With Using The LED Growing Lights To Seedlings And Clones


LED grow lights should be placed anywhere from two to three feet above the growing tops of seedlings and clones.  This ensures that the new starts will not be overstimulated by the intensity of the lights.

Once the plants produce a network of branches the lights may then be lowered to anywhere from eighteen to twenty-four inches for the extensive vegetative period of growth.  Do not move LED growing lights any closer than twelve inches from the growing canopy as this will most likely burn the sensitive new growth due to the amount of radiant heat produced by the diodes.  This problem could be accentuated if the ambient temperature of the grow room is relatively high. Also, when an LED is placed too close to the canopy the effective lighting footprint is reduced leaving adjacent plants without adequate light to thrive.  Note that LED lights that are placed too close to a plant will result in a diminishing returns effect whereby as the light moves closer it has an ever decreasing effect on growth.  Maintain the twelve-inch rule.


The ideal temperature for plants being grown under LED growing lights is between seventy-five and eighty-five degrees.   If supplemental CO2 is being added then the upper limit of this estimate or slightly beyond the upper limit is preferable.

Generally, as they grow room temperature rises the ability of the plant to utilize CO2 increases up to as high as ninety degrees.


As with HID CO2 can increase plant growth dramatically.  Ambient levels of CO2 stand at about 400ppm.   A grow room at seventy-five degrees can make use of CO2 up to 1000ppm.  From this point, the temperature may be increased up to ninety degrees with a corresponding increase in CO2 peaking at 1500ppm.  After this, the plant will reach CO2 saturation and any increase will be wasted.  Note that when operating CO2 at these elevated levels it is recommended that extended periods of time in the grow room to be avoided.


The use of LED grows lights will tend to result in grow rooms that are cooler than grow rooms equipped with HID lighting.  This difference in temperature can also have an effect on humidity levels which in turn have an effect on the growth rate of plants along with other considerations.  A conscious effort will be needed to maintain grow room temperatures along with an awareness of the resulting humidity levels. When humidity levels are low, nearing 50 percent the result will be that the plant will produce narrow leaves which will prevent water in the leaves from evaporating at an acceptable level  This limitation will cause a slowing of growth.

As the humidity levels reach upward to sixty-five to seventy-five percent an optimum rate of growth can be maintained whereby the left surface will increase and transpiration can effectively take place.  As the humidity levels are further raised again the plants’ rate of growth will decrease since now the plant leaf surface will find it difficult expelling water into an environment that is already saturated with humidity.  Another consideration for avoiding high levels of Humidity will be that various molds and pathogens will find the environment more to their liking potentially resulting in disease.


Making the transition from HID to LED oftentimes require that old habits need to be modified.  The two most difficult areas of adjustment are water and fertilizer requirements.  Since LED grow lights produce less radiant heat the rate at which water is released from the plants leaves is reduced.

This accordingly will necessitate that the grower becomes more sensitive to the overwatering potential especially in soil cultures.  There is often an erroneous tendency to maintain the same schedule that was established while growing under HID lighting.


Somewhat parallel to the watering issue is the fertilizer schedule.   By using LED lighting in the garden the grower may experience an increase, a decrease, or no change in growth rate.  So many factors will interact to determine the outcome.  The most important thing to understand is that this is a time when the grower can no longer rely on previously established patterns that were based on a light source no longer being used.

How much fertilizer to use is purely a function of the plant’s ability to absorb nutrients and this can change dramatically.   A new fertilization schedule will need to be established based on the current environmental conditions in the grow room along with observable signs given by the plants such as their overall growth rates, the curling of leaves or the burning of leaf tips.

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