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A Guide to Cannabis Nutrients & Fertilizers

Over the years, there has been an explosion of companies manufacturing different ways to feed your plants. Many of these companies have started to focus their products on cannabis plants. It shouldn’t come as a surprise since cannabis, even when illegal, has been a high-profit crop. Cannabis cultivation is big business.

Depending on your cannabis growing style, the two most utilised forms of fertiliser are liquid nutrients (most are derived from different salts, though liquid nutrient companies use a natural extraction process) or the organics version with amendments. To make choosing nutrients even harder, hundreds of companies out there make these fertilisers. So, which ones should you use?

Why Does Your Plant Need Nutrients?

When it comes to all living organisms, we need things to survive.

Food, water, air, carbon, and many different things keep all living organisms alive. So, how can you plant a rose into the ground, water it, and it will grow just fine but not a plant you produced in coco? It all comes down to what that plant needs.

When you plant a marijuana plant in your backyard, that soil you are planting into isn’t just a blank slab of ground. That soil has bacteria, fungus, and living organisms, all breaking down the material in the soil, making it available for the plant to take up. These are organic nutrients. Microorganisms that provide baseline nutrient levels.

Your plants will take up those nutrients and have a “meal” of sorts, from the germination seedling stage to harvest. Like in any living organism, if something is missing, there will be signs, such as rust spots or extremely light-coloured leaves.

For liquid nutrients, these are usually set aside for cultivators who grow via hydroponic systems, a soilless media, or coco-coir. Some liquid fertilisers are made exclusively for soil and use different extraction techniques. These fertilisers are usually immediately available to the plants. Suppose you notice your plants are suffering from a nutrient deficiency or even a lockout (where there are too many available nutrients for the plant to take up, so it shuts itself down).

In that case, the standard recommendation is to flush the plant and give it a fresh feeding. Doing this will usually correct that deficiency. Since the nutrients are immediately available, this should fix the deficiency in the plant’s new growth.

There is a longer breakdown process for dry amendments and, therefore, longer times between feedings. This is the reason why dry amendments are used primarily for soil. These amendments require microbes, such as bacteria and fungus, to break down. This is beneficial to the plant in many ways. One of the ways is it allows the plant to take up what it needs at that moment. You enable the plant to grow the way it wants to grow.

This will help prevent nutrient lock-out (though, in soil, we have toxicities, where there is too much of a particular amendment available, allowing the plant to take up too much of it). Another way this is more beneficial is the decrease in the amount of water you must use since the micro life in the soil will help distribute that water. This creates what is known as the” Soil Food Web.” You will have microbes break things down, and when your plant is hungry, it munches on what is officially available and what it needs to grow.

The Right Nutrients for Cannabis

To grow to their full potential, cannabis plants should be fed primary nutrients, also known as macronutrients (or NPK):

Nitrogen (N)Nitrogen is a major component of chlorophyll. The compound plants use from sunlight for proper growth and development. It also plays a part in proteins needed for cell development and biochemical reactions that make plants thrive.
Phosphorus (P)Phosphorus is needed for photosynthesis, metabolism, and nutrient uptake. It is especially important for new growth, root growth, and bud formation. A lack of phosphorous (or too much) will ruin your grow.
Potassium (K)Potassium is there to keep your plant growing steadily. It helps control the regulation of water and salt in your plant by handling the opening and closing of the plant’s stomata (tiny pores in the leaves) and creating glucose. If you see weak plants appear burnt at the edges, that is because they’re not producing enough glucose due to a potassium deficiency.

Nitrogen powers the growth of leaves and stems

Phosphorous powers the root, bud and flowers

Potassium powers overall cell function and increases disease resistance

Depending on the plant’s growth, micronutrients may also be needed in smaller quantities. These include:

  • Magnesium (Ma)
  • Calcium (Ca)
  • Sulfur (S)

Also in this list are iron, chlorine, zinc, boron and manganese. These aren’t essential nutrients, and beginners may not need to worry about them unless they spot an obvious deficiency.

Cannabis growers can use these nutrients across a plant’s life cycle. The best cannabis is grown carefully, with a balance struck. For example, using nitrogen to support the plants in the vegetative stage and potassium when blooming or in the flowering stage.

Depending on the type of growth, growing medium, feeding schedule and whether you’re growing indoors in a grow room or outdoors in your garden, not all these nutrients are applicable.

Types of Fertilisers

When it comes to fertilisers (nutrients to a good chunk of the cannabis population), there are two main forms that you can use to ensure optimal plant health.

Salt-based fertilisers are your most common ones. These are typically derived from salts and acids, though companies are starting to extract those same nutrients naturally. This prevents soil from becoming overly saline when a grow is done and the root ball is composted.

Naturally-extracted nutrients are derived from sugar or alcohol extraction as opposed to salts. Emerald Harvest, Cutting Edge Solutions, Advanced Nutrients, Botanicare, and many more companies make some of the best liquid nutrients. Companies that are making more organic liquid nutrients are: Roots Organic, Micro Life, and True Green are just a few.

