Article written by
Dipak HemrajHead of Research and Education
Content reviewed by
Dr. Lewis JasseyMedical Director - Pediatric Medicine
Table of contents
However, one fertilizer type does not fit all, as cannabis plants have different nutritional requirements. Choosing the best fertilizer comes down to find the product (or products) that suits your needs and the environment in which your plants will grow.
Whether you’re using soil, coco coir, or a hydroponic grow also matters, as the soil tends to have nutrients. In contrast, coco coir and hydroponic growing require nutrients to be supplied throughout the growing process.
Timing also matters — the nutrient profile of the fertilizer you use during the vegetative stage will be pretty different from that of the fertilizer you use during the flowering stage.
Whether you choose to grow indoors or outdoors matters as well, as you do not necessarily want to use fertilizers made for indoor growing for outdoor growing, this is because nutrients for indoor growing are often composed of synthetic mineral salts that can damage soil bacteria in outdoor settings.
With this in mind, let’s take a look at what fertilizers are best for various grow types.
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The Importance of Cannabis Fertilizer
Fertilizers are any material applied to soil (or other growth mediums) or plant tissue to supply the plant with nutrients and improve its health and yield. Fertilizers can be synthetic or organic and are distinct from liming materials or other non-nutrient soil amendments.
The three main compounds found in any fertilizer include nitrogen (N), phosphorus (P), and potassium (K). Other micronutrients that may be added include:
- Boron (B)
- Copper (Cu)
- Iron (Fe)
- Manganese (Mn)
- Molybdenum (Mo)
- Zinc (Zn)
- Chlorine (Cl)
- Nickel (Ni)
Macronutrient fertilizers tend to contain NPK, whereas micronutrient fertilizers tend to have nutrients like boron, copper, iron, and so on. Mycorrhizal fungi can also be added to soil, coco coir, Rockwool, and other inert growth media to help improve nutrient absorption.
If you are using soil, consider pH, the soil’s nutrient profile, aeration, texture, and infestation levels. For example, loam soil is the best kind of soil for cannabis. It consists of silt (40%), clay (20%), and sand (40%).
There are many different types of soil explicitly made for growing cannabis, and these soils will have many nutrients in them already. With these cannabis-specific media, you may not need to use any fertilizers in the beginning stages of soil grow.
Although there are differences between cannabis varieties (cultivars or “strains“) in terms of the nutrients they need, there are some general rules to go by, assuming there is virtually no nutrition in your potting mix (i.e., an inert growing medium such as coco coir or Rockwool).
We won’t be detailing micronutrients as these are not often needed, and if they are, they are used very sparingly. Less is definitely more when it comes to micronutrients.
Seedling or Cutting Stage
Using little to no fertilizer in the early seedling stage is best. Rooted cuttings are often deficient in nutrients after propagation, so feeding gently with a 1:2:1 or 1:1:1 NPK ratio may be ideal at this point. But not too much — less is more, especially in a soil grow, where you may not need to feed the seedling anything.
During the vegetative phase (around four weeks indoors, up to 12 weeks outdoors), cannabis requires an NPK ratio of 3:1:1. Nitrogen can help improve the growth and strength of the plant’s roots and increase yields and quality in the long term.
Early Bloom (Flowering)
It is best to reduce the amount of nitrogen during the flowering stage. An NPK ratio of 5:10:7 is ideal. Micronutrients like calcium and magnesium may also be helpful at this point.
An ideal NPK ratio is around 1:3:2, with more phosphorus and potassium.
Late Bloom (Flowering)
Reduce nitrogen further — some growers even suggest no nitrogen. An NPK ratio of 4:10:7, or even 0:3:3, is recommended.
Flushing (Final Stages of Flowering)
This is the last two weeks of growth when no fertilizers should be added. Instead, you want the plant to use all nutrients in the growing medium fully. This will also improve the flavor of your plants and ensure no remaining fertilizer in the bud itself.
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6 Best Marijuana Fertilizers
Now that we’ve covered how nutrients are used throughout the growing process, here are some of the best fertilizers for your marijuana plants.
Good Quality Soil Designed for Cannabis
Soil contains many nutrients in it already, and many feel that it can improve the flavor of cannabis. There are many brands out there, including CANNA (which makes coco coir as well), BioBizz, Dr. Organics Living Soil, and more.
Organic Fertilizers for Outdoor Grows
If you are in an area with good quality loamy soil (or using loamy soil in a pot), you do not need to add synthetic fertilizers to the mix. Mother nature is providing the nutrients for you.
Instead, utilize organic fertilizers like worm castings, blood meal, fish meal, or bat guano for nitrogen; bone meal or rock dust for phosphorus; wood ash or kelp meal for potassium; and dolomite lime for calcium or magnesium.
Kyle Kushman’s Vegamatrix
Kyle Kushman is a legendary breeder and grower who understands nutrients. He has developed several different types of high-quality organic fertilizer for different stages of growth, as well as other products like enzymes and amino acids to boost the strength, quality, and yield of your cannabis.
Vegamatrix is excellent for many growing media, including soil, inert growing mediums like coco coir, and hydroponic systems, and is fantastic for indoor and greenhouse growing.
Canna Coco A & B
CANNA’s Coco A CANNA’ssuited to go with their brand of coco coir and is simply one formulation for the vegetative stage (Coco A) and one for the flowering stage (Coco B). Simple and great for a beginner using coco coir as their growing medium.
Advanced Nutrients Bloom, Grow, and Micro
Advanced Nutrients makes good value products, and its trio of Bloom, Grow, and Micro is ideal for those looking for an affordable, pH-balanced set of nutrients for indoor growing.
Dyna-Gro has several great products that can be used for cannabis and other types of plants, like ornamentals, vegetables, and herbs.
The company’s website also gives instructions on how to use its products to grow weed, which is fantastic for those new to growing cannabis and those with more experience but who want to find the ideal formulation for their plants. It is an excellent choice for indoor growers.
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Professional vs. Homemade (Compost)
Many people opt to make homemade fertilizer by composting natural materials like:
- Grass clippings (nitrogen)
- Tree leaves (nitrogen, trace nutrients, and they attract earthworms if growing outdoors, which is even better)
- Weeds made into a garden tea (nitrogen)
- Manure (nitrogen, but best used in small amounts)
- Coffee grounds (traces of NPK)
- Tea bags (nitrogen)
- Eggshells (calcium)
- Banana peels (potassium)
- Bones and bone meal (phosphorus, calcium, and other nutrients)
- Rock dust (phosphorus)
- Various kitchen scraps (different nutrients depending on the material)
Homemade preparations can be sustainable and cheap, but making the right mix can be complex and lengthy.
Professional fertilizers — where all the hard work of creating a cannabis-specific nutrient profile is done for you — can save plenty of time and effort and can ensure that your fertilizer isn’t too “hot” (i.e., contains too many nutrients for your plant, burning it out, and damaging growth).
However, a homemade fertilizer can be excellent for outdoor growing as the materials are biodegradable and do not necessarily damage the soil’s ecosystem.
The Bottom Line
There are several different fertilizers available on the market. The fact is, any one of them can be used to grow cannabis if you know what you’re doing with them.
However, as different fertilizers are usually made with growing certain types of plants in mind, it is often best to find one that is specially formulated for cannabis growth or gives instructions on how to do so. This makes growing simpler for cannabis growers all around, whether they’re newbies, intermediates, or experts.