Introduction

Growing microgreens is forgiving compared to growing mature crops. As microgreen farmers, we often harvest our crops long before they’re capable of developing nutrient deficiencies, even without adding fertilizer to the soil. However, understanding the basics of plant biology will help us fix crop problems before they arise AND learn how to boost yields with fertilizer. This blog will provide a super high level overview of the 17 essential plant elements and then focus on the big three - nitrogen, phosphorus, and potassium.

Before we begin, I can already hear the cacophony of negativity. “I don’t have a biology background.” “Microgreens don’t need supplemental nutrients to grow well.” “Fertilizer is a waste of time and money.” “I didn’t major in biology in college for a reason.” Let me just say, you’re wrong. You’re capable of learning basic plant biology and I’m going to teach you. Supplemental nutrients for your microgreens are both easy and economical. This article focuses on the former topic. Another blog (How to Fertilize Your Microgreens for Bigger Yields & More Revenue!) focuses on the latter.

Overview

According to the University of Florida IFAS Extension website, scientists Arnon and Scott (1939) and Meyer and Anderson (1939) outline what it means for a nutrient to be essential in plant growth – a given plant must be unable to complete its lifecycle without the nutrient; a life cycle being vegetation, flowering, and fruiting. The function that element serves must not be replaceable with another element. Lastly, the element must be directly involved in plant metabolism or a component of an essential plant compound. For example, nitrogen is vital and irreplaceable in chlorophyll.

Different elements can be repeatedly mobilized by the plant and incorporated into new tissue while other elements are fixed in place. This distinction will help diagnose different nutrient deficiencies. If a plant is deficient in an immobile nutrient, new plant growth will exhibit the symptoms. If a plant is deficient in a mobile nutrient, the old plant growth will exhibit the symptoms. Table 1. outlines which elements are mobile and immobile.

There are 17 essential plant elements. Plants source carbon (C), hydrogen (H), and oxygen (O) from the soil, water, and air, but the remaining elements must be present in the plant's environment for uptake by the root system. As you can see from the charts below, C, H, and O are the vast majority of what plants need. Zooming in, we see that nitrogen (N), phosphorus (P), and potassium (K) are the next most important elements. They are the macronutrients. We will focus on these three for this article because they'll have the greatest impact on your microgreens.

N-P-K Overview

If you don’t want to get bogged down in too much of the N-P-K plant science, here is the main point to remember about each one.

Photosynthesis relies on nitrogen, which is considered the “vegetative” element. Proper nitrogen availability leads to bigger and greener plants.

Phosphorus is vital for early plant growth and root formation. Later in life, it's critical for fruiting and flowering. Phosphorus is the least important of the macronutrients for microgreen production.

Potassium is regarded as the “quality element.” Potassium isn't in any plant structure, rather it helps move water and sugars around the plant. Proper potassium levels are important for improving the appearance and shelf life of your microgreens.

Reading Fertilizer Labels

We’re not going to get into the efficacy of fertilizer use with microgreens in this article. However, we want you to know how to read the N-P-K info on nutrient labels. Fertilizer companies will advertise their products’ N-P-K content on the front of the packaging in large integers. The three macronutrients will always be listed as N-P-K. They will be listed by their percent weight contribution. The back of the package will outline the specific sources of each nutrient. Let’s look at two common microgreen fertilizers, Gaia Greens 4-4-4 and Ocean Solution 2-0-3.

Gaia Greens 4-4-4 is a solid fertilizer you can mix into your soil before planting. It contains equal amounts of nitrogen, phosphorus, and potassium - 4% each by weight. The nitrogen is present as 3% water soluble nitrogen and 1% water insoluble nitrogen. The label does not indicate the form of nitrogen - nitrate, nitrate, ammonium, urea, or otherwise. Phosphorus is present as phosphoric acid, and potassium is present as potash. For our purposes, it's not important to know the difference between, say, nitrate and nitrite. Likewise, you don't need to concern yourself with the ingredients - bone meal, feather meal, gypsum, and so on. The main takeaway is to understand how much N, P, and K one fertilizer has compared to another fertilizer.

Ocean Solution 2-0-3 is a liquid fertilizer you can dilute with water and use to water your trays after germination. Compared to Gaia Greens, Ocean Solution has half the concentration of nitrogen, no phosphorus, and less potassium. Does that mean Gaia Greens is objectively a better fertilizer? Not exactly. Gaia Greens is a stronger fertilizer, but we need to consider the cost per use and the efficacy. The main consideration is the uptake rate. Plants uptake nutrients via their roots. Nutrients must be water-soluble or dissolved in water to enter the plant. The nutrients in Ocean Solution, although not as strong, are immediately available for uptake. The nutrients in Gaia Greens won’t be as readily available for the plants. Microgreens grow so fast that a weaker, more available fertilizer might be better than a stronger, less available one.

