The best fertilizers for cannabis




With increased popularity and legalization of growing cannabis, the entire industry followed so you can find hundreds, if not thousands of fertilizer or nutrient companies and products specializing in cannabis.


In this article, we’ll try to cover the importance and need of using nutrients, we’ll go through all types of nutrients and try to help you choose the best nutrients for your next grow.


What is the importance of fertilizers?


All fertilizers contain food or nutrients in forms of various minerals, sugars, amino acids and other micro or macro elements. With proper use and dosage of your fertilizers, you can enhance and regulate the growth and increase the yield, potency, aroma and flavour of your cannabis plants.


As cannabis plants go through different grow phases they require slightly different feeding schedules. Plants in vegetation don’t need the same nutrients as they need in the flowering stage so using proper nutrients at the right stage is very important.


Cannabis plants need certain micro and macro elements in order to achieve optimal growth and health. Micro and macro are used to describe the quantities of elements that plants need. There are three major macronutrients present in all fertilizers: Nitrogen (“N”), Phosphorus (“P”), and Potassium (“K”). Nutrients for different stages of growth have different ratios of these elements in order to best suit the plant needs for that stage.


Micro elements or trace elements include: Calcium (“Ca”), Magnesium (“Mg”), Sulfur (“S”), Manganese (“Mn”), Boron (“B”), Zinc (“Zn”), and Copper (“Cu”). Micro elements are present in most fertilizers too but in much lower concentrations than macro elements.


Is it necessary to use fertilizers?


Although it is possible not to use any additional fertilizers and still end up with a good and quality harvest, adding nutrients will surely increase the yield, the quality and overall health of your plants in all stages.


Having good and rich soil, or making “super soil” or “live soil” will drastically decrease or entirely eliminate the need for using any additional fertilizers as all the needed nutrients will already be present in the soil.


Homemade or professional


As long as you have all the micro and macro nutrients and their ratios are adjusted to the current stage of your plants development it doesn’t matter if your fertilizers will be homemade or store bought.


Although, especially for inexperienced growers, mixing your own nutrients and getting all the ratios and mixes right can prove to be a challenging task so it might be much easier and better for them to use professional fertilizers.


Professional fertilizers have correct nutrients for every single stage of your plants development – rooting, vegetation and flowering and even the transitional stages between those, so it’s easier to adjust your feeding schedule.


Liquid fertilizer vs dry


Liquid fertilizers are easier to use and can be used both mixed with water when watering or as a foliar solution for fast acting effects. Dry fertilizers release slowly and can be mixed with the soil or added to water during watering. Because of their slow release, the effects they provide will be visible later than when using liquid ones. Dry fertilizers also have a longer shelf life so, for growers that have smaller grows, they might be a better choice.


Hydroponics fertilizers vs soil fertilizers


Usually, fertilizers that are used in hydroponic grows can also be used in soil grows because they are already soluble and readily available and many fertilizers can be used in both soil based mediums and soilless mediums. Using any soil based medium fertilizers in hydroponic grows isn’t recommended because of the salt build up that can happen and potentially cause a lot of problems so we advise you to check your nutrients before buying and using them. It is important to mention that organic soil fertilizers won’t work well in your hydroponics grow because they take time to active and decompose in order to make the nutrients available.


Which fertilizers work well for cannabis?


As long as you’re giving your plants all the needed micro and macro nutrients, and they are in correct ratios, any fertilizer will work. Growers often use other fertilizers, commonly used when growing flowers or vegetables but they often have incorrect ratios or lack some of the micronutrients that cannabis plants can use. Adjusting the dosages and ratios, you can end up with a decent enough fertilizers but it’s advisable to use nutrients and fertilizers that are made especially for growing cannabis as they will give your plants optimal nutrition and health.


Depending on your grow style philosophy and methods, you may want to use different fertilizers and different methods of application. You may mix your nutrients with the soil, you may use them in a hydroponic setting, you may add them to water during watering or you may use them as foliar sprays. Whatever your prefered method may be, keep in mind that not all strains and plants need and use the same amounts of nutrients in every possible setup. Start below the recommended dosage and build up with keeping an eye on your plants and how they react to the feeding. If you notice any irregularities or issues like deficiencies or nutrient burns, adjust your feeding schedule accordingly.


