You have finally mastered the basic concepts of cultivating marijuana.  After hours of reading, days of planning and months of actual growing, you can now claim that you know your way around a grow room. Naturally, you want to raise the stakes and go for something new.

If you are now going through a “where do we go now?” spot, this is the article for you. Luckily, in marijuana growing, there is infinite room for improvement. Below, we will share some advanced tips for marijuana growing, that go beyond the standard grow guides!

Use CO₂ to your Advantage

It is no secret that many growers supplement their gardens with carbon dioxide (CO2) to enhance grows. Contrary to humans and animals, plants inhale CO2 and exhale useful oxygen. Therefore, giving them more of it can indeed increase yields by up to 20%. What is not so obvious, however, is how. As in most things related to growing marijuana, there is a right way and a wrong way to do things. Supplementing your plants with extra CO2 will help them grow bigger if certain conditions are met.

Spoiler Alert: simply sticking a can of CO2 in your grow room, will not be helpful on its own.

CO2 and Plant Evolution

Millions of years ago, when conditions for humans on Earth were not exactly friendly, the atmosphere contained about 1500 parts of CO2 per million. To put that into perspective, nowadays the levels are 403 PPM. While this was bad news for humans, plants thrived in this climate. The point is that their capacity for growth has stayed the same ever since. Instead, it’s the CO2 levels that have dropped. That’s the key point behind using extra CO2: help your plants realize their true potential and unleash their primitive powers!

A properly ventilated grow room uses up the CO2 levels that are available in the atmosphere. If these levels are below 250 PPM, your plants will wither and die. On the other hand, supplying your plants with 1200-1500 PPM (not more!) can genuinely help them grow to be 30% larger and 20% more productive.

How to make the most out of CO2

The real reason why CO2 is mostly used by pro growers is that it requires more dedication in order to work to 100%. Getting your hands on a bottle or canister of CO2 is the easy part; you can find it on most gardening/hardware stores. Before you get it up and running you might need a CO2 meter to measure the actual levels accurately and a timer to schedule the output – note that plants do not use CO2 at night.

• Let there be (more) light!

Perhaps the biggest deterrent in using CO2 is the fact that it is not so effective when it comes to low-powered grow lights like CFLs and T5s. That’s not to say they’re useless –you just need smaller amounts of CO2. The reason behind this is that CO2 and water are the primary way in which plants process the light they are given. Lower powered lights mean that plants need less CO2 and they are probably getting enough by ventilation alone.

However, in bigger grows where HID, (powerful) LED and MH/HPS lights are used, carbon dioxide supplements can help plants use more light, aiding their growth and yield. In such cases, you should raise the CO2 levels to about 1200-1500 PPM. Aim for 40W-60W per sq. ft for optimal results.

• Place your CO2 canister in the right position

CO2 is heavier than air, so it naturally falls downwards. Use that to your advantage and place them directly above your plants. The CO2 should come into direct contact with the plants so it can be absorbed by the leaves.

• Insulate your grow room

Once you get the CO2 inside your grow room, you’ll want to keep it in. Air-proofing your grow room is highly recommended in order to prevent leaks

• Raise the temperature

Cannabis normally likes regular room temperatures of about 70ºF(20ºC). However, when you are supplementing your garden with CO2, you have to crank up the heat significantly. Temperatures in such cases should be around 85ºF to 95ºF (30-35ºC). Since the room is already insulated and the lights you are using are quite powerful, raising the temperature to such levels shouldn’t be a big problem.

Also, keep in mind that all of the tips listed above are targeted to those who use powerful lights (MH/HPS and big LEDs) and therefore can make the most out of CO2. If you have a smaller-scale operation, you are welcome to experiment. Just don’t expect dramatic improvements.

If you want more in-depth information about CO2 supplements, please visit our page here.

Keep an open mind about defoliation

The benefits of defoliation (or lollipopping) are still much debated in the cannabis growing community. Some people claim that it works wonders and others insist that it can potentially hurt yields. The premise is as simple as possible: you just remove leaves from the lower (shadier) parts of your plant, in order to enhance growth in the top. If done correctly, this technique results in a lollipop-shaped plant (hence the name) that will produce higher yields. Defoliation is an advanced technique and should be done with the utmost care. Much of the bad rap comes from growers who have ended up hurting their plants instead of helping them. So, it is better not to proceed if you are unsure about what you’re doing.

Defoliation is not a one-size-fits-all solution. There are situations in which it won’t help –it may even be dangerous to your plants! You don’t want to try defoliation if

• You are growing outdoors;
• Your plant is already under a lot of stress.

