Cannabis workbook: Indoor growing XXVI

Cannabis workbook: Indoor growing XXVI

By Adryc

Good morning friends of,

Welcome on board to resume our journey through indoor growing. This time we will start a comparison between two parallel crops, with same varieties and using white reflective layers in the grow boxes. On one of them we will use LED lighting and 2 MaxSpect R420R screens  –new model, still on trial, it needs 180 watts per screen, total 360w consumption. Creates, according to the manufacturers, a luminosity that equals 600w, but I’d say it’s more on the lines of 500w, as we saw in other chapters-, and another one of HPS 400w and Xtrasun luminaire.

Comparing LED and HPS 400W White reflective crops

The truth is, and we realized this in the last chapter, that the results were below our expectations. Although, for a first crop, using a new technique that we haven’t mastered yet (in fact we barely even know it), it wasn’t that bad. Now we have gathered information about the different parameters of light spectrum that we should use during the first phases of the plants’ life. I think now we should be able to grow our crop using LED and obtain similar results to the HPS crops, with the consequent savings on electricity.

Nothing better than to start a comparison between the two lighting systems, in the same climate conditions and using the same varieties. This way we can check every week how the plants develop under each light, and whether there are changes in size, etc. We will see if both systems are equally effective, that’s what we really want to find out.

But before we go on, let me say a couple of things about another matter we noticed days ago in this LED crop. One of the problems is the smaller size of the inferior branches. That really held down the productivity, and it might be due to the temperature difference between the upper part of the plant and the substrate. The LED screens produce less heat than the HPS, but it is not that big a difference. With the two fans that they incorporate, the upper part of the plant reaches 28ºC easily, while the substrate in normal conditions stays around 19-22ºC, and with that temperature difference, the middle bit will be in 23-24ºC, which causes the scarce development.

But every problem in life has a solution. I will tell you how to solve it further on, when I receive a wonderful new product that will save us lots of trouble in the future with temperature difference. We will talk about it in the next chapter. And now, without further ado, let’s start with the subject of interest.

Start of the crops

We started two alternative crops, each in its own HomeBox indoor tent, featuring white reflective inner layers, but in different measures, 100x100x200 HPS and 120x90x180 LED. We are going to grow in them three autoflowering varieties, 5 Critical, 4 AK47 and 4 Northern Light.


First step was getting the seeds ready to germinate on October 28th (previously, on the 27th, we placed them amongst wet cotton so they would settle in, temperature held to 4ºC. We put each strand in an individual container to ensure their traceability. We then placed them in a sprouter and the sprouter inside an indoor tent in the dark, with a relative humidity of 99% and 24º temperature.

On the 31st they had all germinated and we placed them in containers of 200cc with a substrate for propagation, starting said propagation with LED white light on November the 1st. We used a photoperiod of 16×8 hrs, as the temperature was adjusted to 26º with a relative humidity of 89%.


On the 7th the plants looked perfect and the roots had not appeared yet through the slits of the container. That’s the ideal state for transplanting the autoflowering strains. So we placed them in their definitive containers. This time, we used a strong substrate with numerous nutrients, the Top Crop Heavy substrate, in 7, 5 liter containers. Once we did that, we watered them with a light hummus tea to favor the rooting and placed each one in its definitive indoor tent, the 100x100x200 one. We placed three plants: 3 critical, 2 NL and 2 AK47 and we initiated the growing phase with a light period of 16x8hrs, HPS 400W, temperature 27,8º and 75% humidity.

We started the alternative crop in an indoor box of the same characteristics except for the LED lighting. We placed in this one 2 Critical, 1 NL and 1 AK47 in similar containers, together with a NL and AK47, these ones in 3 liter containers for a special test that I want to perform on them.

We used the same light period of 16×8 hrs with the two spectrum channels of the screens, A and B, set at 100% of the spectrum. The temperature in this tent was lower, 25,4º the first day. This sort of thing happens with this kind of lighting. That’s why I decided to turn on the lights for both boxes at the same time and turn them off also at the same time. This way the HPS compensates for the outside temperature, heating up the room and also, at the same time, it raises the temperature that the intractor introduces in the LED box and balances the temperature of both, to 27,5% maximum, almost perfect. On the other hand the minimum temperature on both crops have been 20,8%, because in the dark they keep the same temperature of the room.

At this point, in both crops the plants had received the same supplement of hummus tea, and no other supplement of any kind, until the day these pictures were taken: November the 18th. As you can see, all three strains have very similar size, homogeneous in both crops, and with an olive green color. “Guardia Civil green”, as I call it. That’s a symptom of the substrate having more than the necessary nutrients. Personally, I think these substrates are ideal for autoflowering varieties, because they will help us save money on fertilizers. Because of their structure and high water retention they hold reduced risks. But remember, “different strokes for different folks”.

I need to wrap it up (rule of space). As you can see in the pictures, no difference can be spotted yet between both lighting options. It is still too early to reach any conclusion, but soon enough we will be in the flowering phase. That is a critical phase in any crop. We‘ll see how they develop.

But that will happen next week, when I will show you how the plants look. You will be amazed.

And that’s it, friends, my loyal bong full of tasty Syrup is growing impatient, heheh.

Best of smokes from my cove and see you soon!

Bong to your health…



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