Professional Marijuana Grower


Cannabis Watering & Fertilizer Regiments

Posted February 9th, 2018 by Dustin Fraser in ,

Plants rely on water and elemental nutrients to progress through their different developmental stages. From seed to harvest, adequate amounts of both will be required for maximum growth. Cannabis plants grown outdoors utilizing the high performance method are no exception to this rule. They require frequent applications of both water and fertilizer throughout the season.

Water resides within every individual cell of a plant and is a critical ingredient of photosynthesis. During photosynthesis water combines with carbon dioxide and, with a little help from the energy of light, is converted into carbohydrates and oxygen. Carbohydrates serve as the food energy source for a plant’s life sustaining metabolic processes. The oxygen is released into the atmosphere through transpiration causing upward pressure within the plant’s vascular system allowing for more water to enter the roots. Water also serves as a carrier for elemental nutrients in the soil. The nutrients dissolve in the water, come into contact with the roots, and enter into the plant’s vascular system.

Plant Nutrition Breakdown

There are 16 essential elemental nutrients required to grow a crop. Three of which — carbon (C), hydrogen (H), oxygen (O) — come from the air and water, and another 13 that are commonly taken up from the soil. These elements are usually grouped as primary nutrients, secondary nutrients, or micronutrients.

Primary Nutrients

The primary nutrients — nitrogen (N), phosphorus (P), potassium (K) — are needed by the plant in larger quantities relative to the other nutrient groupings.

Secondary Nutrients

The secondary nutrients are calcium (Ca), magnesium (Mg), and sulfur (S).


Micronutrients make up the largest grouping of plant nutrients but are needed in the smallest amounts. This group is comprised of boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), and zinc (Zn).

A proper fertilizer regiment or program will contain a blend of all these elements at appropriate levels for the plant’s stage of development. Fertilizer companies offer products that are specially formulated for specific points of growth. For instance, fertilizers that are designed for rigorous stem and leaf growth during the vegetative stage of development will be higher in nitrogen (N) and are often given the moniker “grow” or “veg”. Products designed to enhance or increase flower production during the reproductive stage of growth are often named “bloom” or “flower”. Fertilizer sources range from completely organic to completely synthetic (inorganic) and there are several brands from which to choose. Before making a fertilizer choice it is important to do research, ask fellow growers, or to consult your local hydroponic store on which fertilizer option would best suit your operation and goals. Providing a balanced fertilizer program throughout the season is an essential component to a successful high-performance outdoor cannabis garden.


To achieve maximum growth and yield potential, cannabis plants will need frequent and adequate watering. It is important that the plants don’t go without water for extended periods of time. Doing so can cause the plants to go into water conservation mode where they close their stomata, stopping respiration/transpiration, and halt the intake of water. This, in turn, reduces the amount of nutrients entering the plant causing an interruption in growth. It is equally important to not allow the soil to stay saturated and overly moist for extended periods of time. This will result in a root zone (rhizosphere) that has compromised levels of dissolved oxygen due to the water becoming stagnant. This can lead to the potential death of roots and beneficial microorganisms alike. The key is to find that happy medium. Provide enough water each time to ensure the entire container is moist. Then let the top part of the soil dry out enough to encourage the roots to grow in search of the moisture below. As the area where the majority of root growth is found dries out the roots will venture into the areas that still contain moisture. If all of the moisture is allowed to dissipate from the soil the roots will stop growing and possibly die back.

As the plants grow and develop throughout the season, the frequency of watering will accelerate. The amount of time between watering will be longest early in the season. During the first month or two outdoors, a plant’s root system and canopy growth will be smaller compared to later in the season. In these early vegetative stages the plants will consume less water and watering can usually take place once every five days. As the plants grow larger more frequent watering will be required. Later in the season this may entail watering every other day.

