Some hydroponic growers don't add any nutrients until the root and first leaves start growing.

During the last 4-7 days prior to harvest most growers won't add nutrients, or will add nutrients at half strength or less. This is to flush nutrients from the plants, it is optional but recommended.

An EC or TDS meter is essential when growing hydroponic marijuana for giving you the ability to measure the amount of dissolved solids in nutrient solution.

This will let you know if the nutrient level has to be adjusted to keep it within the proper range, and will allow you to maintain an optimal level for the plants.

You can increase the EC or TDS meter reading by adding more nutrients to the nutrient reservoir. You can decrease the EC or TDS meter reading by diluting the nutrients in the reservoir by adding more water.

Always take an EC or TDS reading after the nutrients have been added to water, or just after hydroponic nutrient solution has been added to the reservoir. Check the nutrient strength in the reservoir at regular intervals.

If the tips of the leaves turn yellow or brown and dry out during early stages of life, it could be an indication that the nutrient level is too high and/or the relative humidity level is below 40%.

During flowering it is more common for the tips of leaves to dry out. Leaves tend to look more ragged as the plant gets deeper into flowering, because plant energy is focused on flowering, rather than growth.

It is normal for leaves at the bottom of the plant to totally turn yellow and die if they don't get enough light. When this happens cut off the yellow leaves at the stem with a pair of sharp scissors.

Hydroponic Nutrient Solution Temperature

If you were going to maintain a hydroponic nutrient solution at a steady temperature for the entire life cycle of the plant, from germination to harvest, 70-72°F/21-22°C is a good choice.

But depending on conditions, altering the temperature might be more beneficial. For germinating, as well as seedlings and clones that haven't rooted, warmer temperatures are preferred.

Aim for hydroponic nutrient solution maintained at temperatures between 70-75°F/21-24°C for faster growth while germinating and with seedlings or clones, until you can see new root growth.

Some growers say they obtain better results at temperatures as high as 78°F/25°C for water or nutrient solution temperatures during these, the earliest stages of the life cycle.

As you raise the temperature of the hydroponic nutrient solution, you provide an environment more favorable to bacteria, germs, mold, other things that can have a negative impact. It also reduces the amount of oxygen the nutrient solution can absorb.

Warmer nutrient temperatures are generally better for germinating, seedlings, clones. But these early stages of growth are when the plants are most vulnerable to organisms that will attack them.

If you are having any kind of infectious problems related to the water or if you want to prevent them, sterilize the water with small amounts of hydrogen peroxide. Instructions can be found on the germinating seeds page.

As the plant matures it will prefer cooler nutrient solution temperatures. Besides being less hospitable to things that can have a negative impact, cooler temperatures allow the solution to absorb more oxygen, which is beneficial to the plants.

For vegetative and flowering stages, aim for lower nutrient temperatures around 65-70°F/18-21°C. If the air temperature is high, lower nutrient temps help plants cool off from the heat being produced by lighting or other factors, .

Depending on the strain and growing conditions, nutrient temperatures between 60-65°F/15-18°C during vegetative and flowering stages can help the plant grow faster and keep the roots healthy white.

When the hydroponic nutrient temperature starts to get too low (or when it becomes too high) for the good of the plant, it reaches a point where it will begin to slow the development rate.

In a nutshell, initiate growth with warmer nutrient temperatures when starting hydroponic plants, until the point where you see new root and leaf growth. As the plant matures from there, you can decrease the temperature for more optimal results.

Flushing Or Leeching

A reason why it is important to know when the plants will be ready to harvest is because prior to harvest, you will have the opportunity to minimize the amount of nutrient remaining in the plant.

Not everyone flushes (also called leeching) plants prior to harvest, but you may want to. The plants themselves and the hydroponic media or soil the plants were grown in will store some of the nutrients that the grower has supplied them with.

In order to flush nutrient from plants, you feed them water only (pH adjusted) for one or more feedings just before they are harvested.

When timed correctly, you are able to wait until just before you are going to harvest, and give them water with no nutrients. In this way they are allowed to grow for the maximum amount of time (larger harvest) before being flushed.

The plants will use up the nutrients they have stored in them and growth won't slow very much. If nutrients are not flushed from marijuana plants, you will be ingesting some.

This might not be healthy especially if smoked. In addition the resulting marijuana might taste bad, and may also be hard to ignite. Flushing will also reduce the harshness of the smoke, making go down easier and reducing coughing.

If you are growing hydroponic marijuana, start flushing about 4-7 days before harvest. This can be done by changing the nutrient solution and using only distilled water or water filtered via reverse osmosis. Just adjust the pH and don't add nutrients.

