Finally, your cannabis plant is starting to flower.

by Alex Robles

    Do you feel that?  The seasons are changing, the nights are getting longer and cooler.   The days are getting shorter and our cannabis plant senses that fall is here and  the end is near. This change in the photo period/light cycle is what’s going to trigger our cannabis plants’ flowering cycle outdoors.  The plant is going to start to go through some amazing changes and we’re going to need to adjust some things to support her.  In this next section of the home grow series, I’m going to talk about the cannabis flowering stage and harvest time.  

     In order to make a long story short, I’m going to use the example of a cannabis plant that is grown outdoors and ready to harvest 10 weeks after it starts the flowering stage.   ALL REPUTABLE seed banks will give this flowering timeline in the description of the seed you want to buy.  Also, please understand that everyone’s growing conditions are different.  That 10 week flowering time is an average of what the breeder has seen, it may take a little longer for you, don’t freak out.    

Sexing our plant 

     A well trained eye can spot signs of pre-flower on a cannabis plant by the middle of the vegetative stage.  If you want your cannabis plant to naturally show you its sex, you’re going to wait until it’s flowering stage starts.  So before we get too far into when flowering starts, let’s talk about sexing our plants. 

   “Sexing” our cannabis plant simply means we’re going to figure out if our plant is female or a male before the flowering stage begins.  The earlier we know the sex, the more time and money it’s going to save us.  We spend our time caring for the plant and our money on soil, nutrients and water during its lifecycle.  It always hurts when a plant that you’ve cared for all season turns out to be a male and you have to chop him down.  Remember, what we’re looking for is that high value unpollinated (sinsemilla) female plant.  She’s the one that’s going to make all those trichomes or oil glands (Capitate-stalked glands) in a much higher concentration than the male plant.  Remember, when the female gets pollinated, she’s going to use most of her energy to make a seed instead of making trichomes.  This is going to make your harvest less potent but you’ll have seeds for your next grow (silver lining).  With that said, I want to quickly talk about two different ways that I’ve sexed my plants. 

     The fastest way I’ve sexed a cannabis plant is to send a small genetic sample to a testing lab that specializes in this type of plant test.  These labs can test a sample from a seedling and tell me if it’s a boy or a girl.  Just be aware that there is a small cost that comes with this type of lab work.

     Another way I’ve sex a cannabis plant that’s a little more technical and involves making a clone.  For more details about cloning, please visit  In the search window type in the word “Easy way to sex a cannabis plant” for more details about this process.  

The beginning of flowering

      The first two week of flowering are known as a transitional period.  Since the plant thinks that winter is on it’s way, it will start to hormonally change.  A lot of cannabis varieties will go through what’s known as a “pre-flower stretch” and could double in height.  The plants will also look fuller or fluffier, so don’t forget to give your plants enough room to stretch out.  The plant is basically bulking up in order to support the flowers it’s about to start making.  This “stretch” is natural, as long as the plant has enough light and  looks healthy, without any signs of stress or deficiency.   She’s doing exactly what she should be doing at this stage, great job, keep doing what you’ve been doing.  You’re not going to need to change anything until you see actual signs of flowering.  

    NOTE:  There are some really great cannabis grow books and authors that have mislabeled some of the cannabis flower structures.  Please visit “ The Cannabis Female Flower “ by Mel Frank (  He does a masterful job describing these structures and there’s an amazing photo that goes along with it.     

Weeks 3-4

Female cannabis flower stigmas

     After that transition period you’ll start to see the first signs of sex organs begin to grow (week 3-4).  The female cannabis will start to push out thin, whispy white hairs called “Stigmas” (mislabeled as pistils).  These hairs are there to capture male cannabis pollen so they can start to make a seed.  The Stigmas grow in the spot where the leafstalk meets the stock, stem or branch and this is where the buds (flower) will begin to build up.  Each of the buds are made up of a cluster of small flowers called “Raceme”.    

             Male Cannabis Pollen Sacks   

     A male cannabis plant will develop pollen sacks that start their lives looking like tiny hops seed cones.  Soon they’ll multiply and start to look like a cluster of grapes.  The males will usually be taller and flower about 2 weeks before the female.  They do this so they can be above the female and ready to drop pollen when the female starts to develop those Stigmas.  Since we don’t want pollinated females, we remove the male as soon as we see any signs of pollen sacks.

Nutrients & Water

     As the seasons change and cooler temperatures move in you may need to water less.  Check your soil before you water just to make sure they need it.  If your cannabis plant look wilted and is drooping, It may need water.  If the plant just looks droopy, you might be over watering.  

