Example: The seedling to the left is stretching upwards because it is not getting enough light. The plant is trying to “reach” up towards what it thinks is the sun. This stretching is not usually a good thing, because these seedings almost always fall over and will tend to grow into tall lanky plants. Tall, tower-like plants are hard to give proper light coverage in the flowering stage and will tend to get lower yields in most indoor setups. That’s because during the flowering stage (when plant start producing buds), higher light intensity is what drives the production of buds.
For most small-scale indoor growing setups, finding ways to increase the amount of light getting to the bud sites throughout the flowering stage is the most straightforward and effective way to increase your final yields. In order to grow dense cannabis buds indoors, you need strong grow lights. Once your cannabis plant is producing buds, anything you can do to help get more intense lights to the bud sites will tend to increase your yields. Indoor cannabis grow lights provide the highest light levels close to the actual bulb. The further away from the bulb of a cannabis grow light, the less intense the brightness experienced by the plant. Because of this, it is tough to provide bright light to all the buds on a cannabis plant when the colas are uneven lengths or at different heights. It is most effective and efficient to grow cannabis plants so they have a lot of colas spaced relatively close together and at the same height . Cannabis growth patterns are something you have complete control over in the vegetative stage (addressed in the plant training section below) and taking the time to manipulate your young plants to make good use of your indoor grow lights is one of the best ways to increase your yields with the same lights.
Yet after flowering has already started, there’s not much you can do about uneven cola height without possibly hurting your plant, so if your plant is already flowering, you’ve just got to do your best to provide the most intense light possible to all the buds until harvest, without overheating or harming your precious growing colas. It’s important to keep plants cool during the flowering stage, as high temps can actually burn off terpenoids (smell/taste) and cannabinoids (potency), lowering the quality of buds even as you may be increasing the overall yields at harvest. For the best results, you want all your buds directly exposed to intense light. Being in direct light seems to cause buds to swell up much more than when buds are hidden by leaves. In the wild, cannabis buds are pollinated by the wind and need light from the sun to power the growth of seeds. A cannabis bud in the wild which is not exposed to air and light is unlikely to get pollinated, so the plant tends to not put much effort into the hidden middle and lower buds on the plant. Only buds which are exposed to air and bright light will tend to fatten up. Most indoor growers are unlikely to provide too much light to their marijuana plants – cannabis plants can use a surprising amount of light naturally! Outdoors in the wild, cannabis grows best in direct sunlight. Therefore as long as an indoor grower keeps their grow lights the right distance away, they’re unlikely to provide too much light and actually hurt their cannabis garden. CFLs and other fluorescent grow lights are relatively weak and can be kept as close to your cannabis plants as possible while keeping heat under control. LED grow lights generally should be kept at least 12″ away, and 3W or 5W models should usually be kept 18+” away for the best growth. The distance needed for LED lights varies from model to model, so it’s important to listen to the manufacturer’s specifications when it comes to deciding how close to keep LEDs to your plants. Modern LED grow lights are very powerful, and It’s very easy to light-burn your plants with LEDs. MH/HPS grow lights usually should be kept 1-2 feet away, though the distance needed depends on the size of your bulb. How Far Away Should MH/HPS Grow Lights Be From My Plants? With all grow lights, it’s important to have some sort of cooling or exhaust system in place to prevent heat stress and help bring fresh CO2 to the plants. If you keep increasing the light intensity in your grow room (or moving high-power lights closer and closer), you will eventually reach a point where you max out on the light your plants can use. If you consider that light is like food for your plant, maxing out the light is like putting so much food on the table that your plants hurt themselves trying to finish their plates. Plants provided with too bright light can experience light burn even if temps are cool when the light intensity gets too high. Some strains are more susceptible to light burn than others. When you’ve reached the ultimate max of light that your plants can use, you still have a trick up your sleeve to further increase your yields. You can give your plants the ability to use even more of that light (and increase your bud yields even further) by increasing the CO2 levels in your grow room during the flowering stage. So if light is like food for your plant, think of CO2 as a way to give your plants a way to “stretch their bellies” and eat even more food than would normally be possible. The way additional CO2 works is it increases the amount of light your plant can use at very high light levels.
With smaller grow lights like CFLs, a T5, even a 400W HID grow light, it is very unlikely that your light is bright enough to bring your plants to point where they are being limited by CO2. Adding extra CO2 when it’s not the limiting factor of growth is almost always a waste of time and money. For most plants, providing a source of fresh air will give plants all the CO2 they need. But if your plants have maxed out on light, artificially raising CO2 levels in the grow room can help plants use even more of the light and turn it into energy for growth.
Just remember that it takes a lot of light for your cannabis plants to hit this light saturation point. so unless you’re using high powered lights like a 1000W grow light (or high-power LEDs) and keeping the lights incredibly close, your plants are probably able to use all the light they’re receiving. Adding CO2 to the grow room does not directly increase yields. CO2 only increases the amount of energy your plants can produce under very high intensity light levels.