Why use TDS meters?


To measure the concentration of nutrients in your watering solution we use TDS meters. TDS stands for Total Dissolved Solids and it measures the combined content of all inorganic and organic substances contained in a liquid. To be considered dissolved, the solids must be small enough to fit through a 2-micrometer filter. Concentration of those solids in the water is expressed by PPM – parts per million.


By measuring the TDS going in and TDS of so called “runoff” water, we can calculate just how much nutrients are our plants using and can adjust our feeding schedule accordingly.


Difference between growth and bloom fertilizers


As our plants go through different stages of development, they will concentrate most of their energy into growing different things – growing leaves, branches and vegetative growth during vegetation and flowers or buds during flowering.


To adjust your nutrients to your plants needs, you need to use fertilizers that have more Nitrogen (“N”) and Potassium (“K”) and less Phosphorus (“P”) during vegetation, and ones that have more Phosphorus and Potassium and less Nitrogen during flowering.


How often to give fertilizer?


How often are you going to add fertilizers in your feeding schedule always depends on your plant needs and your growing and fertilizing methods. If you’ve mixed right your nutrients in the soil mix, you may need to give additional nutrients only once or twice during the grow, at the beginning or the end of a certain stage.


If you’re using hydroponics, nutrients are always mixed in the water solution your plants are in. Be sure to empty and replace the solution every 2 weeks and adjust it accordingly to your plants needs and their stage of development.


If you’re growing in soil based mediums, most growers tend to fertilize their plants every second or every third watering. But always, keep an eye on your plants, as they may need more or less fertilizers and adjust your feeding accordingly. Soil mixes used for cannabis growing often have enough food to last your plants for at least a few weeks, so keep that in mind when you’re feeding your clones or seedlings.


How much fertilizer to give?


If you’re growing in soil, there’s no need to add any extra fertilizers for the first few weeks as the soil contains all the necessary nutrients needed but many growers like to add additional rooting fertilizers to achieve better root mass development and growth.


Dosages on the professional fertilizers are often too high and not all strains and plants react the same to them or need the same amounts so it’s important to start from ⅓ or ½ of the dose and build up to full dose (or more).


To find the “sweet spot” for your plants you need to keep an eye on them and watch how they react to the feeding. Most times the recommended dose would either be too much or too little so when you notice signs of deficiency – increase the dosage and when you notice signs of nutrient burn – decrease the dosage.


As your plants go through different stages of growth, generally the optimal PPMs are:


  • 100-250 PPM for the seedling or a clone stage
  • 300-400 PPM at first and around 700 PPM at the end of vegetation
  • 1000-1500 PPM slowly increasing during flowering
  • 0 PPM for the last two weeks of the grow


When to stop using fertilizers?


Generally, for the last 2 weeks of your grow you want to give your plants just plain water in order to wash away any leftover nutrients. But, if you notice any signs of nutrient burns on your plants, you may want to stop with the nutrients and give them just plain water for the next few waterings. If your nutrients have built up in the soil and caused a root lock or if you experience severe nutrient burns you may want to flush your plant.


Flushing isn’t just watering your plants with regular amounts of water. The idea behind the flush is to wash away any leftover nutrients from the soil and to do that you’ll need a lot of water. To flush the plant that’s in a 10L container, you should use 3 to 5 times more water – 30 – 50 L. After you’ve flushed your plants, let them dry out for a few days and adjust your feeding schedule.


Which water to use?


Water is just as important as the nutrients you give to your plants. Having good water means having nice and healthy plants. Generally, people use tap water indoors and if the quality of your tap water is good enough so you can drink it, so can your plants.


If your tap water is polluted or heavily treated with chemicals you may want to treat it or use a different water source all together. If your water is treated with Fluorine or Chlorine you can just leave it for a couple of hours, or a day, for it to evaporate or you can filter the water by using a charcoal filter.


If your water is even more polluted you can use reverse osmosis which will remove 95 – 99% of all dissolved salts. With balanced PH it’s a popular choice for many growers because of the simplicity of use and no need to adjust your water every time you use it.


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