There are a few ways to assess whether or not the plants are in need of water. The first is by just looking carefully at the plants. If the leaves and branches begin to droop then the odds are the plants have gone into water conservation mode and it is definitely time to water. Check the soil first because plants that are constantly overwatered will also look droopy even though the soil will still be wet. In this case many of the roots have rotted away and the plant cannot take up water. If this happens, the container needs to be allowed to thoroughly dry out in hopes of saving the plant. With that said, waiting for the plant to become droopy because it desperately needs water is in no way the preferred method of judging how often to water. Allowing the soil to get that dry limits the amount of water and nutrients entering the plant and has a negative effect on growth rates. This should only occur if water is being rationed due to availability or cost.

Another way to determine when to water is by gently sticking a finger into the top of the soil mix. Carefully, so not to disturb any roots, stick your longest finger into the soil as far down as the second knuckle. If the area is completely dried out then the plant may be ready for a watering. Some fabric containers can also help you determine if the plants need water simply by touching them. If the sidewalls of the containers feel wet midway down from the top, the plants likely don’t need water. This is one of the beneficial features that only fabric aeration containers can provide.

There are several aspects to take into account when estimating the frequency of watering. Of course the amount of rainfall will have a direct correlation to how often the plants will need water, but there are other components as well. The composition of the soil mix should be taken into consideration. Mediums that have been amended with materials like compost, earthworm castings (vermicompost), or coco coir will have better water retention characteristics and will have lower water requirements. On the other hand, mediums containing plentiful amounts of inert materials like expanded clay pebbles, perlite, rice hulls, or river rock will be quicker to drain and dry out. The faster the moisture can escape the container the more often it will need to be watered. When watering, whether through drip-line irrigation or by hand via a hose, saturate the soil slowly to allow for even distribution. Allow about 10- to 20-percent of the amount of water applied to flush through and drain out of the bottom of the container. Doing so will ensure that the entire container is properly moistened. It will also help flush out any unwanted excess fertilizer that may be unavailable to the plant at the moment, reducing the possibility of “nutrient lock-out”.

Fertilizer Regiments

Organic Fertilizers

Organic fertilizers are usually derived from living plant or animal material and are frequently the by-product of other agricultural industries. For instance, bone and blood meal of porcine (pork) origin are obtained from the slaughtering and processing of pigs intended for the food market. Similarly poultry manure is often collected from egg laying chickens and those that are destined to end up on someone’s dinner plate. In both of these cases, as well as others alike, the obtained by-product materials are further processed, usually with high heat and steam to eliminate any possible pathogens. By the time the products are packaged they are considered safe for plants, pets, and humans alike. Organic fertilizers that are of plant origin like alfalfa meal and kelp meal (though technically not a plant but algae) are more often than not harvested in a sustainable way with minimal impact on the environment. For products like alfalfa meal, the alfalfa needed for human or animal use is removed and then the rest of the plant is processed into an organic fertilizer product. The key idea behind organic fertilization is an emphasis on sustainability and limiting waste by using as many parts of the animal or plant as possible.

True organic fertilizer products must receive certification from one of a number of organizations dedicated to upholding the integrity of the market. The most popular organic certification at the moment is the listing of a product on the OMRI (Organic Materials Review Institute) database. If a material is listed as OMRI certified then the grower can have some piece of mind knowing that the product is produced in accordance to approved methods. There are also state and federal agencies that certify products as organic. On a federal level products can obtain the NOP (National Organics Program) certification which is overseen by the USDA. Currently, the most popular state certifications come from the CDFA (California Dept. of Food & Agriculture) and the WSDA (Washington State Dept. of Agriculture) organic material input programs. Products that are labeled with one or all of these certifications have been thoroughly vetted and are found to be in compliance with national organic standards.

There is a wide variety of organic material that can be used for plant fertilization. Some popular ingredients include bone meal, blood meal, seabird/bat guano, ground oyster shells, composted poultry manure, feather meal, alfalfa meal, kelp meal, and earthworm castings. A grower can purchase separate ingredients and blend them together to create mixes for each specific growth stage. This is the more difficult way of approaching organic fertilization and will require a decent understanding of the materials and the plant’s nutritional needs. If you wish to blend your own mixes it is advised to use a light respirator or dust mask when doing so. Or you can go the easier route and trust the professionals with your organic nutrient needs. There are several companies that offer pre-mixed granular organic fertilizers utilizing many of the same ingredients listed above. Purchasing pre-mixed blends will be more cost intensive but it will also take the guesswork out of the equation. Pre-mixed products will be specifically formulated or blended to meet the plant’s nutrient needs for each of the developmental stages. Most companies offer separate pre-mixed blends designed for vegetative growth and enhanced flower development. There are even high potassium (K) blends to be used as a finishing product that adds bulk to the flowers before harvest. Using pre-mixed blends will cut down on the amounts of individual bags needed and provide the plants with a balanced nutrient regiment.

The mix to be used for the vegetative growth stage can be blended into the soil mix before the plants are transplanted in the spring. Follow the suggested application rates provided by the manufacturer. They should include simple application rates like, “use such and such amount per gallon of container size”. This will provide a baseline nutrient level that will feed the plant for a good three to four weeks. Blend the fertilizer into the medium in early April when the temperatures are still relatively low. As the weather warms the soil, microbial life will become active and start the process of breaking down the organic matter. Giving the microorganisms a head start will help ensure that the fertilizer will be readily available when it comes time to transplant. After transplanting, the fertilizer should be applied every three to four weeks throughout the season. Applications can be made using the “top dress” method. When top dressing with granular organic fertilizer, spread it evenly over the soil medium’s surface and gently blend into the top inch or so. Be careful not to damage the plant’s roots. Most dry organic fertilizers will include application directions for top dressing. After the fertilizer is applied simply water it in lightly and let the beneficial microbes do their work.

The mix designated for the vegetative growth stages will be used until mid-August, when the plants will begin to flower. At this point, you will want to switch to the mix that is formulated for flower development. If you are going to use a finishing mix do so during the last three to four weeks before harvest. Liquid organic fertilizers such as kelp, humic/fulvic acid, molasses, and fish protein hydrolysate can be used supplementary during the entire season. These can be applied directly to the soil or sprayed on the plant’s foliage and will provide extra food for beneficial microbes as well as readily available nutrients for the plants. However, depending on the location, liquid organic fertilizers may not be the best option for your garden unless there is a cool place to store them. When left outside or in a shed under the hot summer sun these types of products will become biologically active and the microorganisms found within them will begin decomposing the product. This can result in the containers becoming bloated and possibly exploding from the pressure of the gasses being created inside; the smell of which will certainly be horrendous. Believe me, almost nothing smells worse than liquid fish protein baking in the hot summer sun.

The fact that more often than not organic fertilizer materials come from plant or animal origin means they behave in different ways compared to synthetic (inorganic) fertilizers. By definition, organic matter contains plant nutrients that are held together with a carbon (C) bond, commonly referred to as an organic matrix. This means the nutrients will not be completely available to a plant’s roots until the carbon (C) bond is broken. Breaking this bond takes the help of specialized bacteria and fungi whose jobs in nature are to aid in the decomposition of organic matter, releasing the constituent elements held within in an ionic form. This is the form that plant roots are able to absorb. If a high performance garden is to be successfully grown utilizing organic fertilization methods then the grower will need to ensure that there are plentiful amounts of microbial life in the rhizosphere.

There will naturally be a base line population of microbial life already present in the soil if conditions are favorable. But there are steps that can be taken to increase the levels of these beneficial microorganisms. Inoculating the roots and soil medium with supplemental microbial life at transplant time as well as throughout the season can raise their overall levels. Perhaps the best way to encourage robust microbial life throughout the season is by weekly applications of a compost tea. Compost teas can be made from numerous organic materials, the most popular being earthworm castings. The materials are steeped in filtration bags, like big tea bags, and “brewed” in highly oxygenated water for 24-48 hours with the help of an external air pump. The high levels of dissolved oxygen encourage rapid microbial growth which will add to the populations in the medium when it is applied. Having high levels of active beneficial microorganisms will result in an accelerated breakdown of organic material into plant available nutrients. It will also make the plants and their roots more resistant to soil-borne pathogens and disease.

