New cannabis cultivators must learn to identify and treat various conditions in the grow room promptly and accurately. Here are the most common marijuana-growing problems and how to solve them quickly and effectively.
My leaves are turning yellow and falling off. What gives?
This is an indication that your plant is short on nitrogen, an essential nutrient. As a result, the plant is using the available nitrogen stored within its leaves for photosynthesis and chlorophyll production. You may have returned to the garden to find that a few of the most significant fan leaves have become lifeless and the connecting part of the leaf can be flicked off.
What you want to do here is remove the yellowing leaves for a few different reasons. You will want them out of sight and out of the garden as insects are attracted to the color yellow. (This is why sticky strips made for catching flies are yellow.) Another reason to lose the leaves is that they’re useless to the plant and removing them will allow more light to the lower parts of the plant that the fan leaves were covering.
If you find that the newest smaller leaves are becoming bright yellow and brittle, then you need to immediately add nitrogen that’s readily available. Add organic matter that’s in a state of humification, such as worm humus or tea, liquid seaweed, fish emulsions, blood meal or other things that are naturally high in nitrogen.
Why is there a rotten-egg-like smell coming from my grow room?
This will most likely happen when you are growing organically. That foul sewer-like smell is produced by a microbe that is in the growing medium. The bacteria are anaerobic, which means they thrive in environments that are waterlogged with low oxygen—basically, swamp conditions. If you get a whiff of sulfur and rotten egg, then you know this is the cause.
To prevent this, introduce hydrogen peroxide into the growing medium at 3 percent strength. This is distilled water with an extra hydrogen molecule attached, an unstable molecule. Once it is in contact with any bacteria, it will starve the organism of oxygen and kill it. It will also kill any beneficial bacteria you have in your grow medium; however, your roots will revive and the anaerobic bacteria will disappear.
A good tip here is to make sure your growing medium is not waterlogged. If you’re bottom-feeding, never let your plants sit directly in a tray of stagnant water. This is precisely how anaerobic bacteria are formed, and even more so if you’re using organic nutrients.
Why do the leaves of my plant have tiny yellow or white dots on them?
If you’ve noticed under close inspection that your fan leaves and newest growth have tiny yellow blotches on them, then, sadly, you have signs of spider mites. You will not notice these tiny pests with the naked eye; you can only see the collateral damage they leave behind.
A spider-mite infection at any stage of the grow can be devastating, so my advice here is to be careful where you source your clones from. It’s important to limit any potential threats that are being brought into the garden. You’ll also want to reduce your humidity, as spider mites thrive in a clammy environment.
It’s always good to have living predators on standby ready to patrol your garden. Once you have introduced these predators into your grow space, the results will be a slow reduction of the number of spider mites or whatever problematic insects you’re dealing with.
Webbing is a sure sign of a spider mite infestation gone awry
I tried to cut the top of a shoot to create two shoots, but I missed. What will happen now?
Don’t worry, as this is a technique practiced on a broad spectrum by all types of growers. It entails the removal of about 70-80 percent of a shoot so that enough is left behind for the plant to reduce the growth hormone auxin but also promote lateral growth from the lowest parts of the shoot that was cut. It’s called “fimming,” for “Fuck, I missed.”
If you intended to grow two new shoots from one, this can still happen, but you need to wait about 10 days for the plant to recover and become bushy. Then you can start the process to top the plant again.
My once white and fluffy roots are now thin, fragile and brown. What happened?
You’ve got what’s called root rot, and this happens when the growth medium becomes waterlogged. Roots need oxygen to breathe during their search for moisture and nutrients. Again, using hydrogen peroxide will help bring the roots back to life, but so will repotting the plants into a medium that contains plenty of air pockets.
A good idea is to use a 50 percent coco and 50 percent perlite mix as a medium, and adding worm castings, blood meal and any humate rich in nitrogen. You will notice your roots bounce back to life and form new fluffy root hairs, so ensure that the growing medium is dry more often than wet.
