Skafidr's indoor pot grow log 2025 - science!

[Skafidr]

Let's do science!

I meant to start this at least a month ago but heh... it seems I was busy with something else.

I'm wondering two things:

1. Do my grow lights with my shelf suffice to produce a decent tobacco plant indoors ('Setup quality')?
2. What is the difference between sowing the seeds directly in the final pot compared to sowing them in smaller pot, then transferring to a bigger pot, then to the final pot ('Difference in planting methods')?

I'm about to grow two tobacco plants in pots.

Setup quality

I have two sunblaster lights that I used to keep succulent plants alive during the winter a couple of years ago. I also have a shelf that I can adjust the height of each shelf so the idea is to move the lights up as the plants grow.

The hypothesis is that at some point the light will not be sufficient for the plant, given that it'll only be coming from the top. Thus, the hypothesis is that my setup is not sufficient to grow tobacco plants indoors.

Difference in planting methods

I was wondering some time ago what would be the effect of directly sowing in the final container, and Bob suggested I test both approaches: plant directly in the final pot, and use the "classic" method of planting in smaller pots and upgrading pot size as the plant grows bigger. I understand that it is not relevant in the case of normal outdoor growing, but what about just planting inside?

The hypothesis is that planting directly in the final pot will allow a faster growth because, presumably, the transfer to bigger pot disturbs the growth.

The plan

Sow in final pot

• sow the seeds directly in the final pot
• once enough of them have grown, pluck the smallest ones
• repeat after a couple of weeks to keep only one
• take care of it until the end of the experiment

Sow in smaller pots

• sow the seeds in two pots
• once enough of them have grown, take a part of the roots and the soil and transfer it to a medium pot
• once it has grown enough, move the "best" plant from the medium pot to the final pot
• take care of it until the end of the experiment

In both cases, I'll spray water morning and evening to have the top soil wet. Once they have their leaves, a light schedule of 16/8. I'll also be using fertiliser eventually.

I may update the setup by adding a fan and Mylar to it, if I can.

Day 0, January 2nd 2025 (not the day I'm writing/posting this)

Setup

• Final pots: ~4L in volume
• Growing medium: a ratio of 4:0.75 of garden soil from last season : pumice
• Sowing medium: MiracleGro seed starting potting mix
• Sow in final pot:
  • the pot is not completely filled
  • the spot where the seeds are sowed, a tiny bit of seed starting mix has been placed
• Sow in small pots:
  • two pots are started, the "best" one will be moved to the final pot
  • ~1½" pots as the first step, ~5" pots as the second step, the final pots as the third step
  • the small pots are filled with seed starting mix
• A heat mat will rest on top of the "final pot", and the small pots will be placed on top of it; expectation: the heat mat will heat the seeds above and below
• The "small pots" are in a container with a transparent plastic cover, the "final pot" is covered by the heat mat; in both cases, it is presumed that this will suffice to keep the humidity
• Seeds: un-bagged "Turkish" (potentially crossed with Big Red Strong and Little Canadian and/or other plants from the neighbourhood which I'm unaware of) from my last season harvest

Note for the reader: I already have news for my next log entry which I'll create at a later time.

 

[Skafidr]

Day 4, January 6th 2025 (not the day I'm writing/posting this)

Leaves have come out of the seeds in the small pots, but not from the seeds in the final pot. I suppose the reasons why the final pot seeds have not come out include:

• It's dark
• The gap I left for air circulation (because I didn't want mold to grow there) makes it so that it becomes too dry

To fix this, I moved the smaller pots and the heat mat aside, and put a 100w lamp above the final pot with a kitchen plastic wrap to keep the humidity in and let the light go through.

 

[Skafidr]

Day 5, January 7th 2025 (not the day I'm writing/posting this)

The leaves of the seeds in the "final pot" have come out!

 

[Skafidr]

Day 6, January 8th 2025

It's alive! Just posting current state images.

I did not expect these to germinate so fast!

 

[Bottenslam]

These sunblaster lights, what W are they?

 

[Skafidr]

These sunblaster lights, what W are they?

Two sunblasters linked together:

• Model: SBLED36
• AC120V
• 60HZ
• 36W
• Maximum linkable units: 8

I no longer have the boxes but internet searches seems to indicate:

• colour temperature: 6400k
• Lumens: 3900

I'm no pro so I don't really know what this all means; the person who purchased them typically did a lot of research before buying and so I presume it was decent for helping cacti/succulents.

Thanks for reminding me about this, I should have included it in the opening post!

 

[deluxestogie]

I have zero understanding of the specific impact of lumens on tobacco growth, alkaloid production and leaf maturation. Direct sunlight, by the time it reaches the surface of Earth, may reach over 120,000 lumens at noon-time exposure in mid-latitudes, though much lower as the angle of the sun decreases (and zero lumens during the hours of darkness).

