Lighting for Sativa Scrog Grow

Im about to do my first scrog grow (3.5' x 2.5') with 400 w mh/hps lamps, with cool tube. The screen will be about 12 inches above the medium.

It will be hydro, and I want 5 clones of a sativa strain, most likely purple haze (70-90 cm tall according to http://www.marijuanastrains.com/purplemarijuana.html)

Im in the process of designing my grow box, and i want to keep it as short as possible.



Can anyone with experience of scrog growing sativa strains give me some answers/advice on the following?:

If I have the 400w lamp (w/ cool tube) about 18 inches above the screen, will the light stay at this height for the entire grow (up to harvest)?

Or would I need to move the lamp upwards by how many inches the colas are growing above the screen? (example: 18 inches + 4 inch colas above screen = 22 inches from lamp to screen)

Is a 12 inch screen heighth, and 18 inches above that for a lamp good heighths for my strain?


I need this info so i can build my grow box to a reasonable height. I want to have as short of a box as possible without decreasing my yield. The final heighth of my grow box will be: 20 inches (heighth of hydro tank) + 12 inches (medium to screen) + max distance lamp will be from screen

generally with a screen u shouldnt hav to hav the light more than 24 inches away really especially with 400s but depending on when u switch and how full ur screen is when u switch and the strain u run will truly determine how much space u will need i would say a minimum of 4 feet depending on ur bucket height
hope tht helps a bit bro good luck

i have a sativa that has stretched about 12" in about 31 days, shes still stretching up, i had her start flowering dec 1st, let her go about 1 week into flower, and pulled the last bit of growth back under and let it stick up from there, jan 6th, shes still coming up, i keep my light about 14" away from the top branch (air cooled lamp). fwiw, im in a dwc, 8" height is my screen with 1.5" blocks, 400w.

its strain dependent, if you have a stretchy type like mines be prepared to move the lamp up. if i needed to i could go up another 2', and i hope i dont have that much stretch in my plant...

just roll the dice, most plants wont stretch more than 24" from what ive grown (mostly sativa dom).

If your using a properly cooled light you should have the light as close as possible while still covering all your plant. No reason not to as long as you don't have a sensitive strain.

Remember that true sativas generally require a lot more light than indica dominant strains to reach their full, or partial, potential.

How many lights in how much area?

clambaker, I'm also interested in a Sativa Scrog that's as short as possible. What did you decide to go with for height? I was going to try a 250W on a 2'x2' and may be hard pressed to go higher than 36". I was somewhat wondering if for scrog one could save bucket / pot height by having a short(er) pot since the whole grow area can be bucket for roots?

I am just stating a Colombian x Jamaican Lambsbread from Underground Seed Collective (USC). Therefore I am looking on the internet for all the options. My only experience growing landrace strains was when I was young and through bag seed in the ground after germinating in Washington State. I was never successful for several reasons as I was young and immature. Now is different because I am using good soil and lighting. The plants will be in various locations inside and out. I have a small makeshift greenhouse on my deck so I will be able to let those go kind of crazy. I will take some clones and grow those inside under light in small containers to control the growth.

I plan to take make a bunch of seeds from the Col x Jam, but also make seed with my Blue Dream. This cross I will be calling Blue ColJam and I think it will be an easy plant to grow with a very good buzz. I will work the Blue ColJam thoroughly but do not expect any problems. Blue Dream is an easy plant to grow and clone so it's combination with the Col x Jam will be similar once I have worked them a bit.

I will check in as this goes with pictures and details.