Best Fertilizer For Marijuana

If you are growing marijuana and you aren’t happy with the amount of yield you are getting or the growth rate of your plants, then you might need to start using fertilizer.

Marijuana growers often face problems if they don’t know which fertilizer is the best for their plants.

There are several types of fertilizers available for marijuana growers. Some of them include organic, chemical, and natural fertilizers.

Organic fertilizers are considered to be the safest option because they contain no chemicals or toxins.

They also provide nutrients to the plant without harming its roots. However, there are pros and cons to each type of fertilizer and it often comes down to personal preference. 

Soil tests should be conducted before applying any type of fertilizer. This way, you can determine whether the soil has enough nutrients to support your plants. If not, then you can apply some other kind of fertilizer.

If you want to know more about which fertilizer to use for your marijuana then you are in the right place.

We have put together this useful guide to tell you everything you need to know, so keep reading to find out more. 

What Is Fertilizer?

A fertilizer is a material added to the soil of a plant to encourage growth and increase yield. It contains all the necessary elements required by the plant to grow.

These elements include nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, copper, zinc, manganese, boron, chlorine, molybdenum, cobalt, nickel, silicon, and many others.

Fertilizers are usually made up of two parts: (1) an inert component such as sand, peat moss, perlite, vermiculite, or clay; and (2) nutrients like nitrogen, phosphorus, potash, sulfur, magnesium, etc.

What Are The Different Types Of Fertilizers?

There are various types of fertilizer that you can choose from- organic fertilizers, chemical fertilizers, natural fertilizers.

Organic fertilizers are safe for both humans and animals. They are made from natural materials, including composted manure, fish emulsion, seaweed extracts, alfalfa meal, kelp extract, and blood meal.

These fertilizers do not contain pesticides or herbicides, and therefore, there is no risk of contamination.

However, it is important to note that these fertilizers will only work if they are applied at the correct time.

Chemical fertilizers are usually derived from synthetic sources. They are designed to mimic nature’s fertilization process.

Chemical fertilizers are used when the soil does not contain sufficient amounts of nutrients.

They come in different forms, including liquid, granular, and solid. Liquid fertilizers are easy to apply and are very effective.

Granular fertilizers are better than liquids because they allow air to penetrate the soil. Solid fertilizers are especially helpful for plants with deep root systems.

Natural fertilizers are generally made from animal waste products. They are ideal for growing vegetables and fruits because they promote healthy growth.

Natural fertilizers are safe for humans and pets but may cause damage to the environment. Therefore, they must be handled carefully.

But which ones are best? Chemical fertilizers are very easy to use and are readily available in many different stores.

However, once you are more familiar with natural and organic fertilizers and you know how to make your own, you will find that you spend a lot less money. It is also good to know exactly what is going into the soil of your plants. 

Micronutrients And Macronutrients For Cannabis Plants

Marijuana plants require micronutrients and macronutrients to thrive. These nutrients include:

  • Calcium
  • Magnesium
  • Phosphorus
  • Potassium
  • Sulfur
  • Zinc
  • Boron
  • Copper
  • Iron
  • Manganese
  • Molybdenum
  • Selenium
  • Chlorine
  • Nitrogen
  • Carbon Dioxide
  • Water

It is recommended that you use a balanced fertilizer to ensure that all of these elements are present in the correct amounts.

Some growers prefer to use a single nutrient solution over others because they believe that this makes it easier to control the pH levels.

However, there is no evidence to suggest that this is true.

It is possible to buy premixed solutions for cannabis plants, however, you should be aware of what is actually in them.

A lot of times, these products contain only calcium, magnesium, phosphorus, potassium, sulfur, zinc, boron, copper, iron, manganese, molybdenum, selenium, chlorine, nitrogen, and carbon dioxide.

They may have some trace minerals added to them, but they won’t contain any micronutrients such as calcium, magnesium, phosphorus, potassium, sulfur, etc.

If you want to use a premixed solution, you should always check the label to see exactly what is in it.

You can also buy individual nutrients that you can add to water. For example, you can buy a specific ratio of calcium and magnesium.

This means that you don’t have to worry about adding too much or too little of either element.

