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The Best Fertilizer for Outdoor Growing




Growing cannabis outdoors requires great skill and experience. Factors such as choosing the perfect growing environment, the correct spot for planting and the right time to plant can greatly affect your crop.

A vital factor that is often overlooked in outdoor cannabis growing is the provision of nutrients throughout the lifespan of the plants. Read on to learn about the best fertilizer for outdoor growing of cannabis. 

What Nutrients do Outdoor Plants Need?

Growing cannabis outdoors entails many factors including specific rainfall, soil moisture conditions, and even the direction of the sun. The cannabis plants should be planted far from trees, hills or buildings and they should receive the necessary nutrients for their different growth stages. 

What are the best nutrients for outdoor grow?

The three main nutrients for outdoor grow of cannabis plants are nitrogen (N), phosphorous (P), and potassium (K). These nutrients should be applied at the right time, in the right ratios and not excessively to avoid nutrient burn. 

We will take you through your plants' nutrient needs in the different stages of their growth.

Seedling Stage

Cannabis seedlings get their nutrients from the seed they sprout from, and absorb water through their leaves before the development of their roots. 

Your seedlings will not need to be fed until they are about 3–4 weeks old and sprout the first 3-4 true leaves indicating the start of the vegetative stage.

Vegetative Stage

While some farmers start their plants on a light NPK ratio of 2:1:2 to avoid nutrient burn, others immediately fertilizer kickstart them on a  4:2:3 ratio.

By mid-vegetative phase (which is roughly 6 weeks post germination), the pants will require an aggressive increase of this is when the plants are experiencing rapid growth. Most cannabis growers choose a 10:5:7 fertilizer ratio by this stage.

Nitrogen levels should be lowered towards the end of the vegging phase which will prepare the cannabis plants for the bloom stage. A 7:7:7 fertilizer ratio is usually ideal for the last week in the vegetative phase.

Flowering Stage

At the start of the flowering stage, the cannabis plants will need an increase of phosphorus and potassium. A very effective NPK formula ratio is 1:3:2 for early into mid-bloom, and then a 0:3:3 in the late bloom. Adding a last flush of plain water or/and a light flushing solution in the final week improves 0n flavor. 


Because hydroponic growing relies on you to provide all the nutrition, cover all your bases by providing: 

  • An N-P-K mix
  • Calcium nitrate
  • Epsom salt (magnesium sulfate)

Your crops will get the hydrogen, oxygen, and carbon that they need from the hydroponic water but you should be sure to provide the rest, as well as a conducive PH environment. 

Other Soilless Mediums

Soilless potting mixtures which are made up of inert (non-soil) ingredients such as perlite, coco coir, rockwool, peat moss, and vermiculite are often great choices from growing cannabis outdoors. The difference with soil is that all the nutrients the plants need have to be added to them usually via water. From here, the plants can access the nutrients through the roots which yields quicker growth as well as higher yields than in soil where the plant has to seek out the nutrients. 

Other Organic Mediums

You could choose to grow your cannabis in organic mediums such as compost or soil. Organic mediums have a more vibrant composition and accessibility to more micronutrients and other beneficial compounds. Though organic growing may be slower, it definitely results in cannabis that is more potent and smells and tastes stronger.

The Different Ways of Fertilizing Outdoor Cannabis


Composting is the process of creating organic “fertilizer” by decomposing organic materials. Composting usually takes time and typically starts months prior to when it’s needed. It also requires suitable space, preferably away from people because it usually has a very strong odor. 

The main idea behind composting is the decaying of organic matter with the aid of bacteria in the decomposition process which creates a blend called humus. Natural soil uses this same process and composting is just accelerating the process as the mixture of additives increases both the presence and activity of microorganisms and bacteria. 

Good, fertile soil typically contains millions of microorganisms as well as other beneficial life forms like earthworms. 

Liquid Nutrients

Liquid fertilizers are liquid concentrates or water-soluble powders which make a fertilizer solution when mixed with water. To apply them, you will require a watering can or hose-end sprayer. You need to apply liquid nutrients regularly as they only last 1-2 weeks. 

The advantage of this form of fertilizer is that it is quickly absorbed, allowing the plants to access the benefits soon after application. They are a great starter solution and also good for a quick boost in the growing season. 

Liquid fertilizers are also great supplementation for granulated fertilizers because frequent watering may cause leaching. 

