When should you stop using cannabis nutrients?

Knowing when and when not to feed your weed plants (and exactly how much to feed them) as they progress through from seed to harvest is at times slightly overlooked - but nothing short of vital.

Growing great buds doesn't happen overnight, and most new growers won't get it right straight away. There's a certain amount of trial and error that we all need to go through as we get to know our plants and understand exactly what they like, and when they like it.

Can I give you all the answers?

No, but I can offer up the info I've gleaned over the past decade or so since I started growing my own buds, and hopefully help you sidestep some of the more common pitfalls most new growers tend to fall into.

So, when should you stop giving your weed plants nutrients?

Signs that your cannabis plants no longer need nutrients

There are a few situations that can pop up during a weed grow that will tell you pretty much immediately that your plants either don't need any more nutrients or would definitely prefer to be left alone for a while.

The more time you spend growing weed (or gardening more generally), the better you will get at reading these signs, and doing so earlier on will help prevent any issues.

Visual signs of nutrient burn

Nutrient burn is up there with the most common mistakes made by growers, and it's not hard to understand why. Nutrients are the plant's 'food', and we all want to make sure that our favorite ladies are well fed and ready to push out the best buds possible, right?

A lot of the time, the opposite is true. Too much food (or more specifically, too many nutrients) can actually slow growth and hurt your final harvest yield.

What to look out for:

• Leaf tips bending or curling
• Tips turning brown and becoming crispy
• Burnt or scorched edges, especially at the tips
• Leaves exhibiting an unusually dark green hue
• Yellowing beginning at the tips and spreading across the leaf

The chances of nutrient burn happening in good quality, cannabis-specific soil is minimal.

This is much more common when growing with synthetic nutes. If so, you need to use a pH meter and a TDS or EC meter to manage your feed correctly. Without these tools, you're effectively working blind.

How to recognize nutrient lockout

Just as with too many nutrients, not getting enough can also be a serious issue. Other than you simply not feeding the plants enough, this can be caused by (or at least made worse by) other issues, such as incorrect pH levels, a long period without feeding and even the quality of your water.

What to look out for:

• Leaves yellowing, particularly at the edges
• Reddish or purple stems and veins
• Stunted growth
• Wilting, even when the soil is moist
• Leaves becoming dry and crispy

Again, a pH meter and TDS or EC meter will help you monitor your plant's nutrient levels and ensure they are getting the right amount. If you think you are experiencing nutrient lockout, the best thing to do is grab your pH meter and check the levels of the runoff. This will give you a good idea of what's going on in the root zone and how to fix it.

How to identify natural fading during flowering

Now, as your plants work their way through the flowering cycle and into the final weeks before harvest, you'll start to see some natural yellowing and fading of the leaves. This is completely normal and nothing to worry about.

The plant is just using up all the nutrients stored in its leaves. The fading usually starts with the older, lower leaves and gradually moves up the plant.

Understanding the nutrient cycle in cannabis growth

You should already have a solid understanding with the different stages of a cannabis plant's lifecycle but what you may not know is that each stage has unique nutrient requirements. Using the best cannabis nutrients at each phase is key to ensuring healthy growth and optimal yields.

Nutrient needs during vegetative vs. flowering stages

During vegetative growth, cannabis plants need a bunch of nitrogen to power the explosive root and plant structure development, along with a decent amount of potassium and phosphorus to help build strong branches and thick, bushy growth.

Transitioning into the flowering stage means a change in nutrient requirements too - specifically, switching out high-nitrogen products for those with higher levels of potassium and phosphorous.

If you are growing hydroponically or with coco-coir as your medium, always use cannabis-specific nutrients and ones designed specifically for your growing medium. Doing so will help you avoid a whole world of potential problems with lockouts, burns and stunted growth.

How nutrient uptake changes in late flowering

As the end approaches, the plants know what's up. They understand that they really need to pack on some weight and get those buds fat, sticky and ready for harvest.

This means that while they are still using up the nutrients stored in their leaves (and therefore showing signs of natural fading), the buds are really packing on the weight. Some growers prefer to reduce their nutrient feed levels in the final three or so weeks. I don't.

I feed all the way up until I'm ready to flush the plants, and I don't ease off. I have experimented with both methods, and in my experience, I get bigger yields when I feed all the way through to the final flush.

How environmental factors influence nutrient absorption

This is probably the most misunderstood aspect of feeding weed plants correctly, especially with newer growers.

Your plants' environment plays a massive role in nutrient uptake.

The warmer and drier the environment, the more water your plants will drink and the faster they will suck up any nutrients in that water. This means that you need to be extra careful not to overfeed your plants in warm, dry conditions. In cooler, more humid conditions, the opposite is true.

Keep an eye on your plants' environment and adjust your feeding accordingly. This could mean reducing the amount of nutrients in a feed so you can water a little more frequently, or watering with plain water in between feeds to keep the nutrient levels stable.

The importance of pH levels

This is a topic that deserves its own guide, but let's breeze over it here.

The pH of your water and nutrient solution plays a crucial role in how effectively your plants can absorb the nutrients you are feeding them. If the pH is too high or low, it will lock out certain nutrients, meaning your plant isn't getting what it needs to thrive.

In general, you want to keep the pH of your nutrient solution between 5.8-6.2 for hydro/coco grows and 6.0 to 7.0 for organic soil. Monitoring this is less important for soil growers than those using hydro or coco, but it's still a good idea to keep an eye on your pH levels regularly.

Techniques for flushing your cannabis plants

We flush our plants to help with the smell and flavor, that's it. It isn't going to make your buds more potent or increase the size of your yield, and many growers swear by not flushing at all.

I have found that if I use synthetic nutrients and don't flush, the terps can be a little overpowered by a (pretty slight) chemical taste, even after a long cure. Some people report getting headaches when they haven't flushed their weed, but I can't say that has ever happened to me.

Flushing couldn't be simpler.

You just give your plants plain, pH-balanced water to help flush out any remaining nutrients from the soil or medium. Depending on how long you've been feeding synthetic nutes, and the growing medium will determine how long you flush for, but as a rule of thumb, flushing for 3 days should be fine.

Common mistakes when stopping nutrients

As I mentioned above, I feed all the way up to the final flush. Some growers reckon they get better yields if they ease off on the nutes as harvest approaches, but in my experience, this isn't the case.

Why stopping too early can hurt yield

This one is pretty self-explanatory, but if you stop feeding your plants too early, they won't have the nutrients they need to continue growing and developing buds. This can result in smaller yields and underdeveloped buds that don't reach their full potential in terms of size or potency.

Avoiding deficiencies during the late stage

Every growth stage is important, and getting things right during the entire grow is crucial for maximizing the final yield number but it's in the last few weeks when the buds really pack on the beef, and deficiencies at this stage can have a significant impact on your overall yield. Make sure you are regularly checking for any signs of nutrient deficiencies and addressing them promptly to ensure your plants reach their full potential.

How to fix nutrient burn if you stop too late

If at any point you think you have fed your plants too much, there are a few things you can do to fix nutrient burn.

The first is to flush your plants with plain water at the appropriate pH level and then resume feeding them with a lower concentration of nutrients. You can also try using enzymes and beneficial bacteria to help break down any excess nutrients in the soil or medium.