Content updated in August 2022
In this article, learn the basics of Cannabis plant nutrients in order to start growing. For example, how to read nutrients labels, what is NPK, and when to switch to bloom nutrients. We’ll start with one of the easiest ways to grow cannabis at home: plants in containers or pots with a growing medium like soil.
Table of contents
- Types of fertilizers
- Synthetic chemical fertilizer
- Organic fertilizer
- Organic vs synthetic fertilizers
- Micronutrients and Macronutrients for Cannabis plants
- How to read fertilizer numbers
- Difference between Cannabis fertilizers and supplements
- Nutrients for veg stage
- Nutrients during the flowering stage.
- FAQs about Cannabis Nutrients
Plants need more than just plain water to grow. This means that certain nutrients must be there for plants to grow healthy and develop flowers or buds with good taste and aroma. There are many ways in which we can supply our plants with nutrients.
Types of fertilizers
Fertilizers are products manufactured to “feed” the plant with micro and macronutrients. Keep reading to learn about them.
Nutrient schedules for growing Cannabis may include organic nutrients, chemical or synthetic nutrients, or a mix of both. All these options are fine and they have their pros and cons. You can choose the best one for you based on your preference, location, availability, and budget.
Synthetic chemical fertilizer
Chemical or synthetic fertilizers designed for Cannabis cultivation are made with precise NPK ratios, micro and macronutrients for each stage and this makes them a great option. Nutrients in chemical fertilizers are almost immediately available for plants to absorb in order to grow fast and healthy. This becomes really important when nutrient deficiencies need to be corrected quickly. Chemical fertilizers are a great option for growers who want to harvest big, sticky buds and maximize their growing time. Hydroponic weed is usually grown with synthetic fertilizers.
Growers need to follow instructions and schedules for applying chemical fertilizers in order to avoid overfertilization or nutrient burn. Overfertilization may damage, delay flowering or even kill your plants so be careful! Get the Grow with Jane app to plan and set reminders!
Organic fertilizer
Natural and organic fertilizers are naturally produced with mineral sources (limestone), animal waste (manure, guano) or plant-derived substances (compost, seaweed extract). Organic fertilizers have been used for centuries to achieve strong, healthy, and vigorous plants. Some organic nutrients are sold as “raw materials” such as guano or bone meal, which may need to be composted or treated. Guano fertilizers are made with the excrement of bats and seabirds.
There are also elaborate compounds ready to use such as earthworm castings or vermicompost. Worm castings (a.k.a. worm excrements or poop) are used for making vermicompost, a type of fertilizer or humus packed with beneficial microorganisms and organic matter.
Organic vs synthetic fertilizers
Both methods can render great results if they are carried out correctly. Synthetic chemical fertilizers have the advantage of having the necessary elements immediately available for plant uptake. On the other hand, be careful about nutrient excess stress or burn when applying synthetic chemical nutrients. Always follow the instructions and maybe start with a lower dose and then increase it gradually.
Organic options tend to be more environmental-friendly than their chemical counterparts, depending on how they are produced and managed. Some organic compounds may take more time in the soil to transform into the elements that the plant can uptake. Animal manures (rabbit, horse, chicken, sheep, etc) need to be composted before use and have different breakdown times.
Micronutrients and Macronutrients for Cannabis plants
Plants take macro and micronutrients (elements) from the soil, air, and water. The necessary nutrients are divided between macro and micro, meaning that Cannabis plants need macronutrients in larger amounts.
Carbon (C), oxygen (O), and hydrogen (H) are the basic elements involved and plants take them from the air (CO2) and water (H2O). Keep good aeration inside your tent or grow room to make sure your plants are receiving the correct amount of Carbon and Oxygen from the air. A good source of water is also vital for basic plant functions. Water should come from a safe source: tap water is fine, use bottled water if potable water is unavailable in your area. Carbon-based filters and some other water filters are great for Cannabis watering because they filter out chlorine and other components. You can also leave water in a bucket or bottle for 24 hours and then stir energetically for the chlorine to evaporate.
