BennyBlanco said:
Well in a sense there are two kinds of stretch. One is associated with the plant's flowering cycle and the other is associated more with the type of light and where it is in relationship to the plants. The first one is pretty much unavoidable and is a natural part of the process of flowering. Once plants are triggered to flower they go thru a growth spurt known as the stretch phase, this generally takes place in the first two to three weeks of flower but it can vary from strain to strain. What I have noticed in my own experiences is that if I wait until the plant sexes itself in veg by showing pre-flowers, before I switch to flower, then it seems stretch is minimal. They say a plant will double sometimes triple in size during stretch, I myself have never had a plant double or triple during stretch. However, due to the fact that so many have experienced this one rule of thumb on when to switch to 12/12 is to do it when the plant is one third the maximum height your space can handle. So for example if you didn't want your plants to be any more then 6 feet tall you would flower it when it reached 2 feet tall. My take on it, and this is just my opinion based on observing the plants I've grown. If you flower early, before a plant has fully matured say 6 weeks of veg or less. Then yes, it will double or triple. Reason being is that an immature plant is less prepared for flower so when it get's that 12/12 signal it trys to hurry up and beef up the structure to support the coming budsites. The bud sites are key to the plants ability to survive over time so you'll notice the bud sites are a top priority for the plant and a taller plant means more budsites. Now if a plant is allowed to fully mature to the point of having definitively shown it's sex thru pre-flowers it is typically a good size, especially plants that are slow to sex (I've had them take up to 10 weeks). If a plant isn't flowered until it reaches this point I find it will usually only stretch a foot or so maybe two feet, sometimes just a few inches. I think in this case the plant sense there's a fair amount of struture there to work with so it gets started on the budsites sooner and stretch seems less or shorter. What I do find though is the end result in height seems to be the same. In other words say the 2 foot plant flowers to 6 feet tripling in size having only had four weeks of veg, maybe five. Likely if you take that same plant and under the same light, veg it out without trainning or topping until it sexes, it'll be maybe four or 5ive feet and stretch another two feet or one foot. The end result would still be a 6 foot plant. So now you're thinking "Cool that means I can cut my veg in half, harvest faster and still get a six foot plant" To which I say now hold on a second. That in fact is true of a sort the thing is, you don't end up with the same sort of 6 foot plant. The longer vegged one will have the fuller, denser, more developed buds, because it got started on the buds sooner and was therefore able to devote more energy to the buds. Of course in both cases the end result will depend on alot of factors, root developement, soil composition, diet, frequency and amount of water, general harmony in the grow room (good ventilation/circulation of air, good temps, good humidity, pest free. If all of those are optimal you get optimal growth. Any of them get out of whack and growth suffers because the plant will divert energy to deal with the stress created. How much depends on how bad and how long things are out of whack and which things they are. The worse thing you can allow to happen is the loss of alot of leaves at once, leaaves are the factories for the plant processing that light and the water and nutrients into new plant matter. Less leaves mean less energy to spend on bud growth. Now once you are well into flower, say about half way you can worry less about the main leaves and it's normal for them to begin to die off because at this point the budsites have created their own set of factories feeding directly into the bud and so it's less dependent on the plant for energy. However should the plant be in serious trouble the energy will still go to the plant for it's survival. So you still want to really keep everything smooth and healthy. Of course that should go without saying.
Now the other kind of stretch is due more to the improper placement and the type of light. If you have a decent HID light but keep it higher then suggested for optimum growth because the tempurature is easier to manage then that's a situation where you'll get stretch because the plant is sensing the light but at a weak strength, it can tell that if it gets a little taller it will get what it needs. Light disipates rapidly as it travels from the source, the formula to figure it is know as the inverse squared rule which basically says everytime you double the distance from the light source the light becomes only a quarter of it's sources strength. So if you go say a foot from the light, whatever thestrength is there, at 2 feet it will only be 1/4th that strength, at 4 feet it will only be 1/16th as strong. So while to us they seem bright enough that we might think the lights can be up high, they really can't the rule of thumb is for 400W you want to be at least at 12" from bulb to plants. With a 600W 18" and with a 1000W 24" most people get even closer increasing the beneficial range of light for the plant by using air cooled lights such as cool tubes for example. Also the type of light makes a difference, the growth hormones responsible for stretching are light regulated and once the plant recieves the right frenquency and strength of light this hormone is slowed down. In nature the plant uses this to push past bigger plants that are shading it. You'll hear sometimes people talk about HPS stretch. To me this refers to the fact that an HPS light in veg will usually cause more stretch then an MH light. This is because the plant's nature from how it has evolved in nature has it used to growing during the time of year that blue spectrum light is more dominent in the sky. Likewise the time of year a plant flowers red spectrum is more dominent. This has to do with how the angle of the sun in relationship to the earth changes with the seasons. This has caused plants to evolve to prefering blue spectrum light (MH or cool white for fluoros) during veg and red spectrum light during flower (HPS or warm white for fluoros). In reality though in nature they get a blend of both that varies in ratio over the seasons, realizing this, may have taken to using full spectrum lighting which is usually a blend of red and blue spectrum either in a single bulb or thru a mixture of two or more lights. Usually in flower you would have about 2/3rds red spectrum 1/3rd blue. I always felt the best set up would be 3 1000W lights each able to run either HPS or MH. Start them for Veg with all three MH. After a month make one HPS and leave the other two MH then at two months when you are about ready to switch to flower make it two HPS and one MH. Then halfway thru flower, which depends on your flowering time. Switch it to all HPS. This would roughly simulate the changing color temps of light over the course of a season. I have yet to really play with what they call full spectrum lighting in flower but from people I have talked to the claim it produces somewhat shorter but more dense or heavier buds.
Okay I think I about talked stretch to death
