The Twelve Steps of Growth (Part 7) Cannabis Plant Problems

Growing Tips from the 101

Part VII – Diagnosing Sick Marijuana Plants

Listen to Your Leaves

Diagnosing Cannabis PlantsThe leaf of the marijuana plant is the biggest tattle tale on the planet.  This is great news for you because anything that the plant, roots, nutrients or environment is doing wrong the leaves are going to let you know.  It does not matter where the problem exists in your plants or grow environment, that problem will be reflected in the leaves of your plants.  It seems like a simple concept…something’s wrong, the leaves tell you, then you fix it.  It would be great if grow room diagnostics were that simple but unfortunately they’re not.  The plant’s leaves will tell you something is wrong but they will do it with the finesse of a screaming baby.  Much like there is no verbal language between a young mother and a baby there will obviously be no words between you and your plants….but your leaves will be talking.  The challenge for you is to figure out what they are saying.

The first sign of trouble is going to be heartbreaking and you will be confused like young parents up all night with that screaming baby.  But fear not, cannabis plants are pretty tough to kill and chances are you will emerge from your plant woes without even affecting your yield.  After a few grow cycles and a couple problems you will have the same confidence with your plants as seasoned parents do with a child.  Before you know it that young mommy knows exactly what her baby wants by hearing even a whimper and you will know what’s wrong with a cannabis plant just by looking at it.  In this installment of our “Know Before You Grow” series, we will look at 11 common cannabis problems, how to recognize them and their solutions. Your plants will deliver good news as well and we will discuss how to recognize when it’s time to harvest….let’s get started.

