The first and most important nutrient to the marijuana plant is Nitrogen(N). It is a macro element and is extremely mobile. It is what gives the plant it's green color and is the most important in the growth or vegetive stage of your plants life. It is directly responsible for the production of chlorophyl, photosynthesis, and amino acids which are responsible for building proteins within your plant.
Nitrogen(N) is also the biggest mobile element so it can travel anywhere on the entire plant. That means it will show up on the older leaves first as the plant will move what it does have to create the new growth. If the plant is starved for Nitrogen(N) it will start out with the older leaves yellowing working into a purplish color. Unlike a Magnesium(Mg) deficiency Nitrogen(N) starts at the tips and works its way back where Magnesium(Mg) starts with the entire outer part of the leaf yellowing while leaving the veins green.
In the late part of flowering your plants will show a Nitrogen(N) deficiency but this is the one time you leave it alone. Your plant is concentrating on making flowers so let it use its stored Nitrogen(N) and yellow out on its leaves.
Too much Nitrogen(N) can also be a problem with the leaves being dark green and the plant not wanting to mature properly. It can also make a tall lanky plant with extremely weak stems looking like it is going through a drought. Big fan leaves will have the "claw" look to them and new leaves will grow in twisted. To much Potassium(K) or Nitrogen(N) will also show signs of a Calcium(Ca) deficiency because it will lock out that element just like improper PH of your water will. Proper PH of water should be about 6.5 for soil. Hydro and soiless should be about 5.8 and we always germinate our clones in rockwool at 5.5. These are the best number for ALL nutrients to be absorbed into the plant so they are not locked out. Nitrogen(N) specifically gets locked out of plants growing in soil at a PH of below 5.5 and higher that 8. Hydro and soiless locks out Nitrogen(N) at 5.25 and lower with 8.25 and above doing the same.
So what to do if you have a Nitrogen(N) deficiency. Don't worry, easy to fix. Recognizing that you have one is half the battle. So maybe your into strictly organic nutrients. Still easy to do just keep in mind that any organic nutes I am always for adding it as a liquid. For instance blood meal, cotton seed meal, bat guano, fish meal, worm castings, etc. All good sources of Nitrogen(N) but I never mix these things into the soil. The reason I never do is it is very easy to overdo stuff like this because unlike chemicals you never know exactly what you got. First thing I do is to take ingrediants like mentioned previously and make a tea out of it. I have an old pillow case that I can put whatever I want in it and let it soak in my water then I pour this "tea" into my plants. If I overdid it I can simply do a flush and remove it. When it is directly added to the soil in its natural form that makes it very hard to remove.
Let's take a moment to hear what some of our favorite hydroponic grow stores in SLO Counties Central Coast have to say about how they handle a Nitrogen(N) deficiency.
Starting north up in Templeton we talked to Nick at the Garden All Year hydroponic grow store. Nick loves to go the natural organic route and recommends to his customers to hit their Nitrogen(N) starved plants with alfalfa meal and feather meal. These are great solutions for the grower that doesn't want to get into all the chemicals for their plants. He carries several lines of nutrients which will also take care of even the worst Nitrogen(N) deficiencies. Companies like FoxFarm which have their Grow Big with an NPK of 6-4-4 works great but also General Hydroponics and Cutting Edge have their solutions for Nitrogen(N) but combine them with other nutrients to make an all around fertilizer which should help the grower in their overall garden picture.
Our next hotshot grow advisor was south of the Cuesta Grade and he was none other than Grady from the Healthy Harvest Hydroponic Grow Shop in San Luis Obispo. He recommends Aurora Innovations as one of his main lines of nutrients that his store carries. Their Roots Organics liquid nutrients have been a staple in his store for some time now. These nutrients have been an overall program that has helped many growers take their crop to the end with the full potential. For Nitrogen(N) Grady uses Auroras Grow-N with an NPK of 8-0-0. That should give your plant a big shot to green them up. And don't forget Holy Batshit Batman because Aurora also has their Super Nitro Bat Guano with an NPK of 15.5-1-1 rating pretty high on the Richter Scale of a totally organic Nitrogen(N) solution. Just remember with high numbers like these products produce it is very easy to nute burn your plants so be careful and use it in a tea so you can flush it out quickly if you use to much. For hydroponic growers Grady looks overseas to the Dutch with House & Gardens line of nutrients. They use their Nitrogen Boost to give their plants a major green rush to get them over the pale green leaf blues.