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Active and Passive hydroponic systems


Passive and Active grow systems

Over the last several years, hydroponic systems have come a long way. It is not some big secret technique or lost mystery. Instead it is a reliable and relatively simple way to grow marijuana plants. It is far easier and a more consistent method than growing in soil. It only requires the mastering of a handful of basic principles employed through a step-by-step basis. The foundation of all hydroponics is the nutrient solution. It is the key to your growing success and it is the most important thing for any grower to grasp. To put it simply, the nutrient solution is what you water your marijuana plants with. Any marijuana nutrient solution must be created in the correct proportions as well as contain all of the essential mineral elements required for healthy marijuana plant growth. There is not a single thing that can be left out-even something as simple as micro-nutrients such as molybdenum {Mb}, which is required in your solution in a ratio of less than one part per million {ppm}. Fortunately for you, now-a-days, there are a large number of nutrient solutions available and all you have to do is choose the product that suits your required needs the best. We highly recommend Formula Flora as a marijuana fertilizer.

Hydroponic nutrient solutions

The mineral salts used in a nutrient formulation react with one another in concentration, which is why most nutrient solutions are commonly formulated in an A, B & C pack. These packs are only mixed together in a working solution. By keeping specific salts separated from one another, it allows the chemist to have limited or no restrictions and supplies his plants with exactly what they need. Most professional cannabis growers will use separate A, B & C tanks, which has allowed home growers to maintain their own version of professional standards.

Hydroponic systems

Hydroponic systems are divided into two very distinct types: active and passive systems.

Active systems

Active hydroponic systems use a pump to supply the solution to the various marijuana plants on timed intervals. The solution is typically recirculated throughout the system and the plants, which is the biggest difference between the management of systems. Active hydroponic systems are divided into three different types: Rockwool, Flood and Drain and NFT. All three systems have been proven and each has their own unique advantages in certain situations. It is up to each individual cannabis grower to determine which system best meets his or her purposes. All of the major techniques are going to be examined within this guide with the sole intention of assisting growers in determining which will suit them best.

The three main types of hydroponic growth systems are adaptable for a hobby grower. Each has advantages and disadvantages, and can only be decided upon by each individual grower. This is simply an overview of what these systems consist of to allow the grower to decide which system to use. You can recirculate nutrient solutions or use it once, throwing out what is left. It is totally up to you. You must decide which you plan to use before beginning to create your system. If you are choosing to recirculate your nutrient solution, your solution will collect in a tank for reuse later. On the other hand, total loss systems allow the excess to simply turn into waste. Smaller marijuana growers often choose a recirculating system because a total loss system is much harder to scale down to size. Total loss systems are recommended for greenhouses and outdoor operations. We will evaluate recirculating systems because that is what most small marijuana growers will choose.

Flood and Drain [Ebb and Flow]

Flood and drain systems are designed to handle marijuana plants set up in individual units. Management is efficient and easy, but requires work when initially setting this system up. Flood and drain systems are based off of a table with relatively short sides that only hold a limited amount of nutrient solution. Your nutrient solution should get pumped to this table regularly, allowing it to drain as fast as it can. Your marijuana plants will stand on this table allowing the growth medium to soak up this nutrient solution, similarly to pot culture. Your nutrient solution will be soaked up from the bottom pushing the roots to grow down, stabilizing the plant and removing stale air from around the roots. As the plant releases the excess nutrient solution it will pull oxygen-rich air down towards the roots from the top of the plant from a form of suction that this process creates. The interaction of air and moisture around the roots makes this system very effective. The only difficult part to this setup is getting the plumbing right, to where your nutrient solution can once again be pumped in at a later time. Not all pumps allow this to happen, which can make setup more difficult.

One thing to keep in mind is the table needs to be totally level, allowing each pot to absorb equal amounts of the nutrient rich solution. There are tables designed for this purpose on the market, such as the Future Garden and Nutriculture Flood and Drain Tables. Clay pebbles are undoubtedly the best sort of medium for this type of system. The overflow pipe must be set to a level that is half the depth of the pots, allowing each pot to be flooded to that depth with each feeding. You should be sure to control your floods with a timer or automated release valve. In order to set your timer you will have to water your pots to know when the nutrient solution is flowing back out of the pots. It may take several feedings in order to properly time this process and may require future adjustments as your plants continue to thrive and grow. The timer should activate the pump for the appropriate allotted interval at a minimum of four times a day, and potentially twice during each hour during the hottest months of the year.