Bob

 

[ProZachJ]

Those lights are mostly designed for propagation as opposed to full cycle (vegetative + reproductive) growth. While I also don't know the specific light requirements of Tobacco like I do other plants I would guess that if you have varieties that grow to typical heights you will struggle with the effect of the inverse square law in getting adequate light intensity to the l middle and lower leaves of the plant. Again just extracting from my experiences with growing many other plants under artificial light, but I would guess that Tobacco would struggle to bring leaf to mature state if it isn't given the energy needed for full reproductive growth phase.

Not saying the plants won't grow, or that the leaf will be bad, just that it may not be quite the same as leaf grown outdoor or under much higher intensity lights like those used for indoor production of other well known smokeables.

The only way to know for sure is to try it, given there is precious little information on the interwebs about the required PAR levels and effect on various quality factors for Tobacco.

 

[ProZachJ]

https://acsess.onlinelibrary.wiley.com/doi/abs/10.2134/agronj1978.00021962007000040009x

There was a consistent reduction in growth when PAR was reduced to 11.4 E m−2day−1, although the differences were seldom significant.

In the comparisons of leaf weight and area growth between field and phytotron-grown plants, growth of leaves was generally enhanced, though usually not to significant levels, for full sunlight. However, growth at the maximum growth room PAR of 25.0 E m−2day−1 tended to be greater than at 24.9 E m−2day−1 for the shaded field plots. Leaf growth at the lowest growth room PAR of 11.4 E m−2day−1 was nearly identical to that in the shaded plots

Some quick conversion math reveals that the lower threshold level mentioned is around 150 umol m-2/s-1 which those lights should be capable of producing at 18"-24"....so science says I'm probably wrong in my previous post!

 

[Skafidr]

I would guess that Tobacco would struggle to bring leaf to mature state if it isn't given the energy needed for full reproductive growth phase

he only way to know for sure is to try it

That's what I presume: the tobacco will not be able to grow correctly because the lights, at some point, will be too far away and/or blocked by the upper leaves; and as you say, I want to see it for myself!

Your second message got me into a nerd hole. I was not familiar with all of this so I searched a bit and had trouble figuring out what the E was in that article you linked. Thanks to Wikipedia, I found out they're "Einsteins", and are no longer in use today. According to another source, they translate directly to moles.

Could you tell me how you get to 150 µmol m^-2 s^-1? The conversion factor I have is 10^6/(24*60*60), which would give 131.94. Not that it matters much at this point (I'm not here to prove anyone wrong, except myself )

From that I found yet another source giving how much "PAR" one gets per Lumens at a distance ((Lumens * 0.0185)/Distance^2) (plus the chatbot says "between 0.015 and 0.020", so 0.0185 is likely "an average"). So I plugged that into excel to see what distances those values represented, given that I had 3900 Lumens lamps

Old (E m−2day−1)	mol m-2day-1	μmol m-2day-1	New (μmol m-2s-1)		dist [0.015] (m)	dist [0.015] (in)	dist [0.0185] (m)	dist [0.0185] (in)	dist [0.02] (m)	dist [0.02] (in)
11.40​	11.40​	11400000​	131.94​		0.67​	26.21​	0.74​	29.11​	0.77​	30.27​
17.90​	17.90​	17900000​	207.18​		0.53​	20.92​	0.59​	23.23​	0.61​	24.16​
24.90​	24.90​	24900000​	288.19​		0.45​	17.74​	0.50​	19.70​	0.52​	20.48​
25.00​	25.00​	25000000​	289.35​		0.45​	17.70​	0.50​	19.66​	0.52​	20.44​
42.20​	42.20​	42200000​	488.43​		0.35​	13.63​	0.38​	15.13​	0.40​	15.73​

The "old" column contains the values from the abstract, in E, the New column holds the converted E values to "modern" notation. The "dist" columns represent the distances, for the value in Old, at which I'd get those PAR values.

Looks like I get to the same conclusion as you did: given that all of this are rough estimates, ~24" would likely be the max distance a light is efficient.

Now this is for only one light, and I have two, so I suppose those values would be increased a bit, but I don't expect that doubling the Lumens because I double the light fixtures doubles the effects (or extend the effects much futher).

I'd like to reiterate that I'm not an expert here and all of this has been gathered from what I read since yesterday.

Thanks for sparking that! Feel free correct any of my assumptions.

I have zero understanding of the specific impact of lumens on tobacco growth, alkaloid production and leaf maturation. Direct sunlight, by the time it reaches the surface of Earth, may reach over 120,000 lumens at noon-time exposure in mid-latitudes, though much lower as the angle of the sun decreases (and zero lumens during the hours of darkness).