Granular Fertilizer

Granular fertilizer is usually found in the form of granules and worked into the soil or sprinkled around the plant. Granulated fertilizer gets activated once it gets into contact with water and could last between one and nine months. 

Many granulated fertilizers have timed-release, slow-release or controlled-release properties, which just mean that they release the nutrients over a period of time, depending on their coating.  This is very advantageous as the fertilizer may only have to be applied once or twice throughout the growth cycle of the cannabis plant. They also typically do not provide excess nutrients or nutrient run-off.

When to Fertilize Outdoor Plants

Experienced outdoor growers usually start their clones or seedlings between March and April. This allows them at least four weeks in the grow phase which is done indoors before the plants are transplanted outside. 

When summer is at its peak, this is when there is the most intense sunlight and therefore when the cannabis plants experience the most stress. Cannabis plants need the most nutrients starting in late August and stretching into September in most parts of the US. Apart from the excess light and heat, this is the period when outdoor cannabis plants are in the vegetative stage and building their height, leaves, stalks,  side branches, and carrying out the intracellular processes that are necessary for the creation of the large and sturdy structure needed to carry the buds.

Giving your outdoor cannabis plants customized nutrition especially in summers’ full heat requires plenty of water. It is therefore recommended to use a half-strength dose of nutrients in order to not burn the roots by overdosing them with nutrients. 

Alternating feeding the cannabis plants with base outdoor growing nutrients and a quarter strength solution containing kelp and fish emulsion will provide a nitrogen-rich program. Kelp in particular is a plant tonic which stimulates photosynthesis, root development, nitrogen uptake, the growth of helpful root-zone microbes, and stalk and height strength gains. , 

The kelp and fish emulsion formula if:

You’re growing your outdoor cannabis in an area which receives in excess of four inches of rainfall/week.

You’re growing remotely which means you can’t readily access your crop.

You lack access to adequate carried-in or on-site water to carry out liquid nutrients feeding.


Homemade vs Premade Nutrient Mixes

What are the best nutrients for outdoor cannabis?

Nutrient mixes come in different forms. You can choose to mix your nutrients at home depending on what you consider to be important for your cannabis plants in their different growth stages and also depending on the medium you are using to the plants. Mixing your own nutrients requires knowledge on what the plants need as well as how best to apply and in wht ratios.

On the other hand, premade nutrient mixes already come prepared to suit your cannabis plants in their different growth stages. All you need to do is purchase an already formulated mix and apply it.

How to Make your Own Compost

Composting is both a cheap as well as an effective way of keeping your cannabis grow in tip-top shape. Apart from being a bed of nutrients. The soil is an entire living ecosystem which is a habitat for diverse lifeforms. Among this are beneficial microorganisms which live within the soil and work with cannabis to protect it and ensure it thrives.

Predatory nematodes on the other hand can work to defend the roots of cannabis plants against parasitic nematodes, while mycorrhiza in a symbiotic relationship with the plant roots help with breaking down organic matter into nutrients that are digestible. 

These microorganisms found in the soil are able to make the difference between good and great cannabis. Applying compost can be the key to encouraging this rich, healthy soil full of beneficial microorganisms. 

To make your own compost, first acquire a bin you will place at a shaded area of your garden. Place your bin on top of grass or soil so that the compost can have adequate drainage and the microorganisms can get access. Preferably, your bin should have a lid to aid in the retention of moisture and faster breakdown of the compost. 

You can also have another bucket or bin in scraps into it and later transfer to the one in the garden. 

What should go into your compost?

Absolutely anything organic. This mainly includes vegetables, bread crusts, tea bags, and a myriad of leftovers. Other food items that are great for your compost pile are:

  • Blood meal– Adds nitrogen
  • Bone meal – Is high in phosphate
  • Chicken Compost – Organic “slow release” chicken manure compost will increase yields and promote the health of your plants
  • Fish emulsion Great for young cannabis plants
  • Worm Castings– Have balanced nutrient content
  • Kelp Meal– Contains many micronutrients
  • Manures- Cow, rabbit, horse, chicken,  or bat manure are great additives. They should not be added directly to soil
  • Coffee grounds – increase acidic PH of soil
  • Eggshells- Increase the alkaline PH of soil or compost
  • Lime– Also makes soil alkaline
  • Wood Ashes – Rapidly adjusts PH as well as increasing micronutrients in the soil.

