Soil: How much is too much/not enough?

I'm kinda looking for a standard based on a common lighting scheme. I've read 1 gallon per square foot of growing space, but am not sure whether this extends past the footprint of the light source. For instance, I have a chamber that is roughly 3 feet wide. The CFL ballast I use is 2 feet wide.

Using a common lighting scheme (2x4 ho-CFL 8-bulb) how many gallons of soil would be ideal? Does this change with the number of plants?
For instance, under the 2x4 light I can either grow 2 large plants or 8 smaller plants.

And a side issue, I'm still trying to determine whether to grow 2 plants or 8 plants so any recommendations on which would be better would be appreciated.

my standard is 1 gallon per month of growing. maybe a little more.

obviously if you are growing monster trees that changes a bit, but generally for a small indoor it has never failed.

I appreciate the reply but am not sure that answers my question. 1 gallon per month would make sense if I knew how much space you were giving each plant.

1 gallon per square foot seems low (I've also never heard that). A 5 gallon bucket is about ~12in in diameter, so thats 5 gallons a square foot.

The whole more vs bigger plants issue really comes down to veg time and the need to 'train' bigger plants. If you have a 2x4, why not put 3 (or 4) plants in 5 gallon buckets? Just make sure you top them and bend the lower branches out so they grow wide and not tall.

If money is an issue, you can mix your own dirt - $40 will get you about 4 cubic feet of peat moss / perlite, which is like 4-6, 5 gallon buckets. Messy though, peat moss and perlite are very dusty when there dry, and dry peat moss is oddly hard to get wet.

Rahz said:

1 gallon per month would make sense if I knew how much space you were giving each plant.

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1 gallon a month still makes sense, a gallon is volumetric. If your buying pots, be aware that a 1 gallon pot is NOT one gallon - it's a "trade gallon", which is a bullshit measurement (http://en.wikipedia.org/wiki/Trade_gallon) - kind of like how an ounce of gold generally means a troy ounce. A 5 gallon bucket is a real 5 gallons, about the size of a 7 gallon pot. 1 gallon a month seems low though, even 5 gallon buckets will root bind in 3 months (1 month veg and 2 flower) Keep in mind that roots are for oxygen, not just food / water.

Well, I'm currently growing 2 plants in a single 15 gallon pot. I'm trying to decide whether 1 plant per pot that size would be too much (30 gallons of soil under a 2x4 lamp for a 1 month veg 2 month flower).

My alternate plan was to do something closer to a sea of green, giving each plant 1 square foot (8 plants under the 2x4) and shorten the veg cycle to 2 weeks. I had 2.5 gallon pots in mind, comming out to 20 gallons over the 2x4 area.

like someone said above i go with 1 gallon per month of growth. if your going to veg a month and then flower which takes about 2 months you would use a 3 gallon pot. pretty simple math is it not? typically more is better but more could be a waste too. if your gonna do sea of green then 3 gallon would be optimal.

like someone said above i go with 1 gallon per month of growth. if your going to veg a month and then flower which takes about 2 months you would use a 3 gallon pot. pretty simple math is it not?

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Seems too simple. 1 gallon per month, 2 plants = 6 gallons. But what if in the same space I choose to grow 8 plants? It would be then be 24 gallons (8x3). So we're looking at a difference, total of 24 gallons -vs- 6 gallons based on the number of plants? It seems the growing space should factor in which is what I'm trying to get at.

growing space is only a factor if your using the whole space. pots size is going to be determined only by how long your gonna grow the plant and how big that plants root system gets. typically a plant uses about a gallon of medium space per month for root growth. again more would be better but only by so much. if your giving it 3 gallons a month theres gonna be a lot of wasted soil thats not being used. plant health and strain is a big factor because not everthings gonna grow the same. so as a rule of thumb for people that dont know 1 gallon MINIMUM a month of medium.

Rahz said:

Well, I'm currently growing 2 plants in a single 15 gallon pot. I'm trying to decide whether 1 plant per pot that size would be too much (30 gallons of soil under a 2x4 lamp for a 1 month veg 2 month flower).

My alternate plan was to do something closer to a sea of green, giving each plant 1 square foot (8 plants under the 2x4) and shorten the veg cycle to 2 weeks. I had 2.5 gallon pots in mind, comming out to 20 gallons over the 2x4 area.

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I'm reading everybody's thoughts here, and taking all this in, but I just wanted to chime in, and mention-more than one plant per pot is not a good idea.

imchucky666 said:

I'm reading everybody's thoughts here, and taking all this in, but I just wanted to chime in, and mention-more than one plant per pot is not a good idea.

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oh damn did i miss that part? i agree, 1 plant per pot.

pots size is going to be determined only by how long your gonna grow the plant and how big that plants root system gets

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This turns the question to plants per square foot. Using a foot (or more) per month, 3 plants would be 9 gallons in a 2x4 area, 4 plants would be 12 gallons, 8 plants would be 24 gallons. It seems like 8 plants would achieve the fastest veg stage, but what that would translate into I'm not sure. I've done several hydro grows with a single plant in a 25" x 27" enclosure using a Pioneer 8 Jr. 2-3 week veg and the area would be fully vegitated after 2 weeks of flowering. I can do this with soil but am beginning to see it will take a longer grow so now I'm curious about the optimal number of plants per square foot and grow duration. Any advice on that matter would be appreciated.

The pot with two plants was given to me, about to be thrown out but it was a strain I've wanted to grow. I'm hoping the 15 gallon pot I'm using will be kind to them.