How to identify and treat nitrogen deficiency in plants

All plants need access to the right balance of nutrients in order to reach optimal health, but what happens when they can't?

There are various factors that could interfere with your plants' ability to get all the nutrients they need, which would result in your plants getting too little or too much of one particular nutrient.

In this post, we'll be covering what happens to your plants when they get too little nitrogen, which is one of the macronutrients your plants need to absorb so that they can carry out a number of essential plant processes. We'll also show you how to identify a nitrogen deficiency, as well as treat it depending on whether you're growing in soil or hydroponically.

What is a nutrient deficiency?

Before we get into the details of a nitrogen deficiency, it's important to understand what a nutrient deficiency is. As mentioned above, your plants will need to absorb the right balance of nutrients so that they can obtain good health.

That said, there are many factors that could prevent this balanced absorption, from incorrect pH to varying water quality or natural soil depletion. For a full lowdown on nutrient deficiencies, as well as a free downloadable checklist that you should follow before starting any deficiency treatment, check out our guide to common nutrient deficiencies and how to treat them.

Ultimately, your plants will need access to a range of macronutrients and micronutrients. As the name suggests, your plants will need larger amounts of the macronutrients, which include nitrogen, potassium, phosphorus, calcium, sulfur and magnesium. Your plants will also need its micronutrients, but in much smaller amounts; these include boron, copper, iron, manganese, molybdenum and zinc.

If your plants are getting too little of any one of these nutrients, it may start showing symptoms of the associated nutrient deficiency. However, your plants could also be getting too much of a particular nutrient, which may lead to a nutrient toxicity. 

The bottom line is that it can be tricky to diagnose a single nutrient deficiency, as it's actually far more likely that your plants are suffering from a combination of different nutrient deficiencies or toxicities at the same time.

This is why we recommend the prevention route; if you regularly monitor the fundamental parameters of pH, EC and temperature, you're less likely to run into a nutrient deficiency or toxicity.

You can use a handheld option such as the Bluelab Combo Meter or for 24/7 monitoring, you can use a monitor like the Bluelab Guardian Monitor Wi-Fi. 

Why is nitrogen important for plant health?

Nitrogen is one of the key macronutrients that your plants will need to be able to access in larger quantities. That's because nitrogen is responsible for a wide variety of plant health functions and essential plant processes. 

Nitrogen is especially important for plant growth, as it forms a key component of plant proteins and amino acids, which are considered to be the building blocks of your plants' overall structure. This is why poor plant growth is often one of the major visual symptoms of a nitrogen deficiency.

This macronutrient also plays an important role in photosynthesis, the process by which plants use light energy to create chemical energy, using carbon dioxide and water to create sugars while releasing oxygen as a by-product. Nitrogen helps in the formation of chlorophyll, a key component for photosynthesis, as these green pigments help to absorb light. Nitrogen is also used in activities related to enzyme reactions and plant metabolism.

In terms of how your plants access nitrogen and other nutrients, if you're growing in soil, they will obtain this from the natural composition of the soil you're using, as well as any additional fertilisers. In hydroponics, you'll most likely be using a premixed nutrient solution.

It's worth keeping in mind that some plant species will require a different balance of nutrients; some plants will also have different nutrient requirements according to where they are in their growing cycle. It's always worthwhile doing your research before you start growing your crops to help avoid running into any nutrient imbalances. 

What causes a nitrogen deficiency?

There are many possible suspects when it comes to determining the cause of a nutrient deficiency. In the case of a nitrogen deficiency, here is a list of some of the most likely causes:

• Incorrect pH (potential Hydrogen): The pH of your growing environment will determine your plants' ability to get all the nutrients they need. If it's too low or too high, some nutrients will be locked out from your plant. Shop Bluelab's pH products here. Find out more about pH in our article 'pH, EC and temperature - measuring and adjusting your fundamental parameters'. 
• Too little nitrogen is being provided: Your plants will get nitrogen from soil, premixed nutrient solution, fertilisers or additives. It may well be that they're getting too little nitrogen from these sources to suit their current health needs. 
• Natural soil depletion: The nutrients available in your soil will naturally decrease with time, which is why you would make use of fertilisers. In addition, nitrogen is soluble, which means that during times of frequent and heavy rain, it could get washed out of your soil.
• Too much manganese, chloride, potassium or zinc: When present in high quantities, certain nutrients or elements could prevent your plants from absorbing nitrogen in the quantities they need. 
• A damaged or dysfunctional root system: If your plants' root systems have been damaged due to disease or another reason, this could prevent them from carrying out optimal nutrient uptake, which could lead to a range of nutrient deficiencies, including nitrogen deficiency.

The list above is by no means exhaustive, and there could be other reasons why your plants would be suffering from a nitrogen deficiency. If in doubt, it's definitely worthwhile calling in a plant nutrition expert. 

How to identify a nitrogen deficiency in plants

As mentioned above, nitrogen plays a major role in a number of important plant health processes, so it should come as no surprise that signs of poor health are often the first symptoms of a nitrogen deficiency in plants.

Here is a list of the most common visual symptoms associated with a nitrogen deficiency:

• Yellowing lower leaves, while the leaves at the top of the plant are a pale green
• Weak shoots or branches
• In some plant species, you may see purple stripes on the plant stems
• Over time, leaves will turn brown and wither, eventually falling off
• Flowering and fruiting will be reduced
• Stunted plant growth
• Reduction in new leaf growth
• If allowed to persist, this deficiency will drastically affect crop yield

How do you treat a nitrogen deficiency?

Nitrogen is a major component of most nutrient mixes and fertilisers so it may be quite tempting to simply increase the amount supplied to your plants. However, since these mixes contain other nutrients as well, your plants will also get an increased amount of these, which could cause other issues over time.

Instead, we advise that you contact your local grow shop or a plant nutrient expert, as they will be able to recommend a nitrogen-specific nutrient additive that you can use. As with any treatment, make sure that you get the correct product for your chosen growing medium, as these may be different depending on whether you're growing in soil or hydroponically. In addition to nutrient additives that you can apply to your plants' root zone, you may also be advised to make use of a foliar spray, usually containing urea, that can be applied to your plants' leaves.

For soil-based plants, growers should consider mulching with organic matter, such as compost or manure, as this can lead to a steady supply of nitrogen in the long term. However, you should avoid using organic matter that contains high levels of carbon, such as sawdust, as the organisms living in your soil will use nitrogen to help break down carbon, further exacerbating a nitrogen deficiency.

Further resources

If you'd like to find out more about nitrogen deficiency in plants and how to treat it, take a look at these additional resources:

• Common nutrient deficiencies in plants - and how to fix them
• pH, EC and temperature - measuring and adjusting the fundamental parameters
• 7 easy methods to add nitrogen to your soil - The Gardening Channel
• What is nitrogen - plant deficiencies - CANNA UK
• How to fix nitrogen deficiency in plants - The Practical Planter

Featured products: 

Bluelab Combo Meter
Bluelab Guardian Monitor Wi-Fi