Synthetic (Inorganic) Fertilizers

The main benefit of using synthetic fertilizers is the nutrients are already in their ionic form and are immediately available for uptake by the roots. Unlike organic fertilizers, synthetic nutrients do not require decomposition and conversion by soil microorganisms. Synthetic fertilizers are most often manufactured from mineral salts that are mined from the earth and processed into water soluble forms. This makes them a less sustainable choice when compared to organics. However, their ease of use and quick acting reliability makes them a popular fertilizer choice for cannabis gardens indoors and out. There are countless numbers of synthetic nutrient providers to choose from and most offer the same types of products. Synthetic nutrient lines will usually consist of two separate base nutrient products that contain the majority of the nutrients. These products will be split up into one formulated for vegetative growth and one for flower development. Along with the base nutrients most companies will offer a calcium (Ca) and magnesium (Mg) additive referred to as CalMag that is an important part of the nutrient line.  The majority of synthetic base fertilizers do not contain calcium (C) and magnesium (Mg). This is because these two elements do not mix well together with the other nutrients in a concentrated solution. Instead they will need to be added, with the base, to an adequate amount of water so that they can stay in solution. Most synthetic fertilizer lines will have multiple supplement products but all are not essential when growing an outdoor cannabis crop. There are also emerging nutrient companies that are creating all-in-one base nutrients, eliminating the need for numerous inputs. You should do extensive research before purchasing to decide which supplement will most benefit the operation.

When deciding which brand of synthetic fertilizer to use keep in mind that companies with inferior nutrient lines typically do not last long. If a product or line of products does not perform well growers will stop using it and word will spread. Companies and products that have passed the test of time can be trusted to provide consistent, positive results. Consulting with respected growers, combing through the many Internet forums, and chatting with employees or owners of hydroponic shops are all excellent ways to get a finger on the pulse of what is working for others. If a line of products is being touted by numerous groups of growers then the odds are it will work for you. This may require going “top shelf” with regard to price but one must remember that in order to have a successful high performance outdoor cannabis garden no meaningful expense should be spared. Fertilizer is an important part of a productive garden and the best possible products should be used. Since there are so many different products in any given line it makes sense, and is easiest to stick with, using products from a single company’s line. Try to avoid using separate individual products from several different companies.  This is not so much about the quality of different brands, but more an issue of compatibility. Products formulated for a single fertilizer line will be designed to mix and interact favorably with other products in the line. Also, if there is an issue with compatibility the company will provide in the directions special mixing instructions to avoid complications. Bringing in a product from another company’s line may cause unwanted interactions between the elements or drastic pH fluctuations that can cause certain nutrients to fall out of solution.

Using synthetic fertilizers does come with inherent complications. Synthetic fertilizers will need to be mixed with water before they can be applied. This means some sort of tank or container will be required for mixing up a batch. The size of the mixing apparatus should somewhat reflect the number of plants in the garden and the size of the containers but, generally speaking, the bigger the tank the better. Bigger tanks mean fewer fertilizer batches are needed to be mixed for each feeding. A 250-gallon plastic IBC tote is a great choice for mixing larger amounts of fertilizer. They have a large hole in the top where the water and fertilizer can be added and an electric mixing blade can be easily mounted. IBC totes also have a handy discharge valve at the bottom and attachments can be purchased for the addition of a pump to pull the fertilizer solution from the tote to be delivered to the plants. There are even attachments that will circulate the water from the bottom discharge back up to the hole on the top. This is a great way to mix a large batch of fertilizer without a mixing blade and motor.

Some fertilizer companies offer feeding schedules that make the fertilization process less daunting. The schedules are complete fertilization programs broken down into weekly application regiments. These are an excellent reference tool and help take the guesswork out of fertilizing the garden. Lower rates of the concentrated fertilizer can be used for growing outdoors when compared to indoors, so start at half the rate suggested unless the company has a specific feeding schedule designed for outdoors. An EC/ppm meter is helpful when using synthetics. These meters measure the amount of dissolved mineral salts in the solution by determining its electric conductivity (EC) — how well it conducts electricity. A solution with more dissolved mineral salts will have a higher EC. With this number a simple equation will help you determine the amount of fertilizer in the solution in parts per million (ppm), EC x 500 = ppm. A safe ppm to start off with early in the season would be around 300-500 total or 0.6-1.0 EC. Try to avoid a ppm of over 1,000 (EC 2.0) at any time in the season. Adjust the pH of the solution to around 6.0 before applying.

