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How To Flower Cannabis Plants With LED Grow Lights


Flower with LED grow lightsBy Ethan Grow

Many people contend that LED hydroponic grow lights work well during the vegetative stage but not when it comes to flowering. This misconception will become a self fulfilling prophecy if you do not know how to use the technology. Follow these cannabis flowering tips to have a successful grow.

The first thing to remember is that when you are growing indoors, your plants do not have environmental feedback telling them which season it is and what they are supposed to do. You have to tell your plants what season it is and the way to do it is with your lighting. In an outdoor setting, cannabis plants flower in the fall when days become shorter, the sun is lower in the sky and plants are signaled that the annual life cycle is coming to an end. After about 8 weeks of vegetative growth you have to mimic this change in the day cycle. Your light schedule should be changed from 18 hours light to 12 hours light and 12 hours dark. Along with the change in the amount of time the light is on, you must also change the amount of red wavelengths the plants get. This is very easy to do with LED grow lights. All you need to do is add a LED with a high ratio of red wavelengths or all red wavelengths.

Some indoor hydroponic LED grow lights have been designed to work for both vegetative stage and flowering. These LED grow lamps will give you maximum intensity during your entire grow season. The trick is to ADD more red wavelengths when it is time to flower. Doing so will help the plant think that it is autumn and the sun is lower in the sky with more red hues. This will kick off the coveted flowering stage! A 90 Watt All Red UFO light is an ideal and inexpensive choice for getting the added red wavelengths needed. You should add one of these All Red LEDs to each light setup you have. Within a couple days of adding the UFO, you will see your plants go through another growth spurt and start the flowering process.

Another option is to switch from a Veg + Flower light to a BLOOM only light which will have a higher ratio of red vs. blue wavelengths. If this is your preferred method, you will get the most grow area coverage by having a vegging station and a flowering station, each with a designated grow light.

There are also LEDs which have a switch where you can switch on and off the blues and reds. With these grow lights you turn on half the (blue) diodes for vegetative stage and then turn on the red diodes in addition to the blue when you get to flowering. Although this method works, the drawback is that you are growing with half the intensity of the light and hence can grow less than if you had the entire intensity of all the diodes. An All Red LED grow light is always the ideal growlight to add when it is time to flower. However, you can also add HPS or CFL white lights which will have the red wavelengths.

Once you have helped your plants to start flowering, you can maximize your yield by understanding the growth process. During the flowering phase leaf growth slows and flowers start to form after one to three weeks. Fuzzy, white hairs called pistils start to grow. The pistils are attached to the light green pods called calyxes. The calyxes, full of the hair like pistils form dense clusters of buds along the stems of the plant. The buds will continue to swell and produce a resin like material called trichomes in the first four to five weeks of flowering, after which they grow at a slower rate.

The trichome resin glands are in the early stages of formation

The trichome resin glands are in the early stages of formation


Trichomes are milky white & amber and ready to be harvested

Trichomes are milky white & amber and ready to be harvested

Trichomes are granular and are comprised of a stalk with a resin head bulb. It is the trichomes that we seek and we must let them flourish before harvesting. When the trichome resin glands are in the early stages of formation they will be clear. You should harvest when the trichomes start to turn milky white to amber for the most potent THC. This should happen around the sixth week of flowering but depending on the strain of plant you are growing, it could take more time. Once your trichomes have turned milky white to an amber red color, it is time to harvest your plants! Let the plants hang to dry for 3-4 days in a dark room to avoid change of color from light. Follow these tips and you will have successful grows with your LED grow lights!


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  1. I’m currently running 2 300w full spectrum generic LEDs in my 4×4 shower lol yea my shower! The plants 4 2gdp 2 gsc in 5 gal pots are doing amazingly well I live in the desert where it’s 100 plus daily I keep the air flowing in the bath n keep the exhaust fan going and the plants are vegging well!! 2 300w LEDs 100$

  2. Hi I read what you should do if you have an led light with veg and bloom switches but my light has three switches… one for white, or for blue and one for red. Would I keep the white light on for all three months?

  3. Yes, here’s the idea, in the first month your plants are just starting out they need soft lighting and lots of blues to get going you want a 18 hour on and 6 hours off light cycle, in the second and third month you put both on so that they get nice and big and as soon as the second month hits you switch the light cycle to 12 hours on 12 hours off, this will make the plant get nice and big and start to flower, but at this point since its still growing and flowering you want both the lights on, now in month four your plant is as big as it’s going to be and it’s budding so you want to give it full red lights and infrared, that way the buds grow as big as they can and since the plant is no longer growing just the buds getting bigger there is no need for blue waves.

  4. What you want to do is the following, for the first month use only growth, that will give you a very bluish light with some other minor colors but gentle wavelengths for the fragile first part of the growth cycle, then you want to switch both of them on for the next 1-2 month’s depending on when your plant will end its flowering, and then for the last month turn off the growth setting and leave only the bloom, people think that it’s less light but in reality the light that there is less of the plant doesn’t use in flowering so actually you aren’t getting rid of anything what most bloom phases have is when they are turned on they will give u an all red light with some infrared lights(they look like dim lights to the naked eye). The more infrared lights the better the plant does, although most manufacturers only put 2 in there max, but with the all red light wavelengths you should be good.

  5. Quick question, I have a 450 watt grow light with the 2 switches on it that says “Growth” “Bloom”. During the flowering stage do i turn on both or just leave the bloom switch on for just red hues only? Sorry new to this and feedback would help. thx

  6. Today a 10 watt LED at 730nm is used to trigger Flowering. This will cover a 8ftx8ft area. Run for 15 min. after lights out and the Plants go right to that deep sleep needed for this period of growth.. But now you have just re programmed the Plant for 10 hour of sleep instead of the 12hr.. Yep and she will stay in Flower until the end for a much greater yield..It works and works well for both indoor and out grows..

  7. Jethro Clampett on

    Improbable that someone like Klaus would utter a know it all statement like joker above. Speak from experience or shut your pie hole.

  8. RVF Garden Supply is the source for all of your indoor gardening needs. We can cover you from start to finish, from containers and growing mediums such as high quality soil or hydroponic systems, to PH testers, Grow Lights and Portable Grow Tents- all items specifically offered with the home grower in mind.

  9. Depends on many factors – how much weed you need – how much space you have to grow – how stealthy you have to be in your grow. We just got done with a stealth grow – 104 watts of LED lamps (8x13w) that produced and finished 3 plants at 29g, 35g, and 48g dried weight. 4 oz off 104 watts. More than enough to last us 6 months of non stop vaping. We don’t do blunts or dabs obviously. That was our first grow in soil too.

  10. I’ll take a High Pressure Sodium Lamp any day. Give it ten years for this to improve in technology…

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