What is NPK?
The main macronutrients involved in plant nutrition are known by the acronym NPK, they are nitrogen (N), phosphorus (P), and potassium (K). They are necessary for Cannabis plants to grow strong, and healthy, and to achieve a major final crop.
Secondary macronutrients and micronutrients
The secondary macronutrients are calcium, magnesium, and sulfur. Along with basic macronutrients, plants also require these elements to grow healthy.
Micronutrients, such as manganese, boron, sulfur, iron, molybdenum, zinc, and copper, are present in most fertilizers but in smaller amounts than macronutrients.
Silicon or Silica (Si) is a very important element not considered essential but highly beneficial. Silica helps plants grow stronger cell walls and stronger stems and leaves. Adding Silica or Silicon dioxide to your medium ensures strong plant development. Silica is very common in most soils outdoors but plants grown in pots with soil mix, coco, and hydroponic systems need silica additives.
How to read fertilizer numbers
It’s normal to become confused and overwhelmed by the number of different products branded as “cannabis nutrients”. As you learn more about nutrients, you’ll become fluent in reading fertilizer labels. For now, there are just a few things you need to know.
One thing you need to learn if you are planning on using Cannabis nutrients is how to read fertilizer labels.
Most fertilizer labels have three numbers that represent the primary nutrients for plants: nitrogen (N), phosphorus (P), and potassium (K). This is what NPK means. These numbers stand for the percentage of each nutrient in the solution. For example, NPK 4 – 15 – 13 means a fertilizer has 4% of nitrogen, 15% of phosphorus, and 13% potassium.
Cannabis has its own requirements regarding the ratios of each nutrient needed in each stage of development. This means that an all-purpose fertilizer with NPK 16-16-16 may be great for your lawn, but won’t be that good for your Cannabis plant.
There’s not only one correct formula with the perfect NPK ratios, or every brand would be doing the same thing. Instead, there’s a certain balance you need to maintain but the percentages may vary from product or line of products.
NPK Fertilizer
We can find the essential nutrients for Cannabis plants in different fertilizer products. These products are usually created for each of the plant stages. Most of the time, there’s a dose measure and schedule chart on the fertilizer’s label.
Fertilizers with a high % of N (nitrogen) and a lower % of P (phosphorus) and K (potassium): Usually intended for the veg stage. For example NPK 9-5-8.
Fertilizers with a lower % of N (nitrogen) and a higher % of P (phosphorus) and K (potassium): Usually intended for the flowering stage. For example NPK 5-9-9.
Not all fertilizers have the same amount of nutrients! It is essential to read every product label and follow the measure guides and schedules to avoid nutrient excess or deficiency. Observation is vital since the plant will give us physical signs of nutrients’ lack or excess.
Some products are designed to be applied from the beginning right to the end of the crop. Always follow the manufacturer’s instructions!
Difference between Cannabis fertilizers and supplements
Supplements are substances used to improve the physical condition of the soil, to help plants grow, or to increase yields. Some examples are microbial inoculants, wetting agents, humic and fulvic acids, and composts. They may include some micronutrients.
When a product has a very low % of NPK it’s probably a supplement and not a base fertilizer.
For example, products with NPK 1.5 – 0.1 – 3.5 are supplements, not the main fertilizers.
When starting, it’s better to concentrate on having at least one base fertilizer for the veg stage and one for the flowering stage with the above-mentioned NPK ratios (see chart). After this is covered, you can add supplements to give your plants a boost. If you start feeding only with supplements in the flowering stage, plants will probably develop severe deficiencies because P (phosphorus) and K (potassium) ratios are not enough. This may result in poor or no budding at all and very small harvests.
Nutrients for veg stage
The vegetative stage lasts about 4 -12 weeks (or more) and during this period, the plant requires a significant amount of light and nutrients. It’s very important to supply nutrients for the vegetative stage to grow healthy plants.
Marijuana plants need high levels of nitrogen (N), especially in this growth phase, since it is the nutrient in charge of regulating protein production. It is also responsible for the leaves and stems growth, which will be reflected in the plant’s future size and general strength.
Fertilizers for the vegetative stage contain a high percentage of N (nitrogen) and a lower % of P (phosphorus) and K (potassium). For example NPK 9-5-8
The most common nutrient deficiency in the veg stage is nitrogen deficiency. Nitrogen deficiency shows in yellowing old leaves at the bottom of the plant, and the whole plant becomes light green. If the leaves’ tips or edges turn brown, or the green color of the foliage turns darker, the plants could be suffering from nutrient toxicity or overfertilization.
Nutrients during the flowering stage.
The flowering stage in marijuana plants is the period when they grow their flowers or buds.
In this phase, there is high consumption of nutrients, mainly phosphorus, and potassium. To supply the plant with these elements, it is best to apply a fertilizer solution during the flowering stage. Unlike the vegetative stage, when the flowering process begins, the plant needs less nitrogen.
Fertilizers for the flowering stage contain a lower percentage of N (nitrogen) and a higher % of P (phosphorus) and K (potassium). For example NPK 5-9-9
Feeding the plants properly during the flowering phase will result in the healthy development of the plant together with an abundant harvest, which is what every grower wants.
Biostimulants and supplements for the flowering stage increase and optimize the absorption of fertilizers, resulting in thicker, more compact flowers with a better flavor. They also promote the production of terpenes and cannabinoids and increase the natural resistance of plants against disease and stress.
FAQs about Cannabis Nutrients
When should I start feeding my plants with nutrients?
You can start giving your plants nutrients as soon as they have grown 2-3 sets of leaves. Some fertilizer brands start the feeding schedule after 1 week after germination, during the seedling stage, and this is perfectly fine. The dose will be significantly lower for a seedling so be careful to follow the instructions to avoid nutrient burn. Depending on the selected growing medium, nutrients are going to be needed sooner or earlier. Some soil mixes come with nutrients for the first 3-4 weeks, they are called “hot mixes”. Avoid double fertilizing and risk burning by reading carefully what’s on your mix and how to proceed.
Should I use nutrients every time I water?
Some fertilizers are designed to be applied with every watering, other products are meant to be applied once a week with watering and the rest of the week give them only water. Always follow the nutrients chart provided by your fertilizer brand to know exactly how often to fertilize. Keep track of your nutrient schedule to avoid nutrient deficiencies or excesses, which may severely harm your plants.
When to switch to flowering nutrients?
When you see the first signs of flowering stage and the plant starts to develop pistils, the flowering process has started. You may apply blooming nutrients from week 4 or 5 of the vegetative stage if you are planning on switching to flowering soon.
If you are planning on giving your plants a longer veg stag, you can switch to bloom nutrients when the plant is big enough to fit the growing environment. Mind that plants stretch a bit more when the photoperiod changes, calculate their height or consider LST (Low-stress training). Remember to change the photoperiod (hours of light) from 18/6 hours to 12/12 if growing regular seeds to trigger flowering.
How often should I give my plants nutrients?
Some fertilizers are meant to be applied with every watering, other brands advise applying only once a week. Some supplements need to be applied once a month, or within some weeks. Read the instructions and set a calendar reminder on the Grow with Jane app to avoid forgetting or missing doses.
When should I stop giving my plant nutrients?
During the last week (or two) of flowering, many growers stop feeding their Cannabis plants with nutrients and start watering with water only. Growers flush their plants to avoid or minimize “chemical” flavor in the flowers when chemical fertilizers had been used. Near the harvesting date, pistils are going to look brown and curled in and trichomes are going to look rather milky or amber/brown. Read our article to know when to harvest and how to flush your Cannabis plants.
My plants are about 3 weeks and about 5” tall. All I’ve been doing this far is watering and spraying the leaves. What fertilizer should I be using now?
