Expected yield with this setup

Well, ideally you should be able to get at least 1gram/watt. Let's even say .5gram/watt, that's still 900grams. Two pounds.

 

especially with that 1000 HPS, I would ballpark at
 
least 1.5-2 pounds, but that could increase with a
 
number of variables such as pot size, LST, sog/SCROGing,
 
soil and fans, etc.

 

 
LST - Low Stress Training
 
SOG /SCROG - Sea Of Green / Screen of Green

 

 
Experienced growers will tell you that each method
 
will increase yield, please click the links I have provided
 
for you, they have easy to follow examples.

 

I'd argue their estimates of "1 to 2 pounds", as a gram a watt is a rule of thumb that applies only if your footprint is enough to be delivering equal wattage to each plant.


1000 watts HID in an area big enough for 20 mature plants that haven't been constrained is nowhere NEAR sufficient. I barely get enough lumens from 2kW in a 5 by 10 tent, at the edges. That fits 10 plants grown too close together for ideal.

I use the Bigfoot ducted hoods for mine, which are designed with a large footprint (they claim it's the largest footprint hood on the market), yet one of them is barely sufficient to pull recommended light intensity for half the tent, if I drop it to proper levels above the plants...and if you keep the light high enough it DOES have the coverage to get the whole floor, the light intensity at the plants is too low.


I DO however, have to cheer you on using the LED boosters...alone, I've found LED doesn't have the penetration, but coupled with other light sources, it makes the plants happy, happy, happy. My own setup is 2kW HID, and a Solar Flare 220 full spectrum, plus 80 watts of reptile UVA/UVB lights. This one's my first grow where I'm doing it in a tall enough tent to not have to dwarf my plants through manicuring...I WAS running a 4' by 4' indoors with the LED and 1kW HID, bushing them out to 2 by 2 each, then letting them grow to 24 to 30 inches before flowering (only had 6 feet of headspace, and use the same Home Depot buckets you do, which are 18 inches tall)...but was yielding an ounce to an ounce and a half of HIGH quality off each plant doing that. A little more than a QP).

Now look at that, and do the math...1200 true watts, 1400-1600 effective watts to produce somewhere near the proper amount of light in the footprint to mimic sunlight, plants manicured, so there were MANY more colas than a full height plant will usually have, even if the buds are a bit smaller...and I got under 11 grams per sq foot consistently (100 grams per sq meter). Granted, it was good enough that what I didn't keep for myself was purchased for personal use by the manager of my dispensary, instead of going on the shelf.

That's 1400-1600 effective watts on a 16 sq foot footprint. And STILL delivering far less light than natural sunlight. But at least it was consistent light levels to all plants.

If you let your plants get to full height, you MIGHT see about that yield off each plant, on average, since your "edge plants" won't be getting near enough light energy, though the ones under direct light will get enough to deliver 4-5 times more than my "dwarfs".

Remember, light is energy...without enough light, they can't convert nutrients to sugars, so they can't grow energetically and at full health...your edge plants will be getting far less "food" as if they're a human kid with a metabolic issue that denies them the ability to properly uptake and use nutrients....smaller, more sickly, less robust.

"Watt per gram" only applies if every watt worth of light reaches a plant efficiently.

 

A pound to 1-1/4, too many small plants in the area for large yields.  Four plants would give a better yield in this space than 20 crowded small plants.
 
PW

 

Depending on other conditions, I'd estimate that if you were VERY careful and attentive, got everything else right on the money, turned plants daily, "swapped positions" twice a week, so the edge ones were central, and central were moved to the edges, each spending half the week under "the best lighting"...probably close to 150 grams per sq meter of plant footprint...so a fully mature bushed out group of plants COULD blow their estimates out of the water....but far more likely, due to lack of enough light intensity, you're looking at, even if all else was done perfectly, closer to 75-100 grams per sq meter of plant footprint.

What bugs me about it is that if you had the right light intensity, enough headroom to go for full growth, topped them properly, bushed them properly, you could top 7 pounds out of 20 plants, and WOULD top 4, no ifs, ands, or buts. I know you hear "1 gram per watt" and "4 to 6 ounces a plant" all the time, but if you actually look into the pro growers' discussions here and there, especially regarding strain differences, you'll find that under ideal conditions, most strains put out between 250 and 400 grams per square meter of plant footprint at full adulthood on an indoor grow. Since a fully grown plant in good health, well tended, will take up a 3' by 3' chunk of floor space, if you assume perfect roundness, each plant is 80% of a sq meter...which, with 20 plants, works out to 8.9 pounds at the low end, if done PERFECTLY.

But you need the equivalent of at least 4kW in light, positioned properly to do anywhere near that, and, in order to do it, you need more...to mimic a nice sunny Humboldt County, CA midsummer day...if the light meter readings I get in my tent are any indication, that means actually running about 6400 watts equivalency, doing some UV and LED supplimentation (assuming you lay them out in 4 rows of 5, "offset").

BTW, even those numbers are lower than an outdoor grow in a good area, where the average is 350-600 grams per sq meter of plant footprint.

Outrageous, isn't it? But to prove the last, look up the family from outside Olympia, WA on trial right now...72 legal plants between the 5 of them, and their last yield was seized just after drying...over 50 pounds. Which works out to around 12 oz per plant (336 grams)...and that's a CRAP area to grow anything but high desert grasses, with a fairly short "good season".

 

Dry weight is based on light output. Another factor would be your experience at growing.  The benchmark is .5g per watt of light every 30 days (.5 x w/30).  This doesnt come from discussions,  this comes from published expert grower Jorge cervantes (which has been peer reviewed by true experts and is considered the indoor bible)  out of his book,  Indoor Marijuana Horticulture.   I wouldnt try going up higher with lights.  Light loses lumens exponentially as it gets farther away(also explained in his book).  Normal size for indoor plants is 3-4' tall,  you start losing to much light when lights are placed more than 5' high(the lower the better).
 
In addition,  a 3' x 3' space will grow however many plants your experience can fit in that space with the size pots you are using.  6" square pots you could fit 36 plants under a 3' x 3'.  The yield will be based on the light output, so neither method could be considered superior.  It would be relatively the same as 1 plant in a 10-20gal pot because it is dependent on the amount of light you are putting on that space.  
Sea of green is based off this exact logic.  because why would i only want 1 top bud(the top bud is the best),  when i can fit 36 top buds in the same space?   I have been using this method for around 15yrs,  and while i may not hit the coveted 1gram per watt of light(i hover around .6-.7grams per watt),  the quality of bud i get is far superior because i get 36 top buds,  instead of 1 top bud and a bunch of small leafy buds like 1 big plant would have.
 
Hope this helps ya my friend.

 

Should be an exciting grow to get going!