Important points to remember with Flood and Drain

The table you buy or create must be incredibly strong. You must calculate the weight of your pots, your marijuana plants and the volume of water to ensure your table is strong enough to support all of the weight. Here is a simple equation to help:

Length x Weight x Max Depth {inches} = volume in gallons = weight in pounds {0.25 gallons of water = 2 pounds

The difficult part about this system is covering the table before the pots go onto it to prevent algae growth. Ideally, simple white or black plastic can be pulled across the table top before the pots go on. Then all you have to do is cut a small hole for each pot. The effects of this system can improve if you take the time to aerate and warm your solution before you give it to your marijuana plants. An aquarium heater is typically enough to maintain the proper temperature for your medium solution, 65-72 °F (18-22 °C). If you use an aquarium air stone, you will also have the proper oxygen to improve your results. If you would like to improve your oxygen further, Oxy can also be added to your tank. The flood and drain system can also include rockwool cubes, and is also recommended when handling large quantities of marijuana plants. If you plan to use this, however, your guidelines will change because of the high fluid retention levels. First, you will only need to flood your pots to just touch the bottom of the cubes. This will change even the way a table is designed, placing an overflow pipe much lower than on standard tables. The timer will also need to be set for shorter periods of time. You will want your rockwool cubes placed on something to keep them up off of the table, allowing excess moisture to efficiently drain after each flooding. It is crucial when using rockwool cubes that plants receive the same exact amount of your nutrient solution.

Nutrient Film Technique [NFT]

This system is often called NFT and allows marijuana growers to grow their plants in shallow plastic gullies filled with streams of flowing nutrient solution. This system is amazing and is widely accepted when growing large plants such as marijuana plants. It can be adapted for smaller plants, but it is not recommended to downsize when growing larger plants such as marijuana. If you plan on using this system for commercial marijuana growth, we suggest you reference "The ABC's of NFT" by Alan Cooper. Initially NFT designers must decide what type of channeling to use. Any piping should be fine, so long as it is lined with or coated with plastic. Ideally, for larger plants such as marijuana plants, your gullies should be up to 8" (20 cm) in width. If you place a strip of plastic film within the gully and around the marijuana plants, it will act as not only a liner but also a cover to prevent light from reaching the growing channels. This basic setup for an NFT system shows how inexpensive and easy this system really can be.

Once each of your marijuana plants are in the channel, you should pour your nutrient solution into the top of the channel, allowing the solution to flow downstream where it can be collected in the tank. Even with the simplicity of this system certain things must be taken into account before you begin. First, you want your tank as large as you can possibly and practical get it. The reason for this is the pH and conductivity of your nutrient solution will constantly fluctuate, and the bigger the tank the less your plants will feel the negative effects. It also decreases how often you need to check your solution. For large, commercialized marijuana crops you should have at least one half gallon (2 L) of volume in your tank for each marijuana plant you have within your system. Smaller marijuana growers should increase their volume to 0.8 to 1.5 gallons (3-5 L) for each plant in their system. In other words, the bigger the tank you can get, the better. You will still need to make sure your nutrient solution is properly oxygenated, but this should be an easy goal to achieve. Normally the second valve is always open which allows the marijuana plants to come in contact with a constant supply of the nutrient and the first value is closed enough to control the flow of water. As the solution returns to the tank, that process should be enough to easily oxygenate it.

The plumbing for this system allows it to easily adjust for other systems like rockwool. If you need to make any adjustments to the nutrient solution, you can easily close the secondary valve, stopping the flow of water to the plants. During the adjustments open the first valve fully to increase agitation, allowing adjustments to almost instantly take place. Just make sure there is not more water in your system than what you tank is able to hold because if you somehow lose power, your entire system can flood. Your nutrient solution should flow down the gullies at a rate of one quarter to one half gallon (1-2 liters) each minute. You can use an empty plastic drink bottle to measure how long it takes to fill, in order to adjust your water flow. Remember this will need to be adjusted through your first valve while your second valve stays open. We recommend you run the NFT system for one to two days before adding plants in the gullies to make sure nothing leaks.

