nitrogen bro thats all the big N.
Nutrient Problems
Nitrogen Deficiency
Cannabis is a fast growing plant species and requires generous amounts of nitrogen throughout growth and early flowering. Nitrogen is regarded as belonging to the group of three primary nutrients essential for plant growth. The other two nutrients in this group are phosphorus and potassium. These will be dealt with here separately. Nitrogen is stored mainly in the leaves and shoot tips, which is why it is inadvisable to remove healthy leaves on plants, as these are the "storage house" for important nutrients. The production of enzymes, proteins, chlorophyll and other vital ingredients for healthy development are all dependent on nitrogen. Chlorophyll lends plants their green color which is why yellowing leaves are a telltale sign of N deficiency.
Causes:
A serious pest infestation of aphids, white flies, or spider mites that suck out the leaves leads to deficiency symptoms.
Too small container size for adult plants is one of the most common mistakes in cannabis growing. Especially in light intensive situations such as balcony or garden grows the plants will quickly yellow and wilt. Don't be too lazy and repot your plants. You can do this up to the third week of flowering even.
Poor soil quality. The second major cause for a deficiency. The importance of using quality grade horticultural soil cannot be stressed enough. Do not use topsoil from the forest if you are not certain about it's nitrogen content. Decomposed leaf material contains no nitrogen (obviously since these are the yellowed leaves shed by the trees!) and makes up for a large percentage of forest topsoil. Also loamy and sandy soil are mainly devoid of important nutrients. If you do utilize such soil in guerilla grows, etc. then make sure to supplement it with long term acting fertilizer, or enrich it with a mix of organic nutrients (bat guano, composted soil, etc.) that have sufficient quantities of nitrogen to support plant growth.
A pH imbalance will block nutrient uptake in the root zone. Make sure that you keep the pH within the acceptable range for soil or hydroponics.
Lack of fertilizing. A minimum of fertilizing on soil is usually necessary to boost plant growth, since cannabis tends to grow faster than the roots can assimilate the natural nutrients in soil. In low light situations or indoors this is less of an issue than in a greenhouse/outdoors/or in a setup using CO2. With high quality soil and a good container size you can probably do without any grow fertilizer if you are cultivating short to medium sized plants.
Symptoms:
The lower leaves yellow between the veins until the entire leaf is eventually yellow. It wilts and dies.
The symptoms spread upwards affecting all sun leaves and then the smaller and younger leaves as well.
Plant growth is inhibited. The plants remain short and underdeveloped if nitrogen deficiency is severe in the growth phase.
During flowering early deficiency can lead to a significant decrease in yield. Plants that are in the last 3 weeks of flowering do not require nitrogen if they have remained reasonably healthy up to that point. A yellowing and shedding of leaves during the final weeks of flowering is quite natural among otherwise healthy plants and should not be held up by heroic dosages of nitrogen (which would result in many undesirable complications such as: mold, sudden stop in bud development, dying of pistils, over-fertilization, rejuvenation/leaf growth in buds).
Appearance of male flowers on female plants.