(Psst: The FTC wants me to remind you that this website contains affiliate links. That means if you make a purchase from a link you click on, I might receive a small commission. This does not increase the price you’ll pay for that item nor does it decrease the awesomeness of the item. ~ Daisy)

Once upon a time, there was a tomato growing in my garden. It was beautiful and the first tomato of the season. Red and round and perfect, I was so looking forward to biting into it, letting that homegrown goodness slide down my taste buds. I watched it carefully, and when the day came to harvest it, I did so.

I then turned it over to admire it from that angle, only to discover that my beautiful tomato was rotten nearly halfway up. The rot started from the blossom end and was nothing other than blossom end rot, a calcium deficiency that affects tomatoes, watermelons, and a host of others. I was so bummed! But facts are facts, and I was simply out of luck. 

Nutrient deficiencies in plants are very similar to nutrient deficiencies in humans.

If you don’t get enough of them, you end up with problems.

Remember, plants need certain nutrients in order to grow healthy and produce fruits. A lack of any of those nutrients will interrupt the process and foil our food growing plans. This is a fairly large topic, so I’ll handle it in installments. Let’s take them one by one, starting with the majors. In this article, I’ll discuss how to diagnose and deal with problems arising from NPK nutrient deficiencies. The next in the series will tackle the secondary nutrients, with the micronutrients handled in the third. 

First, let’s discuss the diagnosis.

This process is the same regardless of the issue and is the tool that will lead us to the source of the problem. Observation and note-taking are the methods used. Ask yourself the following questions and record your observations. Some gardeners keep a pocket notebook for this purpose.  

  • What plant exactly? Tomatoes and strawberries, for example, have different pests.
  • How do the leaves look? Are the affected leaves older or younger? Are the veins differently colored than the leaf portions between them? Do the leaves have spots or edge curling? Is there a general yellowing, aka chlorosis? 
  • Are there signs of pest predation such as rabbits or insects? 
  • What about the environment? Has it been wet and damp, hot and dry, something else? 

Don’t forget to check the soil pH!

Doing so will tell you if it’s within the range that the plant can take up nutrients.

Most vegetables prefer a pH in the 6.5-6.8 range. Too much higher or lower, and the plant simply can’t absorb the nutrient, similar in concept to being in a pantry filled with cans and not having a can opener.

Also, keep in mind that nutrients must be available in a form the plant can use. Simply dropping the element into the soil in elemental form isn’t enough. Most solutions will involve fertilizer or compost for the quickest results. And remember: too much of a good thing can be a bad thing.

I once over-fertilized a potato bed with nitrogen, thinking that the excess would simply remain in the soil unused. However, I was wrong. I had the most beautiful plants I ever saw, but when I went to dig the tubers, there wasn’t a single potato to be found. Not one! Excess nitrogen had gone to leaf formation and inhibited tuber growth. An entire summer’s work for nothing.

A professional lab test will tell you the levels of the three major nutrients but be aware that most labs don’t test for secondary or micronutrients. 

So let’s assume you’ve investigated your problem and ruled out both disease and pest predation. What’s left? Figuring out if there’s a nutrient deficiency.

(You’re going to need to know how to free QUICKSTART Guide to home canning for more information.

What you need to know about nitrogen nutrient deficiencies

Nitrogen is necessary for chlorophyll production, which is necessary for photosynthesis. This is the single most used nutrient in most plants and will drain from soil fairly quickly. Signs of deficiency are: general chlorosis of the entire plant, i.e., extremely pale color, upright leaves are light green/yellowish. Stunted growth. Leaves can appear burnt in extreme deficiency. The older leaves will die off quickly. This is because the plant will scavenge nitrogen from the older leaves for younger growth. 

What are the solutions to a nitrogen deficiency?

Add composted manure or a high nitrogen fertilizer to the soil. Coffee grounds or a green manure crop such as borage, clover, or vetch can help, or if you’ve got time, plant nitrogen fixers such as beans or peas. Some gardeners will rotate crops, planting nitrogen fixers between seasons for this purpose. Compost materials high in this element include grass clippings, fruit and vegetable scraps, and coffee grounds. Tea bags are also good. In other words: your compost greens. 

