Marijuana (Cannabis)

Intermediate Marijuana Hydroponics

Carbon Dioxide
Number Of Plants
Two Growing Areas
Water Supply
Various Extras
Grow Hydro Index

Carbon Dioxide (CO2): This section became so large it was moved to a page of its own. It can be found here.

Cloning: This section became so large it was moved to a page of its own. It can be found here.

EC, TDS, PPM: EC stands for electrical conductivity, TDS stands for total dissolved solids, it is measured in ppm, parts per million.

EC and TDS meters are a method of measuring the amount of dissolved solids in nutrient solution. For hydroponic growers this translates to how strong a nutrient solution is.

If a hydroponic nutrient solution is too strong, it will slow the growth rate and might eventually kill a plant.

If a hydroponic nutrient solution is too mild, it will limit the amount of nutrients available to the plant. Low levels will not kill a plant but can slow the growth rate down.

An EC or TDS meter is essential when growing hydroponic marijuana. Being able to measure the amount of dissolved solids in nutrient solution, and keeping them within the proper range, will allow you to maintain an optimal level for the plants.

Always take an EC or TDS reading after nutrients have been added to the reservoir, then check as necessary. See this for more about nutrients, ec, tds, ppm.

Germinating: This section became so large it was moved to a page of its own. It can be found here.

Heat: Grow lights get hot and heat can be a problem. The more watts of light you have, the more heat those lights generate. Even 250 watt mh or hps lights can heat a small area beyond acceptable limits.

When marijuana is grown indoors under grow lights, most strains will grow best somewhere in between temperatures of about 70-80°F or about 21-26°C, during the day period when the light is on.

If the temperature gets too hot, above about 85°F or 29.4°C, it could have a negative effect on the plants by stopping growth or killing them.

Daytime temperature below about 66°F or 19°C, can slow growth, with the growth rate slowing more as the temperature decreases. Most indoor marijuana plants will die if the temperature drops to about 40°F/4.4°C or less.

One way to cool the air is an exhaust system that draws hot air out of the grow room. Another way is by using air conditioning.

There are also air cooled lighting systems to remove some of the heat produced by lights, before that heat can affect the grow area.

During the dark period when the light is off, marijuana plants will do best if the temperature drops several degrees, but less than by about 10°F, rather than staying the same or increasing.

Humidity: In general, relative humidity readings between 40-60 percent are best. At low humidity levels plants can wilt and the tips of the leaves can dry out and die.

High levels of humidity over 60% are actually very good for marijuana plants, especially young plants and after transplanting. But high humidity levels can promote problems like mold.

In order to not to encourage growing conditions for mold, the humidity level should be kept below 60%. If mold is a problem in your grow room, humidity should always be kept below 50%.

An inexpensive hygrometer can be employed to measure humidity. A humidifier can increase humidity and a dehumidifier can be used to lower humidity.

Lighting: This section became so large it was moved to a page of its own. It can be found here.

Media: Since you aren't using soil in a hydroponic garden, most types of hydroponic systems used to grow marijuana like deep water culture, drip systems, ebb & flow systems, etcetera need a substitute so the roots have somewhere to anchor the plant.

This substitute for soil is referred to as growing medium or media. The media will provide no nutrition, it is just a support for the roots. All nutrients come from the nutrient solution.

There are various types of media available to grow hydroponic marijuana in. Rockwool is one common type of media, but there are others.

In most cases, the media you choose is up to you, unless your hydroponic system requires a specific type. Follow what the manufacturer of your hydroponic garden recommends.

There are small rockwool, oasis, sure to grow cubes designed for starting clones or seeds on. You can germinate seeds right on these. Once you've grown a crop or two you can experiment and see if changing media has any effect.

Rockwool has to be prepped prior to being put in a hydroponic system, check out the grodan website for instructions.

Number Of Plants: The harvest size of an indoor crop is determined by the amount of light and the area the garden covers.

2 plants of a particular strain grown in a 3 x 6 foot (or 0.9 x 1.8 meter) grow area under a 600 watt grow light will produce as much marijuana as a larger number of plants grown in the same conditions.

Unless you have a specific reason to do otherwise, for most people, growing the minimum number of plants possible will be the best way to proceed. Less plants will almost always mean less work and less cost.

The author of this guide flowers 2 plants at a time in a 3 x 6 foot (or 0.9 x 1.8 meter) grow area. Sometimes with a 250 watt, but usually with a 400 or 600 watt mh or hps bulb, and a small amount of supplemental led lighting around the dark edges.

If you are growing with a 1000 watt bulb, consider flowering with 1000 watts of mh or hps, and perhaps a lesser amount of supplemental led or fluorescent around the dark edges, in a 4 x 8 foot (or 1.2 x 2.4 meter) grow area with 2 plants.

In many areas, drug trafficking charges are determined by the number of plants being grown, regardless of the amount of marijuana that each plant will produce.

In these areas, a plant that produces eight ounces at harvest time is considered the same as a plant that produces one-eighth of an ounce at harvest time.

Even if you had a permit to produce medical marijuana for yourself, once you grow more than a set number of plants, in certain jurisdictions, you are considered to be cultivating with intent to traffic.

So growing 2 fairly large plants, that will produce several ounces of marijuana per plant, might be a better idea than growing a larger number of smaller plants, that will produce lesser amounts per plant.

Nutrients: This section became so large it was moved to a page of its own. It can be found here.

Odors: Growing and smoking marijuana will produce odors. Sometimes they can be strong enough to attract attention of people who don't need to know what you are doing.

If you would like to eliminate the smell at its source when growing and/or smoking marijuana, a variable output ozone generator is a very good method.