I noticed spiderwebs forming around the leaves. What is this?
This is not a web from a spider that has somehow entered the garden, but instead a full infestation of spider mites. These pests can lay eggs and multiply in a short time in the right environment, so controlling that situation with clinical effect is necessary.
When you inspect your plants, you need to look at each one in the garden and remember that the spider mites are so small that they can move from plant to plant using the air currents from the fans in the room.
Get a magnifying glass and get close up and personal in order to identify their presence; once you do, you can then try and control the problem with predators that will depopulate the spider-mite colony.
There are tiny gray flies on the surface of my growing medium. Where did they come from?
These little fly larvae can be frustrating, and they can even be inside the soil or coco from a grow store. There is not much you can do about these apart from setting up sticky fly traps. You can also keep the top of your grow medium dry and maintain constant air flow, as adult flies cannot lay their eggs in dry growing medium.
Supporting branches by using a screen increases yields substantially
I’ve been told to use a screen on my next grow for a more significant yield. Why should I do this?
Using a screen at canopy level is a growing technique in which leaves above the screen are kept and leaves below the screen are removed. The screen not only adds support for heavy branches; it also allows you to expand your canopy greatly by training your plants during the vegetative stage.
The idea with a screen is to pull the new trained shoots through each square strategically, so that when the plant flowers, the area above the screen is dedicated to producing dense buds. When you have efficiently filled every square of the screen and removed the irrelevant lower growth, the plant will now focus all its energy on the upper canopy above the screen.
Why are my temperature and humidity so high?
There can be several factors why you cannot get your temperature under 80°F and your humidity is uncontrollable. This is not good and can lead to all sorts of problems, particularly during the flowering period. If you have your ventilation system dialed in, it should remove and recycle the air in your space between 15 to 20 times per hour. One reason that many grow rooms fail is that the ventilation is not on par with what is required to remove the hot, stagnant air and to bring in carbon dioxide.
The other reason why your temperature can be sky-high is that you have your lights too low. Hot air will rise, and cool air will sink. You should have cool fresh air blowing in from an intake fan that is smaller in volume than the outtake fan. The space should perform as a vacuum—dispelling hot air from the grow lights and ballasts and replacing it with fresh air from the lowest part of the space.
Another tip is to keep your carbon filters and wall fans on even during the lights-out period. If you consider how the hot temperature and high humidity level build up, you can see that the heat cannot escape and adds to the moisture that forms on the walls and the surface of the plants. This is how powdery mildew and mold become a threat, so make sure you have constant fresh-air cycles and persistent blowing fans that mimic nature.
There’s white powder all over the leaves when I check my plants. What is this?
This is called powdery mildew (PM), a living spore that attaches itself to the surface of your leaves. This fungus will grow on fresh foliage and can cause problems to an entire grow room in a short time. PM travels through the air and requires wet and damp conditions with little airflow.
This unwanted fungus can be treated with acidic-based washes, or with hydrogen peroxide and then rubbed off. It can take several days to entirely remove a PM infection, so keeping a close eye on your plants is essential at this stage.
Root-bound plants should be transplanted into fresh growing medium.
What do I do about the rusty-brown and yellow spots on my leaves?
Rusty-brown spots on the lower leaves are your plant’s way of telling you that it is deficient in calcium and magnesium. Calcium plays a huge role in the cell division of plants, alongside potassium. Use Epsom salts to boost your nutrients, or get a Cal-Mag supplement from your grow store.
The grow shop told me that my plants are showing a deficiency and that I should feed them trace elements. What do they mean?
Well, nitrogen, phosphorus, and potassium are the three primary nutrients for your plants. The other remaining nutrients, called micronutrients or trace elements, are calcium, magnesium, sulfur, manganese, boron, zinc and copper. Cannabis requires this full lineup of nutrients to be able to do complex jobs deep down at the cellular level.
My plants are root-bound. What should I do?
