Light, Temperature, Nutrients, and Your Grow


Light quality denotes the color or wavelength of the light. Blue light has shorter wavelengths and is best for vegetative growth. While red light has the longest wavelength and is best for flowering.

When it comes to light intensity, every plant differs in their requirements and adaptations to tolerate different levels. If you are thinking about moving a plant to a higher intensity light environment make sure you do it gradually so the plant has time to build up a waxy coating on its leaves to protect against sun burn. It is also important to stay within that plant’s limitations, so do you research and find out what type of light intensity your crop needs.

Light duration is the measure of light exposure. When starting plants indoors, light duration should be approximately twelve to fourteen hours.

Photoperiod is the duration of continuous darkness, and most plants’ flowering growth phase is triggered by photoperiod. Plants can be divided into Short-Day plants, Long-Day plants, and Day-neutral plants. Short-day plants respond to extended periods of darkness. Long-day plants respond to shortened periods of darkness. Day neutral plants enter the flowering growth phase despite the increased or decreased duration of uninterrupted darkness.


The most influential temperature factors that affect plant growth and vigor include: the average daytime and nighttime temperatures and the difference between them; as well as, the maximum and minimum daily temperature. These are fairly straight forward in an indoor growing environment where you have the ability via heating, air conditioning, venting and fans to control these and the swings associated with them. However, this becomes a bit trickier when you take the growing scenario outside, especially in mountainous regions.

It is always important to take into consideration the microclimate of your outdoor gardening space. Factors that affect your garden’s micro climate include elevation, exposure, and thermal heat masses. For every 300 ft increase in elevation, there is about a 1˚ F decrease in temperature. Exposure is greatest to the south and least to the north. And lastly consider objects that could act as “heat sinks” that increase the temperature of your garden during both the day when the sun is beating down on it, and at night when it is radiating the collected heat from the day time.

So how exactly does temperature affect plant growth and vigor? The most important factor here is whether the crop is cool or warm season plant. Germination of cool weather crops occurs between 40˚ F and 80˚ F, while warm weather crops germinate between 50˚ F and 90˚ F.

Generally speaking, as temperature increases both photosynthesis and respiration increase until that plant’s upper-temperature limit is reached. At this point, respiration exceeds photosynthesis. In other words, the plant is consuming more sugars than it is making, and growth and vigor come to a screeching halt. In addition, because your crop is burning more sugars during increased respiration the sweetness factor, or Brix level, of your produce is decreased. Your flowers will show signs of increased respiration with fading colors and a shorter flower life.


Nutrient requirements differ during vegetative and flower growth cycles. During vegetative growth, your base nutrient needs to be nitrogen rich. This is because nitrogen promotes chlorophyll production, which is the key ingredient for vigorous vegetative growth. Two other nutrients, magnesium (which is at the center of each chlorophyll molecule), and calcium (which provide structural stem growth and support) are key elements needed in higher quantities during the vegetative growth phase. During vegetative growth, excess sugar is produced for use during the flowering growth phase.

During the flowering stage of the plant growth cycle, it is phosphorus and potassium that are needed in higher quantities. Phosphorus acts as a flower growth enhancer, while potassium, acts as a ripener, or finisher at the end of growth. During flowering, excess sugar created during vegetative growth are utilized. You will see these nutrient needs reflected in most nutrient lines where most Grows are nitrogen rich and Blooms are phosphorus and potassium rich.