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Choosing and using marijuana fertilizers

A plentiful harvest overflowing with healthy buds is the goal of most cannabis cultivators. Light, oxygen, and water are three of the keys to reaching that goal, but fertilizer is just as essential to increasing bud growth. In this guide to choosing the best marijuana fertilizer, you’ll learn why fertilizer is important for marijuana plants along with how and when to use fertilizer to boost flower production and increase yields.

What is fertilizer?

In simple terms, fertilizer is plant food made from natural or industrially produced substances that growers apply to soil and plants to optimize growth. The nutrients in fertilizers may be beneficial to many different plants, including potted houseplants, flowers like roses and hydrangeas, and cannabis.

Fertilizer is plant food made from natural or industrially produced substances that growers apply to soil and plants to optimize growth. Photo by: Gina Coleman/Weedmaps

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Why is fertilizer important for cannabis plants?

Essential plant nutrients present in fertilizers may help cannabis cultivators raise a healthier crop of marijuana plants with more abundant leaf growth and, eventually, flowers. If you want to grow big buds, the right cannabis fertilizer can help you reach that objective. Without a good fertilizer, the buds on marijuana plants may not reach their full growth potential. Further, marijuana grown with fertilizer will probably be healthier overall, which can translate to more pleasant and full-bodied flavor in the buds.

What nutrients do cannabis plants need?

A cannabis garden needs a combination of essential nutrients and trace, or micro, nutrients. The best marijuana plant food will offer a balance of a vital trio of nutrients.

The big three primary nutrients that marijuana plants need to grow are NPK — short for nitrogen, phosphorus, and potassium. NPK are the collective building blocks of any cannabis fertilizer, as well as any thriving marijuana plant. Cannabis plants also need carbon dioxide and oxygen, which they obtain through airflow, and hydrogen, which comes from water.

Nitrogen, phosphorus, and potassium are the collective building blocks of any cannabis fertilizer, as well as any thriving marijuana plant. Photo by: Gina Coleman/Weedmaps

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Marijuana plants also require secondary nutrients, which include sulfur, calcium, and magnesium.

Finally, there is a more expansive group of trace, or micro, nutrients that boost marijuana plant growth. These essential micronutrients include zinc, manganese, iron, boron, chloride, cobalt, molybdenum, and silicon, among others.

How and when should you fertilize cannabis plants?

Marijuana plants need different levels of nutrients depending on their growth stage. In general, marijuana fertilizer should be applied at least once weekly, along with an ample supply of pH-balanced water.

As a rule of thumb, the ideal pH balance for marijuana grown in soil ranges between 6.0 and 6.8. Hydro, or hydroponic, growers should keep their water pH in a range of 5.5 to 6.5. On average, marijuana plants need a gallon of water each day per pound of anticipated flower.

Plant growth is equally dependent on the work of fertilizers and nutrients. Here are some guidelines for applying fertilizer during different stages of growth.

  1. Seedling: Minimal or no fertilizer. You may want to wait until your plants have sprouted a few leaves before administering the first dose of primary NPK fertilizer.
  2. Vegetative: For Week 1, use an NPK ratio of 2:1:2 — that’s two parts nitrogen to one part phosphorus to two parts potassium. By Week 7, consider increasing the NPK ratio to 10:5:7, followed by a 1:1:1 ratio in the late vegetative phase.
  3. Flowering: At this juncture, stop feeding nitrogen to the plants and focus on elevating the phosphorus and potassium levels. It is useful to fertilize plants during the early flowering stage but not as effective in the latter weeks after true buds have formed.

In addition to weekly feeding, marijuana plants require regular watering with pH-balanced water. As a rule of thumb, the ideal pH balance for marijuana grown in soil ranges between 6.0 and 6.8. Hydro, or hydroponic, growers should keep their water pH in a range from 5.5 to 6.5. On average, marijuana plants need a gallon of water each day per pound of anticipated flower.

For even better results, make sure to research the best feeding schedule according to the weed strain you are growing.

What is the best type of weed fertilizer?

If you want to grow an organic garden, choose a natural marijuana fertilizer containing the following materials:

  • Worm castings
  • “Good” bacteria and fungi
  • Forest humus
  • Fish meal
  • Blood meal
  • Bat guano (aka a mix of the above elements, in addition to kelp meal and molasses, which maximize the benefits of the other ingredients)
  • Biochar (aka a rich blend of carbon and charcoal)

Integrating these ingredients into regular soil can help you create a super soil with a diverse wealth of primary, secondary, and trace nutrients. While you can also purchase commercial fertilizers in liquid or powder form, natural materials often provide the most powerful nutrients.