Nothing is cut and dry. Gaia Greens could be better for longer growing microgreen varieties, like celery and basil. Ocean Solution could be better for faster growing microgreen varieties, like radish and pea. You’ll have to do your own testing. Hopefully, though, you now have a basic understanding of essential plant nutrients, how to spot deficiencies, and how to read fertilizer labels.

Nitrogen (N)

• Nitrogen is a core component of amino acids, co-enzymes, nucleic acids (DNA/RNA), and chlorophyll. Remember that amino acids are the building blocks of protein. Chlorophyll a and Chlorophyll b are the main pigments found in chloroplasts, which is where photosynthesis occurs. Nitrogen is also an important element in ATP, the primary molecule used for transferring and using energy for all life on the planet.
• Plants assimilate nitrogen as either nitrate (NO3-) or ammonium (NH4+). Fertilizers will provide nitrogen as either form or as urea, which will break down into ammonium.
• Although nitrogen is the most abundant element in Earth’s atmosphere, nitrogen is the most common deficiency among crops.
• Nitrogen directly impacts the protein content of plants such as grains.
• Nitrogen is a mobile element, which means deficiencies will appear on older leaves first as the plant tries to prioritize the health of new growth.
• According to Mosaic, a crop nutrition, fertilizer, and research company, most plants need a constant supply of nitrogen throughout their lives – not just during certain growth periods.

_**Signs of Nitrogen Deficiency**_

• Yellow-Green Leaf Color (Chlorosis)
• Stunted Growth

Common Nitrogen Fertilizers

• Calcium Nitrate [Ca(NO3)] (15.5.-0-0)
• Potassium Nitrate (KNO3) (13-0-44)
• Ammonium Nitrate (NH4NO3) (34-0-0)
• Urea (45-0-0)

Phosphorus (P)

• Phosphorus is a component in nucleotides, the basic building block for DNA and RNA.
• Phosphorus promotes early plant growth and root formation through its role in cell division. Research shows that high levels of phosphorus are present in apical meristems of plants – the leading growth points of the root and stem.
• As a plant matures, phosphorus is prioritized for flowering, fruiting, and seed development. Phosphorus is also the key component of adenosine di- and triphosphate (ADP/ATP), the molecule used for storing and transferring energy in all organisms.
• Plants take up phosphorus as H2PO4-, HPO42-, or PO43- depending on the pH of the soil.

Signs of Phosphorus Deficiency

• Slow Growth / Stunting
• Purpling Foliage
• Poor Flower, Fruit, & Seed Development
• Leaf Tips Dying

Common Phosphorus Fertilizers

• Monoammonium Phosphate (12-61-0)
• Diammonium Phosphate (18-46-0)
• Superphosphate (0-20-0)

Potassium (K)

• Potassium in needed by plants in roughly the same quantity as nitrogen.
• Potassium is necessary for numerous plant processes.
  • Increases root growth and drought tolerance.
  • Activates dozens of enzymes involved in plant growth.
  • Translocation of sugars from the leaves to other, non-photosynthetic structures.
  • Facilitates the movement of water throughout the plant.
  • Associated with disease resistance.
  • Regulates the opening and closing of stomata.
    • CO2/O2 gas exchange
    • Releasing water vapor, which cools the plant’s internal temperature
  • Potassium is called a ‘quality nutrient’ because it impacts many of the defining features that make a crop pleasing to humans – starch and protein content, shelf life, size and quality of fruits, and disease resistance, which effects health and appearance.
  • According to Mosaic, “plants generally absorb the majority of their potassium at an earlier growth stage than they do nitrogen and phosphorus.”
  • Potassium is highly mobile, which means signs of deficiency will appear in older leaves first.

Signs of Potassium Deficiency

• Tip & Margin “Burn”
• Weak Stalks
• Easy Lodging – Tipping/Stem Breaking
• Wilting
• Interveinal Chlorosis
• Necrotic Spots

Common Potassium Fertilizers

• Potassium Nitrate (KNO3) (13-0-44)
• Potassium Sulfate (K2SO4) (0-0-50)

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Resources

Table 1.

Nutrient Mobility Inside Plants
Mobile	Immobile
Nitrogen (N)	Calcium (Ca)
Phosphorus (P)	Iron (Fe)
Potassium (K)	Manganese (Mn)
Magnesium (Mg)	Zinc (Zn)
	Copper (Cu)
	Boron (B)
	Molybdenum (Mo)
	Sulfur (S)
	Nickel (Ni)

Primary Photosynthetic Pigments for Green Plants:

PubChem - Chlorophyll A

PubChem - Chlorophyll B

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