How to Grow Cannabis in Hydroponics

Growing cannabis has become so much more accessible across the world thanks to the invention of indoor growing and hydroponics. People can now grow easily in their homes without the mess and inconvenience of using soil.

Setting up a hydroponics system should be easy, which is why we have created this guide. Once you start learning how to use hydro you'll realise it is a very effective and productive method for growing cannabis.

What is Hydroponics?

Hydroponics is the process of cultivating in an inert, soil-less growing medium with a system that uses nutrient rich, oxygenated water to feed and keep a plant alive.

There are a number of hydroponics system designs available today on the market that all use a slightly different methods but the concept is more or less the same. The main difference between these systems is the way they deliver the nutrient solution to the roots. Most of these systems use a pump on a timer but there are also methods that use gravity and floats.

Some of the commonly known techniques used in hydroponics are deep water culture (DWC), nutrient film technique (NFT), drip system, ebb and flow, and aeroponics. For this article we will be taking a general look at how to grow using hydroponics so you know the basics before setting up. It is not as difficult as you might think.

Hydroponics VS Soil

Hydroponics is a great method for growing cannabis indoors. If you come from a soil growing background then it might be a bit hard to get your head around the idea of growing with hydroponics because 'it's easier to grow in soil, right?'. This is not necessarily true. Hydroponics has become easy to set up and requires just a few strict practices from you. 

With hydroponics, the grower is in charge of giving the plant everything it needs to survive. Soil is a little different because the growing medium already contains food for a seedling to grow in its early stages. Soil contains a number of essential macronutrients and micronutrients that are not available to plants in a hydroponics system. 

Store bought cannabis soil mixes hold normally have enough nutrients in them for the early stages of growth. Nutrients usually deplete once a cannabis plant is a few weeks into its vegetation cycle and need to be added. Plants growing in hydroponics need feeding much earlier on. 

Let's take a look at some of the pros and cons of using hydroponics over soil. Each has its own advantages however hydroponics has been proven to be extremely positive for cultivation, even though it can be a little more expensive.

Cannabis grows faster in hydroponic systems during its vegetation phase due to the easy uptake of readily available nutrients. In soil, roots have to spend energy to find nutrients when they could be using it for plant development.

Soil also means growers have less control over what is happening down in the root zone. The retention of water and nutrients in soil can mean it takes longer for plants to filter through problems if they do occur.

Roots are very delicate and should never be disturbed if possible. One of the drawbacks of using hydroponics is that roots do not have the same protective home as they do in soil, making them way more sensitive to sudden changes in the environment. It should not be a problem so long as you keep the proper conditions.

How to Grow with Hydroponics

In this section, let's run through the basic elements you should be focusing on if you are learning how to grow using hydroponics. Each system will have its differences, but this information can be applied to most hydroponic grows. Setting up your hydroponics system will usually take place indoors but can also be set up outdoors.

Light, oxygen, water, humidity and small amounts of nutrients are a cannabis plant's basic requirement. If the environmental conditions are adequate and well maintained, there is little else needed for it to grow a big, healthy cannabis plant.

Your Grow Space

The first thing to consider is where your hydroponics system will live. In most cases using a grow tent is the best option because a big part is already set up for you. Once you have your tent, place it somewhere that is clean and clear of hazards. An empty spare room is good if you have one.

One of the most common frustrations with hydroponics is water spillage so it is important to protect whatever flooring there is in the space. This can be achieved by covering the floor with plastic sheeting and using trays under the hydroponics system.

Raising your hydroponics system above the floor level can be beneficial for a number of reasons.

• Draining water is much easier.
• You can access the system for maintenance.
• It keeps the reservoir at a more stable temperature.

Choosing a System

Amongst all the hydroponics systems that exist today, you need to choose one that will suit your needs as well as the space you have available.

The main difference between the hydro systems used today is the way they circulate the oxygen and water/nutrients. The main things to consider before choosing a system are:

• Efficiency -  growing with hydroponics relies on electricity which is used by the lights, pumps, fans and timers. Choose low consumption equipment such as LEDs.
• Costs - hydroponics systems can be built at home or bought pre-made from a store. Constructing one yourself is usually cheaper but requires prior knowledge to make sure it is done correctly.
• Space - your setup should be big enough for the amount of plants you want to have. Make sure the area is used to its full potential so you don't waste energy or space. Extra space should be allocated for your reservoir, lights, ventilation, etc.
• Automation - nearly everything can be automated which minimizes manual labour. An automated system still needs to be checked daily.

