I learned a lot from my first grow and wanted to share some things I think are important. There is so much more to learn, it is exciting!
I made some mistakes along the way but "mistakes are the tuition to success". Every time I make a mistake, I will do my best to learn from the mistake so that it will never happen again. Mistakes help you grow in many ways ;)

I had some trouble with
Even Node Spacing:
You can control your node spacing by...
LST
Mainline
Scrog
FIM/TOP
Temps
Light distance
"Too much distance between internodes is not a good thing. Some strains, like sativa varieties, may naturally grow taller and stretch more than other strains. However, if the internodal distance is too long, branches and stems become weaker. This means that buds will have to be supported during flowering, with the risk that the branches will snap otherwise."

"If we want to prevent stretching, we’ll need to know what causes it first. Genetics can play a major role here, but for our current intents and purposes, we can throw it out. Beyond your choice of strain, you don’t have much control over the plant genes. What you do control is the environment! The two primary factors you’ll be monitoring are heat and light."
https://www.theweedblog.com/how-to-grow-dense-and-bushy-marijuana-plants/

Cation Exchange Capacity
"Cation exchange capacity (CEC) is a measure of the soil’s ability to hold positively charged ions. It is a very important soil property influencing soil structure stability, nutrient availability, soil pH and the soil’s reaction to fertilizers and other ameliorants"

"The clay mineral and organic matter components of soil have negatively charged sites on their surfaces which adsorb and hold positively charged ions (cations) by electrostatic force. This electrical charge is critical to the supply of nutrients to plants because many nutrients exist as cations (e.g. magnesium, potassium and calcium). In general terms, soils with large quantities of negative charge are more fertile because they retain more cations (McKenzie et al. 2004) however, productive crops and pastures can be grown on low CEC soils."
http://www.soilquality.org.au/factsheets/cation-exchange-capacity

This video really helped me understand:


Relative Humidity
"the amount of water vapor present in air expressed as a percentage of the amount needed for saturation at the same temperature."
"In all stages of cannabis growth your plants will have a constant need to intake water, and the amount of water they need fluctuates with the humidity in your grow room. When the humidity is high, cannabis plants use their leaves to absorb moisture from the air which causes them to drink less water from their roots. Conversely, when the humidity is low, they will pull more water in through their roots.
Since humidity changes how much water your plants drink, and the water you give your plants have nutrients in them, being in control of humidity gives you increased control over your plant's nutrient intake."
http://www.growweedeasy.com/humidity

Vapor Pressure Deficit
"Vapour-pressure deficit, or VPD, is the difference (deficit) between the amount of moisture in the air and how much moisture the air can hold when it is saturated. Once air becomes saturated, water will condense out to form clouds, dew or films of water over leaves."

Herbin Farmer has a helpful video about it:

 

Powdery Mildew
Powdery mildew is not systemic. Its endophytic. 
Spores remain dormant until conditions are right. 
UV-C light will kill spores. 
PM can stunt growth. 
PM produces ascospores, a sac-like ascus enclosed in a fruiting body called a chasmothecium (pictured). 
Liquid water on leaves inhibits spore germination. 
“Unlike most fungal pathogens, powdery mildew fungi tend to grow superficially, or epiphytically, on plant surfaces. During the growing season, hyphae are produced on both upper and lower leaf surfaces, although some species are restricted to one leaf surface only. Infections can also occur on stems, flowers, or fruit. Specialized absorption cells, termed haustoria, extend into the plant epidermal cells to obtain nutrition. While most powdery mildew fungi produce epiphytic mycelium, a few genera produce hyphae that are within the leaf tissue; this is known as endophytic growth.
Conidia (asexual spores) are also produced on plant surfaces during the growing season. They develop either singly or in chains on specialized hyphae called conidiophores. Conidiophores arise from the epiphytic hyphae, or in the case of endophytic hyphae, the conidiophores emerge through leaf stomata.”
http://www.apsnet.org/edcenter/intropp/LabExercises/Pages/PowderyMildew.aspx

 

Conidiophores

Conidiophores

Foliar spray
I learned why you shouldn't foliar spray with the lights on...
", intense light can produce light reflection from water droplets that causes your leaves to burn."
http://www.ilovegrowingmarijuana.com/how-to-foliar-feed-your-marijuana-plants/

"foliar spraying burn happens when the curved surface of the droplets of water create a lens, magnifying the light and burning small spots on your leaves where the droplets were"
https://forum.grasscity.com/threads/foliar-spraying-burn.170215/

Fungus Gnats:
I had some fungus gnats get into my tent and realized that the only plant affected was the plant that didn't have cover crop yet. I think the cover crop might have helped deter the fungus gnats because the gnats might not be able to get into the soil as well. I added some diatomaceous earth to the affected soil and it seemed to work.
http://www.growweedeasy.com/fungus-gnats

I think that is about it! Can't wait to see what I learn in the next round! If you have any suggestions for what I should be learning, please let me know! Thanks!

Learning Goals for next round:
Learn more about how LEDs work
Learn more about IPM (Integrated pest management)
 

Much Love,
Herbal Visionz