One upside of synthetic fertilizers is that they tend to work faster than organic fertilizers. They may also be less time consuming and make a good choice for growers who prefer not to get their hands too dirty.

Bottom line on weed fertilizer

Using the right fertilizers and nutrients in the right quantities at the right time are essential to achieving an optimal cannabis grow. Ultimately, the best fertilizer for cannabis is the one that works for your schedule, budget, and level of desired effort. Growing cannabis requires a delicate balance of the right nutrients, so make sure you give your plants the attention they need and they will reward you with delicious, healthy buds.

The Most Popular Fertilizers for Growing Cannabis [Guide]

With an increase in the number of states where people are legally allowed to grow marijuana, it was inevitable that the fertilizer market would take off. Without the right fertilizers and nutrients, there is no hope of your weed producing fat buds. While you need to be careful not to overdo it and cause nutrient burn, a lack of fertilizer will ultimately harm your plant.

In this guide, we look at the best fertilizers and provide a quick guide on making your own.

Vermiculite and Perlite

While these materials are often considered to be interchangeable, they are different entities. They are both relatively sterile inorganic products but look and act differently. Perlite is hard and porous and is made by heating volcanic glass to an extremely high temperature. Vermiculite is soft and spongy and made by heating mica to an incredibly high temperature.

Perlite is normally white, traps water, and has a slightly alkaline pH. Vermiculite is tan or brown, absorbs water, and has an almost neutral pH. The two materials are often sold together despite their differences, and the combination absorbs water up to four times its weight.

These materials are ideal for preventing your soil from hardening when it dries.

Most importantly perhaps, vermiculite and perlite provide calcium, magnesium, and potassium, which gets into the soil and nourishes your marijuana. If you have a hydroponics setup, you can create a fertilizer that includes 50% of perlite and vermiculite, with the rest made up of peat moss and water. If you are using soil, you only need 10% of perlite and vermiculite in your fertilizer.

Human Urine

As bizarre as it sounds, your urine is a fantastic fertilizer for your marijuana plants. Fresh human urine is high in nitrogen, one of the key nutrients in weed growth. The breakdown of your urine depends on your diet. If you follow a ‘Western’ diet, the nitrogen, phosphorus, potassium (NPK) ratio is 11-1-2. For reference, blood meal is 12-2-1.

As urine contains a lot of salt, it must be diluted to a ratio of at least one-part urine, 10 parts water. DO NOT URINATE DIRECTLY ON THE PLANTS! It will probably kill them. If you plan to use your wee on potted plants or seedlings, dilute the urine to a 1:20 ratio in water.

It should go without saying that you must only use your urine if you are healthy. Don’t use it if you are on medication or have a urinary tract infection. By the way, if you are grossed out by the thought of using urine, how do you feel about bat guano or cow poop?

Wood Ashes

Yet another unexpected fertilizer, wood ash contains ample potassium and lime for your plants. Believe it or not, you can even use the ashes from your fireplace, assuming you have burned wood. You can lightly scatter the ashes on your plants, or add them to a compost heap. One issue is that the ash will produce high amounts of salt and lye if it gets wet.

It is also important to note that ashes from hardwood trees, such as maple and oak, contain more nutrients than ash from other trees, on average. Wood ash also acts as an effective pesticide by keeping slugs, snails, and other soft-bodied invertebrates at bay.

Bat Guano

A fancy term for bat poo, guano has been used as a soil enricher for eons. You can also use manure from other animals including chickens and cows. Bat guano is often worked into the soil or made into compost tea. Bat guano’s NPK ratio is 10-3-1 which vegetative stage. Chicken manure releases nutrients slowly and can enhance yield.

Fish Meal

Fish meal is typically made from ground-up parts of the fish that are inedible. The result is a fine powder that can be added to your soil. Fish emulsion is pressed fish oil. When combined with the meal, it prolongs the release of the nutrients. Fish meal is high in nitrogen. Alternatives include blood, bone, and soy meal.

Worm Castings

This is what comes out of an earthworm once it digests soil or other organic components. It is laden with tiny organisms and loaded with nutrients. It is commonly added to compost tea because adding it directly to weed, especially during the flowering stage, could result in your marijuana tasting like worm feces.

