Why are my marijuana plants growing so slowly

I planted three tutankhamun plants over a month ago and all the plants are from 4 inches to 6 inches tall. Two are very bushy, one isn’t. I started with two 12 inch pots and one 8 inch pot in a 2 foot by 3 foot metal closet I had painted flat white. I added a 1000 watt LED light that has all the light bands, including infrared and uv. When I started, I had the light approx 1 1/2 feet from the plants, and have since raised it to over two feet to try to coax them to grow higher, but to no avail. I am not really giving them any fertilizer. Once in a while I will give them the three part PH Perfect fertilizer, but have been giving them Super Thrive, a growth formula with B1. I just dug one up yesterday because the leaves are now turning yellow at the tips on all the plants, but the leaves themselves are a medium to dark green. I am using 40 hours on and 8 hours off, switching the lights from the timer to the plug directly. I have been using the defoliation method and once in a while, take some of the fan leaves so the leaves underneath will get light. That is why they seem to be getting thick. Why are the plants taking so long to grow and are growing so slowly? Also, why are the tips of the plants yellow while the leaves themselves are green? Can anyone help?

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First off welcome to the forum @vinnya
Ok first off switch lights to 18 on 6 off
nowhere on the plant will you get 40 hours of sun per day
And stop pulling off the leaves
Sounds to me like your stressing them out to much
Why did you dig the one plant up ?
Can you post a picture
It will help me help you
Also the first 3-4 weeks the plants have slower upward growth as they work on there foundation ie the roots


Ok, let’s start with why I am using the 40/8 method. The plants themselves consider one day 18 to 21 hours, right? Well, by extending it to 40 hours, the plants have longer light cycle which should make them grow more. It doesn’t hurt them, they still are very green, they just aren’t growing fast at all. Defoliation is suppose to work. But maybe you are right. Maybe I should wait until they are bigger, but the only problem with that is, WHEN? The last time I planted, I had a four month grow cycle and they wound up being about 21 inches tall. Now what I want to know is, how do I speed up the cycle? How do I make them grow faster? Like I said, I have a 1000 watt LED light, which is more than enough for three plants. They should be over one foot by now. Do you think it is the light? I was using cfls before that and it totaled about 1800 watts, with the same results. There has got to be a way to speed up growth. Also, why are the tips of my plants, all of them, yellow, while the leaves themselves are medium to deep green? I hardly fertilize them. This has become an ongoing problem and I don’t know what to do. I’ve enclosed some pics, including the closet, light and plants, including the size, next to a tape measure. The first pic is of the closet and light. The second and third, top and side views of one of the girls in the 12 inch pot. The forth and fifth are top and side views of the second girl in a 12 inch pot. The sixth and seventh are top and side views of the girl in an 8 inch pot. The others are side views with the tape measure so you can see their exact height.You can see they actually look very healthy, except for the slight yellowing of the ends of the leaves. Let me know what you think.

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@vinnya they aren’t growing because they are in an unnatural light pattern. They will grow much faster if they can get some darkness, every day. Switch them to 16/8 for a week and see what happens. If we are wrong you can switch them back to your light pattern.

COPY/PASTE: This “Support Ticket” into your forum post.
Answer these simple questions the best you can.
If you do not know, or do not use something; Just say so = NA

Strain; Type, Bag seed, ILGM… name of strain:

Age from Sprout:

Soil in pots, Hydroponic, or Coco / Brand and type of Soil & Size of Pots:

How often do you water and how do you determine when to do so?

PH of water and runoff or solution in reservoir:

What is strength of nutrient mix? EC, or TDS:

Indoor or Outdoor:

Light system, size and height from plants:

Temps; Day, Night:

Humidity; Day, Night:

Ventilation system; Yes, No, Size:

AC, Humidifier, De-humidifier:

Co2; Yes, No:

Add anything else you feel would help us give you a most informed answer. Feel free to elaborate, but short, to the point questions and facts will help us help you

Also here is a Deficiencies & Excesses Chart to help you identify what is wrong with your plants




They need sleep time so to speak, they do a lot of growing when lights are out @vinnya these guys know and can help you for sure imho, 18/6 is best


I don’t know. I heard of someone using 30/8 and his plants were fine. Are you sure? Can it be something else, like the light or the fact I am defoliating the plant?

From my limited experience, everything I have ever read is 18/6 for photo period plants… my last grow I did 14/10 and my photos went into flower before I wanted them too… my next grow is gonna be 18/6… then when I want to flower, ill go 14/10 for a week maybe 2, then 12/12… like @bob31 said, try it and you can always go back… but from a biological standpoint, plants need dark… a lot of biological functions are happening when lights are out… just like people, we need rest to function… good luck!:+1:… defoliating when the plants are young is probably not a good idea, wait until they are stronger and heartier… and even then, you don’t want to defoliate too much, leaves are important for photosynthesis and again, the biological functions of plants… imho


could be anything… fill out the support ticket so we can stop guessing and try and help you with educated answers


I agree with @Countryboyjvd1971. In my experience plants do most of their growing in the dark. I’m not a plant whisperer or anything, but if you look at the photosynthetic process it makes sense. I bet there’s even some time lapse videos on YouTube that will support.

Not saying 30-40 hours of straight light won’t grow a plant, but I bet not at same rate as something like 18/6 or 20/4. There’s always the thought that you shouldn’t want to run your lights anymore than needed too. Energy cost and life expectancy should tell you that.


They ARE getting eight hours of dark after 40 hours of light.


Please forgive me for being a bit blunt but if there weren’t some issues to begin with you wouldn’t be here asking questions. Questions are GOOD! We are all hobbyist growers (except for our Mods) and have a lot to learn. :grin:

That said: your plants are small because they are on an unnatural light cycle. In effect, they’ve gotten roughly 1 weeks worth of night cycle instead of a month. Much of the growth occurs in darkness when nutrients are transported to the roots for use by the plant.