Root-bound pots may look good, and many naive growers will show them off with pride without realizing that their plant has become restricted. When growing in a fabric pot or a pot with air holes in the bottom, roots will have a chance to come into contact with air and, as a result, react by pruning themselves. Fibrous roots will multiply and turn back on themselves and repeat this process like a spider does when building the structure for a web.
Prepare a larger container with a new medium into which to transplant. Wet your existing grow medium and turn the plant upside down with your fingers around the base of the main stem, carefully removing the entire root ball and placing it into the new medium.
When I touch my grow medium with my hands, the soil is cold and wet. Is this good or bad?
Cold temperatures are never good when it comes to growing cannabis. A cold medium can mean several things: poor air circulation, inconsistent wet and dry periods, the breeding of anaerobic bacteria, roots unable to take up phosphorus efficiently or sparse microbial life.
You want your grow medium to be warm, and a good tip here is to use felt pots and have a temperature of 75°F around the base and tops of the plants. Lifting your pots off the ground and making sure they’re not touching the cold floors can make a big difference. Add a heater set at a low temperature to keep the air nice and warm for the roots. “Big roots mean big fruits,” as the adage goes, so keep the roots and microbes warm and happy.
If you are hand-watering or bottom-feeding, use half as much nutrient solution twice as often. This can be more beneficial in the long run than finding out the hard way and having to work backward to find out where you went wrong.
Good luck in growing your killer plants, and I hope these diagnostics have helped you already.

Looking for the basics of how to grow marijuana? Here are the tools and information on how to grow weed affordably and effectively. All you need is a small discreet space and a little bit of a budget to get started on your indoor pot production.
Grow Tools
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The first thing you’ll need is a place to grow. I recommend getting yourself a decent grow tent. They’re cheap, made to grow inside of and can be put up and taken down quickly by one person. Some tents come with packages that include all kind of complicated hydroponic equipment. Your best bet is to purchase only what you need inside the tent and to learn how to grow weed without the expensive plastic. Some even have separate chambers for vegetative growth and cloning, making them perfect for people living in one-bedroom apartments or studios with limited room to grow.
First, you’ll need a growlight. I like HID (High-Intensity Discharge) lighting – HPS (High-Pressure Sodium) or MH (Metal Halide) systems with ballasts, bulbs and reflectors. If heat from these lights will be an issue, there are also LED (Light-Emitting Diode) and CFL (Compact Fluorescent) systems you can employ. Be sure to get a light that covers your tent’s footprint and invest in a decent timer to control when your light turns on and off.
You’ll also need an exhaust fan and activated carbon filter to reduce heat and eliminate odors. Be sure to get one that’s rated for your tent’s size with the proper ducting size. A clip-on circulating fan will keep air moving and stop it from being stagnant. A thermometer/hygrometer is also a must for keeping track of temperature and humidity.
If you don’t have access to marijuana seeds or clones from a dispensary or friend, you’ll need to get some cannabis seeds mailed to you. Don’t have them mailed to the same place you plan to grow if you’re not growing legally. Don’t just learn how to grow weed, learn how to be discreet and not brag or bring attention to yourself.
A simple loose and airy soil mix in 3-5 gallon buckets are great for beginners and much more forgiving than any hydroponic system. Be sure to cut holes in the bottom of the buckets and use saucers under them to catch any overflow. You’ll need to purchase nutrients to feed to your plants as they grow and a watering can as well.
How To Grow Weed  

After you’ve planted your seeds or rooted your clones, it’s time to get them growing. Lower your reflector so that it’s closer to the plants rather than making them stretch to reach for light. Raise the lighting system as your plants grow. Set your light timer to be on for 18 hours per day and off for 6 hours. During this vegetative stage, the plant will grow leaves and branches but no flowers (unless it’s an auto-flowering plant).
