Cannabis plants require different nutrient ratios for their various growth stages. If you want to make the most of your grow, it’s important to understand how cannabis plants use nutrients during different parts of their development.
Cannabis Nutrients: An Overview
All plants require nutrients to grow. If you’ve ever watched a plant perk up after fertilization, then you know how much of a difference it makes. It’s crucial to understand how to fertilize them effectively, with both micro and macronutrients.
Macronutrients are the building blocks of plant development. They form the majority of the plant’s matter. Macronutrients include carbon, hydrogen, nitrogen, phosphorous, and potassium. The first two are so common that it’s rare you would want to supplement them.
Nitrogen, phosphorous, and potassium, however, are so commonly supplemented that they have a shorthand: N-P-K. You’ll see this on many fertilizers, in a format like “N-P-K: 1-3-3.” This means that the fertilizer provides one part nitrogen per three parts phosphorous and three parts potassium. Feeding the right N-P-K ratio to your plants is an important part of maximizing your crop.
Micronutrients are things that a plant needs only in tiny amounts. Everything from iron to zinc to molybdenum are used by plants. Micronutrients are usually used for hidden but important processes like enzyme function and amino acid production. If you’re using a general fertilizer supplement, it’s unlikely that you run into a micronutrient deficiency. It’s not impossible, however. You can also run into micronutrient overloads, which cause a variety of problems with your grow.
Every stage of the growth cycle needs its own blend of macro and micronutrients. Keeping an eye on your plants will help you transition your fertilizer smoothly from phase to phase. This is key to harvesting good bud at the end of the process.
How to Fertilize Cannabis
There are two primary methods for growing cannabis – hydroponic techniques and soil-based techniques. These two styles require different fertilization methods.
Hydroponic growing involves an inert growth medium, so plants do not receive any nutrients from their roots unless placed there by the water. Every time water runs through the growth medium, it should contain fertilizer. Otherwise, your plants can suffer from nutrient deficiencies in as little as a few days. The fertilizer used in hydroponic systems is always going to be liquid fertilizer.
Liquid fertilizer is the most common type recommended today. It offers the most control over what your plants receive and when. Liquid fertilizer comes with instructions that explains how much of the fertilizer should be added to a gallon of water. You then use this fertilized water to water your plants. Hydroponic systems should always use fertilized water.
On the other hand, soil-based grows can use solid or liquid fertilizer. Solid fertilizer typically comes in little pellets that are designed to be spread across the top of the soil, mixed into soil, or dissolved in water – the type that stay on top of the soil leach nutrients into the water every time you water. Solid fertilizers that mix into soil should be included in the mix from the first transplant. Many growers agree that the heaviest concentration should be towards the bottom of the pot, so the plant grows to reach them. The type of solid fertilizer that dissolves into water works similarly to liquid fertilizer.
When using liquid fertilizer in soil systems, remember that the soil typically will already contain nutrients. Soil tends to hold onto nutrients very well. This can quickly cause problems for your plants. If there are too many nutrients in your soil, they can overwhelm your plants and prevent any nutrients from being taken up.
To avoid this, don’t use liquid fertilizer every time you water. Instead, you should fertilize at most every second watering. If you use highly-amended soil, then you can fertilize as little as once a week. If you’re fertilizing often and notice symptoms of nutrient depletion, you’re overfertilizing. You need to flush your soil for a few days to fix the nutrient lockout you’re experiencing. Keeping the balance takes some practice and an understanding of your own cannabis plants. It’s better to under-fertilize and have slightly smaller plants than over-fertilize and potentially poison them.
Finally, for the two weeks before harvest, don’t fertilize your soil-based plants at all. Water with pure H20 to flush out all the extra nutrients. This forces the plants to use the nutrients they have already taken up and depletes their resources. These resources are often concentrated near the cannabis buds, so clearing them out gives the bud a cleaner, tastier flavor.
Seedlings and Clones
Seeds come pre-packed with all the nutrients seedlings need to get started. Seeds contain some basic plant-starting nutrients in the same way that bird eggs have a yolk. It feeds the tiny organism until it’s able to feed itself.
This means that you should always use caution when you begin to supplement your plants. Starting too early can actually hurt your seedlings. Nutrient lockout happens when there are too many nutrients in the soil, and they more or less “plug up” the plant’s roots. Clones can face the same problem, with the added strain of developing roots from nothing.
Once you see your cuttings or seedlings developing multiple roots, add a half-dose of a 1-1-1 fertilizer to their water. A half dose references the recommended amount of fertilizer per gallon of water. Add only half the recommended amount to the same volume of water, then water as usual. Keep an eye on how your plants react. Ideally, you’ll see growth rates speed up.
Seedlings and clones get a 1-1-1 ratio of N-P-K because they need all-around-support. They’re focusing on developing roots, not foliage or flowers. They will be getting foliage support shortly, once they enter the vegetative stage.
During this phase, you’re prompting your plants to grow as strong and leafy as possible, to support flowers later. Vegetation requires large amounts of nitrogen to grow well. There are lots of fertilizers on the market that offer a high nitrogen level – a good ratio would be 3-1-1 or 9-4-5.
Start with a half dose when the plant shows its second or third pair of true leaves. Over the course of a week, increase until you’re using the full amount recommended by the fertilizer. This allows the plant to continue developing a strong root system without suffering from shock or nutrient lockout from the extra nitrogen now available.
Continue this for the duration of the vegetative phase. That can be anywhere from two weeks if you’re doing the Sea of Green method, to two months if you’re taking it slow. Keep an eye on your plants to make sure they aren’t showing any signs of nutrient deficiencies, and above all keep a regular routine.
Once it’s time to switch over to the flowering stage, you’ll need to transition your fertilizer. Flowers require much more phosphorous and potassium than does greenery. However, you’ll still need to supplement with nitrogen, as you must feed the plant mass you already have. A good ratio might be 1-3-3 or 3-8-8 N-P-K.
Once again, it’s important to taper your plant onto the new fertilizer. In this case, you can drop to a half dose of your old fertilizer and a half dose of your new fertilizer when you change the lights to flowering. This gives the plant time to switch its focus from vegetation to flowers. Taper onto the flowering mixture over the course of a week until you are using no vegetation fertilizer and a full dose of the flowering mix.
Troubleshooting Cannabis Nutrients
There are plenty of specific problems your cannabis plants might display regarding micro and macronutrients. Here are some of the most common nutrient problems and how to fix them:
- Stunted growth, yellowing leaves, potential leaf-burn: Nutrient lockout. Flush your soil and test the soil pH. If the soil pH is too high, it can prevent your plants from using the nutrients in the soil. If the soil pH is above 6.5, then you have a pH problem, not a nutrient problem.
- “Burnt” leaf tips, twisting leaves: Nutrient burn. Flush soil with clear water and reduce the amount of fertilizer added to soil.
- Pale bottom leaves, pale color climbing from the bottom up, reddish stems: Nitrogen deficiency. Check soil pH in case you’re approaching lockout, then add more nitrogen to the soil.
- Purpling leaves, dark brown leaves, spreading dead spots: Phosphorous deficiency. Check your soil’s pH, as a true deficiency is almost always a sign of pH problems.
- Dull, very green leaves with burnt tips and brown spots: Potassium deficiency. Check for lockout and supplement additional potassium.
Fertilizer helps your plants do all the things they need to do to stay alive. By carefully fertilizing and flushing your plants, you can keep them growing healthy and strong through harvest. The best buds come from growers who know how to fertilize well, and you can do that too.