Plants have various growth cycles. As mentioned earlier, you may leave grow lights on for 24 hours when your plants are in the vegetative phase. Meanwhile, plants grown for their flowers, fruits, and vegetables require a dark period to enter the flowering phase.
A: In general, you should not leave grow lights on 24/7. Plants need a light-dark cycle to develop properly.
' plants do require a daily respiration period of at least 6 hours per day (for seedlings) and ideally 8-10 hours for more mature plants. Therefore we do not recommend providing more than 14-16 hours per day of light, even if you are growing long-day-loving varieties and trying to induce flowering/fruit from them.
You can bloom an autoflower indoors under 12, 18 or 24 hours of daily indoor light. Or you can bloom autoflower plants outdoors where they will bloom happily irrespective of how many daily light hours are received.
It is ideal to keep a grow light on for about 12 to 18 hours. Too much light in various growth phases can interrupt a weed plant's natural process of growth and dormancy. Worse, light exposure for a whole day can damage and kill your plants.
Vegetative
The vegetative light cycle of cannabis is when plant growth truly takes off. Much like a human adolescent, the plant will achieve most of its vertical growth during this time. Lasting between 3 to 16 weeks, the vegetative stage requires full-spectrum light for 18 hours and 6 hours of darkness.
Sufficient lighting is essential for all stages of growth, but sometimes you can overdo it - leading to light stress in plants. This can cause a variety of issues with your plants. This can get tricky, because you absolutely need intense lighting to produce strong root systems to develop fruits and flowers.
Myth #14: LED Lights Can't Damage Plants
The reality is that modern LED grow lights can produce a very high level of light and it can cause photo-bleaching and burn leaves. This depends very much on the plant, but a PPFD of 800 is enough to damage some plants.
Once you're in the process of hardening them, you can turn off the lights while your seedlings are outside during the day. But, you shouldn't stop using them completely until after you've moved the seedlings outside for good.
After the plants reach the final stage of grow, and get to their full size, we do not need to use the grow light that much. Even though they've already stopped growing, you shouldn't ditch the grow light completely. A fully-grown plant would still need about 12 to 14 hours of light per day.
It could destroy your plants, so if you leave them under your grow lights for too long, you'll just end up with dead and wilted plants. A sign that a plant is absorbing too much light is yellow spots on its leaves.
For “seedlings”, if space (and time) permit, better yields can be obtained from a 6-8 week veg period. Alternatively they can be switched straight after germination, however they are biologically incapable of budding until about 3 weeks of age.
In optimal conditions, plants should be kept in their vegetative stage for approximately 60 days. This time period should give the plant the opportunity to maximise yield and acclimatise to growing conditions.
While some plants will tolerate 24 hours of light, most plants need both light and darkness. With that in mind, running a grow light around the clock can damage the photoreceptor cells of a mature plant, which perform vital internal processes at night.
In the vegetative stage, LED grow lights should be between 12-24 inches away from the top of the canopy. During this stage, more light is needed for photosynthesis, so the light source should be located closer to the plants.
The most apparent sign is leaf burning. This typically causes the yellowing of leaves at the top of the plant but the veins stay green, and the leaves take on a yellow or brown, burnt look.
Symptoms of excess sunlight on indoor plants
Strong sun and heat cause the breakdown of chlorophyll in the leaf. Damage appears as pale, bleached or faded areas. These areas eventually become brown and brittle. Symptoms are more severe when strong sun is combined with dry soil conditions.
The light you use should come with specific instructions. But as a general guide, here's a few tips. To be effective, grow lights really need to be on for at least 8-10 hours a day. This can vary up to 16 hours, depending on the conditions.
The first and the most important symptom of light burn is yellow leaves. The green leaves of the plant turn yellow. This happens to the leaves at the top of the plant and starts from the tip of the leaves. If you have noticed this symptom, it is time to take action.
Once you decide on your vegetative timetable, it is time to think about how you will switch the light cycle. This plant has been in flower for two weeks and displays young, white flowers. Most growers use an 18-hours on/6-hours off light cycle for the veg phase. Some prefer to use 20 on/4 off, which is also acceptable.
Even though plants are in their bloom stage and thrive off the "RED" light emitted by the Bloom mode they still require some blue and green light to really thrive. Always have both switches ON (VEG and BLOOM) once you plants are in the Blooming stage.
Vegetative Stage
For this, a healthy dose of blue light is your best bet. A higher concentration of blue keeps plants a little shorter.