You can also buy a liquid fertilizer that contains all of the above-mentioned nutrients and other things like kelp extract, seaweed extracts, fish emulsion, alfalfa meal, molasses, yeast extract, and many other ingredients.

There are even some companies that sell complete nutrient packages for cannabis plants.

The most important thing to remember when buying a fertilizer is that you should look for something that has been tested by independent laboratories.

It is very difficult to test a product yourself, especially if you are not familiar with how to perform lab tests on plants

Types Of Natural Fertilizer

If you want to try some natural fertilizer then these are our top recommendations: 


Horticultural Organic Vermiculite by GARDENERA - Medium Grade - Natural Soil Additive for Potted Plants - Orchids - Hydroponics - Terrariums (1 Quart)

These two products are used as a source of nutrients for your cannabis plants. They help to improve the quality of the soil and increase the yield of your crops.

These products are very effective when it comes to improving the overall health of your plants.

They are also known to help with root development. So if you are looking for something to boost the growth of your plants, these two products will do the trick.

Perlite is a porous material made from volcanic glass that has been exposed to extreme heat. It is white and has a mild alkaline PH. It traps water and feels very hard.

Vermiculite is much softer with a spongy texture. It is made from mica that has been heated and is also able to absorb water.

It has a neutral PH. Whilst these materials are different, they are often sold together. When used together, they can absorb a lot more water than if you use them individually. 

The main use of these fertilizers is that they stop the soil from becoming too hard as it gets dry.

They also provide important nutrients for the soil including calcium, magnesium, and potassium. This helps your plant to thrive and flourish. 


Premium Double Sifted Clean Hardwood Ash (Natural Fertilizer, Aquaponics, Change Soil Ph Levels, Boost Organic Tomato Plants and Compost) 2 Pound

If you burn wood in your fireplace then you can collect the ashes and use them to fertilize your marijuana plant. It contains a good amount of potassium and lime.

If hardwood was burned then the ash will contain more nutrients than if softwood was burned.

Make sure the ash does not get wet before you use it, as it can create high salt levels once it comes into contact with water. 

Wood ash is very simple to use- simply scatter it over the plants or add it to your compost heap.Wood ash is also very useful as a natural pesticide as it can keep soft-bodied invertebrates away from your plants. 


Down to Earth Organic Bat Guano Fertilizer Mix 7-3-1, 2 lb

Guano is another word for poop, and bat poop is a great fertilizer. You can also use manure from chickens, cows, and other animals.

It contains nitrogen, potassium, and phosphorus. The slow-release manure is the best for improving the yield of your plants. 


Down to Earth Organic Fish Meal Fertilizer 8-6-0, 5 lb

Fish meal is a mixture of the inedible parts of fish that have been ground up into a fine powder.

This can be added to the soil of your marijuana plant to provide nitrogen and other nutrients.

By combining the fish meal with fish emulsion (pressed fish oil) you will prolong the release of the nutrients into the soil. 


Dr. Verm's Premium Worm Castings - Organic Soil Builder and Fertilizer (2 LB)

Worm castings are what are released from a worm after they have digested organic components like soil.

It contains lots of nutrients that are ideal for adding to compost.

It is best not to add the worm castings directly to soil as it can impact the flavor of the weed, so make sure you put it into a compost tea. 


Charlie's Compost 10lb

Compost is one of the most common types of natural fertilizer, and it is the easiest to make.

Simply collect kitchen waste like vegetable peelings, eggshells, and leftovers (not including dairy or meat products).

Over time, this will break down into a mulch-type material that you can add to the soil of your plants.

The soil will be enriched with important nutrients which will help your plants to grow faster and yield more.

The other added benefit is that you reduce the amount of rubbish that you are sending to the landfill. 

You can add any organic material to your compost heap, so if you have animals like chickens you can add their manure to the compost. You can also add worm castings as above or even bones.

It is best to mix up the compost well and you can do this easily by turning the heap with a pitchfork.

This not only maximizes decomposition but also creates an even spread of nutrients. 

After three months, your compost should be ready to use. You can purchase compost towers for your garden which makes it easy to manage the compost. 


This might sound strange, but human urine is a really good fertilizer for marijuana. It has a high nitrogen content which can boost the growth rate of your plant.

