Like any craft worthy of the name, growing cannabis well takes commitment, creativity, and experimentation. But the right knowledge doesn’t hurt either. The botanical science of cannabis is an ancient one, yet it’s still evolving today. Most home growers, however, just want to know what works and what doesn’t. What their plants need and what they don’t, in order to bloom into massive, potent flowers for harvesting. So let’s state the obvious. Growing healthy cannabis plants means knowing what the most important nutrients are, what they do for your plants, and how to get it to them.
This isn’t a grow guide that’s going to sing the praises of this or that fertilizer, this or that soil mixture. Instead, it’s going to drill down all the way to the elemental level of cannabis nutrition.
There are many different methods to grow healthy plants. And each has their own set of pros and cons. The nutrients listed below are fundamental to every method. They’re the 16 most important nutrients for healthy cannabis plants.
Air, Water, and Light
Focusing on the fundamentals was no joke, and it doesn’t get more fundamental than these three nutrients. It’s easy to get bogged down in the long list of soil nutrients and completely forget that the absolute most important nutrient for healthy cannabis plants, is light.
And in order for that light to be any good to your plants, it needs the support of the carbon in the air, and the oxygen and hydrogen in water.
Breathe in The Air
You can’t eat if you can’t breathe, and plants are the same way. Lucky for them, and lucky for us, we each inhale what the other breathes out.
It’s a pretty good relationship and one that began its course at least 2.7 billion years ago when photosynthetic organisms saturated the earth’s atmosphere with oxygen.
But you need oxygen, while your plants need carbon dioxide. They don’t want the oxygen atoms, they want that delicious carbon, baby!
Carbon is essential for the photosynthetic process. No wonder it accounts for just around 45 percent of the dry weight of the cannabis plant.
Circulating air is the best way to get carbon to your plants to keep them healthy. If you’re growing outside, you don’t have to worry about it.
But indoor growers working in confined areas may want to invest in a CO2 generator.
Because we can’t make our own food like green plants do, we tend to forget that light is actually the key ingredient in a healthy plant’s diet. It’ll die without it.
Green plants get their food through the process of photosynthesis, which basically means “light making.”
Plants synthesize the sugars they need to grow using the energy in light, which is made of photons. Cool huh?
Your cannabis plants will thrive if you give them long hours of bright, direct sunlight. As much as you can give it, really.
That’s why the natural habitat of cannabis is the tropic regions of the planet. Plenty of water there, plus longer days than farther toward the poles.
Back in the dark days of cannabis prohibition, you’d be able to tell in a single puff if your weed was grown indoors or outdoors.
Fortunately for today’s growers, the unique light spectrum of sunlight can be virtually recreated with special grow lamps.
Today, you’d be hard-pressed to tell the difference between indoor and outdoor bud.
Water, Water, Everywhere!
Water, though obviously an important nutrient for your cannabis plants, can be tricky to administer in the right amount. Humidity control is key.
That’s why expert indoor and outdoor growers know how to use different synthetic polymers called “hydrogels.”
These non-toxic gels are soil additives that soak up and retain water when it’s available. And when the soil dries up, they release the water steadily back to the plant.
They’re cheap and essential kit for growing healthy plants. You can find them at any garden or home store, and most store-bought soil already has them.
Water is an important nutrient for cannabis plants not just to keep them firm and prevent them from wilting.
Water, or H2O, contains oxygen and hydrogen. And these account for another 45 percent of the dry material of your cannabis plants. So yeah, water is important!
N-P-K: The Holy Trinity of Soil Nutrients
Air, water, and light; you get those from the environment in which you grow your plants. But of course, there are many hugely important nutrients in the soil you’re using to grow your cannabis.
Of the roughly 16 essential nutrients that support virtually every plant in existence, there are three that are the most important.
Your plants need these three nutrients in larger quantities than the rest. That’s why when you purchase commercial potting soil mix, the package is labeled with 3 numbers, indicating the percentage of the three most important nutrients for healthy plants: nitrogen (N), Phosphorus (P), and Potassium (K). N-P-K.
As a general rule, go strong on the phosphorus and potassium, and dial back the nitrogen, and you’ll get plump, sturdy, fast-blooming, mega-flowering and overall healthy cannabis plants.
If your soil is nutrient-deficient, the number one culprit is likely nitrogen. And that’s a problem because cannabis uses nitrogen to build all kinds of important things.
Nitrogen forms the building blocks for the plant’s proteins, its chlorophyll, its enzymes, basically everything that makes the plant function.
But above all, nitrogen helps cannabis create its legendary cannabinoids. And where would we be without those!