     If I’m using bottled nutrients, I’ll check the manufacturer’s recommendation for flowering and then cut it in half for the first week.   I do this to make sure it’s not too strong and possibly burn the plant.  If I’m top dressing soil amendments I’ll look for one that has a 2-8-8 NPK.  Whichever way you feed your plant, keep a close eye on her for deficiencies, some varieties of cannabis get hungrier when flowering starts and are known as” heavy feeders”.  On the flip side of that, keep an eye out for “nutrient burn” (too much nutrients) because other varieties won’t need as much nutrient to keep them looking great.  Here are some quick notes about the macronutrients.  Remember to cut out all nutrient feedings the two weeks before harvest and give them water.   

  •  Nitrogen (N) –  The cannabis plant in flower uses less nitrogen since there isn’t a lot of vigorous growth happening.  The plant is growing flowers but it’s not building too many new branches, leaves and roots.  At this point the nitrogen is mostly being used for things like making chlorophyll for photosynthesis.  So don’t forget to dial back the Nitrogen when flowering starts.  
  • Phosphorus (P) is primary nutrient that is used in large amounts during the cannabis plants life cycle and is known as a mobile element.  It’s needed in photosynthesis because it helps the plant change the energy it gets from the sun into sugars.  These sugars will make the different chemical compounds used in root, leaf and stem growth, but it’s a vital part of dense bud development during flowering.    Phosphorus will also help the plant cope with the stress of drought, frost, pests, and disease easier.
  • Potassium (K) is another vital primary nutrient that a healthy cannabis plant will use throughout its lifecycle and is also essential for photosynthesis (the building of sugars).  It lets the plant metabolize (chemical digestion) those carbohydrates (sugars) to make different proteins and amino acids that are used in different plant processes.  Potassium helps carry water throughout the plant and this allows it to be less stressed during dry periods and improves the plants resistance against frost by working in the plants sap.  It will promote consistent, even and strong growth and when combined with Phosphorus it will also help strengthen the root system.   Potassium is needed during flowering to increase the density, weight and number of buds.

The Trichomes

     The trichomes are the oil filled glands that grow on the surface of the buds/flower and lower smaller leaves (sugar leaves).  These trichomes are where the cannabinoids like THC and CBD are made and housed.  This is also where the terpenes are made, which give cannabis it’s aroma and flavor.  The burning of the trichomes is what is giving us the euphoric effects of cannabis, NOT the bud/flower.  The bud only exists to give the trichomes a place to grow, that’s why we want to encourage big healthy bud growth. The bigger the bud, the more surface area for trichomes to grow which leads to a more potent harvest.  If you want more information about the anatomy of the “Trichomes” please visit the article I mentioned that was written by Mel Frank (      

Warning Signs

     It’s normal to see a few yellowing or dead leaves at the bottom of our plants.  Since those leaves aren’t producing a lot of energy because they get too much shade.  The plant senses them as dead weight and will let them die.  Once again, this is NORMAL,  it is NOT normal to see yellowing or drooping leaves this early.  That leaf death is usually seen at the end of week 7 or beginning of week 8.  Most likely it’s a sign of a deficiency or disease, whatever it is you need to move fast because it could affect your harvest.

The likely causes:     

  • PH – If your water PH is lower than 5.5 or higher than 7 it could be causing nutrients to be locked out or not absorbed.
  • Nutrient Deficiency –  Check your feed dosages if you’re feeding your plant bottled nutrients, you could be under or over feeding them.  If you’re using a “Super Soil” or enriched soil mix in a container, it could be depleted.  I use a liquid fish emulsion with kelp and molasses at half to a quarter strength.  The idea is to keep my plants well fed for the next couple of weeks without having nutrient build up just before the flush.  Different nutrients will show different symptoms of deficiency, so it’s a good idea to learn what they look like.   
  • Pest – Check your plant daily if you can, for any signs of pest pressure.  For example, chewed leaves or brown spots are some signs of caterpillars.  A small cluster of fine webbing could be signs of spider mites moving in to infest your cannabis flower.  .       

Pest control during the flowering stage

    Our plants are under constant attack by pests but as they move into flowering we’re going to have to pivot a little bit when we’re planning our IPM (integrated pest management).  During this stage I rely less on foliar sprays and more on biological predators to spearhead my IPM.  Here are a few reasons why:

  • Foliar Sprays – I don’t recommend using any kind of foliar spray during flowering.  It doesn’t matter if it’s for pest/pathogen control or supplemental nutrient feeding.  DON”T do it, you run the risk of introducing moisture into the bud and causing fungus to grow in that bud.  Which makes it smokable because you should NEVER SMOKE cannabis with fungus on it.  The trichomes and bud will also take on the taste of whatever you sprayed which could make your bud taste bad.   
  • Biological Predators – The two predators that I use for pest control when my cannabis plants are in flower are the Green Lacewings Larvae and Trichogramma Wasp.  The Green Lacewing Larvae is a great general predator that will actively hunt a large variety of softbody pests like the two spotted spider mite and boring mites.  The Trichogramma is a tiny parasitic wasp that helps control moth eggs that develop into damaging caterpillars.  These predators help break up the moth’s life cycle by laying its eggs inside the moth egg and preventing the moth egg from hatching into a caterpillar.  I also use nematodes to help control any soil dwelling pest also.    

