Meet the Secondary Macronutrients and the Micronutrients Your Plants Need

By on March 17, 2013

Tricia adds micronutrients to her soil, based on the results of a lab soil test.

Micronutrients are essential for your plants, says Tricia in our video about secondary macronutrients and the micronutrients.

You know about the major nutrients, N-P-K. Those are the symbols for the building blocks: nitrogen, phosphorus and potassium. They’re represented by the three numbers on the front of fertilizer boxes or bags. For more about them, check out our video here.

With the lesser known micronutrients (like “molybdenum”—if you can spell that you can probably win a Spelling Bee) you’ll need a lab soil test to know if any need to be added to your soil.

Let’s have a quick look at the major mineral nutrients, and then get to know the micronutrients and find out what they do for your plants.

Mineral Nutrients—Do You Know the Seconday Micronutrients?

Soil has varying amounts of minerals. When it rains, or we irrigate our gardens, the minerals dissolve, and the plant roots absorb the minerals.

Our friends N-P-K are the primary macronutrients.

Also important are the secondary macronutrients:

Calcium builds cell walls. Add it via limestone powder, gypsum, oyster shell, or Calcium 25. Problems caused by low calcium include blossom end rot in tomatoes. Before you add calcium, check your soil pH in order to choose the best calcium source for your garden; oyster shell will raise the pH, but gypsum will lower pH.

Magnesium supports chlorophyll production. Add it via dolomite, K-Mag or Azomite.

Sulfur builds protein. Sulfur is released when “greens” like vegetable scraps and lawn cuttings decompose. Add it via gypsum, iron sulfate, and sulfur.

Meet the Micronutrients

We say “micro” because plants need only small amounts of them. Sometimes they’re even called “trace elements”. They all have a role to play, though.

Let’s find out what they are, what they do, and how you can add them to your soil.

Boron is a boss (or regulator) of other nutrients. Plants need it for seeds and fruit. Add it via powdered boron.

Copper helps plants reproduce and boosts metabolism in roots.

Chloride is another aid to plant metabolism. 

Iron assists in producing chlorophyll.

Manganese breaks down carbohydrates, cooperating with enzyme systems.

Molybdenum (in addition to being hard to spell) aids nitrogen use by plants.

Zinc helps change carbohydrates into sugars, and it’s in plant growth enzymes too. Add it via zinc oxide, zinc sulfate, and zinc chelate.

How Do I Supplement for Micronutrients?

Want a supplement for the plants growing in your garden? One that contains many of these micronutrients? Try kelp meal, glacial rock dust, Azomite or (for fastest results) liquid kelp.

Now that you know the basics of secondary macronutrients and the micronutrients, go get a lab test on your soil. Once you have the results, use organic fertilizers to add what you lack—and you’ll be on your way to a garden full of healthy vegetables and bountiful harvests.

For more information about nutrients and organic fertilizers, read the Fertilizer Solutions Chart in our Fertilizer catalog, or download the chart as a PDF here.

Secondary macronutrients and the micronutrients are small but essential building blocks for the plants in your organic garden!

  Comments (6)


What micro-nutrients do you recommend for trees?
Do you ever fertilize tree leaves or plant leaves?

Posted by dave on Apr. 02, 2013 at 8:38:06 PM

Dave, Different trees have nutrient preferences (such as avocados and zinc or citrus with manganese and iron), but a good micro-blend (like Biolink Micronutrients  can supply small enough amounts that it will not over-feed.
Foliar feeding trees is usually fine as long as done when the leaves have sufficient time to dry before the sun hits them. Sometimes it leaves a residue film on the leaves that people do not like.

Posted by on Apr. 04, 2013 at 11:19:29 AM


Charlotte, would the biolink be perfect for citrus? The garden store recommends citrus growers blends but it is not organic.  Also how often and when do you use it?

Posted by Joe on Jun. 24, 2014 at 11:27:06 PM

Hello Joe,

Yes, biolink would work on citrus, the label says “as needed”. We also carry some certified organic fertilizers formulated for citrus. Such as: , and

Posted by on Jun. 25, 2014 at 8:42:24 AM


What kind of soil test does your lab perform? I am reading The Intelligent Gardener and all of his discussions are based on Mehlich 3 test results. Our testing was done by PVFS so I wonder how they compare.

Posted by joanie on Sep. 22, 2014 at 8:37:39 AM

The soil tests offered at PVFS uses the Ammonium Acetate extraction. There is a lot of information on the web regarding soil testing. Really depends on the location of the lab, whether in the West or East…, what soils they are testing.
I am not sure where you are located but here is a link with a lot of information,

Posted by Suzanne at Peaceful Valley on Nov. 07, 2014 at 10:43:11 AM

+ Show More Comments

Leave a Comment