How is understanding changes made to your garden useless? I agree, it’s useless to compare to others and it’s only part of the equation, but it’s extremely useful information for a grower. But growing the most weed you can from your garden is not everybody’s goal, some people want to look at fuzzy hairs.
See, I knew it would get some push back
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Im not interested in getting into a fight, but here are a few points to consider:
1) Watts from the wall or actually reaching the plant or from the label on the fixture?
2) What about efficiency - LED vrs CMS, HID, etc Big differences here.
3) Distance from the light to the canopy = inverse square law.
4) oops - skip this one - different metric
5) Are we talking average watts over the life of the grow or peak watts used in flower or fixture label watts? I dim my lights to different levels depending on growth stage - and it changes with each grow/strain. Plus I raise and lower the lights depending on canopy heights.
7) Are you growing 12/12 or 18/6 or 24/0? How long in each stage if you change from veg to flower?
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Genetics - some strains handle more light, some less. You can have the exact same lights, nutes etc and two different strains will produce wildly different yields.
9) The secrete to huge gms/watt numbers is to just veg longer. Thats all it takes. Veg 3 months instead of 1 month, and your plants will be much larger and you will have huge gm/watt numbers.
10) There are more, but thats plenty
As you said - most of that has to do with not being able to compare grows from different people - but there is still reason why its not useful for your own personal tracking.
#9 is the one that really kills gm/watt for me. Just grow veg longer - without changing anything else - and you will get some trees, and your gm/watt numbers will be insane.
I managed a solid 5 gm/watt (depending on how you measure it) just by vegging for 3 months one time. I ended up with a single surviving plant in my tent (males), and wanted to really fill up my scrog screen, so I kept vegging until I did. Ended up with 1200 gms dry.
My lights were never turned up over 250 watts in flower, and were kept to under 80 early to 200 max late during veg. So if you take the average watts - call it 225 even though it was actually lower - that works out to 1200/225 = 5.3 gm/watt. Or take my peak watts 1200/250 = 4.8. Or take the label watts on my driver 1200/320 = 3.75 - which is still a very big number for gm/watt.
I decided that the only metric that makes sense for me is grams of dry yield per day of growing. If I yield 1000 grams dried, and it takes 150 days, thats 6.6 grams per day of growing time. My cost per day doesnt change much from one grow to the next. The only significant variable is the time it takes to get from seed to harvest.
Having a huge harvest isnt all that great if it takes months to get there. I find I get more grams per day of growing fast, small autos than I do from photo period plants that have larger yields, but take much longer to finish.
When I was growing in soil I averaged around 4-5 gms per day. When I switched to hydro I went up to the 5 to 6 gm/day range. Now that Im growing using aero Im in the 7 gm/day range.
That grow with the big yield - my largest harvest - took over almost 6 months so 1200/174 = 6.8 gm/day. Even though that was my largest harvest, that wasnt my best gm/day by a good bit. I grew three autos and managed 7.7 gm/day over just under 3 months. But the gm/watt on that auto grow looked like crap in comparison. I had about 700 grams dry for the same 320 watt fixture, so my gm/watt number was less than half for a grow that actually netted me more meds.