It’s safe to say that your cannabis plants “know” how important nitrogen is for them, too. They eat as much of it as they can get their roots on!
And that’s why the classic beginner mistake is to add too much nitrogen to the soil. You end up overfeeding the nutrient to your plants, and that will slow its root growth and its flowering.
Nitrogen makes your plants “mature,” and you don’t want them to grow up too fast, now do ya?
If you take a look at commercial potting soil mix, the first of the N-P-K number indicates the amount of nitrogen.
When it comes to making your own soil, there are a few tried and true methods to feed it nitrogen if you think your plants are deficient.
Blood meal or fish meal will provide a ton of nitrogen to your soil at a low cost. So will using plant sprays made with liquid seaweed.
If nitrogen is the bodybuilding nutrient that helps your plants grow up (literally), phosphorus is what makes it flower. It’s bloom food.
Unlike nitrogen, it’s better to risk over-feeding this nutrient than to play it safe. Phosphorus helps the plant produce the unique enzymes and nucleic acids that go into producing cannabis flowers.
If your plants reach maturity with low phosphorus, you’ll see smaller flowers and end up with less product.
Ironically, however, phosphorus deficiency is what turns cannabis plants purple. And folks love their purple weed!
But that’s a sign of a buildup of anthocyanins. Not necessarily a bad thing, if you don’t mind slow-flowering plants and desire the purple coloration.
The best way to get phosphorus to your plants is by using bone meal. Phosphorus dissolves into the soil at a slow rate, so the risk of giving too much too fast is pretty low.
Sometimes, however, you may need to get some phosphorus to your plants quickly. In that case, look for “Blood Food” soil, which has no nitrogen but lots of phosphorus and potassium.
Potassium is the nutrient that gives your plants their strength. It accounts for around one percent of the total dry weight of cannabis plants.
Your plants need potassium to breathe and make proteins. They also need it to keep up the internal pressure that helps your plants stand tall and strong.
Deficiencies in this important nutrient will reveal itself through dead spots on leaves, flimsy stalks, and problems falling over. Low K also leaves the roots more vulnerable to disease.
The best way to give your plants this important nutrient is by mixing wood ash with your soil once a month before you plant your seeds.
With potassium, timing is everything. Mix the wood ash too soon, and water will leech out most of the nutrient. Put it in too late, its higher concentration will burn your seedlings!
Conventional wisdom has it that a few pounds of ashes per plant is a good ratio. And remember to get your ash from burning wood only.
Two Important Macro-Nutrients
Soil also provides two more super-important macronutrients for healthy cannabis plants.
Milk does a body good because the calcium in it helps you build strong bones. But plants need calcium for a different reason.
Most of the calcium in cannabis plants is used for defense. The calcium acts as a shield against other toxic elements that can poison and kill your plants.
There are lots of toxins in the soil with similar structures to calcium that try to imitate it. But calcium stands at the door like a bouncer at a club.
Calcium deficiency will make the leaves of your plants twist up and deformed. So use dolomite limestone to make sure your soil is well supplied with calcium before you plant.
Even though it never stays around in the final product, Sulfur is essential for healthy cannabis plants.
All the proteins made by the cannabis plant are built of two indispensable amino acids. And sulfur goes into making those.
But this one is tricky, because sulfur is a very common soil pollutant, especially in North America.
You’re more likely to have too much sulfur than not enough. And too much will kill the plant’s chlorophyll, which it needs to turn light into food.
Calcium protects the plants from the excess sulfur. And cannabis plants can definitely benefit from it at key stages in the grow process.
You can add it to your soil using gypsum or plaster of Paris. But use it sparingly if you’re going to use it at all.
Important Micro-Nutrients for Healthy Cannabis Plants
The above nutrients are what makeup virtually all of the tissue of your cannabis plants. But there’s still 0.5 percent of that tissue which is composed of “micronutrients” found in soil.
So while these may not be the “most important” nutrients, it’s hard to say they aren’t important at all. In fact, your plants would be in deep trouble without them.
We won’t go into the details of each. Suffice to say that most of these ingredients are trace metals that plants need to conduct the electricity powering their cells. Interestingly, botanists still aren’t sure about the role of some of these elements, like iron and boron.
All of these metal nutrients are toxic at anything higher than trace levels, and your plants don’t need more than very small amounts.
It’s likely you have too much of them in your soil than too little. Signs that you have too much of these elements include yellowing, dead, or deformed leaves.
If you think you may have too little of these trace nutrients. Add some chelating agents to your soil. These convert the metals into soluble versions (called “salts,” FYI) that roots can actually absorb.