Growing cannabis outdoors is an exciting and fulfilling experience - every cultivator wants to look out and see a vibrant, healthy garden of cannabis plants in full bloom. To ensure maximum vigour, growth and yields, it’s essential to understand the nutrients your plants need. Cannabis plants require a balanced diet of macronutrients, micronutrients, and other important elements to thrive. Understanding how to deliver these nutrients is critical for a successful harvest.
For first-time growers, there’s a caveat regarding cannabis nutrients: different strains will have different needs. Sure, the primary nutrients each strain or type of cannabis needs remain the same, but quantities may differ depending on the genetics. Photoperiod strains will have different needs than autoflowering varieties. You’ll use the same nutrients for outdoor growing as indoor growing, but delivery routes will vary depending on where you situate your grow.
We’ll break down the different nutrients, including macronutrients (the main ones) and micronutrients (secondary, but still important) outdoor-growing cannabis plants need, and look at the options for the best nutrient delivery.
Why Cannabis Plants Need Nutrients
Popeye was famous for eating spinach to get an all-important surge of strength. Aside from being a clever trick to get kids to eat their veggies, this was scientifically correct (even though the effects were exaggerated). Spinach contains nitrate, and muscles benefit from nitrate. Like Popeye or any athlete who supplements for performance, cannabis plants perform better when given the nutrients essential to their growth.
Grow two cannabis plants side by side, providing one with all the nutes it needs while withholding nutes from the other. The supplemented plant will flourish, while the nutrient-starved plant will likely die.
NPK: The Vital Macronutrients Your Cannabis Plants Need
Macronutrients are the primary nutrients that plants require in large quantities, and they are essential for the growth and development of cannabis plants. Without the three main macronutrients listed below, you have a slim chance of producing any decent yield. The three primary macronutrients required by cannabis plants are nitrogen, phosphorus, and potassium, often referred to as NPK. The concentrations (amount of nutrients) in which you feed these to your plants are known as the NPK ratio. It’s important to note that your plants’ nutrient needs will change at every growth stage - the same nutrients in different concentrations will assist in different ways.
Nitrogen (N) is essential for vegetative growth and is responsible for developing leaves, stems, and branches. Nitrogen is needed to produce chlorophyll, which is necessary for photosynthesis. Cannabis plants need nitrogen at every stage, but especially during the vegetative stage. This is when the nutrient ratio is tipped in favour of nitrogen. Nitrogen can increase plant resistance to diseases and pests and even assist in resisting frost. A nitrogen deficiency can lead to stunted growth, yellowing of leaves, and reduced yields. That’s bad enough, but a lack of nitrogen can lead to plant death.
Phosphorus (P) is another essential macronutrient for your cannabis plants. Like nitrogen, it’s vital for photosynthesis and new growth. Also, it aids plant root development, flower production, and overall plant health and yield. A lack of phosphorus can cause slow growth, weak stems, and poor bud development.
You’ll give your plants phosphorous during the vegetative phase, but when the flowering stage kicks in, you should increase the amount of phosphorous.
Potassium (K) is vital for the plant’s stress tolerance and helps regulate water uptake, ensuring proper plant hydration. During flowering, your plants need higher amounts of potassium to increase bud size and density. Too little or too much potassium will cause your plants to suffer; potassium deficiency can lead to yellow leaves and decreased yields. You’ll increase your potassium while increasing phosphorous and decreasing nitrogen at the end of pre-flowering to boost bud production and quality.
Micronutrients Are Important, Too
While macronutrients are required in large quantities, micronutrients are only needed in trace amounts. However, they are still critical for plant growth and development. Micronutrients include boron, copper, iron, manganese, molybdenum, and zinc.
- Boron (B) is required for cell wall formation and calcium uptake
- Copper (Cu) is essential for photosynthesis and overall plant health.
- Iron (Fe) is required to produce chlorophyll, responsible for the plant’s green colour and photosynthesis.
- Manganese (Mn) is essential for enzyme activation and nitrogen metabolism
- Molybdenum (Mo) is required for nitrogen fixation
- Zinc (Zn) is essential for root development, hormone synthesis, and enzyme activation.
This is not an exhaustive list; experienced growers use these micronutrients and more. While micronutrients are required in small quantities, they are arguably just as important as macronutrients for healthy cannabis cultivation. A deficiency in any of these micronutrients can lead to numerous issues, including stunted growth, yellowing of leaves, and poor flower development, to name just a few. Some beginners overlook micronutrients, focusing almost entirely on ‘the big three’ (NPK). However, adequate supplementation with the above micronutrients will benefit your plants more, so don’t skip these!
Dosing And Scheduling Nutrients
Pre-made plant nutrients come with instructions on dosages and recommended feeding schedules. These will tell you what nutrients to give, in what concentrations, and in what ratio for each life cycle stage. These are general guidelines, as nutrient requirements may vary slightly depending on genetics, conditions, etc. Overfeeding nutrients can cause many issues, so start with a low dose and increase as/if necessary.
Nutrient Delivery Systems for Outdoor Cannabis
There are several different delivery systems for providing nutrients to outdoor cannabis plants, including soil, hydroponics, and foliar feeding.
Soil is the most common method of growing cannabis outdoors and arguably the most forgiving. Cannabis plants grown in soil can absorb nutrients over time as they break down, making it easy to release nutrients slowly. Soil amendments can also be used to adjust the nutrient content of the soil, ensuring that plants have access to the necessary macronutrients and micronutrients. It’s hard to overstate the importance of monitoring the pH levels of your soil regularly to ensure that the plants can absorb the nutrients effectively. Consider buying a pH meter to keep accurate tabs on your soil.
There are different types of potting soil you can use for cannabis, each with different qualities:
- Sandy soil: Good drainage and high oxygen levels, but poor water retention means nutrients can get washed away easily.
- Silty soil: Good water retention and adequate drainage, contains minerals and nutrients.
- Clay soil: rich in nutrients and minerals, retains water well but is heavy, difficult to work with and has poor drainage.
- Loamy soil: nutrient-rich with good water retention and drainage, but it can be expensive.
You can buy balanced soils suited to growing cannabis or make your own. When growing in soil, it’s recommended to have a soil tester and an NPK tester. These can be picked up fairly cheaply, allowing you to test your soil regularly. This means you can add amendments as necessary, taking some guesswork out of optimizing nutrient levels.
Hydroponics is a method of growing cannabis without soil, using a nutrient-rich solution instead. Hydroponic systems allow for precise control over nutrient delivery, ensuring that plants receive exactly what they need. However, hydroponic systems require more maintenance and monitoring than soil-based systems. They can be more challenging for novice growers.
Foliar feeding is a method of nutrient delivery that involves spraying a nutrient solution directly onto the leaves of the cannabis plant. This method is becoming increasingly popular among outdoor cannabis growers due to its ability to quickly boost nutrients to plants and address any nutrient deficiencies quickly.
Foliar feeding can be beneficial for outdoor cannabis plants that are growing in poor soil or facing adverse weather conditions. It can also be used to address specific nutrient deficiencies quickly, providing a targeted approach to nutrient delivery. The downside of foliar feeding is that overuse of this method can lead to nutrient burn and damage to the plant. It should therefore be used sparingly rather than as a go-to nutrient delivery method. With foliar feeding, it’s essential to monitor the pH levels of the nutrient solution carefully and ensure that the solution is well-balanced before applying it to the plant.
Compost Tea
Compost tea is a nutrient-rich solution made by steeping compost in water. It is a natural and sustainable nutrient delivery method that is becoming increasingly popular among outdoor cannabis growers. Compost tea is an excellent source of micronutrients, beneficial bacteria and fungi that can improve soil health and plant growth.
Most cannabis growers use aerated composted tea. Aerated compost tea uses oxygen to support the growth of beneficial bacteria, which help clean and nourish your plants' soil. Click here for a good compost tea recipe.
Compost tea is great because it’s natural and sustainable and can improve soil health and plant growth. It comes with the advantage of being easy to make and inexpensive, albeit somewhat time-consuming to brew.
The Importance Of Having An Ecosystem
Setting your garden up for more than just cannabis plants goes a long way to creating an ideal environment for your plants to succeed. A working ecosystem containing cover crops and more allows self-replenishing nutrients, and that’s good news for you as your garden will help keep everything topped up. Good soil and the right balance of additional plants will attract beneficial insects to help nourish the environment, meaning a healthier garden and healthier plants.
Don’t Forget To Flush!
Nutrients are crucial to healthy plant development and optimizing yield, but you don’t want a buildup in your buds come harvest time. Remember to flush your plants with pH-neutral water for one or two weeks before harvest. This will force your plants to consume excess nutrients, resulting in a smoother, better-tasting end product.
Nutrients For Outdoor Cannabis – Conclusion
Nutrients are essential for growing healthy cannabis plants. Whichever method you choose to deliver nutrients to your outdoor plants is up to you. While cannabis plants can be grown without nutrients, a solid nutrient regimen will almost certainly provide better results come harvest time.