EDITOR’S CHOICE – Homegrown CannabisCo

Homegrown CannabisCo are the masters when it comes to seeds. Offering a massive variety of cannabis seeds that are well categorized, not only does this company create a resource for superb quality options including feminized seeds, it also provides extensive growing information for those looking for some support along their journey.


Experienced gardeners know that organic material will ultimately grow back into the soil, and take with it the nutrients in the original matter. You could compost kitchen waste and other organic materials and expect to be rewarded with wonderfully fertile soil. As well as boosting your plant’s growth, composting reduces your landfill contribution and enriches the soil in your locality.

Your compost heap can contain anything; as long as it is organic.

This means the food you throw out, chicken manure, worm castings, and bone meal. After you have created your compost heap, turn the compost with a pitchfork (daily if possible) until the contents have been properly mixed. By doing this, you maximize decomposition and reduce the time it takes for the heap to become usable. As a rule of thumb, you can expect it to take three months for your compost to become usable.

You can also create a compost tea, which is basically a liquid version of your compost heap. You need organic molasses, organic compost, water, a bucket, and a few other materials. It normally takes around three days to make, and you should use it as soon as possible.


If you have a hydroponics setup, it means you are using a growing medium such as Rockwool or coco coir instead of soil. As a result, you need store-bought nutrients made especially for hydroponics. These nutrients will contain no organic matter as they are provided through minerals, and should contain optimum NPK ratios.

With marijuana, you need high nitrogen, medium phosphorus, and high potassium during the vegetative stage. During the flowering stage, you need high phosphorus and potassium, and low nitrogen. What you buy must also contain various micronutrients such as iron, copper, boron, sulfur, manganese, and magnesium.

Carbon Dioxide Boosting

The process of photosynthesis involves plants using oxygen, sunlight, and carbon dioxide (CO2) to create energy. When you increase the CO2 in your grow room, you boost your marijuana plants’ growth. One of the simplest ways to achieve this is by using white vinegar and baking soda. Set it up so that one drop of vinegar falls into a bowl of baking soda every two minutes, and marvel at the CO2 increase in the room.

In an outdoor setting, you need to improvise as the smell of vinegar could land you in trouble with the authorities. A useful CO2 increasing technique involves placing a large plastic bag over the plant. Then, fill an empty plastic jar with baking soda until it is 25% full. Put the open jar beneath the tent created by the plastic bag.

Pour a tablespoon of vinegar into the jar until it begins to foam, a sign that it is generating CO2. Reseal the bag, allow the plant to breathe for a quarter of an hour and add more vinegar to what’s left of the baking soda. Stir with a stick and leave the bag over the plant for at least four hours.

If you are growing indoors, you could invest in a CO2 cylinder or a generator.

Synthetic or Organic Fertilizer?

There are tried and trusted products such as Miracle-Gro that are worth buying if you are a novice grower. Over time, however, you will learn that pre-packaged products are expensive and wasteful, not to mention bad for the environment. Once you learn how to create your own organic fertilizer, there’s a danger you will get addicted!

As well as saving a small fortune, you learn so much more about plant nutrition, and gain an understanding of what your plants need, and when. Eventually, this knowledge will lead to larger yields and more potent buds. The key is to determine what nutrients each organic element brings. For example:

  • Nitrogen: Worm castings, bat guano, human urine, and chicken manure.
  • Phosphorus: Bone and fish meals, rock dust, and banana peels.
  • Potassium: Fish meal, wood ash, and kelp.
  • Calcium: Clay, gypsum, and limestone.
  • Magnesium: Epsom salts and dolomite.

When Should I Stop Fertilizing?

Make sure you create a feed chart to discover what happens when you feed specific nutrients to your plants at set growth stages. If the leaves of your marijuana plants are turning yellow or look burnt long before harvest, it could be a case of nitrogen burn. Check your feed chart to see if it is a likely reason.

If your plants are being overfed, perform a flush with pH neutral water, but don’t do it in the week before forcing the plants into flowering.

Keep an eye out for deficiencies but resist the urge to add extra fertilizer. Marijuana plants often need fewer nutrients than you think. Perform a flush any time from two weeks away from harvest, or else your weed could taste of fertilizer!

Final Thoughts on Marijuana Fertilizers

If you see yellow leaves near the base of your plants as harvest time approaches, there’s no need to panic as that’s a normal occurrence. It is all too easy to overfeed your plants and cause nutrient burn, an issue that could damage your plant permanently, at least in an aesthetic sense.