A variable output ozone generator will allow you to adjust the amount of ozone that is produced. When put on a timer you can eliminate the smell of marijuana and other odors.

Ozone is comprised of three oxygen atoms (O3), oxygen in the air we breathe is comprised of two oxygen atoms (O2). After about 90 minutes any ozone not used to eliminate smell will break down into regular oxygen (O2).

Ozone can be dangerous to humans and animals, especially those with any kind of breathing disorder. Therefore it is best to keep ozone away from areas where people and pets spend a lot of time.

An alternative method is to use exhaust fans, these have the advantage of also being used to remove heat from the grow room. If you plan on using an exhaust system, make sure it is vented to an area where the smell won't attract attention.

Placing the end of an exhaust duct on a roof or other space that is seldom used by other people is a good idea. You can put carbon filters on exhaust fan ducts to remove odors before the air is exhausted.

pH: The pH of the nutrient solution should be somewhere in between 5.8 and 6.2 on the pH scale, for best results.

You will need a pH meter or pH test kit to check the pH and some pH-up or pH-down solution to adjust the pH when it gets out of range.

See the page about pH and hydroponic marijuana if you would like to learn more.

Seeds: Info about germinating marijuana seeds is here. Info about how to produce marijuana seeds is here. Info about seed strains is here.

Temperature: Strains that originated in cool areas prefer a lower temperature than strains that originated in warm areas. Most indica strains prefer slightly cooler temperatures that sativa strains.

Depending on the stage of life the plant is in, an indoor marijuana plant grown with grow lights will have a preference for different air temperature ranges when the light is on.

Germination: 70-80°F or 21-26.5°C.
Unrooted Clones: 75-85°F or 23-29.5°C.
Seedlings: 70-78°F or 21-25.5°C.
Rooted Clones: 70-80°F or 21-26.5°C.
Vegetative: mainly indica 70-76°F or 21-24.5°C.
Vegetative: mainly sativa 72-80°F or 22-26.5°C.
Flowering: mainly indica 72-76°F or 22-24.5°C.
Flowering: mainly sativa 74-78°F or 23-25.5°C.

Measure the temperature at the top of the plants, where they are closest to the light and the temperature is the highest.

For germination and new seedlings or new clones, try to keep the night time temperature fairly close to daytime temperatures.

During vegetation and flowering, when the light is off, the temperature should drop at least a few degrees for the benefit of the plant. The temp can drop as much as 10°F at night, without harming the plants.

If the temperature drops more than 10°F at night, it can slow the growth rate of plants during veg and extend the required flowering period, resulting in a late harvest.

The temperature should not go below 60°F/15.5°C or above 85°F/29.5°C when the light is on, or growth will slow down drastically or stop.

If these extremes are exceeded for an extended amount of time, the plant may be permanently damaged or killed.

Plants grown under strong light, like sunlight, with supplemental carbon dioxide, prefer slightly warmer temperatures between about 80-85°F or about 26-29°C, during the hours the light is on.

Transplanting: This section became so large it was moved to a page of its own. It can be found here.

Two Growing Areas: An alternative to growing in one area is to set up two or three separate growing areas. The hydroponic setup the images in this grow guide were taken from has three growing areas.

Grow area 1 is for germinating, cloning, seedling stages.
Grow area 2 is for vegetative and 12/12 light stages.
Grow area 3 is strictly for flowering plants.

The life cycle of the plants is timed so as soon as those that are in the flowering area are harvested, plants that have just started flowering (in grow area 2) are moved into the flowering section.

With one grow area dedicated to flowering, the length of the flowering period (from the time the plant starts to flower until it is harvested) of that strain determines how often a crop is harvested.

A strain that has a flowering period of 8 weeks, will produce a crop that can be harvested every 8 weeks. With a strain that has a flowering period of 10 weeks, a crop can be harvested every 10 weeks.

The main drawback is the extra room needed for the different grow areas. Some growers might be limited to a single grow area because that is the only space available.

Since the flowering plants need absolute darkness during the dark phase, the light from the other grow areas can't reach the flowering plants.

These areas will have need to be isolated from each other and other sources of light either by using curtains, or something similar, or by being located away from each other in different rooms.

Any available sunlight will help in the growing process. The vegetative area can be open to extra light at all times but there must be a way to block out all sources of light for twelve hours a day in the flowering area.

Water: In most cases, you can not run a hydroponic system on tap or well water. City 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 will also kill hydroponic marijuana plants.

Well water can contain concentrations of minerals that will harm or kill hydroponic marijuana plants. The two options available to most hydroponic growers are reverse osmosis or distilled water.

The two most common types of water for hydroponics are distilled and reverse osmosis. Distillation is a process of heating the water and catching the steam. Reverse osmosis is a filtration system.

Both types of water are very clean, when measured with an ec or tds meter, the readings should be under 100 µS with an EC meter or 50 ppm (NaCl) with a TDS meter.

You can buy a good reverse osmosis water system for under $200. They are not hard to install and maintain if you have a basic understanding of plumbing.

If you are not inclined to install a water filtration system yourself, you can hire a plumber. It should take an hour or so for a professional plumber to install.

Water treatment companies will install and maintain reverse osmosis filtration in your house for a fee. You can also purchase distilled or reverse osmosis water in most supermarkets.

----- Do not use chemicals to clean anything that the water and nutrients will come into contact with, like the inside of nutrient reservoir for a hydroponic garden. Use hot water to clean these.

----- You can use hydroponics to grow outdoors but temperatures must remain within the tolerance of the plant. That means in most parts of the world, you would only be able to grow for several months of the year. Evaporation of nutrient solution can be a problem.

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