When can seedlings be put under lights or in the sun?


Not sure whether to grow your cannabis seeds in the sun or under light? This article explains how much light you need, how to keep your seedlings from falling, and when to plant them outside.

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

For those who grow indoors, cannabis seedlings can be placed under light as soon as they emerge from the soil or growing medium.

How Much Light for Cannabis Seedlings?

When using HID lighting (usually a metal halide lamp), young seedlings should be kept at least 50 cm from the light bulb.

With compact fluorescent lamps (usually 100 W or more), there should be a space of about 15 cm between the top of the young seedlings and the bulb.

Using normal fluorescent tubes (18-36 W), the seedlings can only be kept a few centimeters away from the light source.

Cannabis seedlings growing under lights should always get 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 considerably.

Are your cannabis seedlings falling over?

When cannabis seedlings grow large and then fall over, it is almost always the result of growing in a static air environment.

Seedlings intended for outdoor growing should be kept in a sunny window for the first week or two after emerging from the ground.

When you’ve grown your second or third set of serrated leaves (after the round cotyledons that originally emerged from the seed), the seedlings are usually sturdy enough to thrive in direct sunlight.

Seedlings can be held through a sunny window until they are ready to grow outside.

When should you plant your cannabis seedlings outside?

If the outside temperatures are suitable, the seedlings can be accustomed to direct sunlight by exposing them to outdoor conditions longer each day.

From around three hours outdoors, at the sunniest time of day, the seedlings can be left outdoors for an additional hour each day, so that they can be left outdoors permanently within around two weeks.

  • Disclaimer:

    Cannabis growing laws and regulations differ from country to country. Sensi Seeds therefore strongly recommends that you check local laws and regulations. Do not act contrary to the law.


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Robert Dunfee