If you are using a store-bought fertilizer, begin with half of the recommended dose unless there are clear signs of nutrient deficiency. The amount of nutrients your plant needs depends on the marijuana strain. When using organic fertilizer, start small and gradually increase the dose as and when it is needed.

Although you can use ready-made fertilizers as a novice, it is best to educate yourself on the topic and learn how to create organic fertilizers. Not only will it be better for the soil, and the environment in the long-term, it also helps you gain valuable insight into the world of gardening. The more knowledge you possess, the more likely it is that you will grow bigger plants and enjoy greater yields.

EDITOR’S CHOICE – Homegrown CannabisCo

Homegrown CannabisCo are the masters when it comes to seeds. Offering a massive variety of cannabis seeds that are well categorized, not only does this company create a resource for superb quality options including feminized seeds, it also provides extensive growing information for those looking for some support along their journey.

Cannabis Fertilizer – The Best Marijuana Fertilizers and Nutrients

If you’re looking for the best cannabis fertilizer products out there, don’t sweat it! We did all the research for you. First we spent hours reviewing the products out there and over the last few years we’ve refined this list based on feedback from the 2,000+ readers that visit this page each month. Then we negotiated a special deal just for our readers:

Take 5% Off Nutrients from Reefertilizer – Exclusive discount code: fertilizerforless


Reader Feedback: Top Two Alternatives for Your Plants

If you’re in a hurry, these two products below are the best sellers out of our list and the feedback from our audience has been 100% positive for both Fox Farm and Advanced Nutrients. Click the images below to buy now or scroll down to read our full review of the best weed fertilizers on the market.

Check Price on Fox Farm Nutrient Trio

Check Price on Advanced Nutrients Big Bud

Organic & Traditional Fertilizer Options

Table of Contents

Our Top Choices & Product Reviews

Top Fertilizers for growing your Marijuana Plant

Available on Amazon

To make it easier for you to choose the best fertilizer to feed your marijuana plants, we have listed our top 5 best fertilizers you should check out, below. Now we’re going to dig in and tell you why these are our top five favorites!

We’ll list the pros and cons of each fertilizer, complete with a stars rating on products that have free shipping with Amazon Prime. Now let’s get started!

1. Cutting Edge Solutions Uncle John’s Blend Growing Additive

Our first review is Uncle John’s Blend, which is a 0-0-2 formulated for use in hydroponic solutions. The great thing about this cannabis fertilizer is that it can also be used as a foliar spray early on in the grow season to give an additional boost to your weed plants!

We rate this 4 out of 5 stars, but only because it isn’t an organic fertilizer. If that doesn’t concern you, this one really packs a punch and it has a perfect 5 stars on Amazon at the time of writing.

When it’s closer to your 12- hour light stage and flowering time, add in some of their Bloom fertilizer product for professional results and a healthy plant!


  • It increases your plants’ metabolic rate for a more healthier and lively marijuana plant.
  • Has a complex, potassium based mixture that stimulates healthier photosynthesis cycles.
  • It also has a low molecular weight, and helps maintain the metabolic rate of growing marijuana plants.
  • Available in either bulk sizes or smaller 1-6 gallon sizes.


  • It’s somewhat pricey
  • If you’re one of many organic weed growers – just be aware that this fertilizer isn’t using an organic compound

Application: Twice a week.

2. Fox Farm Liquid Nutrient Trio Product

Next up on our list is a review for Fox Farm – a leader in the organic fertilizer industry. This advanced formula will save you time because you don’t have to worry about trying to figure out what to feed and when!

This trio of fertilizers and plant nutrients gives you the right NPK formula for each stage of growing. We rate this one a 5 out of 5 stars for being the ultimate choice for beginner marijuana growers who want to keep things organic!


  • Used in sequence at each growing phase, cutting out the guesswork
  • It’s an organic product
  • Features a 3-step growth system that aids cannabis plants from initial planting to their final stage of growth.
  • Contains a root stimulator which isn’t a common formula.


  • None that we’re aware of!
  • Just be sure to follow the stages correctly

3. Advanced Nutrients Big Bud Liquid Fertilizer

Our next review that we have is Big Bud, which was specifically formulated for cannabis grows by Advanced Nutrients.

It’s made to work well with coco coir and other hydroponic mediums, so we definitely give this one a 5 out of 5 stars for sure!