Some hydroponic growers will change the water two or more times before harvest because the plant and media may still hold nutrients after the first flush. There are products available to help flush hydroponic and soil plants quicker.

With soil you need to change to distilled or reverse osmosis water about 7-14 days before harvest. With coco coir start flushing about 7 days before harvest. With amended soil where you don't add nutrients, there is no need to flush.

Amount Of Water For Hydroponic Marijuana Plants

For germination and unrooted clones the amount of nutrient solution water a hydroponic plant needs each day is about 1/5 of a gallon or a bit less.

For seedlings and rooted clones the amount of nutrient solution water a hydroponic plant should get each day is about 1/4 to 1/2 of a gallon.

For early vegetative growth the amount of nutrient solution water a hydroponic plant should get each day is about 1/2 to 1 gallon.

For later vegetative growth and pre-flowering the amount of nutrient solution water a hydroponic plant should get each day is about 1 to 2 gallons for a plant up to 4 feet/1.2 meters in diameter. A larger plant needs more water.

For flowering the amount of nutrient solution water a hydroponic plant should get each day is about 1 to 3 gallons for plants with a canopy of up to 4 feet/1.2 meters in diameter. A larger plant needs more water.

Something else to take into consideration is the further the temperature rises over about 76°F/24.4°C, or the humidity falls below 60%, the more the plants water needs increase.

The amounts stated above have worked for the author, and will give you a rough idea of how often to discard and put new nutrient solution in a recirculating system or adjust the flow rate in a drain to waste system.

If you are currently growing a good way to tell if you are providing enough water is, to increase how often you change the nutrient solution with a recirculating system, or increase the flow rate with a drain to waste system.

Try it for a week or two, and if the plants do better with more frequent nutrient solution changes or an increased flow rate, you might want to maintain the increase in the amount of water the plants get.

With a recirculating hydroponic garden the nutrient solution will be supplied to plant roots, usually via pump, then the pump will turn off and the nutrient solution will flow back into the reservoir.

As water is absorbed by the plants or evaporates, your water reservoir level will drop. When it does, it is a good idea to replace it on a regular basis.

It is usually better to add water with no nutrients when you top up the reservoir tank for a recirculating, or deep water culture, hydroponic system. This is something you can experiment with.

With a drain to waste hydroponic system, nutrient solution is supplied to the plant roots then rather than flowing back into the reservoir, it is discarded.

As water evaporates and is delivered to the plants, your water reservoir level will drop. When it does, you will have to replace it. With a drain to waste system, add nutrient solution at full strength when you top up the reservoir tank.

Always measure, and if necessary adjust, the pH and strength of the nutrient solution after topping up the reservoir in either a recirculating or drain to waste hydroponic system.

If you have a recirculating or dwc hydroponic system, you may notice that after you change the nutrients, the pH rises. Then a few days after the nutrients were changed, you see the pH will start to fall.

When you observe this kind of pH rising after changing nutrients, then the pH lowering a few days later, it is a good indication that you are not changing the nutrient solution often enough.

Start changing the nutrient solution more often, so the nutrient solution is discarded and replaced before the pH starts to decline, or just when it starts to decline. Your plants will grow faster and be healthier.

List Of Materials
ec or tds meter
meter calibration solution
optional plant flush
optional water chiller
optional aquarium heater
optional reverse osmosis filter

*** nutrients: A good choice for a 1 part hydroponic marijuana nutrient is maxigro and maxibloom. They are in powder form, you add water, so that you are not paying for shipping a large container that is mostly water.

Maxigro can be used by itself as a 1 part nutrient for germinating, clones, seedlings, vegetative growth. Maxibloom can be used by itself as a 1 part nutrient for flowering.

Maxigro and maxibloom are employed by myself, and more experienced gardeners, but they will be especially appreciated by novices who want a nutrient that is easy as possible to work with.

FloraGro, FloraMicro, FloraBloom Hydroponic Nutrients

3 part nutrient systems are used in all stages of life, but the amount of each particular part is varied depending on the stage.

For people who want more control over the relative amounts of the various nutrients being supplied to their plants, multiple-part nutrients are the way to go.

The flora series (floragro, florabloom, and floramicro) are a good example of a 3 part nutrient system for hydroponic marijuana growers.

There are other brands of hydroponic nutrients that will also provide good results like those stated above. You may want to try various brands to see what works best for you setup.

If you have a multi-part nutrient, you can vary the ratio of each part, but keep the total strength of the nutrient solution within the levels stated, in the nutrient strength section on this page.

