Plant Nutrients Explained: Everything You Ever Need To Know
Ready for a test?
With paper and pencil, make a list of ALL nutrients that plants need to grow properly.
We’ll wait…no cheating!
Here’s the list to check yourself against:
There are more elements here than you listed, I bet! To fully understand how plants grow and how we can help them grow better, we have to understand what they need to grow.
In this article, we’ll dive into everything a plant needs from a nutrient standpoint. Let’s get started!
Fertilizer is Deeper than N-P-K
We are all aware of the importance of good fertilizer for plants, gardens, and lawns. Just as with animals and humans, plants have to have proper “nutrition” if they are to be at their best. And most people are aware of the “N–P–K” numbers printed on all fertilizer bags. These, in order of printing, represent the nitrogen, phosphorus, and potassium (sometimes referred to as potash) percentages contained in that particular fertilizer.
For instance, 10–10-10 fertilizer is 10% nitrogen, 10% phosphorus, and 10% potassium. And, on the same subject, 100 pounds of 10-10-10 is exactly the same as 200 pounds of 5-5-5! No difference.
Let’s briefly review what the numbers stand for, and the importance of each element.
Nitrogen is the first and to some degree the major nutrient for strong, vigorous growth, dark green leaf color, and photosynthesis. Plants that are almost all leaf, such as lawn grasses, wheat, oats, small grain crops, and golf course grasses need plenty of nitrogen. The first number in fertilizers (N) for these crops and others should be especially high, especially for grass since it must continually renew itself due to being mowed often.
When buying fertilizers for grasses, look for an analysis that starts with a very high “First number” in the N – P – K numbers. 30 – 0 – 0 is often used, but any combination with a high “first number” can be used.
Just remember, 100 pounds of 30-0-0 is exactly the same as 200 pounds of 15-0-0. Even if you chose 10-10-10, you could get the same 30 pounds of actual nitrogen by applying 300 pounds. And, with the 10-10-10, you’d also be applying 30 pounds of phosphorus and 30 pounds of potassium. That would probably be overkill for grass.
Phosphorous is used by plants largely for root growth and development. Flowers that are well fed with phosphorus will have more blooms, and fruits ripen better and faster. Phosphorus is important to flower bulbs, as well as to perennials and recently established trees and shrubs. Since trees and shrubs do not need as much nitrogen as grasses and leafy vegetable crops, a small first number and a larger second number are often seen in fertilizers intended for these plants, shrubs, and bushes.
Potassium is a general nutrient for all plants, improving the overall health and strength of the plant. It improves the plant’s ability to withstand temperature extremes, and to a lesser degree, stress from drought. Potassium also helps plants resist diseases.
Because most soils have some available potassium, the third number is sometimes smaller than the first two. However, it is important to note that if the soil does not have available potassium, as some don’t…a smaller third number may not be desirable.
Calcium is important for general plant vigor and promotes the good growth of young roots and shoots. Calcium also helps to build cell walls. As cells weaken, the vascular system of the plant starts to collapse, reducing the uptake of all of the major elements. The symptoms show up first at the growing tips of both the shoots and the roots.
Calcium is an immobile element, meaning that when there is a deficiency, the plant can’t translocate calcium from the older leaves to the younger leaves. New growth at the leaf tips and margins begins to wither and die back, and the new leaves are often deformed.
Magnesium helps regulate the uptake of other plant foods and aids in seed formation. As it is contained in chlorophyll, it is also important in the dark green color of plants and for the ability of a plant to manufacture food from sunlight.
Magnesium is necessary for the formation of sugars, proteins, oils, and fats, regulates the uptake of other nutrients (especially phosphorous), is a component of chlorophyll, and is a phosphorus carrier.
Deficiency symptoms include mottled yellowing between veins of older leaves while veins remain green. Yellow areas may turn brown and die. Yellowing may also occur on older leaves. Leaves may turn reddish-purple due to low P metabolism, and decreased seed production often occurs.
Deficiencies are most likely on leached sandy soils and where high levels of N and K have been applied.
Turf: Green or yellow-green stripes, changing to cherry red. Older leaves are affected first. Increased winter injury.
Broadleaf: Leaves are thin, brittle, and drop early. Older leaves may show interveinal and marginal chlorosis, reddening of older leaves, with interveinal necrosis late in the season followed by shedding of leaves. Shoot growth is not reduced until the deficiency is severe. Fruit yield is reduced in severe deficiencies; apples may drop prematurely.