There are hydroponics systems which host only one plant but most systems have a shared reservoir. Shared systems means roots can get tangled together, so if you have a problem with one plant is tricky to separate it from the rest without hurting another plant. However, shared systems make it much easier to control the feeding schedule and the overall well being of your garden.

Grow Medium

In hydroponics the growing medium is not as responsible for providing the nutrients to the plant, like it is with soil. The growing medium is there to give the plant support and to deliver nutrients to the root zone.

Starting seeds in jiffy pellets and keeping them in a propagator until the tap root shows is recommended before planting them into your grow medium.

Most hydroponics systems work well with a mix of clay pellets and perlite as the base medium but there are many others you can use too such as coconut fibres, rockwool, vermiculite, sand or gravel, to mention a few.  

Clay pebbles and perlite both have efficient water and air absorption. They also allow oxygen to pass around the root zone which helps to avoid problems such as root rot.

Tip: Even though it is a commonly suggested growing medium for hydro found online, we advise you to avoid using rockwool. It holds moisture for way too long and increases the risk of overwatering/drowning your plants.

Lighting

Growing indoors means you have to organise the lighting yourself. It's safe to say cannabis plants need light whether they are grown in soil or with hydroponics. Basically any kind of grow lighting can be used for hydroponics.

Much of it depends on the space and how it will affect your grow environment. Use lights that do not generate too much heat, such as LEDs. They will save you money in the long run and make temperatures much easier to manage. HID lamps produce a lot of heat which can create problems for your grow.

Blue spectrum light is mainly used for vegetation, whereas a red spectrum during is used the flowering phase. We recommend using a full spectrum light for the whole duration of your grow so you cover all spectrums. Most LEDs are full spectrum but double check it to make sure.

Getting the lighting set up correctly for your hydroponics system will also determine what yield you end up with. Choose a light that will give enough coverage for the size of hydro system you install. A hydroponic system will not be as beneficial if the amount of plants hosted in it do not have enough light.

The rule of thumb with LEDs is to use 30 standard watts per square foot of grow space. That means if you have a space that is 6 x 6 feet (36 square foot) you would need to multiply it by 30, which would give you 1080w. The equivalent HID wattage would be around 500-600w.

Glookies from Barney's Farm growing in hydroponics under LEDS, Coughy from GrowDiaries

Irrigation

It is a good idea to hand water gradually in the beginning until roots are well established within the system. Once rooted, plants can make use of the circulation.

Using a pump on a timer to push oxygenated water from the reservoir is how most hydroponics systems work. Usually water is pumped from a reservoir at intervals, which floods the root zone and then drains back into the reservoir.

Creme de la Chem! - DWC

Drip systems differ in that they transfer the nutrient solution to the top of the growing medium rather than the bottom directly to where the roots are.

Less water more frequently is the way to go. Roots can easily become drowned if they are submerged in water for too long, or can get seriously affected if they dry out too much. Problems like these will likely start to lock out nutrients, resulting in stunted plant growth and other deficiencies.

Set up your timer so that roots are watered every 15 - 20 minutes. The key is to prevent them from growing too much in search for water or nutrients as a way to conserve energy.

Roots will grow wherever they can to find water and may end up blocking the system.

Tip: If you are using tap water it can be left to sit for 24 - 48 hours before use so chlorine evaporates.

pH Levels

The pH levels are super important to determine the acidity or alkalinity of the nutrient solution in the system. Certain minerals are absorbed at different pH levels so carefully monitoring it will help you give plants what they need at the right time.

The ideal pH range for a cannabis plant in hydro is 5.5 - 6.5. Adjustments can be made throughout the stages of growth when plants require different nutrients. Cannabis can absorb a wider array of available minerals when there are slight fluctuations in pH.  

Adding nutrients to water make it more acidic and reduce the pH levels substantially, depending on the concentration. After mixing nutrients into water, the solution should be allowed to sit for about 15 minutes to allow the pH to stabilize before measuring again.

Then the pH can be adjusted by adding pH up(+) or pH down(-), which can be found in all hydroponics stores. Tap water is usually slightly alkaline. If your pH is too high, add a small amount of pH down (usually 1ml per gallon) until you have reached the desired level and vice versa. 

Tip: Check pH levels on a daily basis.

Nutrients & Feeding

Feeding cannabis plants in hydro means you are able to make a balanced solution without worrying about excess salts building up around the roots.

As we mentioned earlier, plants will need feeding from the early stages of vegetation because they do not have the same nutrients available like they would in soil. Start by giving them half the recommended amount stated on the nutrient product label.