NFT system management

Very quickly after your system starts functioning you will notice root mats within the nutrient channel. This allows bare roots to come in contact with the nutrient solution directly, making this the biggest asset and biggest downfall of the NFT system. You will find incredible growth and unparalleled marijuana plant performance, assuming your nutrient solution can meet these requirements:

Correctly formulated for NFT

In regards to nutrient solution, NFT is considered the most demanding form of hydroponics. With no medium in place to work as a buffer, the solution demands a near-perfect balance with all elements required for good plant growth. It is recommended that growers insist on a dual-pack, liquid formulation like Optimum or Power Grow, which is specifically formulated for NFT systems. Making sure that you select a solution that is fully chelated of trace elements, is one of the most important things for an NFT system.

Correct pH and Conductivity

Once more, pH and conductivity are far more important to an NFT system over a passive system. Your pH level should be maintained at 6 and requires checking and adjustments on a daily basis. Your conductivity needs may vary during various stages of the crop. If you are looking for a solid starting point, you want to be around 2 milliSiemens, which is typically full strength for various products, such as Formula Flora and Power Grow. Be advised that you may need to increase this with your crop when the plants are producing buds. Your nutrient solution needs to be constantly agitated. This will ensure maximum aeration as well as temperature when heated with an aquarium heater to 65-72 °F (18-22 °C)

Rockwool systems

Once your marijuana plants are in the SBS cubes, you need to treat them in several different ways. If you wish to continue growing in rockwool, the next step would be to transplant your marijuana plants into larger 3" (7.5 cm) cubes. You will want to soak the wrapped cubes in a fairly weak, slightly acidic solution such as Formulex. This will ensure that cubes are properly wetted. Carefully remove smaller cubes from your SBS trays and place them in holes at the top of the wrapped cubes. Keep in mind that it is important to label your plants clearly. You will want to place the plants in a warm, sunny place to grow. Be sure to check the moisture daily, and provide your plants with a sprinkle of your nutrient solution as needed. Check the bottom of the larger cubes regularly and once you notice new roots, it is time to consider planting them once more. Now that your marijuana plants are further along and a good bit bigger, you may want to consider selling or discarding your smaller, less desirable specimens before continuing the process. Same as before, you have the option on how to plant your marijuana plants. You can use a garden or pots of soil, but the best way to grow them is with rockwool.

Culture Slabs

Rockwool culture slabs are available in a great variety of shapes and are well suited for commercial growers. Ideally a home grower will use a 3" (90 cm) or 4' (120 cm) slab. These culture slabs will be wrapped in plastic, which will provide superior performance. By no means should this plastic ever be removed. Make sure to place your culture slab on a thoroughly cleaned surface. Ideally, this would be its final location as well, because once everything is planted, it will become impossible for it to be moved. Special attention should be paid to your drainage. You can easily achieve this by placing a small board under the rockwool culture, forming a slope from end to end. The easiest way to handle slabs is to use the Aqua tray, which will hold the slab firmly and also has drainage holes built in. Carefully place your culture slab into an Aqua tray. At this point you want to mark out the locations of your marijuana plants. Once you have traced an outline of the cubes on the desired locations, take a sharp knife and gently cut an X within the square. Do this to all of your marijuana locations drawn on the slab. Mix up a minimum of 2.5 gallons (10 L) of your nutrient solution and pour this slowly into one of the openings on the top of the slab.

Continue this process until the slab is full. Note that the side will bulge out, making it abundantly obvious that the slab is full. It is recommended that you let the slab sit overnight, but you can plant in as little as one hour. Before you plant, lift the lower end of the slab from the tray and use a sharp knife to make several small puncture holes within the plastic, to allow excess solution to drain. The best way to supply nutrients to your slab is through a dripper system, which growers should activate at least twice a day and should be left to run until excess solution is flowing out of the slab. You can also use a watering can to water your slab on a regular basis if you so choose. If you decide to use a watering can, the same rule of thumb applies: watering it until excess water begins to flow from the slab.

