How Plants Use Nitrogen & Ways to Detect Deficiencies

Plants use the nitrogen they absorb through their roots from soil or potting mix with nitrates and ammonia to create amino acids that become proteins that help them with growth and their metabolism to survive. Their metabolism is what converts light, water, and nutrients into the molecules they need to survive. Just like human bodies which use nitrogen as one of the building blocks to form proteins via amino acids. 

Nitrogen is found in every part of the plant including the leaves, stems, fruits, roots, and even the seeds as it is used for:

• Germination

• Photosynthesis

• Growth

• Nutrient absorption and uptake

• Life function including developing chlorophyll

• Assisting in surviving environmental stresses like drought

In fact nitrogen is the most common element found in plants because each part uses it. 

Fun fact: Nitrogen levels impact flower size, quantity, and quality helping to attract pollinators.

This is why it is important to make sure that your plants, whether they’re vegetables like tomatoes, rare tropical houseplants, or cacti in a decorative rock garden, get enough nitrogen. Here’s some of the ways to determine whether your houseplants and gardens have enough nitrogen, how to measure the levels, and add nitrogen back in when there is a deficiency.

The signs of a nitrogen deficiency in a plant include:

• Foliage yellowing at the tips and then spreading throughout the rest of the leaves.

• Smaller than expected or than the average fruits, flowers, and foliage.

• Less annual growth, or stunted growth during the normal non-dormant period.

Nitrogen helps with creating food and new cells via amino acids, so when there is a lack of it the plant cannot grow as large or as healthy. The reason the leaves turn yellow from a nitrogen deficiency is the plant moving the available nitrogen to newer leaves leaving the older ones unable to phosynthesize as well as a plant without a nitrogen deficiency.

There are multiple types of nitrogen testing kits you can buy online, at hardware stores, and home and garden shops. Three popular kits include:

• Colorimetric tests where you collect a sample and match the result to the color on the matching chart. If the color matches a nitrogen deficiency, you’ll need to add more.

• Nitrate testing strips test the soil or potting mix for nitrogen letting you know if there is a good amount, not enough, or excessive levels. The difference here is that nitrate is the compound found in the potting mix or soil itself while nitrogen is a gas that is in the air, most people intermix them in casual conversation when talking about plant nutrition.

• Sap tests can also be done where you use a nitrate testing strip or a Cardy meter in the sap vs. the soil or potting mix. 

If any of the testing methods above show your plants need more nitrates, it is easy to add more.

Adding nitrogen to garden soil or potted plants is easy and inexpensive. For outdoor plants, try adding organic materials like mulch or compost to the garden on top and mixed in. These materials are rich in nitrates and may also have phosphorus and other nutrients plants need.

Fertilizing plants is another way to get outdoor plants enough nitrogen, or plant a mix of “nitrogen-fixing” plants like clovers, alfalfa sprouts, and beans. These plants absorb the gaseous nitrogen from the air and push it into the soil where the other plants can absorb it as a nutrient.

To add nitrogen to houseplants, start by adding plant food to the potting mix as it will contain other nutrients that may be missing if there is a nitrogen deficiency. If it's been about a year or two since your houseplant has been replanted, it could be time to increase the pot’s size so the plant does not become root bound, which also means replacing the potting mix. Choose one that has nitrogen and other nutrients and problem solved.

Nitrogen is an essential nutrient for plants to grow and is found in all parts of the plant. If you notice leaves yellowing at the tips and then spreading, or stunted growth, your plants may have a nitrogen deficiency. Get a testing kit and see. If there is one, add fertilizer to your outdoor garden or use plant food for potted plants. Nitrogen deficiencies are nothing to worry about in plants as they are easy to remedy.