Hi Todd! We recommend starting with any cannabis fertilizer intended for the vegetative stage. This is also a good time to start with some supplements with micronutrients. If you need grower support and personalized advice, please download our free growing app https://growithjane.com/. Just write an in-app message and we’ll be happy to help! As Grow with Jane app users, you also access our growing community where you can share photos, ask questions and more. https://social.growithjane.com/
Thanks for reading and commenting! Happy growing!
Calag and root doctor to start
What fertilizer should I be using my weed plant it’s about 7 to 8 in tall knows about 13 14 ft tall
Try pure blend pro grow then bloom at bloom I’ve been having great results and it’s not 100$ a gallon 👍👍
Thanks man that helps a lot have been watching vids for 3 years and 1 article was better they don’t explain npk in vids because they want you to watch more
Hi Aouni! I’m happy to know that the article was useful for you! Thanks for reading and commenting, happy growing!
This doesn’t exactly tell me what number nutrients I should purchase other than final stages bloom,
Jessi
Hi JT! This is because each brand has different N-P-K concentrations for each stage and also micronutrients added may differ. If you need grower support and personalized advice, please download our free growing app https://growithjane.com/. Write an in-app message with info about your grow and we’ll be happy to help and give recommendations! As Grow with Jane app users, you also access our growing community where you can share photos, ask questions and more. https://social.growithjane.com/
Thanks for reading and commenting! Happy growing!
There is an infographic & the entire intro is about which number/ratio of nutrients are for which stages (veg & final bloom).
The author spent so much time & thought writing this article to begin with, so show some courtesy & appreciation by actually reading it next time.
Nitrogen 1st number shit i plant it with a coupme green beans till about 2 to 3 feet tall when u grow a green bean plant it naturally enriches the soil with nitrogen . key nutrient in veg stages AKA all stages before u decide okay she is big enough let the magic begin lol then push bloom nutrients…but if u do companion plant green beans make sure they are diseaee free and bush variety..no pole dont wanna choke your pretty girl..yank those suckers out and enjoy mother nature’s symbiotic blessings . now thats what i call true Romance lol xohappy buds much love frm Oregon
Excellent site. Lots of useful info here. I am sending it to a few friends ans also sharing in delicious. And certainly, thanks to your effort!
Good lecture
Hi Osman, thanks for your kind words! happy growing!
Pure blend pro grow and bloom follow directions go at 1/2 what they recommend and see if u need higher Or lower amazing nutrients love it makes 100$ tps junk
My plant has been growing on my porch in a miracle grow mix. She has grown to be about 2 feet thus far (about 14 weeks) She is my first plant—I do now know how to best nurture her from here. i feel like she should be bushy but I don’t know! Do I pinch the center top like a tomato plant to encourage bushing out? What do I need to do to encourage her to produce flower?
Hi Michelle! Outdoor plants flower when days grow shorter, in Autumn. Here’s an article with lots of tips for each stage of growth. https://growithjane.com/cannabis-plant-life-cycle-stages/
If you have specific questions about your plants, please download our app from http://www.growithjane.com and contact us via in app message, so you can also share pics and any info you think would be helpful. We’ll be happy to take a look and share some personalized advice! Thanks for commenting and happy growing!
Google YouTube low stress training hurry while shes young and flexible no haircuts increase yeild and bonsai that bitch baby xo
Hey there… newbie at growing. My babies are about 6 ft high… dont know why. Trimmed and topped at Ppropriate times. They r sativs. Seeds in pots outside under green house. Long white hair like leaves growing up where I’m guessing cones are forming. What should I be putting in soil for nutrients now? Combating bugs and keeping soil right moisture. Lost 2 already to root rott.
Hi Amy! I’m sorry you lost some of your plants to root rot, it’s very common. If you want to have free personalized advice, please download our app from http://www.growithjane.com and contact us via in app message, so you can also share pics and any info you think would be helpful. We’ll be happy to take a look and give you some tips for your grow!
