GROWING WITH LED’S
BY POETRY OF PLANTS (IG @poetryofplants)
When cultivating under LED lighting, a cultivator might be tempted to execute a similar methodology to HPS
cultivation. This strategy can lead to frustrating results due to the environmental dierences, higher usable
lighting levels and subsequent higher photosynthetic rates that stimulate growth with less room for error. The
focal point of heat created by a bulb also helps burn o latent load (RH) which doesn’t occur with a properly built
LED xture, which diuses heat into the ambient environment created a more evenness to environment but also
can cause higher relative humidity. Also, with LEDs more input energy goes into created light than heat (which
is the case with HPS).
This increase in light will stimulate higher photosynthetic rates, leading to higher transpiration rates anda higher
demand of feed solution, all of which add more water into the room. When specifying dehumidiers it’s important
to match the dehumidication potential with the volume of water added. With LEDs, it is safe to assume that the
peak water demand per day will be 1 gallon per sq ft of canopy. Remember this is PEAK water demand, daily
water demands will in reality be less and dependent on pot size, cultivar type, and plant age. For example, a
2-week-old plant will require less water than a 6 week-old plant.
PPFD ENVIORNMENT
Because of the higher photosynthetic and growth rates, plants that recieve a higher ppfd will require more food.
It is recommended when rst cultivating under LEDs, for the cultivator to match PPFD levels used under HPS
and make gradual increases of both light and fertilizer PPM during subsequent runs. It is also recommended
that the cultivator uses a quality PAR meter that measures PPFD (umol) to understand how much light they are
giving the plant.
APPROPRIATE BASELINE LIGHTING LEVELS
HOW TO ASSESS APPROPRIATE PHOTOSYNTHETIC RATES
Use a laser thermometer to measure leaf surface temperature. Under LEDs the leaf surface temperature should
be at or around ambient canopy temps (2-3 degrees dierential). Transpiration generally cools the leaf surface,
so if your leaf surface temp is climbing 2-3 degrees higher than ambient canopy then the light energy is not
being turned into phytochemicals (which is desired) and instead is being reected back as heat (undesired and
used to cool down the plant). If the plant is heating up above the ambient temps then you need to dial down the
light intensity until the stress is resolved. If this occurs for multiple days, then you should also dial down the
fertilizer concentration, feeding the plant more water to help cool without leaving a buildup of salts in the media
(which will choke the roots, aka osmotic root pressure). You should also perform daily pour through run o tests
to make sure the media isn’t becoming acidic and the EC levels are close to solution EC level).
WEEK 1
FLOWER
2
FLOWER
3
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4
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5
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FLOWER
PPFD 450 550 650 750 750-850 850-950 850-950 850-950 850-950
RH 60-70% 65-70% 60-65% 60-65% 60-65% 60-65% 60-65% 50-55% 50-55%
SLT 72f-75f 72f-75f 72f-75f 75f-78f 75f-78f 78f-82f 78f-82f 68f-72f 65f-88f
WEEK 1
FLOWER
2
FLOWER
3
FLOWER
4
FLOWER
5
FLOWER
6
FLOWER
7
FLOWER
8
FLOWER
9
FLOWER
UMOL 200-300 300-500 500-600 600-700 700-750 750-850 850+ 850+ 850+
PHASE MOTHERS CLONE PHASE 1 VEG PHASE 2 VEG
UMOL 300-600 75-125 125-200 200-300