  • Offers a great hydroponic option
  • It perfect for any strain type
  • Great for first-time and also seasoned growers
  • Great price
  • It enhances terpenoids and phenols
  • Has minimal risk of overfeeding


  • Generally, this fertilizer is close to perfection. Nothing to dislike really.
  • Only available in .25 to 23 liter sizes

4. Flower Fuel 1-34-32 NPK

Talk about flower power! This one boasts a special blend of trace minerals and micronutrients, along with highly bio-available forms of phosphorus and potassium at a 1-34-32 NPK ratio.

Mix 1/4 teaspoon per gallon of feed water. This marijuana fertilizer also works well with coco, soil or any nutrient base! This one gets a 4 out of 5 stars rating because it’s not 100% clear if all ingredients are organic and you’ll need to keep a close eye on PH levels immediately after use.


  • Great for any flowering plants and not just for marijuana
  • Has all the macro and micronutrients that your plant needs
  • Not prone to overfeeding (but definitely still possible)
  • Over 40 proprietary ingredients for improved essential oil and resin content


  • It’s a bit pricey, but it does treat 200 gallons of water
  • You need to be cautious during the preparation to ensure the plant will get its needed nutrients

5. General Organics Go Box

Here’s a beginner’s perfect choice! This complete kit has 8 unique products that all serve different needs in a hydroponic cannabis operation.

Perlite or vermiculite growers will appreciate this one for it’s easy application! We give this one a 5 stars rating, but only if you’re starting on a small scale because there is no bulk option.

  • It’s a complete kit for hydroponics
  • Balances out PH levels
  • And it’s reasonably priced
  • May cause fertilizer burn according to reviews
  • Only suitable for smaller grow ops

General Cannabis Info

Is it legal to grow cannabis from clones or seeds in your state now? If so, you’re sure to be excited to get started with this special plant soon!

There are all kinds of tutorials to help you out, but we’ve highlighted some the best cannabis fertilizers shipping from Amazon right now!

Whether you’ve already started growing marijuana or are just planning to get started, knowing what the best fertilizers and nutrients are is crucial to the health of your plants! The cannabis plant is known for replenishing soil, but if you’re looking for the dankest buds with a rich terpene profile, you’ll definitely want to give them that added boost!

It may seem that everything is of equal importance when it comes to growing marijuana, but fertilizers and nutrients play a vital role in your plants’ health, growth potential, and potency. So, it is equally important that you choose the right fertilizers with the right nutrients to help your plant flourish! Read on for more information on caring for marijuana clones.

Fertilizers and Nutrients

A cannabis plant needs specific elements which are referred to as the “macro-nutrients” that cover both mineral and non-mineral elements. Micronutrients also play an important role in development and should not be ruled out!

Many commercially available fertilizers have a special formulation of these trace elements along with the macro-nutrients to help boost your soil or hydroponics solution.

The three main macro-nutrients needed by your cannabis plants are nitrogen, potassium, and phosphorus which are found on every bag of fertilizer represented by 3 numbers printed on the front information section of the fertilizer container.

These are often referred to as the N-P-K ratio. These numbers state what percentage of these 3 nutritional needs the fertilizer has and can provide your plant.

Aside from the above 3, there are other macro-nutrients needed by your cannabis plants as follows:
  • Hydrogen
  • Oxygen
  • Sulfur
  • Calcium
  • Carbon
  • Magnesium
In addition, your plant also needs a trace amount of some elements, namely:
  • Chlorine
  • Cobalt
  • Boron
  • Iron
  • Zinc
  • Molybdenum
  • Silicon
  • Copper
  • Manganese

Care Instructions

Read More

With a little know-how, indoor operations can be very efficient and easy to ensure success! Since you can control all the environmental variables like co2 indoors, it’s a great choice for beginners. Plus, you’re able to grow in the cold months from Dec to Feb when an outdoor cannabis grow would be impossible.

Choose a cool, dry area with plenty of ventilation. 70 to 75 degrees is acceptable. You’ll need to ensure your cannabis plants get 18-20 hours of LED lighting during the initial phase.

When it’s time to bud, you can cut this back to 12 hours daily, which encourages flowering. Be sure to look up a complete growing guide and purchase the proper equipment prior to starting.

There are many considerations like carbon dioxide levels, water needs and several additional variables that should be carefully controlled. This LED grow light below gives you an idea of another common area of concern for those new to cannabis. Certain light spectrum’s are needed more or less at each stage of the grow: