Besides the big three (nitrogen, phosphorus and potassium), cannabis needs secondary nutrients (calcium, magnesium and sulfur) and a handful of micronutrients like iron, zinc, manganese, boron, copper and molybdenum. Micronutrients are only needed in tiny amounts, but if any of them runs short you'll see stunted growth, discolored leaves and, in the worst cases, lost buds, and your harvest takes the hit. So what exactly does your plant need?

• Primary macronutrients: nitrogen (N), phosphorus (P), potassium (K)
• Secondary macronutrients: sulfur (S), calcium (Ca), magnesium (Mg)
• Micronutrients: boron (B), chlorine (Cl), cobalt (Co), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo) and zinc (Zn)

Macronutrients vs. Micronutrients: What's the Difference?

Macronutrients are needed in larger quantities, while micronutrients are only needed in very small amounts (a few parts per million). For normal growth, a plant needs a balanced supply of all of these essential nutrients.

So how do micronutrient products actually work? They're often formulated as suspension concentrates (SC) or oil dispersions (OD) because they have a high solids content, and the active ingredients (the micronutrients themselves) tend to be very dense. That makes them prone to settling and other destabilizing forces, which is why choosing the right dispersant is a big deal when a manufacturer builds a stable formula.

Essential Micronutrients: Which Ones Does Cannabis Need?

How many micronutrients count as "essential" depends on who you ask. Like with secondary nutrients, it's partly a classification thing, since some sources lump the secondary nutrients in with the micronutrients. Either way, these are minerals and elements that aren't as abundant in soil and aren't needed in large amounts by cannabis plants, but they're still non-negotiable.

Whatever the source, boron (B), manganese (Mn), zinc (Zn), copper (Cu), iron (Fe) and molybdenum (Mo) always make the list of essential micronutrients. Like every other essential nutrient, each micronutrient has its own job or helps the other nutrients do theirs. Here's what each one does:

Boron:

supports the growth and development of root tips. It also helps plants take up calcium and moves sugars around inside the plant.

Manganese: a key player in chlorophyll production and photosynthesis. It also helps enzymes do their work.

Zinc:

helps stems, leaves and branches develop. The more mature a plant gets, the more zinc it usually contains and needs.

Copper:

helps the plant build proteins and strengthens stems and branches.

Iron:

important for chlorophyll production. Iron deficiency often shows up as yellowing between the leaf veins (interveinal chlorosis).

Molybdenum:

helps the plant process nitrogen.

Other trace elements that some consider essential are cobalt (Co), silicon (Si), chlorine (Cl) and selenium (Se). Not everyone agrees they belong on the essential list, though they do play a role in supporting plant life.

Secondary Nutrients for Cannabis: Calcium, Magnesium and Sulfur

The essential secondary nutrients are magnesium (Mg), calcium (Ca) and sulfur (S). For cannabis to absorb them properly, keeping your pH in the right range is crucial.

These secondary nutrients handle a wide range of critical jobs in cannabis development. They're often building blocks of, or sidekicks to, other nutrients and processes. All of them are needed for plant and root growth, but each has its specialty. Calcium helps move other nutrients through the plant and helps them get absorbed. Magnesium sits at the heart of the chlorophyll molecule. Sulfur is involved in making chlorophyll and also helps with plant metabolism and transpiration.

What Nutrients Do Cannabis Plants Need to Grow, and When Do You Start?

Macro and micronutrients keep your plants growing strong and help keep pests from taking over your grow. You can start feeding cannabis once it has 2-3 sets of true leaves. Some fertilizers are introduced a week after germination, during the seedling stage, and that's perfectly fine too.

Seedlings need a much lower dose, so follow the label carefully to avoid nutrient burn. Depending on your growing medium, you'll need to start feeding sooner or later. Some soil mixes come pre-loaded with nutrients for the first 3-4 weeks; these are called "hot" soils. Read what's in your mix and how to use it so you don't double-feed and burn your plants.

How Often Should You Feed Your Cannabis Plants?

Some nutrient lines are meant to go in with every watering, while other brands say once a week. Some supplements are applied once a month, or only during certain weeks.

When Should You Stop Feeding Cannabis Before Harvest?

During the last week (or two) of flower, a lot of growers stop feeding their weed plants and switch to plain water. This is called flushing, and growers do it to avoid or minimize a "chemical" taste in the buds when synthetic fertilizers have been used.

As harvest gets close, the pistils turn brown and curl in, and the trichomes go milky or amber/brown.

The difference between micronutrients and macronutrients is clear-cut. Plants can get them in several ways, but can they get them naturally? How do plants take in nutrients in the first place, and what are the main natural sources?

Plants pull macro and micronutrients (elements) from the soil, the air and water. Carbon (C), oxygen (O) and hydrogen (H) are the basic building blocks, and plants take them from air and water.

That's why good airflow inside your grow tent or grow room matters: it makes sure the plants get the right amount of carbon and oxygen from the air. A clean water source is just as vital for basic plant functions. Use safe water: tap water is fine, and if the tap water where you live isn't drinkable, go with bottled.

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