Synthetic Composting

Depending on your medium, compost may be an alternative to using synthetic chemical fertilizers or other soil amendments. While chemical fertilizers may provide a quick boost which spurts plant growth, they are often low in minerals, micronutrients, and beneficial organisms which plants need for their long-term growth. Most synthetic fertilizers also damage soil organisms such as earthworms, which upsets both the health of the soil and the ecosystem.

Some composters may choose to boost the level of nutrients of their compost pile by adding synthetic fertilizers. A good way to do this is to first apply your compost to your soil, and then after you have tested your soil in a couple of weeks, you can add some fertilizer as required. Directly adding the fertilizer to the compost pile might not be the best solution. 

Organic Composting

Organic compost is made by decomposing organic matter which is usually used to improve the health of the soil the cannabis has been planted in. Apart from being a rich source of nutrients such as nitrogen, compost adds organic matter and humus that cannot be further broken down to the soil. The humus helps in moisture and nutrient retention in the soil while changing its density. 

How to Avoid Nutrient Deficiencies Outdoors

Depending on the medium you are using, you can do a few things to ensure that you avoid nutrient deficiencies in your cannabis outdoor grow. Some of these are:

Start out right: Whatever medium you are using, ensure that your cannabis plants will be able to access the correct nutrients at each stage of their grow. This could mean purchasing growing mediums that already contain the right nutrient mixes for cannabis plants, or testing mediums like soil and ensuring that whatever is lacking is added. This will go a long way in preventing deficiencies.

Monitor pH Levels – This is especially important in hydro grows through applies to all mediums. Having the wrong PH prevents the uptake of nutrients, even if they are available in the medium. Constantly measure the PH in your water and flush it out with water that has the right PH and the correctly balanced nutrients. 

Monitor the Phosphorus – Though phosphorus is one of the essential nutrients needed by your cannabis plants having it in excess will cause deficiencies of other nutrients like iron. This means that you should keep away from products like PK 14/15 whose higher ratio of phosphorus in relation to potassium could lead to a phosphorus build-up which could have very adverse effects on your plants.  

Use Humates – Humates like Humic and Fulvic acid are a great way to ensure nutrient uptake. These are materials which are naturally found in fertile soil that when added to a nutrient solution, chelate into something which can provide real bioavailability to your plants.

How to Deal with Nutrient Excess Outdoors

When growing cannabis outdoors, incidences of excessive application may occur which negatively impact the plants.  When phosphorus is applied in excess, it might cause iron and potassium deficiencies while an excess of magnesium may cause a calcium deficiency.

Before adding any nutrients to your medium, test the soil by sending a sample to your nearest testing facility. 


What nutrients do outdoor cannabis plants need?

Cannabis plants mainly require three nutrients in larger quantities to stay healthy. These macronutrients are:

  • nitrogen (N)
  • phosphorus (P)
  • potassium (K)

These three nutrients are what feature in most fertilizers as an NPK ratio indicating the quantities of these nutrients present in that mix.  

In addition to these macronutrients, cannabis plants need more than just three macronutrients to thrive. The following micronutrients play vitally important roles in their growth:  

  • Calcium: This micronutrient is important for wall and cell development. It also helps in the reduction of soil salinity as well as improving water penetration in soil.
  • Magnesium: This plays a major role in photosynthesis, carbohydrate metabolism, and the stabilisation of cell walls of the cannabis plant.
  • Sulfur is vital for chlorophyll formation as well as the production of amino acids, proteins, vitamins, and enzymes which protect plants from disease.

Other necessary micronutrients are chlorine, boron, iron, copper, manganese, zinc and molybdenum. 

What are the best nutrients for growing outdoors?

Organic composts are the best method of introducing nutrients to outdoor grows as they work together with nature for the best results.

Compost serves as the best outdoor marijuana fertilizer. This is because it is a natural slow-release fertilizer that is not at risk of burning plants the same way chemical fertilizers do. Compost also improves texture and boosts air circulation. 


Sebastian is a passionate advocate of CBD's therapeutic potential, dedicating himself to exploring its diverse benefits. As a seasoned writer, he eloquently shares his insights and personal experiences with CBD, aiming to educate readers about its transformative power. His life's mission is promoting holistic wellness, with CBD at the heart of his advocacy.

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