Now, what about if you want to use more natural means?

Thankfully, many growers have figured out how to use pure organic means in a pot. We use something called dry amendments, amending before and during the plant’s life, where we sprinkle the amendments on top and scratch into the surface of the soil. These are slowly broken down into the ground, cutting back on the amount of fertiliser you need to use.

In turn, you are no longer just focused on feeding the plants what they need but also on providing the soil directly, making it available to the plant. This also cuts down on the number of feedings required. You’re feeding your plant directly with liquid fertilisers, so there’s nothing to allow the suspension of nutrients the plant will want. With dry amendments, you’re top-dressed roughly once a month, so this has the added benefit of saving money on buying many bottles of liquid nutrients.

Many local companies have created lines of dry amendments products. Gaia Green, Down to Earth, and Build a Soil, are just a few of the larger ones.

How Often Should I Feed my Cannabis Plants Nutrients?

This subject is a little harder to tackle.

Whether you feed with a liquid nutrient solution or dry amendments, every grow cycle will be different. Thus, requiring different schedules. You will feed these nutrients daily or weekly when growing in a soilless environment.

Good companies will have a chart, either on their website or with their products, depending on your product. With liquid nutrients, you will most likely need to adjust the PH of your water, as well, since these nutrients are more available with the proper PH. For liquid nutrients, the appropriate PH range is 5.5-6.2, lowering the PH level as you move into the flower cycle. The general sweet spot is 6.2PH in the vegetative growth stage to ensure healthy plants.

Then, there’s an order you will have to go in as well. The product that will almost always go in first is your silica-based nutrient. If you mix the products in the wrong order, you can throw off the PH and make one nutrient unavailable. Again, good companies will have charts to follow, which will help you immensely. There’s a level of monitoring with each grow cycle. So, use the charts as a guide, but if you notice a lockout, you may need to decrease the amount of fertiliser in the water or increase the amount of time between feedings to avoid nutrient burn.

For dry amendment, you will have a more straightforward yet more difficult time regarding how often you feed.

This can be a little confusing, but it will make sense. In soil, more than likely, you will have nutrients already available and nutrients that are either suspended (soil loves to hold onto things) or still need to be broken down. This means that if you buy a bag of premade soil, you should add a little more amendment to that soil. Adding extra amendment gives the dormant microbes some fresh food to wake up to.

By doing this, you shouldn’t have to feed your soil for another month, on average. Now, if you have a demanding or overly vigorous plant, you may have to shorten the time to two weeks. You don’t want to feed under those two weeks since it takes roughly two weeks for those amendments to break down.

This is what makes dry amendments easy to use. Just sprinkle on the top, gently scratch it into the top layer of soil, and water when necessary. Though, there is a downside to growing in soil. And that’s the deficiencies. If you run into a deficiency, you won’t necessarily be correcting that deficiency for that plant. A good example would be this: you’ve been in veg for 2 weeks. You’re starting to see some rust spots that follow a slight pattern, which looks like a calcium deficiency. So, you go to the store and pick up some seashell powder, adding 1.5 times the recommended amount to the soil.

Unlike liquid fertiliser, it will not be immediately available for the plant (remember where I said it takes an average of two weeks to break down dry amendments?). For this reason, the newer growth will still show signs of deficiency until that calcium is readily available. Doing this will correct that plant’s deficiency, but that excess calcium will be held in suspension, waiting for the next growth cycle.

Which One Should I Choose?

For this question, it is going to be based solely on what method of growing you want to do. If you wish to use coco-coir, you can use either or. Coco-coir is generally blank when it comes to nutrients and PH. But, if you want to use a bucket system with a pump, you would need high-quality liquid fertilisers. Using dry amendments in such a system can easily become messy and costly, and overfeeding can overwhelm your plant roots.

Then, there’s soil. If you want to grow in soil, STAY AWAY FROM LIQUID FERTILISERS! There’s a reason, and it’s that soil loves to hold onto things. It is very good at it as well. Most liquid fertilisers, as I said, are derived from salts. When you add too much salt to soil, you can cause your soil to become overly saline, causing leaching of that soil.

The most effective way of getting rid of salts is with water. Like saline soil, you end up leaching that soil through flushing. So, it is always highly recommended to use dry amendments. More and more companies are premixing these amendments, allowing for more ease of use when it comes to growing in soil. As a result, once you have fed your soil the amendments, you only need to worry about watering your plants after that. So, experiment if you don’t know what to choose.


There has been a growth of companies making different nutrients over the years. With the legalisation of cannabis, the number of companies has increased and will continue to increase moving forward. Depending on your growing style, you’ll choose from two main fertilisers: liquid fertilisers and dry amendments. Choosing which depends on you and the plant you’re growing.

Cultivation information, and media is given for those of our clients who live in countries where cannabis cultivation is decriminalised or legal, or to those that operate within a licensed model. We encourage all readers to be aware of their local laws and to ensure they do not break them.

Chris Staniszewski