On the other hand, lollipopping can work if done properly. If executed in the vegetative stage (not recommended for newbies) it offers a better structure to the plant. The idea is to remove the excess leaves which can create problems with light exposure and create a wider space over which light can be adequately absorbed.

In the flowering stage, defoliation serves a completely different purpose. By trimming leaves you ensure that more light gets to the buds, aiding their development.

We have a whole article dedicated to lollipopping here at HTG! Be sure to check it out for more information on that advanced technique.

Master Plant Training

Plant training is arguably the cheapest and most effective way in which pro growers manage to achieve killer yields. Training your plants is a first-class opportunity to learn more about them and botany in general. But more importantly, it is the most surefire way to ensure the maximum yield your plants have to offer. Each strain has a certain capacity, but with training, you can increase your usual yields up to 40%.

Training has a lot to do with manipulation of a plant’s structure, in order to make the best possible use of available lighting. The natural shape of cannabis is triangular (like an X-mas tree), which is more suitable for outdoor grows, where the light is gloriously provided by the sun. The problem with artificial lighting is that it can not penetrate the bottom layers of a plant, resulting in uneven bud development (the parts that get more light are more productive). The primary goal of plant training is to increase the number of kolas, in order to create a wider surface from which light can be absorbed.

Your plants can grow perfectly fine without any additional input from you. However, training is on every advanced grower’s checklist. There are quite a few methods for you to choose from. For more information, click the link next to each description.

• Sea of Green (SOG) – With this method, you can create an even surface of leaves, maximizing the light intake of your plants.
• Screen of Green (SCROG) – A method similar to the Sea of Green but using a screen over the top of the plants.
• Topping – By careful incisions, you can multiply the main kolas into two, four etc. One of the most efficient training methods.
• FIMming (Fuck, I Missed) – Like topping but more extreme. Proceed carefully and you will be handsomely rewarded.
• Low-Stress Training (LST) – A combination of topping and then training to de-stress the plant and get the most of the light source to grow.
• Super Cropping – This is not a pruning technique but more of a stress test on your plants to create bigger yields.
• Monster Cropping – A fresh approach to plant training, that requires a minimal time investment.

All of these techniques can be applied in conjunction with each other, to achieve the best possible result. They all come with their own pros and cons, so be sure to read our comprehensive analysis for more information on each!

Selective Light Training

Another not-so-well-known growing method, selective light training (or SLT for short), is based on the principle of providing some parts of the plant with more light, in order to manipulate certain proteins into expanding rapidly, leading to improved yields and healthier plants.

Plants typically have more than 1,000 light-sensitive proteins: the phot1 and phot2 phototropin are the ones probably manipulated with blue and minus blue light. Blue causes plant cells to not stretch out, so showering the stem with blue spectrum light gives a more compact plant. On the other hand, minus blue light can have the opposite effects. It can cause plant cells found in leaves and the stem to greatly expand.

How to Use SLT

The quality of the lights you’ll use is not so important here. LED lights are probably best for this operation, as they emit almost zero heat. Instead, you should focus more on getting the lights really close to the stem and let it run uninterrupted. You can do that by attaching the light to a pole and then propping it right in the growing medium. The light sticks should be used through vegetative growth and the first 15 days of flowering.

Take Stealth Seriously

This may seem like a cliché, but you’d be surprised how many people neglect the security of their garden. In most places growing marijuana is still illegal and/or heavily regulated. Keeping your garden operation secret is the cornerstone of success and pro growers know that. So here are some tips on keeping things away from prying eyes.

No Tell, No Smell, No Sell

The core philosophy of proper stealth can be accurately summarized in the above aphorism. There are so many ways in which you can keep your garden a secret, but you must always remember these three rules.

• No Tell – Ideally, you don’t want anyone to know about your grow operation. It’s hard keeping it a secret (especially from close friends) but everyone who knows about it leaves you vulnerable in the future. Pro growers know that silence is the optimal precautionary measure to unexpected troubles;
• No Smell – Do not be careless with air filtration. Make sure that your garden stays as odorless as possible, by using specialized equipment for your exhaust vents. Same goes for you; the stench of cannabis is distinct and can put you in an awkward legal position;
• No Sell – If you are selling your cannabis in legal states, make sure you have all the necessary permissions. Otherwise, selling to make some extra cash is bound to get you in trouble, especially when you deal with people out of your network. Although it may seem tempting, it is still illegal and still not worth the risk. On the other hand, growing for personal use is a lot safer. In any case, it is better to keep things simple.

See no evil…

As obvious as it sounds, not being seen involves more than a stealthy grow box or a conveniently concealed grow room. Unless you live in the woods, the tips below might come in handy!