Week 5-6

     By the time your cannabis plant is in week 5 of flower, it will start to look fuller, with a lot of  white hairs popping up everywhere indicating new bud growth.  When the plant gets thick or full looking, air circulation through the plant is important.  It helps the plant to breath and it helps moisture evaporate.  A lot of times as the plant grows, the big fan leaves will overlap each other in a thatching pattern.  This overlapping can cause moisture to hang out on the leaf surface longer and allow pathogens like powdery mildew to take hold.  If I notice 2 leaves overlapping more than a quarter of the leaf size, I’ll remove one of them.  You have to be careful not to take off too many leaves, the plants not making too many new ones and she still needs them for photosynthesis.  

     When your plant gets into week 6, there’s no denying it, she is in full flower mode.  The buds will look bigger and she’s going to start giving off a beautiful aroma.  You’ll notice a few of the older stigmas that used to be white, have turned an orange or brown color and may have shrunken back a little.  All of that is a normal part of the flowering/maturing process.  Sometimes at this point also buds could get too heavy for it’s branch and needs to be supported with a bamboo stake.  It sucks when a bud breaks the branch it’s on and isn’t able to fully mature.  It’s normal for the buds to put on noticeable hefft daily and look plump.           

Week 7

      If everything is going as planned by week 7 and 8 are the home stretch.  The cannabis plant looks green and healthy.  It’s been using almost all of its energy to build flowers and synthesize cannabinoids and terpenes.  She more than likely has taken on that classic “Christmas Tree” shape with buds looking like beautiful ornaments.  Plus the aroma of all those buds is bliss to a grower.   

Week 8 and the “Flush”

     The two weeks before a harvest is always an active time for the cannabis plant.  This is when I’m going to stop feeding her any nutrients and start the “Flush” by just giving her a lot of water. This “Flush” helps break up the nutrients and salts that may have built up in the soil or on the roots.  This will help your bud have a more honest, pure cannabis taste.  Otherwise, that flower could have a bit of a harsh, chemical taste when you smoke it.

    When I flush a plant, I want to water the plant until you see a lot of runoff coming from the bottom of the container.  I like to see the amount of runoff equal to the size of the container.   If I’m flushing a 3gal pot, I want to see about 3 gal of runoff.  For the next two weeks I’ll water her as needed and about 1gal of runoff is what I’m looking for.   

     The other thing I’m going to start to do two weeks before harvest is look at the trichomes everyday for signs of ripeness.         

Trichome Ripeness…It’s all about timing

     Some growers will judge the ripeness of a cannabis plant by the amount of stigmas that have turned from white to orange or brown color, I don’t.  I use a jeweler’s loupe or a magnifying glass to take a closer look at them.  As the trichomes ripen and mature they change color from clear/transparent (unripe), to milky/cloudy (ripe) to amber (over-ripe).  The tricky part is knowing the right time to harvest a plant.  I also have to remember that the trichomes will keep ripening after I cut her down and start the drying and curing process which should take at least three weeks.  If you want a more energetic high, harvest a little early, when the buds have more milky trichomes.  If you’re a fan of that classic couchlock feeling, you want to harvest a little later, when you have more amber trichomes.   

     A good rule that works for me when it’s harvest time is this: When I see about 30% amber trichomes, it’s time to cut her down and put her up to dry. 

NOTE:  Don’t forget, everyone’s growing conditions are different.  That 10 week flowering time is an average of what the breeder has seen, it may be sooner or take a little longer.

Week 9-10

     By week 9 that female is fattening up the buds, the trichomes are ripening and she’s smelling up the yard.  She knows the end is near and you’ll start to notice more yellowing, dying leaves, don’t panic, this is natural.  You’re doing great, she looks awesome, just keep her hydrated and pest free.  You may need to help support the branches that start to sag or buckle under the weight, I like to use bamboo stakes for this.  Week 9 is also when you should start to think about where you’re going to hang up this cannabis flower to dry after you cut her down.  For a first time home grower, the best spot to dry a small batch of cannabis is a closet in their home.  It’s temperature controlled and manageable size, but I’m getting ahead of myself.

     IT’S WEEK 10, HARVEST DAY.  You did it, that 10 week variety has just the right amount of amber trichomes for your liking.  Take some pictures and cut her down.  But ahhh, you still need to dry and cure that bud.  Could be another 4 weeks before you can truly enjoy your smoke.  I’ll share my best practices about drying and curing in a different article, keep an eye out for.   

    You know I love you very much and remember to Grow Learn and Teach.