Avoid overfeeding and overwatering your plants at all costs. Err on the side of caution as it’s always easier to add more nutrients or water than it is to take them away. Marijuana roots prefer a wet/dry cycle so lift up your buckets and you’ll get a better idea for if they need watering or not by the weight. The first sign of overfed plants is burnt leaf tips. The first rule of how to grow weed is to learn to stay off of its way sometimes.
Anytime space is limited for growing, some basic rules apply: Since square footage is at a premium, plans must take full advantage of each available inch. This means choosing between growing indica-dominant strains such as Hashplant, Afghani #1 or planning on using drastic trellising and training techniques if growing out sativas such as Super Silver Haze, Jack Herer or Kali Mist.
Pruning For Higher Yield

When pruning, start early and often. Cut or pinch branches just above the node where two new shoots will emerge. If you stay on top of this process, you’ll have plants that look like bonsai bushes, with plenty of bud sites but not a lot of stretching out and big gaps between nodes. This is the efficient way to get bigger yields out of small spaces but your vegetating time will increase so factor that into your schedule.
Don’t prune or pinch plants at all once they’ve begun flowering – you’ll only be decreasing your harvest at that point. If the branches are threatening to reach the light, bend them or tie them down to keep them from burning. A trellis system constructed from chicken wire at canopy level (aka the ScrOG or Screen of Green system), will further spread out bud sites and increase your yields considerably. Simply train growing shoots to grow horizontally along the bottom of the screen to fill empty spots.
Flower Power

Indoors, The decision of when to induce flowering in your plants is entirely up to you. If you want to learn how to grow weed, it’s important to determine how much space you have and to factor in the fact that your plants will stretch for at least a few weeks after flowering is induced. I usually recommend one week per gallon of container, so a plant in a five-gallon bucket should get approximately five weeks of vegetative time.
When you’re ready to begin the flowering stage, switch your timer to a 12 hour on/12 hour off light cycle. Be sure never to interrupt the 12-hour dark period with any light. This confuses your plant and can cause serious problems.
Change your feeding regimen to one suited for flowering. Plant nutrients generally come in vegetative or flowering formulations so switch over to a “blooming” solution. Depending on the flowering time of your strain, determine when you have two weeks or so left and begin the flushing process. If you’re growing a 60-day flowering strain, start to flush your grow medium with only plain water around day 46.
Harvesting, Drying and Curing
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Knowing when and how to harvest your buds is as important as knowing how to grow weed.
Use a loupe or a strong magnifying scope to take a very close look at the trichomes; the tiny glandular stalk and head sometimes referred to as “crystals”. Up close, they resemble little glass mushrooms with a stem that forms a bulbous round clear top. Inside that gland head resides the psychoactive compounds (THC, CBD etc). Harvest when the majority of the gland heads begin to go cloudy white and before they’ve gone completely amber. Harvest when they’re mostly amber if you desire a more lethargic stone.
Post-harvest, you will trim and hang up your buds to dry. This process should take about a week or two depending on the humidity and heat in your area. It’s always best to keep this process slower than 3-4 days in order to ensure you aren’t locking in that “green” chlorophyll taste. Add a humidifier to your drying room if you think your nuggets are drying out too quickly. Never leave a fan blowing directly onto your drying colas but make sure air is circulating to avoid mold and bud-rot.
After you’ve determined that your buds are sufficiently dried you’re ready to jar them up for the cure. The stems should snap instead of bending and the outside of the flowers should feel bone dry to the touch. The truth is there is still plenty of water stuck in the bud and the curing process will slowly “sweat” out the remaining liquid.
Always use opaque jars (ones you can’t see inside) and place them in a cool dark place. Open up the jars to determine the level of moisture and leave them open if there’s any condensation forming on the inside of the glass. Slowly but surely, if you open and close the jars once or twice a day, the moist air will be replenished by dry air and the water that’s stuck in the middle of your bud will work its way to the outside and then out into the air altogether. After three weeks to a month or so curing, your buds should burn and taste perfectly.