Bob

I don't have a clue either about the specifics; I think the Lumens are associated to the actual photons, the PAR mentioned previously being associated with a specific range of wavelengths, influencing the "energy per photon" and "quantity of photons". Associated to that is the colour temperature of the light which influences things in the plants, but I don't know either what they influence. Those lights are bright, they nearly light up the whole room decently when it's dark outside! I don't mind not having a great quality of tobacco from those test subjects.

 

[ProZachJ]

Awesome nerding here! I think your calculations look correct.

E m-2day-1 vs umol m-2s-1

The former is not so much antiquated as it is a product of what light source is being measured. It is typically used in outdoor settings to account (average over) for the difference in intensity throughout a day due to angle of incidence, clouds, etc. The meter type used here will keep a running sum. Whereas the latter is preferred for artificial light because an instantaneous measure can accurately be multiplied over the lighting cycle to arrive at totals.

I also got 131.9, I just rounded the requirement up to 150 give a little margin and because I have good feel for PAR levels of 150, 300, 600 etc.

Since I have a lot of experience testing a wide variety of LED lights, I've gotten a good sense of what PAR will be at various distances based on whatever poor (for horticulture) specs a manufacturer chooses to use. I particularly despise when a light supposedly designed for plants gives its specs in color temperature and lumens.

Your average for lumen to PAR conversion is probably functional but exact figures will indeed depend on the precise spectrogram of the light. The trouble with color temperature is that two lights can have the same color temperature but different light curves. Both lumens and color temperature (as measured for artificial lights, not as defined by "pure" black body radiation) are based on scales calibrated in some way by perception and aggregation. Lumens particularly is human eye perception based, which is why it is a great measure when talking about lighting a room for people. However it is entirely possible for a light to seems crazy bright to the eye, but be fairly useless for photosynthesis or visa versa.

Two lights will increase the PAR when they are in the same source location, but it is more likely in practice that the majority of the energy will be applied in increasing the coverage footprint at or near the single light level.

 

[Skafidr]

Okay, thanks for the reply, nice info here!

supposedly designed for plants gives its specs in color temperature and lumens.

What would one be looking for, instead of Lumens and colour temperature?

 

[ProZachJ]

Okay, thanks for the reply, nice info here!



What would one be looking for, instead of Lumens and colour temperature?

Something that most often doesn't exist unless you buy commercial horticultural lights...a PAR at distance chart! However retail sellers/manufacturers are either too skeezy or lazy to provide such numbers. They get away with it because many indoor growers are used to using these bad units from the incandescent and florescent days.

 

[deluxestogie]

Ouch! This discussion is stirring-up PTSD from physics and math classes I "enjoyed" in the late 1960s. It seems applicable to some astrobiology speculations I've recently read.

Bob

 

[Skafidr]

unless you buy commercial horticultural lights...a PAR at distance chart!

Well now I hope I don't have to buy grow lights anytime soon the wallet will take a hit hehe!

 

[ProZachJ]

Ouch! This discussion is stirring-up PTSD from physics and math classes I "enjoyed" in the late 1960s. It seems applicable to some astrobiology speculations I've recently read.

Bob

Sorry @deluxestogie

Before owning any land, and when most indoor growers thought LED grow lights were a scam, I spent years obsessed with this stuff. Now that the knowledge and experience is mostly irrelevant to my personal growing pursuits, I get all excited when I can at least share it with others.

 

[ProZachJ]

Well now I hope I don't have to buy grow lights anytime soon the wallet will take a hit hehe!

Luckily, you can find good lights at decent value on the retail market these days, you just have to research and remember that you almost always get what you pay for and no more.

 

[Skafidr]

Ouch! This discussion is stirring-up PTSD from physics and math classes I "enjoyed" in the late 1960s. It seems applicable to some astrobiology speculations I've recently read.

Bob

Fortunately, I can limit head hurting to only one evening with this stuff! I found myself fortunate enough to be able to understand the basics, though (thanks to high school classes).

Regarding astrobiology, are you meaning that photons had influence on how life developed/develops out there?

 

[Skafidr]

Luckily, you can find good lights at decent value on the retail market these days, you just have to research and remember that you almost always get what you pay for and no more.

I think I remember those I have now were not cheap. We'll see how it goes in a month or two!

 

[johnny108]

Sorry @deluxestogie

Before owning any land, and when most indoor growers thought LED grow lights were a scam, I spent years obsessed with this stuff. Now that the knowledge and experience is mostly irrelevant to my personal growing pursuits, I get all excited when I can at least share it with others.

I worked in a hydroponic shop in the late 90’s: I know all about the metal halide, and high pressure sodium lights, which were power hogs.
Still trying to figure out LEDs….