What you need to know about phosphorus nutrient deficiencies

This nutrient plays a huge role in bud and bloom development. This is essential to the fruiting process! No flowers, no fruits, right? It also plays a role in cell formation, protein synthesis, and fat & carbohydrate metabolism.

Counterintuitively, however, phosphorus doesn’t run off as quickly as nitrogen does, and most soils don’t need much in the way of phosphorus supplementation. Signs of phosphorus deficiency are a short and dark green plant with few or no side shoots. In extreme deficiencies, the plant will turn brown or black. A bronze, violet, or reddish-violet color will be seen under the leaf. Symptoms will appear on the older parts of the plant first.

What are the solutions to a phosphorus deficiency?

Add phosphorus to soil, either via fertilizer or compost materials high in this element. Bone meal, rock phosphate, and manure are commonly used. Fish meal will also work. Manure, especially horse manure, will add all three of the major nutrients. 

What you need to know about potassium nutrient deficiencies

This third major nutrient is important for water regulation and enzyme activity. Water regulation provides structure. This is called turgor, or turgor pressure, defined as the state of turgidity and resulting rigidity of cells or tissues, typically due to the absorption of fluid. In other words, correct water regulation holds the plant upright. Enzymes are necessary for a very high number of chemical reactions.

According to the Penn State Horticulture Department:

“Potassium-deficient plants are easily distinguished by their tendency to wilt on dry, sunny days. The overall appearance of the plant is wilted or drooping. Deficient plants will have a stocky appearance with short internodes. Younger leaves’ growth is inhibited, and they have small leaf blades. Leaves may also be dark to bluish-green, have a bronze metallic shine, or have a wavy appearance. In some species, older leaves show blotchy chlorosis. In monocots such as maize, leaves may have inverted V-shaped chlorosis.”

To correct this problem, finished composts made primarily from food materials can be added. Banana peels are particularly useful. High potassium fertilizers, kelp, or seaweed are fast-release forms. Comfrey liquid or wood ash can also help, but be careful with the latter as it can burn the plants. Check out these high potassium recipes courtesy of South Side Plants!

A simple potassium recipe for your plants

Dry four banana peels and three eggshells. Combine them and add four tablespoons of Epsom salt. Grind the mixture into a powder in a food blender. Pour 75 ml of water onto the powder, shake to combine, and water your plants with the liquid. 

To make concentrated liquid kelp fertilizer, fill a bucket with foraged kelp, cover it with rainwater, and leave to soak for a month, stirring every few days. For added nitrogen, add a few stinging nettle stems into the mixture. 

(Want uninterrupted access to The Organic Prepper? Check out our paid-subscription newsletter.)

Are there other elements needed for healthy plant growth?

Elements that aren’t usually thought of as nutrients but are extremely important to plant health are hydrogen, oxygen, and carbon.

Carbon is incorporated into plant structures. We’re all carbon-based life forms on this planet, and carbon dioxide is absorbed through the stomates. These are openings in the leaves that regulate gas exchange and water loss. We breathe carbon dioxide out for them during exhalation, and they produce the oxygen we require, a very symbiotic relationship.

Carbon also comes from your compost browns. These are dried leaves, twigs and branches, sawdust, straw, cardboard, and paper egg cartons. Hydrogen and oxygen are required for respiration, pH regulation, energy production, and synthesis of both plant structures and carbohydrates, among many other functions. Hydrogen and oxygen are the components of water. Plants will take these elements up via mass flow when we water them.

Plants that aren’t properly watered will wilt and die. The obvious solution is to water them but again, remember: too much of a good thing is a bad thing! Excessive watering brings on root rot and makes plants susceptible to disease. 

If your garden is fighting nutrient deficiencies, check the Big 3 first!

We’ve discussed the symptoms of major deficiencies and some possible solutions. In my next article, I’ll cover the secondary nutrients: calcium, magnesium, and sulfur. These are also discussed in our Urban Agriculture course in greater detail, of course.

How do you manage nutrient deficiencies in the garden? Please tell us in the comments below! 

About Amy Allen

Amy Allen is a professional bookworm and student of Life, the Universe, and Everything. She’s also a Master Gardener with a BS in biology, and has been growing food on her small urban lot since 2010.