Conifer: Needle tips are orange-yellow and sometimes red. Primary needles remain blue-green in young seedlings, but in older plants, older needles and the lower crown show symptoms first. In affected needles, the transition to green may be sharp.
Sulfur helps maintain a dark green color while encouraging more vigorous plant growth. Sulfur is needed to manufacture chlorophyll. Sulfur is as necessary as phosphorus and is considered an essential mineral.
What does sulfur do for plants? Sulfur in plants helps form important enzymes and assists in the formation of plant proteins. It is needed in very low amounts, but deficiencies can cause serious plant health problems and loss of vitality. Plants only need 10 to 30 pounds of sulfur per acre. Sulfur also acts as a soil conditioner and helps reduce the sodium content of soils.
Sulfur in plants is a component of some vitamins and is important in helping give flavor to mustard, onions, and garlic. Sulfur born in fertilizer assists in seed oil production, but the mineral can accumulate in sandy or overworked soil layers. Sulfur deficiencies in soil are rare but do tend to occur where fertilizer applications are routine and soils do not percolate adequately.
We have now covered the primary and secondary elements that plants require for healthy growth. However, do not make the mistake of thinking the other elements needed are to be taken for granted. Au contraire! The so-called “trace elements” can have a far more exaggerated effect on plant growth than just “a trace effect.”
When I ran a 2000-acre farm, I had a few spots on one farm that have extremely low manganese. Until the problem was remedied, soybeans completely died in those spots! That’s hardly a “trace” problem when you’re depending on the soybean crop for your income. Let’s examine the remaining elements needed to provide everything a plant needs.
Boron helps in cell development and helps to regulate plant metabolism. It’s a micronutrient required in very small amounts and there is a narrow range of safety when applying boron as toxicities can occur if too much is applied.
Boron has an important role in vegetable plants. It is needed for protein synthesis, development of cell walls, carbohydrate metabolism, sugar translocation, hormone regulation, pollen grain germination, and pollen tube growth, fruit set, and seed development. Boron is mobile and readily leached in sandy soils and regular additions are necessary for many vegetables, but only in small amounts. Boron toxicity will occur if this element is overly applied.
Chlorine is involved in photosynthesis. Chloride is necessary for gas exchange, photosynthesis, and protection against diseases in plants. When a plant’s leaf pores, called stomata, open and close to allow the exchange of gases, the plant sees an increase in potassium. A subsequent increase in chloride balances out the positive charge of the potassium to prevent plant damage. The exchange of gases between the plant and the air around it is critical for photosynthesis; a deficiency of chloride inhibits photosynthesis, threatening plant health.
Copper is extremely important in plant nutrition if only for the fact that it aids in forming chlorophyll. Plants don’t need much copper, but if they don’t get any, results can be disastrous.
It activates enzymes in your plants that help to synthesize lignin. It’s also part of the photosynthesis process. On top of that, it’s a key for flavor in certain types of veggies, and color in certain types of flowers.
Copper is immobile in plants, so if they are deficient in copper it will likely show up in newer growth. New leaves will begin to cup and you’ll notice chlorosis between the veins. If it’s a serious deficiency, small spots of the leaves will die off and they may wilt and fall off.
Leaf nodes will start growing closer and closer together, creating a squat look to your plant.
Iron assists in the manufacture of chlorophyll and other biochemical processes. Iron is a nutrient that all plants need to function. Many of the vital functions of the plant, like enzyme and chlorophyll production, nitrogen-fixing, and development and metabolism are all dependent on iron.
Without iron, the plant simply cannot function as well as it should.
Symptoms of Iron Deficiency in Plants
The most obvious symptom of iron deficiency in plants is commonly called leaf chlorosis. This is where the leaves of the plant turn yellow, but the veins of the leaves stay green.
Typically, leaf chlorosis will start at the tips of new growth in the plant and will eventually work its way to older leaves on the plant as the deficiency gets worse.
Other signs can include poor growth and leaf loss, but these symptoms will always be coupled with leaf chlorosis.
Manganese is needed for chlorophyll production.
Manganese and Magnesium
It’s necessary to note the difference between magnesium and manganese, as some people tend to get them confused. While both magnesium and manganese are essential minerals, they have very different properties.
