Since Nebula has a VERY EXTENSIVE guide on every possible problem your plant could potentially have I will just give my two cents on how to fix about 90% of the problems that can occur when you are new to the subject.
1. Discoloration of the leafs.
This problem makes most first time growers loose their shit very fast. When you never had to take care of any plant at home it seems weird that there is something dying on a plant.
Main reasons leafs are dying:
- Leafs on the lower part on the plant die first. This is normal and occurs nearly everytime. Do not worry and move on. If you do not lollypop or defoliate it can happen that about 1/5 of lower growth will get dry in the course of the grow. The leafs are just light deprivated and the plant rather uses nutrition on leafs that get hit by more light.
- Leafs turn yellow at the end of the life cycle. This is very much dependent on your nutrient schedule and genetic. Have you flushed your plants? The plant will try to redistribute nutritions down to the roots. The leafs will turn yellow. Its harvest time, and you are pretty much simulating fall in your tent. Its normal. Some plants do not get yellow in the end. Thats also perfectly fine. Yellow leafs, after stopping nutrient supply is a common reaction.
- You are in the middle of a grow, and did everything according to the nutrient schedule as well as the soils instructions about nutrients? You might have a deficiency/toxicity going on. Read more in the next section…
2. pH value
This is actually very important knowledge. Soil is and inert medium. That means it is a living environment and can deal with out-of-order pH-values.
Since I am not a hydro dude, I will just say this: Get your pH straight. Buy some measuring stripes and look closely at the graphic below.
A good example is the tap water where I live. It has a pH value of 7.5 to 8.2. To make it simple: The pH value is responsible for the availabilty of certain nutrients your plant needs. It is similar to humans: If your diet is too one-sided you will get problems! The pH value in an inert medium can be buffered to some degree, meaning that a slight off will be taken care of.
My water will prevent most of the Copper, Zinc, Phosphorous and Iron to be left out in the feeding schedule and this will show in Leaf discoloration, reduced yield and growth and an overall unhealthy look.
Tip from the pro: Get a pH measurement device and dial that shit in. The optimal way would be the use of pH-up/down as a chemical addition to the feeding plan for every watering. You can also use lemon juice concentrate, especially when working with soil.
The perfect pH-value when working with soil is between 6 and 7.
3. The right temperature
The origin of cannabis in nature is pretty sunny and warm. A cannabis plant grows best between 20°C and 30°C. The optimal values would be the area between 23°C and 27°C. Since a lot of homegrowers do not use any climate control their only hope is air circulation and decent ambient temperatures. The temperatures of plants in vegetative growth can be slightly higher, according to the seasons: vegetative growth happens in the summer, where the temps are usually a bit higher. A plant can also go out of this range: A higher than 1500 ppm supply of CO2 and a very bright light can help a plants thriving at temps as high as 35°C! But this should not be the case for newcomers.
My tip: Build a setup according to my guides and check out how it dials itself in. If its in range, you are good to go. Do not expect massive outcomes if your room is always over 32°C!
If your room happens to be under your roof, without air circulation thats connected to active heating and temps are constantly below 18°C you will most likely stun the plant and the growth will come to a full stop. This will be lethal and most likely the death of your plants. A funtioning thermometer will work wonders!
If you read a few month online about growing you will notice that nearly everyone uses nutrition to some degree. The plant needs food to survive. You want it to create a decent amount of harvestable material in the end. Compare it to tomatoes: A food deprivated tomato will stay small and might not taste good. It needs light and the right diet to thrive and grow right. Its the same with weed.
People tend to overnute their plants at first! They read that they should put 5-10 ml that gooey brown stuff per 10l in their water and think: “Wow, that can’t be enough!”
Two weeks after these people usually message me on instagram.
Deal with nutes according to the instruction. That is also important for your soil! Cannabis grade soil is oftentimes prenuted to some extend and still people put in all types of liquids, solids, fungi, worms and FUCKING MOUNTAIN DEW into their soil even when the plant is only 2 cm tall.
Read the instructions and deal according to it.
Its pretty much fool-proof. And less is more with nutes!
5. The Watering plan
This is another controversial topic. I just leave my way of watering here:
I take up to 1/2 of the pots volume in water and flood the pot the plant is in. I do it gently to prevent the water from just pouring out of the bottom of the pot. This builds up airy channels in the soil and water can not be taken up by the plants as effective as before.
This will also create a runoff. When about 15% of the water volume are coming out of the pot you are doing it right, and the soil is saturated with water. Only moist soil will be rooted up!
After that procedure I wait between 2 and 7 days. Depending on the root system and the overall environment (Temperature and humidity) the water will get used up more or less fast. When i can put a fingertip into the soil and it feels very dry I repeat the process. This will oxygenate the soil and prevents the plant from “drowning”. I did that in the past four years and it worked very well for me.
Overwatering and underwatering can look very alike by the way!
If you overwater, the leafs will turn droopy but will still try to hold up at the base on the stem, while underwatered plants will just drop the leafs and crumples. Underwatering will be solved by just watering them. The effect will be visible in a few hours after that and the leafs will look healthy again.
Overwatering a plant is also not lethal: just leave the plant alone for a few days and do the finger-tip test.
If all that does not help you, scroll up and click on the first link in this post.