• The night is your friend – The best piece of advice is not to drag your equipment around at all. However, if you absolutely have to, do it in the nighttime. Also, don’t forget to cover up any suspicious parts; your neighbors might be alarmed if they see you transporting an exhaust fan and duct tape in the middle of the night.
• Pay attention to your trash – Mix up your growing-related trash with other stuff so it doesn’t stand out. A dead marijuana plant sticking out of your trash would be a huge red flag for the trash collectors, your neighbors, and the local police.
• Check your surroundings – Take a walk around your house and check out for any abnormalities. Weird bright lights that shine out of windows in the night tend to raise heads and questions.

Hear no evil…

Your indoor garden will contain a lot of electrical devices and exhausts that will run 24/7. Low-quality components tend to be louder. The main culprit behind excessive noises is usually the ventilation system. Exhaust fans and air pumps of inferior build will cause a racket that might attract unwanted attention.

• Get quality components – Get products that are proven to be quiet. This might come at a price, but the added benefits make this investment worthwhile;
• Keep the ducting straight – Twists and turns in air flow create extra noises. Try to keep your ducts as straight as possible;
• Insulate your fan and your ducting – You can use an insulated box around your fan to keep it quiet. It also makes sense to use insulated ducting for your ventilation systems;
• Have an adequately large intake hole – Sexual innuendos aside, your intake hole should be about four times bigger than your exhaust fan, so the air can flow freely. If the fan is not getting enough air, it will run louder –and break down faster.

Smell no evil!

Cannabis doesn’t smell like much until the flowering stage. But once that phase kicks in, you are in for a treat. Although it is largely a matter of genetics, cannabis will get smelly at that point no matter what. There are indeed some strains that are less stinky (like the Northern Lights Haze or the Blue Mystic), but it is best to be prepared.

When it comes to odor control, you can either use odor absorbing gels (that should be placed outside –but near- your grow room) and carbon filters (scrubbers).

Odor Absorbing Gels

• The inexpensive choice for the small grow room. Not powerful enough for especially stinky strains or big grows;
• Gels should be replaced quite often. It is best to have a few lying around just in case;
• The ONA Gel is the most popular odor absorbing gel. It comes in jars and using it is a breeze. You just open the jar in the near your grow (not in the same room) and it will neutralize odors automatically.

Carbon Filters/Scrubbers

• Carbon filtration is your best option for a total peace of mind as far as odors are concerned. Carbon filtration works by passing the outflow of air from your growing space through activated carbon granules. Activated carbon is charcoal that has been chemically treated to give it a very open structure. The result is a highly porous substance that has an incredibly large surface area, making lots of spaces to trap the tiny odor molecules;
• Installing carbon filters is as easy as mounting them to your exhaust fan. The trick here is to place the carbon filter as far away as possible from the external vent, to avoid unwanted leaks.
• Brand name carbon filters like are better than generic versions. Like with most things in life, you get what you pay for. VIVOSUN and Phat Filters are some solid brands.

We value your need for discretion and we have prepared an article especially about stealthy tips and grow boxes. You can find more information about them here!

Some Quick Tips for the Advanced Grower

Humidity Levels

You should keep your humidity levels at around 90% at all times, except in the case of overwatering. Cannabis roots do not need water every single day, except in very high temperatures. If you have adequate ventilation, there should be no mold or gnat dangers to your plant.

Average watering schedule

• 10 days : 1 Quart (946 ml)
• 20 days : 1.5 Quarts (1419 ml)
• 30 days : 2 Quarts (1892 ml)
• During Flowering : 1.5 Quarts (1419 ml)

Flushing the Soil

Flushing your soil is a useful technique, that is mainly used in three situations

• In case of a nutrient burn, you may need to flush excess components away from your growing medium.;
• In case you want to remove excess salts from your soil;
• When your plant is 10 days into flowering. Removing extra nutrients that still exist in trace amounts, will radically improve the taste and “burnability” of your final product.

Flushing is easy as pie. All you need is a 5-gallon container filled with pH’d water. The process is this

• Empty the water on your grow medium and wait a few minutes. This will allow the nutrients to be dissolved;
• Add more water to your container and repeat. This will clean up any remnants of the first dose;
• As nutrients, compounds and surplus elements decompose, they can be effectively flushed out by the second dose.

Don’t stress your plants too much

Cannabis is very responsive to its surrounding environment. There is a number of factors that can affect your plant’s growth and development, sometimes in unexpected ways. Light, heat, water, temperature etc., can be crucial in the size, yield and most importantly, sex of your plants. Although there are many things you can do with your male plants, it’s the females that give all the smokeable product.

Put simply, pro growers always put their plants under conditions of controlled stress. Training for example, is practically stressing your plant out, to help it develop defense mechanisms. What your aim should be as an advanced grower, is to stress them out just enough.