Yes, you can plant weed seeds in dirt and possibly grow a plant without any fertilizers or special nutrients. But chances are that you don't happen to live in a place with very rich, fertilized soil that carries just the right blend of nutrients needed by a marijuana plant to thrive.
Because of that, I encourage growers to learn about the type of nutrients and special fertilizers needed by a cannabis plant, and at least start with good soil before you get started growing if you're determined not to use any nutrients.
While cannabis plants will grow in a lot of conditions, as a farmer, you are looking to optimize the size, weight, density, potency and overall quality of your buds. In order to do that, you will need to fertilize your cannabis plants in such a way that they can produce at their best.
Cannabis plants which don't get the right levels they need, especially in the flowering/budding phase, tend to grow small and airy buds. In extremely poor conditions, some cannabis plants may just sprout a few white hairs (pistils), and never actually form any real buds at all.
And if you are determined to grow organically with no added nutrients, I encourage you to learn about how you can actually compost your own organic super soil in such a way that you actually don't ever need to add any extra nutrients at all.
Other trace minerals thought to be essential include cobalt (Co), silicon (Si), chlorine (Cl), and selenium (Se). Not all sources agree on their inclusion in the essential group, though they are important to support all plant life.
No matter what source, boron (B), manganese (Mn), zinc (Zn), copper (Cu), iron (Fe), and molybdenum (Mo) are always listed as essential micronutrients. Like the other essential nutrients, all micronutrients either have a unique function or serve to assist in the functions and processes of the other nutrients.
For its part, phosphorous is needed more during the flowering stage and is only required at about half the ratio of N levels during the vegetative phase of development. During this phase, K is needed at between half and two- thirds the level of N.
They do, however, need to be in a significantly higher quantity than the micronutrients, so they are separated here. The essential secondary nutrients are magnesium (Mg), calcium (Ca), and sulfur (S). These nutrients are often unavailable to cannabis if proper pH levels are not maintained (more on that later).
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Cannabis has thousands of unique properties, but like any other plant, it requires the same essential nutrients to properly grow and produce the desired yield of buds. Plants need relatively large amounts of macronutrients, lesser amounts of secondary nutrients, and small to trace amounts of micronutrients to germinate, grow, flower, and produce seed. All told, there are about 20 essential nutrients needed for optimal cannabis growth and development.
What follows is not an exhaustive list, but a sampling of some of the roles of micronutrients and how they aid in the development of cannabis plants:
Essential Secondary Nutrients
Some sources do not separate the secondary nutrients and instead lump them in with the macronutrients since they aren’t needed in the same high quantities as the macronutrients.
The number of micronutrients listed as essential can vary based on the source. Like secondary nutrients, it is somewhat a matter of classification as some list the secondary nutrients as micronutrients. Either way, they represent minerals and elements that are not as abundantly available on Earth and as such are not needed in very high amounts by cannabis plants, but are still necessary.
These secondary essential nutrients perform a wide range of critical functions to proper cannabis development. They are often necessary components or complementary parts to other nutrients and functions. They are all needed for plant and root growth, but they do have specific roles. Calcium assists in transporting other nutrients and aids in their absorption. Magnesium is a critical component of chlorophyll. Sulfur aids in the transport of chlorophyll, but also assists with plant metabolism and transpiration.
The lesser amount required to aid in the proper growth and development of healthy cannabis should not be mistaken as being less important than the micronutrients. The same can be said for the diminutive amounts of micronutrients needed.