Passive systems

A passive hydroponic system will supply the nutrient solution to the marijuana plant periodically and gets distributed by hand. It is also allowed to sit in some sort of reservoir and can be used by the marijuana plants as they need it. Pot culture, which will be fully explained below, is the simplest of all passive systems. These systems are not favored by commercial-grade marijuana growers due to the increased difficulty of properly watering a large number of marijuana plants. However, these systems have much to offer smaller marijuana growers in regards to greater results through simple pot culture. There are fewer things that could potentially go wrong with a passive system, and it also requires a lower financial cost than active systems.

Pot Culture

Pot Culture is referred to as the safest and easiest way to grow using hydroponics. It is a true passive system. This means it is ideal for beginners yet still favored by seasoned marijuana growers due to the remarkable results that can be obtained if the system is set up and used properly. It is very favorable for all species of marijuana plants and virtually all growing situations. It is fairly cheap to set up and extremely difficult to fault as an effective, well-versed growing system.

Theory of Pot culture

Due to the basic principle of capillarity, pot culture is remarkably simple. In essence, it is just filling a pot with a proven medium and using a reservoir to supply the nutrient solution to the marijuana plant. The medium will bring your nutrient solution up into the plant by capillary action, and will maintain a favorably moist environment around the roots of the marijuana plant at all times. While the plant's medium will always be damp, it is going to retain a lot of air spaces near the roots. These high levels of air in combination with constant moisture and free flowing nutrients create the perfect zone for self-optimized marijuana plant growth. This and this alone is what makes pot culture work as well as it does.

The Pot or Container

The first choice a grower must make is which pot and saucer to use. Growers should always use plastic pots. If you choose to use artificial light, white pots are preferable due to how well they can reflect the light back to the marijuana plants. Large marijuana plants will grow best in a pot around 4 gallons (15 liters), but smaller plants will only require a pot about half that size. The reservoir under the pot should be deep enough to hold the necessary water for the marijuana plant. The Hydro pot is great for large marijuana plants, and is found at most hydroponic suppliers. The pot has a 3.5 gallon (13 L) limit, plus comes in a bright reflective shade of white and comes with its own saucer. This Hydro pot is ideal for large marijuana plants. If you would like more information regarding how pot culture works check out the Simple Steps to Successful Pot Culture that is a bit further along in this guide. Most garden centers have multiple choices available for medium sized plants; just do not forget the saucer, as it is a key component to this particular method of growth.

Growing medium

Once you have chosen your pot the next choice is growing medium. The purpose of the growing medium is to hold air around the roots, keep the medium moist and hold the plants root system in place. If your medium performs all of these tasks effectively, your hydroponic growth system will produce successful results. This shows why the right growing medium is so incredibly important. The three main options for pot culture as far as growing medium will be chosen by each individual grower by the variety of marijuana plant, the cost and local availability of each of the supplies.

Perlite [Pearlite]

This medium is, simply put, just awesome! It is incredibility effective, extremely light weight and cheap. Through the process of exfoliation, volcanic rock is processed through a furnace and becomes Perlite. The capillarity of Perlite is exceptional, thus making it highly recommended for use as a marijuana plant growing medium. The process of lifting moisture from your water reserves to keep your growing medium moist is capillarity. Occasionally Perlite will attract algae, which will make the Perlite look green, but it is no cause for concern. If it starts to look unsightly you can sprinkle dry Perlite on top to cover it. Perlite is available in quantities up to 25 gallons (100 L).

Green Mix

This medium, developed in Denmark, is specially blended from various types of rockwool to give growers the best combination of air to moisture within their pots. That is what makes this growing medium stand apart from its competition today and will for years to come. It holds exponentially more water than its competition without losing its air to water ratio. This growth medium may not be as viable as its current competition when it is compare simply by cost. Check out your local nurseries to find out which ones carry Green Mix.

Expanded Clay [Clay Pebbles]

Clay pebbles are specifically made for planting. They are sterile, reusable indefinitely and light weight. Clay pebbles are perfect for nearly anything grown in small containers, especially marijuana plants.

Simple steps to successful Pot culture

Assuming you currently have marijuana to be transplanted, you can delve into pot culture with your seedlings or cuttings.

