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Are Yellowing Leaves During Late Flowering A Problem?

Yellowing leaves during later flowering, are arguably the most frustrating thing to happen to, newbie, cannabis growers. After all, you thought you were doing everything well, and you were in the clear. You are now ready to be soon able to enjoy your buds. However, it’s week 9, and flowering starts, and to your horror, you notice that the lower cannabis leaves are yellow. Some of them even looking like they will die!

Spoiler alert, yellow leaves during late flowering is likely caused by a nutrient deficiency. (most likely Nitrogen)

What did you do wrong! Can this be fixed? Does it even need to be fixed?

Find out more in this article where I will tell you the following:

  • Other Reasons For Yellow Leaves
  • Why Nitrogen is Necessary
  • Symptoms of Nitrogen deficiency
  • How to Fix a nutrient deficiency

And More . . .

Other Reasons for Yellow Leaves

There are several other reasons for yellow leaves on cannabis plants. Although similar, each of these problems has different symptoms than the typical plant nitrogen deficiency. Those reasons are soil PH is too high or low at the root level and over or under-watering.

Soil PH Not At The Right Level

No matter how well you fertilize or prep your cannabis plant, a cannabis plant’s leaves may become prematurely yellow if the soil PH is not at the correct level. The reason for this is that weed will have a harder time absorbing nutrients when soil PH is not up to par.

How Can You Discover and Fix This?

Bluelab PENPH pH Pen Fully Waterproof Pocket Tester, Easy Calibration, Double Junction Probe for Improved Accuracy and Durability
PH Tesing Pen

All you have to do is check the soil or water, if you are growing hydroponically, with a PH pen. This article on PH pens for soil and hydroponics will tell you how you can best do that.

How Is This Different From A Nitrogen Deficiency Right Before Harvest?

With a soil PH problem the fan leaf will tend to be yellow spotted, striped or patched, and burned around the edges. You can differentiate this from a nitrogen deficiency because the yellowing leaves are all over and are not grouped at the bottom of the cannabis plant.

Not Watering Correctly (Over and Under)

Over Watering

Overwatering is a common mistake that many newbie growers make, which is not surprising. When you start, the newbie generally tends to be over-attentive to their cannabis plants. However, overwatering may lead to your cannabis plants not getting enough oxygen, which results in the roots being malnourished. Yellow leaves throughout the plant are the main symptom of this.

Under Watering

This is another reason for yellow leaves. Surprisingly, unless you forget or something happens that makes you unable to water your plants, under watering is less likely to occur than overwatering.

Other Reasons

There are several other reasons for yellowing leaves (other than an N deficiency) that are listed below.

  1. Light Burn
  2. Heat Stress or Too Cold
  3. Other Nutrient Deficiencies like magnesium deficiency and Iron deficiency
  4. Not Enough Light for seedlings.
  5. Pests-The spider mite, as an example, can cause a yellow leaf to appear.
  6. Bud Rot

Click Here for an excellent overview of recognizing and fixing each of the above problems.

Why Does Cannabis Need Nitrogen?

Nitrogen (”N”) is one of the essential plant nutrients as it helps with the following:

  • Production of DNA
  • Forms the amino acids, which start the process of building essential proteins
  • Develops chlorophyll

All of these are essential for vibrant cannabis plants and buds.

How Can You Tell If you Have a Nitrogen Deficiency?

Nitrogen affected leaves will normally be yellow and somewhat brownish. They also will be soft and tend to fold inward. The biggest difference between a nitrate deficiency and other reasons for yellow leaves is that a nitrogen deficient fan leaf will start with the older leaves near your plant’s base, and the upper leaves will tend to look normal.

This indicates a nitrogen deficiency because when the older leaves do not have enough nitrogen, they will sacrifice themselves for the newer or upper leaves. The plant is essentially eating itself to get all of its required nutrients. At the final stages, the lower affected fan leaves will eventually fall off.

Is a Yellowing Leaf Always Bad?

First of all, it is not always bad when your leaves start yellowing during late harvest. This often happens during the eighth or ninth week during the flowering stage. Most cannabis plants are ready to harvest in around eight to nine weeks. So, If this happens when you are almost ready to harvest, it is not an issue.

It is a problem though if it starts to happen too early. For example, it could be a problem if 6 weeks into flowering yellow leaves appear. If the yellowing starts too soon, it will eventually start to creep up to the younger, healthy green leaves. If left unchecked, all of the leaves will eventually become yellow, which will eventually result in either the plant dying or if it doesn’t die, you’ll have, poor quality and smaller buds.

How Can I Fix A Nutrient Deficiency?

The following guidance is based on the assumption that the supposed N deficiency is actually a problem that needs to be addressed. Because, as I stated earlier, a cannabis leaf yellowing is natural and perfectly acceptable during the late flowering stage. However, if the deficiency signs occur too early (I.E., during the vegetative state) and you get you will want to fix this problem ASAP.

To fix it, you simply add organic or synthetic fertilizer to your plants. An all-purpose growing fertilizer should do this for you. However, the results are often not as precise as you might prefer. So, it is best to apply specific nitrogen-based fertilizers. For the organic route, older poultry manure should do the trick




Espoma GM25 Organic 3-2-3 Chicken Manure, 25 lb
Organic Nitrogen Source



Too much nitrogen leads to toxicity, which can be as big or a problem as a deficiency. It should go without saying that follow the instruction for using the fertilizer.

Final Thoughts

If you follow proper growing procedures, nitrogen deficiency should not occur. This means prevention should be your number one goal. So, apply a general grow fertilizer and plant food. Also, check your soil ph, don’t over or underwater, etc. Above all, watch your cannabis plants like a hawk to see if any nutrient or other problems. And when, and if a problem occurs, be sure to nip it in the bud before it gets worse.