How many plants can I put under a 400 watt HPS?

Trader Bill

Trader Bill

Active Member
Hi all. I'm new to the board.

Here's my situation.
I have a 400watt HPS mounted to a hood attached to a 6ft PVC frame that I built so I could raise and lower my light as needed via the chains that attach the hood to the frame.

I'm running a deep water hydroponic system that features four 20 gallon tubs that have spots for 4 plants per tub. So as it stands right now I can have 16 plants going at once.

My plants are growing incerdibly fast and it seems to me that 16 plants under one 400 watt HPS might be too much. They're already crowding each other and im just under a month into my operation.

So can I have 16 plants under one 400 watt HPS?

How close can you crowd the plants together?

Will I get better yield from fewer plants that I grow larger? Or should I crowd up smaller plants and get a fast harvest of many plants? This is my first time growing so thanks for the info.
 
High4Life

High4Life

Well-Known Member
4-6 Plants Work Best Under A 400w . I Found 6 Is Tightly Packed With Not Much Ligh Getting Through To The Sides , 4 Plants Works Perfect ..h4l
 
D

Dutch1976

Well-Known Member
I say 9 small-medium sized plants. Top the plants as soon as you see the 4th node. A few days before you put them into flowering, strip the lower half of the plant and watch those colas explode.
 
kearners

kearners

Well-Known Member
thanks man this really helped me i was going 2 make a thread to find out how many plants i could have!! ill be checking this out again soon!thanks...
 
J

jEthereal

Active Member
It all depends on how TALL the plants are when you switch to 12/12.

You could EASILY do 16 plants under a 400w HPS. How so, you ask?

FLOWER AT 6"!!

If it is done right then you'll be able to have a bunch of mini-cola plants.

16 plants x 1/2oz expected yield =

One question - What's the 'footprint' of your tubs? ie - How much space (LxW) do your tubs take up when you have them arranged how you want? 4x4? 5x5? etc....

Your spatial 'footprint' when growing with a 400w HPS should be around 4x4. It's YOUR choice on how to accommodate your plants into that space.

There isn't really a 'set' number of plants that are appropriate with a certain wattage.

So to say 4-6 plants WITHOUT offering the SIZE of said plants is a very inaccurate statement when trying to help a newbie.

jE
 
High4Life

High4Life

Well-Known Member
Unless your doing a sea of green for advantced newbies or mini growers *

4-6 normal plants is all a 400whps is good for
 
kearners

kearners

Well-Known Member
thanks a lot i just spent a long long time looking for advice on this area but ye really helpd, i owe ye one!! peace out!!
 
White Widow Woman

White Widow Woman

Well-Known Member
Trader Bill said:
Hi all. I'm new to the board.

Here's my situation.
I have a 400watt HPS mounted to a hood attached to a 6ft PVC frame that I built so I could raise and lower my light as needed via the chains that attach the hood to the frame.

I'm running a deep water hydroponic system that features four 20 gallon tubs that have spots for 4 plants per tub. So as it stands right now I can have 16 plants going at once.

Hey Trader Bill - I like growing in 4 separate sections just like that in a square, but mine are all 2 weeks or so behind each other. And I tried DWC but my tubs were bigger than 20 gals. I used 1-400w HPS over the 2 tubs of newly added plants and 1-400w MH on the other side over the tubs with plants that were further along. My footprint for each tub was 24in X 36in then times 2 = 48X36 or 4ftX3ft (because they are lined up side by side) --- so each light was only covering a 4x3 area which is perfect for a 400w light. Plus there's a little bleed over, since both lights are facing each other.

My plants are growing incerdibly fast and it seems to me that 16 plants under one 400 watt HPS might be too much. They're already crowding each other and im just under a month into my operation.

So can I have 16 plants under one 400 watt HPS?

How close can you crowd the plants together?

Now in answer to these questions, you need to bear in mind it would be nice to know the height of your plants currently or to see a picture. Anyway I have 2 smaller rubbermaid 18gal tubs that I use as cloners and they measure 22inX16in, so if yours are in similar dimensions and you have 4 of them arranged in a square - then your footprint is about 44X32 or less than 4ftX3ft --- this is just fine for 1-400w light, that is covering several plants all of similar height.