  1. Light Burns / Heat Stress
  2. Over Watering
  3. Underwatering
  4. Powder Mold
  5. Spider Mites
  6. Root Rot
  7. Nitrogen Toxic
  8. Boron / Calcium
  9. Zinc / Sulfur
  10. Magnesium / Potassium
  11. Underwatering
  12. Nitrogen Toxic
  13. Phosphorus
  14. Powder Mold
  15. Boron / Calcium
  16. Harvest Time
  1. LIGHT BURNS & HEAT STRESS – We touched on this topic in the previous installment of our ‘Know Before You Grow” series but the topic is worth revisiting as it will happen more than once.  We often plan our first workout for a crop when the plants reach the lights.  That same scenario happened in our project trailer.  We transplanted late so we postponed the plants first-week workout until they bushed up a bit.  Toward the end of week 2, the upper leaves got a little toasted.  At that point, we raised the lights and worked the plants.  When leaves are light burned they will curl up at the edges and turn yellow.  Even if your lights are high enough off the canopy your plants can still get too hot.  If your leaves curl up at the edges and it’s hot (over 80 degrees Fahrenheit) in your room your plants are displaying signs of heat stress.  If your plants are burned from the lights the solution easy….simply raise the lights.  Heat stress is a more difficult problem to address.  At the very least you will need to add a fan or two but I have seen clients have to add power and air conditioning to their room.  If you recall in our previous articles and videos we have been obscenely repetitive about room temperature, humidity and air flow…..this is why.  Heat stress is a challenge we take on too many times in too many rooms.  We have even seen clients pull off an amazing grow of dank buds in a room built in Autumn.  They harvested twice over winter and spring then lost two consecutive crops to heat stress when summer temps rolled in and they had no power for an air conditioner.  Usually, heat can be overcome but it can be a room killer if not taken seriously.
  2. OVERWATERING – If your plants are in aeration grow media (coco and perlite) and your pots are elevated above your drain trays which are connected to a drain then you should never experience an overwatering problem.  If you have decided to re-invent the wheel with your own “soil” and chose to forgo the drain system because you’re good at estimating then you are most likely plagued with over watering problems.  The plants’ roots deliver oxygen to the plant so if they are sitting in undrained water the plant is drowning.  The leaves will curl down even at the stem like its branches and stems can no longer hold themselves up.  Yellowing will appear as time goes on.  The best and obvious solution is to not water for a while.  You can also increase the airflow in your room and crank up the dehumidifier to try and dry out the plants faster.  If there are no drain holes in your pots put some in them and figure out how to direct the water out of your room.  You can also use a small dowel stick or straightened coat hanger to poke holes in your soil and aerate your pot.
  3. UNDER-WATERED PLANTS– A plant that is starving for water will look similar to a plant that is drowning.  The leaves will look sad and droop down but unlike an overwatered plant the stems and branches of an underwatered plant will stay straighter and the leaves will droop around them.  An overwatered plant’s stems will droop with the leaves.  An underwatered plant will turn yellow more quickly than an overwatered plant.  Hopefully, you will have recorded or at least remember your watering times and amounts making easy to determine whether you gave the ladies too much or too little to drink.  
  4. POWDER MOLD – The humidity of your room must stay under 50%.  There’s really no way around this.  Too many times we come across new growers that are so excited to show us all the white resin dripping off their plants.  We arrive to find a room with no dehumidifier, 70% humidity and the plants are not dripping in resin….they’re covered in powder mold.  In the first half of the grow cycle powder mold is quickly eliminated with neem, leaf polish or a mold eliminating spray like Safer’s 3 in 1.  But later in the grow cycle and after buds have formed these solutions are no longer an option.  Some products say that they can be applied right up to harvest but you (and anyone who smokes your weed) will taste the products in every hit.  There are little green LED lights available in any grow store (and on our site as well) that will allow you to detect problems like powder mold on your leaves a bit earlier and every day you stay ahead of it helps.  The green lights allow you to see the mold spores earlier than with the naked eye.  The mold will start as little white dots and circles on a few inner leaves.  Within a couple days it will spread throughout the plant, within a few days it will spread throughout your room.  Neem and leaf polishes are not only solutions but preventative maintenance as well.  We spray our plants with neem into week 3, keep our plants’ leaves thinned for air flow and keep our rooms’ humidity below 50%.  We do all of these things with powder mold on our minds.
  5. SPIDER MITES – These treacherous mites are probably the quickest killer of crops we will discuss.  They are also extremely challenging if you do not get them all the first time.  These mites are not called spider mites because they are arachnids with 8 legs.  They are called spider mites because of the webs they make in marijuana plants.  They lay millions of eggs and offspring reach sexual maturity in days so they can kill a plant overnight and eliminate an entire crop in days.  These mites love the underside of leaves where you cannot see them and if you do not kill all the eggs with your treatment you will be greeted days later with a larger army of mites now immune to your first treatment.  Solutions range from vacuuming your leaves with a shop vac (no kidding) to purchasing ladybugs and releasing them in your room.  Spider mites will look like little white dots on your leaves and will be more prominent on the underside of leaves. Spider mites are like ants in that they never travel alone.  They will be easy to recognize because where there is one there is many an infestation will become very obvious very quickly.  To rid your room of them ladybugs are a great solution and so is neem or products like Bugblaster.  You can also spray your pots and soil with bug killer then spray your leaves lightly with water, the mites cannot hang on and die when they hit the bug killer.  If your mites appear close to harvest you can simply crank open the valve on your CO2 tank and leave the room.  Overloading the room with CO2 will kill the mites but not the eggs so this is only a solution when you’re within a week or two of harvest.
