So these three plants are about one month old now (from seed). I'm expecting to have them in veg for at least another month or so, i guess, but i need to get some height going. I just transplanted them from one gallon into the 3 gallon pots this past weekend. They are very short and stocky. Mars Hydro says between 18-24 for veg. I had the lights at about 18-19 from the plants, but I'm wondering if i raise them up to 24, will that make the plants start to stretch, and get taller? Just curious. Trying to learn. Have a great day everybody.
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Sorry for the long read but it‘s more than just set the light at x distance from the plant. There’s a balancing act between light, temp, and humidity.
Light
Photosynthesis depends on the availability of light. Generally, as light intensity increases, so does photosynthesis. However, for each plant species, there is a maximum level of light intensity above which photosynthesis does not increase.
Download the Photone app and use a diffuser (piece of printer paper) over the phone’s front camera or use a PAR meter.
Set the light intensity to 100 PPFD at 18/6 light/dark schedule. for seedlings and clones.
Adjust to 463 PPFD in veg (3-4 nodes) at 18/6 light/dark schedule.
When your auto begins to flower turn up the light to 617 PPFD but leave schedule at 18/6.
If you’re growing photos when you flip 12/12 for flower, you have to turn up the light to 917 PPFD. 12/12 is 50% the light of 18/6 so to give the same amount of daily light you have to turn up intensity by +50%.
Daily Light Integral (DLI)
micro Mols per second = PPFD
PPFD * .0036 (3600 (sec in an hour) / 10^6) = Hourly Light Integral (HLI): example: 600 * .0036 = 2.16
HLI * hrs of light per day = DLI: example: 2.16 * 18 = 38.88
Maintain 38-40 DLI in veg and bloom.
Temp
Although not a direct component in photosynthesis, temperature is important. Photosynthesis occurs at its highest rate between 65° and 85°F and decreases at higher or lower temperatures.
Ensure your light and other equipment isn’t heating your leaves too much. Ck with a IR thermometer. I prefer 75-85F leaf surface temp. I’ve heard others go higher. Sample various places around the plant.
If leaf temp is too hot raise the light and readjust intensity to your PPFD requirement.
As the plant grows raise the light, ck leaf temp, and adjust intensity.
Humidity
When a leaf's guard cells shrink, its stomata open, and water is lost. This process is called transpiration. In turn, more water is pulled through the plant from the roots. The rate of transpiration is directly related to whether stomata are open or closed. Stomata account for only 1 percent of a leaf's surface but 90 percent of the water transpired.
Transpiration is a necessary process and uses about 90 percent of the water that enters a plant's roots. The other 10 percent is used in chemical reactions and in plant tissues.
Transpiration is responsible for several things:
Transporting minerals from the soil throughout the plant.
Cooling the plant through evaporation.
Moving sugars and plant chemicals.
Maintaining turgor pressure.
The amount and rate of water loss depends on factors such as temperature, humidity, and wind or air movement. Transpiration often is greatest in hot, dry (low relative humidity), windy weather.
Once your light intensity and leaf temp is set, set the grow space relative humidity (RH). Heat and humidity go hand in hand to keep the plant transpiring.
Use a dehumidifier or humidifier that has a humidity sensor and can turn on/off the device to maintain a RH range.
Look up your leaf temp on a vapor pressure differential (VPD) chart and set your humidity measured at the canopy in the range for your stage of growth.
Set the RH for the max leaf temp. When the plant cools at lights off the VPD should remain in the range for the RH setting.
Example: if my max leaf temp is 81F in mid/late flower, set the RH to 40% so when the lights are off and the plant cools to 73F it remains in the VPD range. If I set the humidity to 50% (which is in the VPD range for a max 82F leaf temp), when the plant cools at lights out it would fall outside the VPD range.
This is important: If relative humidity is low, the VPD can be too high, which may cause stunted growth. On the other hand, a low VPD correlates to high relative humidity, and can result in disease and mineral deficiencies.