Ofcourse there will be lots of crowding as flowering continues, so your buds may not be as tight lower down; due to less light getting to them. Also they will slow down their vertical growth soon. Normally they almost double in height the first few weeks and then they begin to fill in more than grow taller (buds forming) - but this IMHO is a do-able situation with some cfl side lighting and by lollipoping the bottom growth.

Will I get better yield from fewer plants that I grow larger? Or should I crowd up smaller plants and get a fast harvest of many plants? This is my first time growing so thanks for the info.
Click to expand...

Yes, you could get a better yield from letting fewer plants grow taller/vegging longer for height - but you can also get a great yield from growing lots of smaller plants (SOG). That dear sir is all personal preference. But I have never heard of this 'Fast Harvest' that you speak of. The plants are gonna take 7-8+ weeks of flowering reguardless of their height - unless you have chosen a strain that finishes sooner.

Let me finish by saying that 8 plants under a 400w light, creates some pretty good buds - go down to only 4 plants and you get some great perfect buds!


:mrgreen:
Widow
 
Trader Bill

Trader Bill

Active Member
jEthereal said:
It all depends on how TALL the plants are when you switch to 12/12.

You could EASILY do 16 plants under a 400w HPS. How so, you ask?

FLOWER AT 6"!!

If it is done right then you'll be able to have a bunch of mini-cola plants.

16 plants x 1/2oz expected yield =

One question - What's the 'footprint' of your tubs? ie - How much space (LxW) do your tubs take up when you have them arranged how you want? 4x4? 5x5? etc....

Your spatial 'footprint' when growing with a 400w HPS should be around 4x4. It's YOUR choice on how to accommodate your plants into that space.

There isn't really a 'set' number of plants that are appropriate with a certain wattage.

So to say 4-6 plants WITHOUT offering the SIZE of said plants is a very inaccurate statement when trying to help a newbie.

jE
Click to expand...
Hi all. Sorry it took me so long to respond.

I have all four of my tubs pressed together into one rectangle that is 45in x 31in.

The biggest plant is 19.5 inches. The rest of the plants range from 18 inches to 13 inches.
 
Trader Bill

Trader Bill

Active Member
White Widow Woman said:
Yes, you could get a better yield from letting fewer plants grow taller/vegging longer for height - but you can also get a great yield from growing lots of smaller plants (SOG). That dear sir is all personal preference. But I have never heard of this 'Fast Harvest' that you speak of. The plants are gonna take 7-8+ weeks of flowering reguardless of their height - unless you have chosen a strain that finishes sooner.

Let me finish by saying that 8 plants under a 400w light, creates some pretty good buds - go down to only 4 plants and you get some great perfect buds!


:mrgreen:
Widow
Click to expand...
Hiya. When I mentioned getting a faster harvest with smaller plants I was speaking in the context of having a shorter vegetative period before going to 12 on 12 off to make em flower.

I think i'm going to try for 4 plants per HPS, and get myself a second HPS so I can do 8 at a time.
 
T

tpemiles

Active Member
for a 400w hps, should it still be around 2 in. away from the top of the plant during vegetation? and then how far should it be from the top of the plant during budding? and with a 400w hps with 30w extra blue spectrum, thats all i would need right? sorry about all the questions. just dont want to fuck up lol
 
mared juwan

mared juwan

Well-Known Member
an hps needs to be AT LEAST 14 in away from your plants. That 2 inch stuff is for CFLs. Please don't put your light that close. You will kill your plant quick.
 
T

tpemiles

Active Member
it won't grow too high too fast if its 14 in away?
and how much does it normally grow after you start budding? i just want to make sure i have the right height when i build my room. i only want a small garden, just for personal use.
 
J

jEthereal

Active Member
tpemiles said:
it won't grow too high too fast if its 14 in away?
and how much does it normally grow after you start budding? i just want to make sure i have the right height when i build my room. i only want a small garden, just for personal use.
Click to expand...
You can expect to double or TRIPLE in height. Sativas will stretch more. Indicas usually double their height, if even that.
 
T

tpemiles

Active Member
i thought it would get too stretched out and not bud well but i honestly dont know anything so thank you!
should the light still be at least 14 in for budding? Is it all the same distance with hps?
 
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