These guys know what they’re talking about. 18/6 or 16/8 is where you want to be. I use 16/8 myself.


Put your plants on 18/6 and stop pulling leaves off.

We KNOW 18/6 works and we KNOW the leaves are your solar panels that convert all that light into growth.

If I’m reading your post correctly, you have not yet succeeded in growing a normal, full sized plant. So, I urge you to use proven methods until you get a plant to grow right. Then you can experiment with alternative methods.

And 6 inch plant don’t need defoliating under any circumstance.

Good luck with your growing!


I forgot about the leaves, thank you @PhantomFarmer!


The lights being on 40 hrs is too long… would you like to be up 40 hrs before you had 8 hrs sleep? You and I wouldn’t function too well with that schedule… fill out the support ticket and these guys will provide sound info. @vinnya

  1. The strain is feminized tutankhamun grown from seeds
  2. Approximate age is about 6 weeks
  3. Pots. 2-12" pots, plastic. One 8 inch pot, clay.
    Soil- 1-12" pot (on left in pic) and 8" pot use 1/2 Sunshine naturally organic planting mix, 1/2 Bumper Crop organic soil builder with fungus, topped with about 1/4 inch of Happy Frog soil. 1-12" pot (on right in pic) is 1/2 Happy Frog (also with fungus) and 1/2 Sunshine naturally organic planting mix and Bumper Crop organic soil builder with fungus.
  4. I water every two to three days, depending on how dry the soil is. I usually test it by sticking my finger down as far as it will go to determine wetness of soil. I use a pint container to water all three plants. Since the LED light does not produce much heat, I found it better to give it less water than more since I have had problems with root rot before.
  5. The last time I checked the PH, which was yesterday, it was 6.3.
  6. I really do not fertilize the plants too much since they are too small, so I use a capful of Super Thrive, which contains Vitamin B1 for the root system, and kelp, along with a very light fertilizing I did last about a week ago, using 2 of 3 parts of PH Perfect (nitrogen part, I ran out of the bloom portion), a half a teaspoon of (half of the small scoop) of Miracle grow(to replace the potash and phosphate missing, along with zinc, boron, copper manganese and molybdenum, and iron missing). I usually use a tablespoon of blackstrap molasses as well to stimulate the healthy bacteria in the soil, but I haven’t use that in the last couple of days since the ends of the leaves started to turn yellow, despite the fact the leaves themselves are a medium green.
  7. They are indoor plants (see pics above for more info)
  8. Light system is a 1000 watt LED light that has the full spectrum, including UV and Infrared. I had it about a foot and a half above the plants, then moved the light to about two feet above the plants to stimulate them to stretch more.
  9. Daytime temps vary from 85 degrees F with the door closed to about 74 degrees F with the doors open. Night time temps are around 70 degrees or a couple of degrees less.
  10. Yes, AC in the spring, summer, fall and into part of the winter, depending on how warm it is outside. I live in a basement, so I use the AC to take out the moisture and dust from the air. No humidifier. Not necessary since the basement is already pretty damp.
  11. No C02. I tried that with my other plants by using vinegar and baking soda, but it didn’t do enough.
    Final comments
    I have had these problems before when I was using 1800 watts of cfl lights. They just seem to perform poorly and I have to extend the grow cycle to about 4 months, and the flowering time is also extended by a couple of weeks, and I NEVER finished the plant completely. The trichomes would not completely develop and the smell would not be there also. I grew blueberry for that exact reason, for the taste and smell but that never happened as well. It was pretty good, probably about 18 percent thc, but not as good as it should be. I usually get about 2 1/2 to 3 ounces per three plants, which isn’t very good also.
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Thanks for doing the Support Ticket

How many gallons would you say the 8 and 12 inch pots hold? @vinnya

We recommend a 5 gallon pot for a photoperiod indoors. I’m thinking right off the bat that those pots are pretty small and your plants are probably root bound.

When you water plants they should be watered until they produce runoff. Do you have holes in those pots to allow proper drainage? My plants were taking over a gallon of water 2x a week at that age.

How are you checking your pH? Can you post an amazon link or take a pic of your meter?

Happy Frog is an organic nutrient enriched soil (Which I highly recommend)

The sunshine planting mix is

Canadian Sphagnum Peat Moss
Composted or Aged Bark
Bark and/or Other Forest Products
Earthworm Castings
Seafood & Shrimp Meal Compost

Have you ever done a slurry test to see what pH this mix would pH to?


@bob31 beat me to pot size. You have to use some trickery to use pots 3 gallon or less well. If you’ve had them in 12” pots the whole time I’d guess half your problem is they are/were spending a lot of time expanding roots, which generally is period of slow plant growth. It’s usually better to start them in something small like a party cup and then transplant to 3-5 gallon.

Light cycle is going to be another if not the biggest factor. We’ve already covered that. Also probably a reason you had trouble with the cfl. What is the actual power draw or model of your led? It’s probably not 1000 Watts, so that will tell us more.

As far as feedings go, it likely wasn’t the molasses that caused your burnt tips. Probably the miracle grow. Being consistent with what you’re using to feed and how you’re applying will make your life a lot easier and your plant a lot more healthy.


I was gonna ask you to talk about the lights @dbrn32 thanks for jumping in. @vinnya gonna be growing BOM contenders here before you know it!

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I wouldn’t be surprised if you over fertilized a bit. The medium you’re using had some nutrients anyway and then you added something.

Looks like you’re well on the way to bigger, better plants.


If you can’t beat them, may as well join them right?!