In order for a plant to photosynthesize and produce sugars to feed itself and grow, there must be a readily available supply of Nitrogen within the grow medium. During the growing stage plants will require Nitrogen in order to grow lush thick leaves, which over time will naturally want to darken to aid photosynthesis further. There is a big misconception that during the flowering phase, it is a good idea to cut off the Nitrogen uptake of the plant and allow it to feed solely on the Phosphorus and Potassium. Often bedroom growers and beginner growers can be challenged with a cannabis plant which has become a distained yellow and looks lifeless. It is debatable if the plant has any Chlorophyll A+B left inside the leaves, amino acid production, plant vigour and new growth have totally given up.
When this does happen the grower can often be left panicked and extremely unmotivated to finish the grow. It seems like it is easier to get hold of some clones and throw a sea of green project together where your yellow crisp plants currently stand. I remember when I was much younger growing plants that were totally yellow by the end and not being any wiser to why. Understanding what has caused the yellowing of the plant and what further problems can lead from this, then makes the job of maintaining adequate Nitrogen levels within the garden easier.
You may notice that when a good organic or veganic grower harvests their plants, there will be only vibrant green leaves growing, even upto the neat trimming job. If you consider how many new leaves and shoots the plant will produce once flowering is induced, then it makes zero sense to cut off Nitrogen. The feed you may find on a nutrient for the growing phase will be something similar to 5-3-4 then during flowering the ratio will change to something similar to 2-7-8, then later a heavy feed of Phosphorus and Potassium. Many growers find using 0-13-14 for the last part of flowering highly beneficial in pushing for weight.
A one part solution feed can often cover all the angles of the plants requirements. The plant will still feed accordingly to what it needs and when it needs it. If you can make an effort to ensure there is a high Nitrogen content within the grow medium or through liquid feed, you should never see a yellow leaf during the entire grow. A yellow leaf or multiple yellow leaves is not something you see in nature or is it something you really see on amazingly grown cannabis plants. I would personally recommend using something with a ratio such as 7-6-5 all the way throughout. During the transition phase, the cannabis plant actually uses as much Nitrogen as it does Potassium until harvest. Recent studies have shown that Phosphorus is the least element used during the flowering phase, in comparison to the high levels of Nitrogen and Potassium. Hopefully this is a reminder to those overzealous growers who go high with Phosphorus and Potassium levels.
To begin with once there is a lack of available Nitrogen, the plant will remove it from the leaves one by one, until it has the necessary amount to continue growth. The colour of the once so waxy dark green leaf will become a pale yellow. The yellowing can occur very quickly and the pale will become a dark yellow. Similar to when you see a yellow leaf falling off a tree in winter, when there is no need for the tree to support the leaves. The tip of the leaves will grow inwards and over a short time, the connecting leaf can be broken off with the touch of a finger.
If you come across this then by knowing how many leaves have become yellow and useless, is an indication to what levels of available Nitrogen there are. If you return to your garden after 3 days and find nearly all of the fan leaves have yellowed during that time, then you will know that is how quickly the plant used the Nitrogen. Imagine being in a gym and being pushed to work at your fastest rate. With a decrease in water or protein, your performance will be majorly affected. This is the same scenario with cannabis plants and should be treated with the same severity.
There is a high level of Nitrogen and Auxins within our urine. This is a simple solution that should be mixed 1 part urine to 9 parts water. When used without water, this can have adverse effects and create bad smells.
Many organic nutrient companies sell a powerful strong smelling fish mix. This can have all of the essential minerals the plant needs, as well as a rich source of Nitrogen. Be Careful when using a fish mix outdoors as it can attract insects and other curious animals, due to the overbearing aroma.
Something I personally love to use as it is highly beneficial from seed until bloom. You can purchase bat guanos which can be a ratio of 10-10-8 and these types are amazing. Other bat guanos are more heavy with Phosphorus and Potassium, however it depends on the location of the source. Indonesian Fruit Bats guano will generally produce rich levels of Phosphorus and Potassium whilst seabird or Peruvian bat guano will have a high Nitrogen ratio.
If using dry sea weed to mix into the grow medium then this is a great way of allowing a Nitrogen rich nutrient, to slowly buffer and break down into the medium. In addition liquid seaweed feeds can be cheap and most effective. Seaweed fed directly into the roots or as a foliar spray have instant results and often promote thick lush leaves and stems.
Generally from horses and used for outdoor projects, horse manure similar to compost is going through a process of breaking down. Once in the medium and encouraged by the right atmospheric conditions, Nitrogen will be readily available through a longer period of time. A ratio of tested horse manure tea read 1.1-0.8-1.3.
Using alongside bat guano will set you up for the healthiest plant you may have ever seen. Worm castings are basically the excrement of a worm, once it has eaten through soil. The worms job is to simply aerate the earth's soil and as it does so by recycling what is considered as refined compost soil. Considering that the worm has now produced something from the soil which has had years of life force growing within, worm castings are super rich in all of the essential elements and microbes a plant needs from start to finish.
By Stoney Tark