Magnesium is a part of the chlorophyll molecule. Plants that are lacking in magnesium will become pale green or yellow. A plant with a magnesium deficiency will show signs of yellowing first on the older leaves near the bottom of the plant.
Manganese is not a part of chlorophyll. The symptoms of manganese deficiency are remarkably similar to magnesium because manganese is involved in photosynthesis. Leaves become yellow and there is also interveinal chlorosis.
However, manganese is less mobile in a plant than magnesium so the symptoms of deficiency appear first on young leaves. It’s always best to get a sample to determine the exact cause of the symptoms.
Other problems such as iron deficiency, nematodes, and herbicide injury may also cause leaves to yellow.
Molybdenum helps plants to use nitrogen. In non-legumes (such as cauliflowers, tomatoes, lettuce, sunflowers, and maize), molybdenum enables the plant to use the nitrates taken up from the soil.
Where the plant has insufficient molybdenum, the nitrates accumulate in the leaves and the plant cannot use them to make proteins. The result is that the plant becomes stunted, with symptoms similar to those of nitrogen deficiency. At the same time, the edges of the leaves may become scorched by the accumulation of unused nitrates.
In legumes such as clovers, beans, and peas, molybdenum serves two functions:
- The plant needs it to break down any nitrates taken up from the soil—in the same way as non-legumes use molybdenum.
- It helps in the fixation of atmospheric nitrogen by the root nodule bacteria. Legumes need more molybdenum to fix nitrogen than to utilize nitrates.
Zinc is used in the development of enzymes and hormones. It is used by the leaves and is needed by legumes to form seeds. The function of zinc is to help the plant produce chlorophyll.
Leaves discolor when the soil is deficient in zinc and plant growth is stunted. Zinc deficiency causes a type of leaf discoloration called chlorosis, which causes the tissue between the veins to turn yellow while the veins remain green. Chlorosis in zinc deficiency usually affects the base of the leaf near the stem. Chlorosis appears on the lower leaves first, and then gradually moves up the plant.
In severe cases, the upper leaves become chlorotic and the lower leaves turn brown or purple and die. When plants show symptoms this severe, it’s best to pull them up and treat the soil before replanting.
It’s hard to tell the difference between zinc deficiency and other trace element or micronutrient deficiencies by looking at the plant because they all have similar symptoms.
The main difference is that chlorosis due to zinc deficiency begins on the lower leaves, while chlorosis due to a shortage of iron, manganese, or molybdenum begins on the upper leaves.
The only way to confirm your suspicion of a zinc deficiency is to have your soil tested. Your cooperative extension agent can tell you how to collect a soil sample and where to send it for testing.
How to Test Your Garden’s Soil
By now, it should be obvious that plants are actually miniature chemical factories that require a strict balance between primary, secondary, and trace nutrients.
And, they will perform poorly when these chemical nutrients are not in the correct balance. The obvious question is…
How do I know how to fertilize my garden?
The answer seems impossible for the average person to know. Well, the good news is….it isn’t hard at all! Many laboratories and even most state extension offices offer soil testing that can pinpoint exactly what any garden needs and even modify their recommendations for specific crops.
So, to get your garden, lawn, or farm ready for a new season, do this:
Take soil samples. You will need ½ to 1 pint of soil per sample. Now, don’t take one sample from one spot in your garden and send it in. Rather, take multiple samples over the area and go get a representative sample of the entire area.
Send the sample to a trusted and established laboratory for their recommendations. There are always forms to be filled in, so contact the lab of your choice first to get the proper forms.
Fill in the forms very specifically, indicating what crops you intend to grow, any known problems from previous years, and any concerns that you have.
When the report comes back…it may be difficult for you to read and interpret, so never hesitate to re-contact the lab with your questions. They will be glad to help.
Apply exactly what is recommended. Everything. Exactly. And, you should do it as early in the spring as possible because the added nutrients will not be readily available to the plants until they undergo certain chemical reactions in the soil. Earlier is better.
Your soil needs something, and you will never know what it is without that all-important soil test. With it, you can look forward to the best garden of your life!
There are fertilizers out there that contain all of the elements — primary, secondary, and trace — needed for your garden or lawn. I never plant a garden using a fertilizer that has only the “Big 3” numbers of N-P-K on the label. Instead, I use fertilizers that have all of the nutrients. And my garden always looks amazing.
About the Author
Randy Williams is a retired farmer who used to run a 2,000-acre farm.