A high performance outdoor cannabis garden will need to be fertilized one or two times a week when using synthetics, with regular watering between feedings. Using lower feeding rates will help ensure that you don’t over fertilize. If you have the ability, the fertilizer can be distributed through the dripline irrigation system. Just make sure to run some water through the lines after each feeding to avoid any fertilizer salt build-up in the emitters. Feeding can also be done with a hose and a sprayer or watering wand. This will require an electric (or gas) water pump that is strong enough to move the solution to the containers. Regardless of the method used the solution should be applied to the soil until it begins to flow out the bottom of the container. Only foliar feed as needed to fix minor nutrient deficiencies or to apply some type of specialty product. When watering between feedings allow 10 to 20 percent of the water to exit the bottom of the container. This will reduce the amount of residual fertilizer salts that can build up in the soil by flushing them out. Without regular flushing these mineral salts can accumulate and cause fertilizer imbalances in the medium resulting in unwanted but avoidable consequences.

Collecting some of the water runoff and testing the EC/ppm levels is an excellent way of determining if the plant is being fed too often or at too high a rate. If the EC/ppm is higher than what the previous feedings was then you may need to cut back on feeding strength or frequencies and flush with normal watering until the number is lower. As is the case with organic fertilizers: feed with the vegetative cycle products until August and then switch to the flowering cycle products. If you wish to use a finishing product do so a few weeks before harvest and allow time for a good week of straight water flushing.

Hybrid Method

The hybrid method of plant nutrition is a tried and true approach utilized by growers in nearly all sectors of horticulture. This method is an excellent fertilization program when it comes to growing cannabis. This approach utilizes both the organic and synthetic forms of plant nutrition giving the grower, and the plant, the best of both worlds. The reason the hybrid method is so effective is the organic components being added to the soil medium help to build and sustain populations of beneficial microorganisms. The beneficial microorganisms in turn help break down the organic matter, releasing the nutrients held within for consumption by the plant. They also help create a healthy root zone that is less capable of supporting

harmful soil pathogens. As the organic fertilizer works below the surface creating a healthy root environment, the applications of synthetic fertilizer provides fast acting, reliable plant nutrition, making the hybrid method so effective. The grower is developing a sustainable microbial population that increases the health and potential of the soil while at the same time supplying adequate plant nutrients that go to work immediately, resulting in a healthier plant that is more productive. Feed the soil and the plant.

When utilizing the hybrid fertility method apply both organic and synthetic fertilizers at half the suggested rate. Top dress with the organic nutrients once a month and apply a compost tea on a weekly basis. Apply the liquid synthetic fertilizer solution weekly at half, or even a third, of the suggested label rates. Foliar applications should be made only as needed or if desired for a certain product. Similar to the other fertilization methods, switch from vegetative to flowering products in August as the plant begins to flower. When done appropriately, the hybrid method will result in an extremely healthy plant that delivers a high quality, exceptional yield.

Supplies Needed For Watering & Fertilization

Watering Supplies

  • Reliable Water Source
  • Irrigation Lines
  • Water Hose & Sprayer or Wand

Organic Fertilizing Supplies

  • Container for Mixing Ingredients (if you create your own blends)
  • Dust Mask
  • Measuring Scoops

Compost Tea Supplies

  • Large Bucket or Small Tank for Mixing
  • Aeration Pump and Air Stone
  • Compost Tea Ingredients
  • Large “Tea Bags” or Nylon Stockings

Synthetic Fertilizer Supplies

  • IBC Tote or Tank for Mixing Solution
  • Mixing Blade & Motor or Pump for Recalculating Mix in IBC Tote
  • High Powered Pump for Delivering Solution
  • Irrigation Supplies (ie) Hoses, Watering Sprayer or Wand
  • EC/ppm Meter
  • pH Meter
  • Measuring Cups or Container

This article is an excerpt from Outdoor Performance Cannabis written by Dustin Fraser and published by High County Publishing. For more information visit

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