For a hydroponic system, only get nutrients specifically intended for hydroponic applications. They have a balanced primary, secondary, trace element formula that even most soil growers will like.

*** ec or tds meter: An inexpensive meter like this functions very well and makes measuring nutrients solution strength easy. It can display both EC and TDS levels.

The EC levels on this meter are displayed in µS/cm, and TDS is calibrated to NaCl standards. It also measures the temperature of the nutrient solution, or other liquids, in degrees F or C.

Calibrating this particular meter is a bit difficult without instructions because of the location of the calibration set screw. A step by step guide can be found here.

*** meter calibration solution: EC and TDS meters are calibrated prior to leaving the factory, but will drift with use and need to be calibrated regularly, every 6-12 months or so.

Calibrating EC and TDS meters doesn't have to be performed as often as with pH meters, which should be calibrated every week or two.

For EC and TDS meters that will be measuring hydroponic nutrient solution, calibration solution like this is recommended. It can be used to calibrate either EC or TDS meters.

*** optional plant flush: There are products to help flush nutrients from hydroponic, soil, soilless marijuana plants at a quicker rate than they would naturally.

Clearex has been used for flushing hydroponic plants, starting 3 days prior to harvest rather than 7 days prior, with good results. This gives the plants a few more days to grow.

In addition to flushing just before harvesting, most plant flushing products can be employed earlier in the life of the plant if you think too much nutrient has built up.

*** optional water chiller: A water chiller will lower the temperature of water or nutrients solution, if it becomes necessary to do so.

A 1/10 hp water chiller is good for chilling a reservoir that has a capacity of up to about 25-50 gallons of water or nutrient solution.

For larger reservoirs or to cool the water or nutrients solution more quickly, a water chiller model with a larger hp rating is required.

*** optional aquarium heater: A submersible aquarium heater will help raise the temperature of water or nutrient solution for a hydroponic system when it gets too cool.

A rough idea of the wattage that the heater should be is 5-10 watts per gallon of water or nutrient solution the reservoir holds. The higher the wattage, the more quickly it will raise the temperature.

*** optional reverse osmosis filter: A reverse osmosis system to filter water is a good idea for providing clean water, that is ideal for hydroponic applications.

There are fairly inexpensive models, considering how important water is to hydroponics, that do a very good job and do not cost much to operate and maintain.

If you have a basic knowledge of plumbing they are easy to install. If not a plumber should be able to hook one up for you, in an hour or so.


1 --- Watering house or garden plants with discarded hydroponic nutrient solution will at least double the growth rate, if you usually water your plants with regular tap water with no nutrients.

2 --- Nutrient can build up on the inside of a reservoir and other things it comes into contact with. Before draining a reservoir, wipe the inside and any easy to access items with a clean cloth, scotch-brite, or something similar.

After cleaning whatever is easily accessible, drain the reservoir. After being drained you can put hydrogen peroxide in a spray bottle and spray a coat over the inside of the reservoir, for sterilization purposes.

3 --- It can not be stressed as to how important nutrients are to the success of your crop. Nutrients, pH, and temperature are the 3 top problem areas when growing hydroponic marijuana.

If you experience a crop failure it will probably be due to one of these factors. New growers tend to make the nutrient solution too strong thinking plants will mature quicker.

Too strong of a nutrient solution will kill your plants. If you under fertilize, plant growth will be slowed but they will stay alive. If you aren't sure, use less nutrient rather than more.

Related Books

Grow Great Marijuana
Very good choice for simple and accurate instructions about growing hydroponic marijuana. Does not cover advanced techniques, but if you have no experience, this is the first book to look at.
Grow Great Marijuana

The Cannabis Encyclopedia
Easy to read with comprehensive focus on growing and consuming for medical and recreational purposes. This will be of interest to growers, patients, caregivers, consumers, or anyone interested in consuming, growing, or producing cannabis products.

Over 2,000 color images on 596 pages. Loaded with recent information covering all aspects of marijuana. The grow section explains hydroponics and soil growing, growing indoors, outdoors, and in greenhouses.
The Cannabis Encyclopedia

Part 01) Full nutrient article is this page.
Part 02) Nutrient introduction is here.
Part 03) Water is here.
Part 04) Preparing nutrients is here.
Part 05) Measuring nutrients (EC, TDS, PPM) is here.
Part 06) Nutrient strength is here.
Part 07) Nutrient temperature is here.
Part 08) Flushing or leeching nutrient is here.
Part 09) Amount of water for plants is here.
Part 10) Nutrient list of materials here.

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