Thanks for contacting us and happy growing!
I may need you help on a couple things, glad I found you…
Hi Dennis, thanks for reading and commenting! If you have specific questions about your plants, please download our growing app from http://www.growithjane.com and contact us via in-app message. There, you can share pics and info about your grow. We’ll be happy to take a look and share some personalized advice!
I have one plant turning yellow
Hi! Yellowing leaves may be a sign of Nitrogen deficiency, but also a lot of other things! If you have specific questions about your plants, please download our app from http://www.growithjane.com and contact us via in-app message, so you can also share pics and more info about your grow. We’ll be happy to take a look and share some personalized advice!
Can I send u a photo?
Hi Ellic, to get personalized advice on your plants and send photos, please download our app from http://www.growithjane.com and contact us via an in-app message. We’ll be happy to help! Thanks for commenting and happy growing!
Lot of good informaation. Nice blog.
Hi first time grower. Just put my seeds on paper towel in sealed plastic container. I am planning on using miracle grow soil and miracle grow fertilize for veg. Plants. Was going to start indoors grow with house led lights. Is this process a good start?
Hi Russell, we do not recommend any soil with “extended-release” nutrients, because they continue to release nitrogen for up to 6 months. This may cause nutrient burn and slow growth, it’s just not good for cannabis. Try other soil mix and add any veg fertilizer for cannabis and you’ll get better results. The rest sounds good!
You can share your progress with us using the Grow with Jane app. Best luck with your grow!
Thank you for providing this knowledge I was searching for this information.
I just planted one single seed in bonsai soil & it grew in 5 days! Is it okay to continue growing it on bonsai potting soil?
Hi Robyn! There are many types of bonsai potting soil with mixtures of different elements, but most of them are not suitable, or at least not the best option, for cannabis. If the plant is already growing in this medium, it’s ok, you can transplant it to a bigger pot filled with potting soil for cannabis. Thanks for reading and commenting!
On week 9 of a clone and starting to see what I believe are white pistils. When do I change her light cycle(indoors tented) and when do I start budding nutrients?
Hi Olivia! You can start right now with the 12/12 light cycle, your plants are ready. If you want your plants to be bigger, extend the veg cycle until reaching the desired size. Cannabis plants can grow in size from 30% to 50% in the first two weeks of the flowering stage so calculate this size and the distance to the light source as well. When you change to 12/12 you can start giving your plants nutrients for the flowering stage as well. Thanks for reading and commenting, happy growing!
A good read. Lots of useful info and photos about growing cannabis. It will be helpful while writing articles on my website. Good job! I’ll be back for some marijuana advices!
Hello, my plans are about seven months old and are in the firing stage. I stopped giving them tomato feed about a few weeks ago is it safe for me to continue giving them tomato feed before harvest after I stopped already?
Hi Aaron! It’s safe to continue to give your plants nutrients, especially if you see stunted growth. Many growers flush their plants before harvesting as a rule of thumb but new studies suggest it could be only beneficial if the plants were already overfertilized. So if your plants are under fertilized now, you can give them what they need. It’s up to each grower’s preference and the nutrients they use to flush or not. Plants growing in containers or pots run out of nutrients quickly after flushing but plants growing on garden soil can access nutrients even if you are not fertilizing them. For personalized advice about your plants, please send us an in-app message from the Grow with Jane app and our Grower Support team will be happy to help! Thanks for reading and commenting, happy growing!
That tip about letting tap water sit for 24 hours, then stirring vigorously to let the chlorine evaporate is a great tip, I always forget to pick up gallons and end up using bottled drinking water. This will save me a few bucks over time
Hi CannaPete! Usually, this works for lots of growers who use tap water for irrigation. Depending on the concentration of chlorine in the tap water, it may take more than 24 hours and a lot of stirring to evaporate all of the chlorine or at least reach a concentration that is not damaging to the plants. Aerating the water with an air pump also gives good results. Thanks for reading and commenting!