The other nutrients included in the urine will depend on your diet, but it could contain phosphorus and potassium which will also be very useful. 

If you are going to use urine as fertilizer then make sure you dilute it first, or the salt content will be far too high.

Aim for one-part urine to 10 parts water for mature plants, or one-part urine to 20 parts water for seedlings. You should never urinate directly onto the plant as this could kill them. 

If you are taking medication, if you are unwell, or if you have a urinary tract infection then do not use your urine to fertilize your plants. 

Compost Tea

To make compost tea, take some of your compost and place it in a separate bucket.

Then, add water and molasses sugar and leave it for three days. The compost tea will then be ready to add to the soil. 

Tips For Using Fertilizer

The most important thing when it comes to using fertilizer is keeping a record of what you have done.

This is important for getting to know your plants and their needs. It is even more important if you are using homemade, organic fertilizers. 

Create a feed chart to show which nutrients your plant has had at which point of its growing cycle.

Keep an eye out for different effects, good and bad, so you can adjust the fertilizer if needed. 

A common mistake that people make is using too much fertilizer. It is best to start small and add more if you need it, or you could risk causing problems like nitrogen burn.

This could cause the leaves of the plant to turn yellow (remember, yellow leaves just before harvest are normal, but at any other time of the growth cycle it is cause for concern). Marijuana plants don't need as much fertilizer as you might expect. 

Around two weeks before you are due to harvest your marijuana, perform a flush of the soil to prevent the taste of the fertilizer from tainting the plant. 

If you are using a chemical fertilizer of a store-bought fertilizer mix then do not go straight in with the full dose.

It is best, to begin with, half, and work your way up while you monitor the effects of the fertilizer. 

How To Read Fertilizer Numbers

If you are buying a chemical fertilizer then you will need to read all of the packaging to decide whether it is suitable.

The number of nutrients will be displayed in a number format such as 4-15-13. This is the NPK. 

The NPK tells you how much of each of the three main nutrients are included in the fertilizer- nitrogen, phosphorus, and potassium.

Depending on the point in the growth cycle, your plant will need different levels of these nutrients. If the packaging shows an NPK of 4-15-13, this means it has 4% nitrogen, 15% phosphorus, and 13% potassium.  


And there you have it, some of the best fertilizer options for marijuana! Whichever you choose, you should see an improved crop and a healthier plant.

Be sure to use the tips we suggested earlier to increase your chances of success too!

Best Fertilizer For Marijuana

Frequently Asked Questions

Get your last-minute questions answered below!

How Can You Boost The Growth Of Your Plant?

As you probably know, plants create energy using a process called photosynthesis.

This process requires plenty of carbon dioxide, so if you provide the plant with more carbon dioxide then you can increase the rate of photosynthesis. 

This is easy to do if you are using a growing room. All you need is white vinegar and baking soda. Set it up so that the vinegar drops into the baking soda at a rate of one drop every two minutes.

This will increase the amount of carbon dioxide in the room and you will notice an increase in the growth rate of your marijuana. You could also purchase a carbon dioxide cylinder or generator. 

What Are The Stages Of Fertilization?

Each plant that you grow has its growth cycle. Different nutrients are needed at various points in the growth cycle to help the plant flourish and reach its full potential. 

If you are growing marijuana there are two phases of the growing cycle that you need to be aware of when it comes to fertilization - the vegetative stage and the flowering stage.

During the vegetative stage, the plant will need plenty of nitrogen and potassium, and a medium amount of phosphorus.

During the flowering phase, the plant will need higher levels of phosphorus, plenty of potassium, and lower levels of nitrogen. 

There are also important micronutrients that will benefit the plant through the growing cycle- iron, copper, boron, manganese, magnesium, and sulfur. 

How To Test The Soil?

The first step to using fertilizers is to test the soil. This allows you to see how much nutrients are in the soil so you can determine how much fertilizer to use.

You can conduct a simple test by mixing one part water with three parts soil. Add a few drops of food coloring to the mixture.

Wait until the color changes completely. If the color remains unchanged, then the soil is rich in minerals. If the color turns orange, then the soil needs additional nutrients.

If you enjoyed this article, then you might like to read our post on the 'Best Weed Grinder'.

Scott Peters
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