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lighting for cannabis seedlings

Lighting for cannabis seedlings

“When can cannabis seedlings be put under lights or in the sun?” is a common and sensible question that is often asked by novice cannabis enthusiasts after germinating seeds indoors under lights.

Seedlings intended for outdoor growing should be kept by a sunny window for the first week or two after emerging from the soil.
If cannabis seedlings grow tall and then fall over, this is almost always a result of growing in an environment with static air.

If outdoor temperatures are suitable, seedlings may be acclimatised to direct sunlight by giving them progressively longer daily exposure to outdoor conditions.
Cannabis seedlings growing under lights should always be given a gentle breeze from an oscillating fan (a small household fan on the lowest setting is fine), as constant gentle movement will strengthen their stems significantly.
If using normal fluorescent tubes (18-36w), seedlings can be kept within a few centimetres of the light source.
When using HID lighting (usually a metal halide lamp), young seedlings should be kept at least 50cm from the bulb.
With compact fluorescent lamps (usually 100w or more), a distance of around 15cm should be maintained between the top of the young seedlings and the bulb.

Seedlings can be kept by a sunny window, until they’re ready to grow outside.

When cannabis seedlings have grown their second or third set of serrated leaves they are usually hardy enough to flourish in direct sunlight. Learn when that is and how to do that now.

Lighting for cannabis seedlings

Outdoors

Outdoors
If you’re growing cannabis outdoors with seeds, you should wait until a few weeks after the spring equinox to put your seeds outside. In the northern hemisphere this means seeds go outside in-or-after April, In the southern hemisphere seeds go outside in-or-after October.

What keeps cannabis in the vegetative stage?
Cannabis is a “photoperiod” plant, which means the amount of light received each day decides when the plant starts flowering or making buds. This article explains how much light a day your photoperiod cannabis plants need to grow and start budding, so you get to a happy harvest day. What about auto-flowering strains?
The indoor grower will need to artificially induce flowering/budding in plants by changing the light schedule so the plant receives only 12 hours of light a day, and 12 hours of uninterrupted darkness.
Outdoors
Indoors

Here’s an example of LST to keep a plant short:

What do I need to know about light cycles and flowering my marijuana plants? Plants keep getting bigger and bigger with long days, and start making buds when you give them long nights.