Thanks Alecia!
Hi CannaPete, thanks for reading and commenting! Happy growing!
My tap water has chloramine that unlike chlorine doesn’t gas off when sitting exposed to air.
Do you have any suggestions?
Hi Bruce, I recommend using water filters with catalytic carbon or activated carbon. Activated carbon filters work fine but they need more time in contact with the water than catalytic carbon, which is more effective at removing chloramine. Reverse Osmosis filters are an excelent option, but quite expensive. RO filters take out not only the chloramines but also all the minerals in the water. RO filters highly effective but you need to add all the essential nutrients back in solution with fertilizers, including not only NPK but also calcium, magnesium and all the micronutrients. Thanks for reading and commenting! Happy growing!
does dry banana peelings hurt seedlings
Hi Doug, I do not recommend adding anything that has not been previously composted to a seedling as it may rot and attract pests and fungi diseases. In the best case, it won’t do anything. Worst case, it may cause a fungi infection and kill the seedling in a few days. The banana peelings (and any other “natural” inputs) need to be composted and disintegrated for the plant to be able to absorb its nutrients. This process takes time and consumes energy. I recommend composting them first and adding them as compost to your plants without the risk of damage. Some growers add this to “living soils” but that must be in conjunction with some macro and microorganisms added on purpose to help decompose the materials.
Here’s an article about how to take care of seedlings, I hope it helps https://growithjane.com/cannabis-seedling-grow-healthy-plants-avoid-stunted-growth/
Thanks for reading and commenting. Happy growing!
Can I be directed to a good site for step by step how to grow Marijuana
Hi Dylan, here’s our basic cannabis growing guide for beginners with step-by-step instructions, pics, and tips. You can then find detailed guides step by step on each growing stage of the plant (germinating, seedling, vegetative, flowering, harvesting). https://growithjane.com/cannabis-growing-guide/
I hope you find them useful! Thanks for reading and commenting!
My plants are about 2 and a half months old and they are getting brown spots on the leaves can you help me with this project
Hi JC! Send your pics and questions through the Grow with Jane app and our Grower Support Team will take a look! You can also join our Community via the app to share with other growers worldwide.
Download free at https://growithjane.com/
Is 13-4-5 ok?
Hi Sedekick! It may be suitable for the vegetative stage but it depends on how the product is made, your media and other things. You can send the details of the product and your grow through the Grow with Jane app and our Grower Support Team will take a look! You can also join our Growing Community via the app to share with other growers worldwide.
Download free at https://growithjane.com/
I am in week 3 going into 4, I was giving my plant fish fertilizer but it is only 5-1-1 my plant looks very healthy its growing in a indoor tent, the buds look sweet but This is my first grow. So not sure if i need to go to the stronger phosphate and potassium? Please advice thank you inadvance cheers
Hi Jim! Fish fertilizer high in nitrogen is good for the vegetative stage but too much nitrogen in the flowering stage can result in small flowers and poor yield. Try switching to another fertilizer with less nitrogen and more phosphorus and potassium, it doesn’t need to have huge amounts of it, as it may be perjudicial too. If you need personalized advice on a specific produc, you can download the free growing app at http://www.growithjane.com and join the community or message us from there, we’ll be happy to help! Thanks for reading and commenting! Happy growing!
I transplanted ta 7 gallon pot. She is showing pistols already, outdoorsin Cali, Now that I have to give more gallons of water, do i increase the nutes 1 tsp per gallon us what i was giving, do i go to 3 tsp if it takes 3 gallons of water now?
Hi Sandra! Yes, exactly. You need to increase the nutrients proportionally to the amount of water. It’s easier to calculate it as you say, increasing the tsp of nutrients per gallon of water. Thanks for reading and commenting, happy growing!
Cool site
Hi Scott! Thanks for reading and commenting! I’m happy to know you like the site. Happy growing! 🙂