Cannabis needs a few important minerals in order to survive. The main ones you will hear about are nitrogen (N), phosphorous (P) and potassium (K) and can often be found labelled clearly on nutrient products as an N-P-K ratio. These three macronutrients are found in fertilizers for both hydroponics and soil and are used throughout a cannabis plant's cycle.

The way nutrients for hydroponics differs to those for soil is through the addition of essential micronutrients. Solutions for hydro have smaller mineral compounds dissolved in them than regular nutrients used for soil do which makes absorption much more efficient. Soil nutrients should not be used in a hydroponics system.

Plants only require very small amounts of these micronutrients and they include sulfur (S), calcium (Ca), magnesium (Mg), zinc (Zn), iron (Fe), copper (Cu), chlorine (Cl), manganese (Mn) and boron (B). As roots uptake the necessary minerals to the plant it creates an imbalance in the quantities of readily available nutrients.

This means the concentration of the solution in the reservoir is always changing. It varies depending on the stage at which plants are at as well as other factors like temperature. More nutrients can be added, however it is recommended to simply change the reservoir after 2-3 weeks to avoid disturbing the roots.

Hydroponics Grow Tips

It can't hurt to have some extra knowledge before starting. The more you know in advance, the better prepared you are for any possible problems. Knowing how to take proper action before the situation worsens will prevent further problems later on.

• Put airstones in your reservoir - keeps the water moving and provides oxygen to the roots.
• Filter the water - depending on the quality of your tap water, you may want to use a reverse osmosis filter.
• Adjust the pH daily - a stable pH leaves less room for problems such as nutrient burn/lockout.
• Keep roots in the dark - roots are shocked easily and begin to grow algae if they are exposed to light.
• Clean your equipment after each grow - reduces the risk of pests, fungus and other problems.

Buy a PPM/EC meter to measure your nutrient concentration. Cannabis plants will under perform if the nutrient solution is too diluted, and may become deficient or burnt if it is too concentrated. An EC meter will give you an estimate idea of how many dissolved solids there are in the water. Hard tap water has a higher pH will eventually get build up of these dissolved solids because they cannot be absorbed by the plant.

Problems/Solutions

You may run into some issues along the way that could make the difference between a successful grow or a failed one. It can be helpful to know what problems may arise so you can prevent them before they get too serious.

Problem 1. Leakages

One loose connection in your system could cause spillage and in a worst case scenario, cut off feeding to your plants. Not checking your system regularly can leave problems like this unnoticed until it's too late.

Solution - Run water through your system before planting anything in it to make sure all valves and tubing is properly connected and sealed. Reinforce or fix areas you might be worried about using tape or sealant.

Problem 2. Blocked pipes and failed pumps

Sometimes hydroponics systems can fail because of blockages in the tubing, either from residue build up or roots. This can lead to overflowing as well as roots being submerged for too long or not receiving nutrient for an extended period of time.

Solution - Flush the system with water at least every 2 weeks before adding a fresh solution. Avoid using hard water which has a lot of dissolved minerals in it that will accumulate in the reservoir and tubing.

Problem 3. Root rot

If you notice any strange smells coming from your reservoir, check the roots to see how healthy they are. Roots that are turning brown are a sign of rot. They become slimy and stop absorbing oxygen. Leaves start curling in (both up and down) and become discoloured. Plant growth slows down.

Solution - If it is still in the vegetative phase, you can carefully cut off roots that look infected but be aware this could seriously stunt your plant. Provide more oxygen to the root zone. Avoid temperatures that are too warm.

Conclusion

Hydroponics systems are one of the most recommended ways to grow cannabis indoors because of their easy set up and maintenance. Remember, your garden needs your full attention, so don't get lazy and make sure you check your grow room everyday.

Choosing the right hydroponic system for you requires you to just experiment and have fun learning in the process. It can be a tough switch if you are used to growing with soil, but it is relatively simple once you get the hang of it.

External References

The Techniques of Hydroponic System. - Mariyappillai, Anbarasu & Arumugam, Gurusamy & V B, Raghavendran. (2020)

Automation in Hydroponics Farming Ecosystem. - Wagh, Jagruti & Patil, Rajendra & Vishwakarma, Anil & Chaudhari, Vijay. (2020).

Adjustment of Phosphorus Concentration to Increase Growth and Yield of Cherry Tomato Using Hydroponic Drip System. - Hidayat, Cecep & Frasetya, Budy & Syamsudin, Ilman. (2018).

This article was updated January 2021.