Successful cannabis growers know getting the soil right is half the battle. A good harvest is planned and prepared before the seeds have even touched the soil or grow medium, and if you lay your groundwork correctly (pun totally intended!) you may not even need to add cannabis soil amendments like liquid fertilizer later on.
A super soil such as Roots Organics Formula 707 is a great way to ensure happy, productive plants. You can also create your own super mix, adding plenty of organic compost, sea kelp, and other special ingredients such as vermicompost and bat guano.
A word about hydroponic growing
Hydroponic growing is a popular way to grow weed for those who do not have the space to grow the plants in pots or grow bags. The simplest explanation is that hydroponic systems keep the root system immersed in highly oxygenated water, which is saturated with hydroponic nutrients in the right proportions to promote growth and a generous harvest.
Hydroponic cannabis plants are kept in carefully controlled conditions of light, temperature, and cleanliness, and they tend to give very successful crops even in very small spaces.
This article will focus on traditional soil-based growing, so we will leave the general hydroponics discussion for another day.
Now let’s talk in great detail about what should go in your soil, pots or grow bags so your cannabis plants grow and produce beautifully.
Nutrients for optimum cannabis growth
Cannabis plants require a lot of nutrients, which they can get from enriched soil or from the hydroponic solution we mentioned earlier. Some are required in large amounts, and those are known as macroelements, while others are required in very small amounts to keep your plants healthy – these are called microelements.
The macroelements a cannabis plant requires for good growth are Calcium (Ca), Potassium (K), Magnesium (Mg), Nitrogen (N), Phosphorous (P) and Sulfur (S). You can use a test kit to make sure your soil has all of these, and add amendments as needed to ensure your plants are given the very best nutrition from the start.
Microelements are required in tiny amounts, but if they are not present your plants will not thrive as they should. Microelements include Boron (B), Chlorine (Cl), Copper (Cu), Iron (Fe), Manganese (Mn), Molybdenum (Mo) and Zinc (Zn). A good fertilizer should make sure you’re covered with all of these advanced nutrients – this is what makes the difference between an amateur grower and an award-winning pro.
Plants need protein to grow well, but they don’t synthesize them very well or easily, which is why you can give your plants a huge boost by providing them with amino acids. Plants absorb amino acids through the roots or leaves, and experts tend to prefer foliar sprays to give cannabis plants a healthy dose of protein in a way they can easily absorb.
Amino acids are super important to get good harvests, because they stimulate chlorophyll production, make plants more resistant to disease and pests, and generally make them stronger at a cellular level.
Stages of cannabis growth
Cannabis plants have different needs according to the stages of growth they go through. Let’s focus on the most important ones for you: vegetative stage and flowering stage.
A cannabis plant will need lots of air, lots of room and lots of light during the vegetative state – make sure it is getting 12-15 hours of sunlight or 18 hours of fluorescent light daily. During the vegetative stage, a small cannabis plant will engage in vigorous root growth, develop a thick stem, and grow many of the highly recognizable, beautiful, serrated green leaves. It should get taller, too, up to 3-4 feet. This stage takes 3 to 6 weeks, and during this time the plant will need more Nitrogen and Potassium, and regular amounts of Phosphorus.
Bat guano is an excellent natural source of Nitrogen for the soil, but it can be extremely strong and concentrated, so use it very sparingly or as part of a balanced mix of organic nutrients. If your plants are kept under 80 degrees you may need to up the Nitrogen a little more. In any case, a testing kit is your best friend when it comes to knowing what is in your soil so you can add the necessary cannabis soil amendments.
A quick warning for new growers and a reminder for more seasoned ones: gender is everything when it comes to cannabis plants. Once your plants are tall and lush, it’s time to check carefully for markers of their gender – remember only female cannabis plants produce the buds we all know and love, and that a male plant can destroy your entire crop.
Also, remember there are occasional hermaphrodite plants with both gender markings, and the pollen from those can ruin your crop. Seek and destroy all male plants (or at least put them far, far away from the plants you want to flower!)
At this stage, you have beautiful plants full of gorgeous leaves, and the time to flower and bud is approaching. Make sure your cannabis plants have everything they need to succeed in producing big buds full of THC and CBD!
During the flowering stage you want to go easy on the Nitrogen, and increase Potassium and Phosphorus for a higher yield. Too much Nitrogen during the flowering stage will slow down and reduce the development of buds, while giving the survivors a nasty taste. Cut back on the Nitrogen the moment you see buds start forming.
It’s generally understood that Phosphorus will make your plants grow more flowers (as in the number of flowers), while Potassium helps each of those flowers become bigger. Keep them balanced, and do not go overboard – too much of a good thing is dangerous, and overfeeding may result in damaged roots and even dead plants. Experienced growers recommend that you use HALF of the amount of fertilizer recommended by the company that made it – start slow and add a bit more if needed, it is definitely better than adding too much and killing your plants at the most crucial stage.
You might want to try Uprising Bloom or Terp Tea Bloom by Aurora Organics, 100% organic supplements designed especially for this growth stage, to give you maximum yield and fragrance.
Other aspects to consider besides nutrients
Besides giving your plants appropriate nutrition at every stage, keep in mind the other crucial factors that make a cannabis plant vibrant, happy and productive.
The soil in your pots or grow bags should be loose, fluffy and well aerated. It should hold enough water for the roots to absorb what they need, but not become waterlogged. If your soil is hard, compacted or drains poorly, your plants will suffer.
Keep the soil in optimal conditions by preparing it well from the start with a good amount of organic compost. Worm castings, also known as vermicompost (or “worm poo”) are an ideal additive to improve the soil texture and aeration, and they also provide many micronutrients that are slowly released into the soil during the entire lifespan of your cannabis plants.
A soil pH tester should be part of your grower’s toolkit – if you don’t have one yet, go get it now. Even if your soil has every nutrient your plant requires, in the optimal amounts and ideal proportions, the wrong pH levels may make it impossible for your poor cannabis plants to access the nutrient buffet you so lovingly set out for them.
For those who forgot their highschool chemistry lessons, pH levels measure the acidity of the soil – the scale goes from 0 to 14, where 7 is completely neutral, like water. The lower the value, the more acidic the soil is, and higher values indicate basic (alkaline) solutions.
Cannabis plants like a very slightly acidic soil – test and amend your soil pH regularly, using these guidelines for the optimal range:
If you’re growing in soil, be it direct, pots or grow bags, pH should be between 6.0 and 7.0
If you’re growing in coco coir, it can be a little lower, between 5.5 and 6.5.
The same pH levels work for hydroponic weed: between 5.5 and 6.5
Plants need water to be able to absorb nutrients, as well as needing it to hydrate. Let’s state this a different way: if your plants do not have enough water, they will not only dry out, they will also be malnourished. Have we impressed this on you enough? Water frequently and abundantly, and make sure the soil is draining appropriately so your plants don’t sit with “wet feet”.
Light and air
The light requirements of cannabis plants deserve a whole article, but let us at least remind you that during the vegetative phase plants will need 12-15 hours of sunlight (or 18 hours of fluorescent light if you are growing indoors). Shorter light hours will signal to the plant that it is time to start flowering, and no grower wants plants flowering if they’re just a foot tall – those mini harvests may look cute, but it is heartbreaking to spend all that time and effort to get such a tiny harvest. Mind your light hours, and supplement with artificial lights if needed.