  6. ROOT ROT – Roots are easily affected by water with bacteria in it.  We use Mycorrhiza products in our nutrient diet to maintain a healthy relationship between our plants’ roots and the bacteria around them.  Products like Mycorrhizae and Great White are excellent nutrients to make sure root rot is something you never experience.  But if you do encounter root rot keep in mind that the damage to your roots is permanent.  Your plant can recover and make new growth but the roots that rotted are useless.  Your plant will look like it’s overwatered with leaf and stems drooping and yellowing.  However, the leaves will not be able to hang on and the plant will start losing leaves as soon as they yellow. The roots will be brown and slimy instead of white and clean.  And root rot stinks….the smell is awful.  If you see the above symptoms and your soil has a wang to its aroma…you have root rot.  Typically root rot is seen only in hydroponic systems but it can happen in soil and soilless media as well, especially when overwatering occurs.  “Aquashield” is a popular treatment for root rot but in most cases, growers end up scrapping the affected plants and starting over.
  7. NITROGEN TOXICITY– Nitrogen additives are great for a vegging plant.  However, that same blue additive that your plants loved so much when they were babies can kill them now.  Leaves will begin to look very dark and growth will slow.  The tips of some leaves will point down at the tip.  Their downward curl will be abrupt even at a 90-degree angle.  Nitrogen toxicity creates a unique bend commonly referred to as claw leaf.  The plant may have the symptoms of a nutrient burn as well.  The most common cause of nitrogen toxicity is a lack of knowledge.  Cannabis plants require very different nutrients at specific times.  Most every nitrogen toxic plant we have encountered was simply caused by the grower using nitrogen-rich nutrients during the grow cycle or not discontinuing use of nitrogen once the plants enter the flowering cycle. The solution is simple….stop using nitrogen.  Flush your plants with ph balanced water and get them on a proper flowering/budding diet.
  8. BORON/CALCIUM DEFICIANCY– The two most telling signs of calcium or boron deficiency are big brown spots on the leaves and new growth will be retarded, small and yellowed. Leaves will also crinkle at the edges like the plant is heat stressed.  A cannabis plant needs boron to process calcium effectively so both boron and calcium problems will show the same symptoms.  PH balance being too high can also cause these issues so flush your plants with PH balanced water and return them to their diet slowly.  Adding a trace element replacing product like “Cal-Mag” to their diet will most likely eliminate the problem.
  9. ZINC & SULFUR DEFICIENCY– These deficiencies will start off looking the same as consistent yellowing of the leaves will begin.  Sulfur deficient leaves are unique in the way that they will show stress from back to front instead of tip to the base like most other problems.  Zinc deficient plants will also yellow consistently but their leaves will curl much like they are heat stressed then the leaf will yellow between the veins and fall off.  After a couple days, buds will start to die on both zinc and sulfur deficient plants.  The solution to both problems is to flush your plants with PH balanced water and return them to their diet adding a trace element replacement like Cal-mag.  A zinc deficiency will disappear within a couple days.  Sulfur deficiencies will take a few days to show signs of repair.
  10. PHOSPHORUS DEFICIENCY– Phosphorus is needed for growth in flowering marijuana plants.  The first sign of a phosphorus deficiency is that the plant stops growing, if not treated the leaves will turn a gray/pink/purple color that is unmistakable to phosphorus deficiencies.  The solution is again to flush your crop with PH balanced water and return them to their diet.  If you are using nutrients heavy in zinc or iron you may want to back off a bit as too much of some elements will make the plant deficient in other elements.  If your water was properly PH you can add phosphorus to your plants’ diet.  Phosphorus deficiency is rather common, the plants cannot seem to get enough of the stuff.
  11. MAGNESIUM & POTASSIUM DEFICIENCY – These deficiencies are marked in the beginning just like the others with yellowing leaves and stunted growth.  The leaves of a magnesium deficient plant will completely yellow while the veins within the leaves remain dark green….it’s usually unmistakable.  Potassium deficient leaves will scorch and curl around the edges.  The solution is the same.  These are problems caused by unbalanced, incomplete or overdosed nutrients.  PH your water and return to their diet adding in a product like Cal-mag.
  12. HARVEST TIME  – We are going to talk in depth later in this series about trichome tips and how they change throughout the flower cycle.  More importantly, we will discuss their importance at the time of harvest.  There is a bit more to trichome harvest sequence than clear, milky, amber…harvest!  But we’ll get to that later.  For now, we’re going to keep on the topic of leaves.  The cannabis tattle tales that leaves are will point out all the popular problems we covered and many more issues….but they will deliver you some good news once in awhile as well.  One of the best time leaves can give happy news is at harvest, they can also save the day as well.  The whole trichome thing isn’t as clear cut as milky, amber then harvest and I have postponed or expedited many harvests because of what the leaves were saying, not what the trichomes were saying.  Your leaves will yellow when the plant is ready and they will yellow like autumn leaves would as opposed to looking nutrient burned or deficient.  More than once with dark amber trichomes I delayed harvest because the leaves were lush and healthy.  The leaves were right each time.  More than once I have hurried a harvest because the leaves in the entire canopy had run their course.  And each time the leaves were right.  Of course, you want to give center stage to the trichomes at harvest time but the leaves will never let you down.

The leaves do most of the talking for the plant and just like that young mom with a new baby, you have to listen to and learn their cries.  But you get their smiles as well.  When all is good your leaves will be a color of green that you can smell and their odor will be so thick you can see it in the air.  They will be beautifully peaceful when the lights are off and reaching for the lights when they are on.  It may sound cliché but on those days you will feel just like that young parent when their baby smiles.

Welcome to the Green Rush!

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