Pot culture [Perlite]

You must make sure the holes within the bottom of your pot are small enough to where Perlite will not wash out. If the holes are too large, something as simple as duct tape can be used to shrink the holes but not cover. You will still need small holes in the pot to get the nutrient solution to the roots. Once Perlite is in the pot, make sure it is thoroughly damp with water from a watering can or your personal hose. Once your Perlite is wet, you will no longer have to worry about Perlite's dust [warning below]. Use your hand to make a hole in the middle in the pot for your seedling or cutting. Add more Perlite if needed to firmly pat down your marijuana plant, similarly to how you would plant with soil. Make sure to water until the saucer below the pot is full, topping off as necessary. With young marijuana plants, they will typically only need water every three to four days, but as they grow the watering could become as often as daily. Between watering's, allow the saucer to become completely absorbed by the plant without allowing the saucer to become bone dry. We recommend you flush your marijuana pots with clear water until the water comes out of the bottom of your pot, about once a month, removing loose sediment and salt deposits.


Perlite contains a lot of dust and should only be handled outside. Take special care to ensure you to do not inhale any of the dust, as it is hazardous to your health. Green Mix is also a known skin irritant and should only be handled with gloves.

Maintenance of marijuana plants in Pot culture

Maintenance of marijuana plants when using pot culture is incredibly easy. The only tools you really need are a drum filled with nutrient solution and a large watering can; simple huh? Marijuana plants should be watered every two or three days. Your saucer should become dry but not completely dry out between waterings. Ideally, you will want to water just as the saucer becomes empty, allowing for maximum air around the roots. If you would like to automate your hydroponic system, you can formulate drippers which can lead to each pot that you have, and pump the nutrient solution in on a timer. We typically do not recommend this because each plant requires different nutrient amounts. Greenhouses can be the one exception to the rule, but regular home growers should think of pot culture as a hand watering system. Marijuana plants require nutrients to be fed to them containing a CF value of 2mS {20 CF} along with a pH level of 6. You will want to check your reservoir solution weekly, although the values should remain stable throughout your growing season. If you notice the conductivity increasing in your solution, use clear plain water for a few days until your saucers show a decrease in conductivity levels. The best way to check the conductivity levels in your saucers is by using the Conductivity Truncheon. If the levels get too high, you may have to flush your entire crop to lower the levels. Several gallons (liters) of water may be required to remove the excess salt buildup.

Pot Culture [Green Mix]

Green Mix blends multiple fibers within the medium to both repel and absorb water at the same time. This allows the soil to hold moisture incredibly well yet still remain aerated around the roots. Lignite and clay are also added to allow a neutral pH to be easily maintained. At that point, the grower simply needs to use a high quality nutrient solution when watering their marijuana plants. This is part of what makes Green Mix so nice to use. It is very similar to how you would grow marijuana plants in soil. If you would like to transplant new marijuana plants into Green Mix, here's how. Find a suitable pot and fill it half way with Green Mix. Use the same size and depth recommendations as previously mentioned. Use your nutrient solution to water the Green Mix until thoroughly wet. Gently place your marijuana seedling into the pot, adding additional Green Mix if necessary until your plant is fully supported. Water the plant again with the same nutrient solution until it runs through the pot and drains from the bottom. Now place your pot within the saucer, making sure that the saucer has nutrient solution. You will want to add more nutrient solution to the saucer instead of the pot when watering the Green Mix solution. This is because of its extraordinary capillarity. Green Mix fed marijuana plants will drink larger quantities of the nutrient solutions than marijuana plants using other growing mediums. The saucer should be near empty when you water it again.

Recycling the growing medium

Perlite should be flushed thoroughly between each set of crops, making sure to remove all old roots. Some growers may opt to use a simple diluted bleach solution to further assist in sterilizing the Perlite, although this will require an additional flushing to ensure the bleach does not taint the upcoming crop. If you chose to not reuse your Perlite, mix it into your personal garden. In order to use clay pebbles indefinitely you must gently bleach them in between crops, flushing them thoroughly to remove any and all traces of bleach. We do not recommend that you reuse Green Mix. Instead, add it to your potting soil or garden bed and enjoy the wonderful results that this additive will give you.

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