400W bulb... 5 plants... How tall?

I'm trying to decide when to switch over to flowering. I have a 400w metal halide bulb with a decent reflector, and some mylar on the walls. I have 5 white widow plants, and I want to maximize the 400 watts without going overboard (I don't want the plants to get so big that the light can't handle the task anymore.) I assume they will roughly double in size during flowering... so given my lighting setup, at what height should I start to flower?

Not sure how others will feel, but I think 2.5-3ft is as tall as I'd want to grow a plant with a 400 due to light penetration concerns. You could maximize yield by using SCROG or supercropping.

since you got the right start invest in the hps bulb for your unit if you have the proper ballast that can run both types. i dont know it it could handle 3 footers! maybe but you might want to top them and tie down branches, this will allow it to get more light on more surface area. mine are about one and a half foot now, flowering with the 400w. you could go a bit taller but i love the branch tie down thing- so much more surface area and my plants arent streching as bad as they told me after that 12/12 switch

smokinskins said:

since you got the right start invest in the hps bulb for your unit if you have the proper ballast that can run both types. i dont know it it could handle 3 footers! maybe but you might want to top them and tie down branches, this will allow it to get more light on more surface area. mine are about one and a half foot now, flowering with the 400w. you could go a bit taller but i love the branch tie down thing- so much more surface area and my plants arent streching as bad as they told me after that 12/12 switch

Click to expand...

My ballast is meant for an hps bulb, right now I'm using a MH conversion bulb... I have a 400 HPS for later . So maybe I should shoot for 30"-36" plants. I'm a little nervous about the tie down thing... how do you tie the branches down, and when do you start that? Right now I'm only 2 weeks into veg.

southpawprof said:

My ballast is meant for an hps bulb, right now I'm using a MH conversion bulb... I have a 400 HPS for later . So maybe I should shoot for 30"-36" plants. I'm a little nervous about the tie down thing... how do you tie the branches down, and when do you start that? Right now I'm only 2 weeks into veg.

Click to expand...

they will strech with the switch so plan on it, but i topped mine and its the best thing i ever did! branches- not sun leaf stems will grow like crazy. i have some thread taped to the pot thats it! branching will promote alternate branching as they try to get light from under the sun leaf and twist. i did mine one at a time when they reached up to the canopy from top to bottom to allow light to penatrate the plant in the center, down to the lower levels. all of a sudden its a bush not a stick! topping will make branches, tie down when they reach the top or if you want to move it out of the way to let other spots share light. i topped anywhere between 4th and 6th node and those plants have major more bud than the one i left alone!