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Why Are Your Autoflower Leaves Turning Yellow?

If you’re growing autoflowering cannabis plants and your leaves start to turn yellow – aka chlorosis – it’s a sure sign something’s wrong. Some plants take on different hues over and above the traditional green you’d expect, and you get some stunning colour combinations – but yellow’s not one of them. Read on to find out the most common reasons why your autoflower leaves are turning yellow and what you can do about it.

Think of yellow cannabis leaves as your plant sending up a flare to let you know there’s a problem. Yellowing can indicate several issues, so you first need to run a diagnostic of your plant.

You need to know exactly what’s caused the yellowing in your instance so that you can take the appropriate remedial action. Knowing how to check your plant goes a long way to determine the problem, so let’s glove up and start there.

autoflower leaves turning yellow

Where you see the Yellowing Matters

The location of the yellowing is important. For example, if your weed plants display yellow at the bottom, on lower leaves nearer the soil, this indicates a nutrient deficiency. You’ll likely see yellow at the tips of the leaves, which will, in time, work its way across the leaves until the yellow reaches the stem.

autoflower leaves turning yellow

If the yellowing is prominent towards the top part of the plant, however, this is most likely an indication of an environmental problem. Too much light, heat, or even plant infections will start nearer the source – so, up high and on the outermost foliage of the plant.

When you see the Yellowing Matters

What stage is your plant at? Are you at the seedling stage, vegetative or flowering? This is important because your plant’s needs change throughout its life cycle, so deficiencies will be known through the plant’s appearance, depending on the phase your plants are in. Where the yellowing occurs may better help you figure out why your autoflower leaves are turning yellow.

At the Seedling Stage

Finding yellowing leaves at the seedling stage is unlikely to be a sign of nutrient issues because seedlings don’t generally require additional nutrients. At this stage, yellowing is more likely to indicate insufficient light exposure or problems with your watering habits. Seedlings need plenty of light, adequate heat and moisture, so make sure you’ve ticked these boxes. If not, take immediate steps to remedy these issues for your plants’ good.

At the Vegetative Stage

If you’re finding yellow fan leaves during the vegetative stage, this is most likely your plant signalling a nitrogen deficiency. Younger plants are also susceptible to light burn and heat burn, so be prepared to make some adjustments. Indoor growers may want to consider raising the light away from the plants a little more to avoid this damage.

At the Flowering Stage

At this life cycle stage, your marijuana plants will have different requirements for nutrients and supplements. Potassium, magnesium and calcium are all required in the correct measure. Ensure you’ve read the nutrient instructions correctly and are following the proper regimen. If not, ramp up or down the nutrients gradually and cautiously. We’ll talk more about nutes for autoflowering cannabis later on.

Taking Action on Yellowing Autoflowers

Once you’ve determined where the yellowing is occurring and which phase your plant is at in its life cycle, it’s time to take appropriate action to remedy the issue. But what’s causing it, and how can you tell? Here are some of the most common causes of why your autoflower leaves are turning yellow.

Incorrect Watering 

Water is essential to healthy plant growth, but too much or too little can damage plants by harming the root system. Both overwatering and underwatering are common mistakes which are easy to make since watering is such a delicate balancing act. Fortunately, the plant will tell you which mistake you’re making with watering by displaying differing symptoms for each.


The root systems will begin to drown if you’re overwatering your plants. Then you can add the dreaded root rot to your list of problems, and you do not want that. For more information on how to fix overwatering or root rot, there’s a handy article on each for your information on our blog.

Lighting Issues

You’re growing autoflowering cannabis, but is your lighting schedule on point? Are your plants receiving too much light or too little? Check your environment for excess shade or light leaks interfering with dark periods. Autos are sturdy and should flower without changing the schedule, but make sure you’re armed with the right information on lighting for autos.

Nutrient and PH Problems

Incorrect PH is a good indicator that your nutrient levels are off. If you’re growing in soil, you have more protection against PH imbalances than if you’re growing in hydroponics or coco. In soil, aim for PH up between 6.0 and 7.0. Hydro and coco setups will want to seek nearer PH levels between 5.5 and 6.5. A PH imbalance means your roots won’t get the nutrients they need, which could lead to nutrient lockout and explain why your autoflower leaves are turning yellow.

cannabis nutrients

You should already have a PH meter in your equipment arsenal to test the Ph of your growing medium, but if you don’t, get one and test your levels. If they’re off, flush your plants with water and then resume feeding with a light solution, ensuring you’re following the guidelines for correct amounts.

Nutrient Schedules for Autoflowering Cannabis

Bear in mind that autoflowering cannabis requires less nutrient support than photoperiod cannabis. There are various factors dictating this, namely:

  • The size of the plant, as autos are usually smaller
  • Genetics, as autos contain Ruderalis genetics meaning they’re generally hardier
  • Accelerated growth rates – autos reach the flowering stage within a few weeks

As well as choosing the proper nutrients, you must correct the delivery schedule for growing cannabis. If you don’t use the right amount, this could lead to deficiencies that also cause your plants yellowing. Cannabis nutrients usually base their recommended dosage on photoperiod plants, so if you’re using them for autoflowering weed, use a fraction of the manufacturer’s recommendation. It’s easier to fix undernourishment (by adding) than over nourishment.


Seedlings don’t require additional nutrients. They’re far more prone to nutrient burn, so it’s best to give water only at this stage.

Vegetative Phase

Give 1/8th strength vegetative nutrients from day ten, increasing to ¼ strength towards the end of the veg phase. This will provide the necessary nitrogen at this stage to promote stalk and leaf growth.

Pre-Flowering Phase

Ramp up your vegetative nutrients to around ½ strength to maximise the vertical growth of your plants and increase yield potential. The pre-flowering phase sees your plants take on accelerated growth and will benefit from the additional nutrients at this time.

Flowering Phase

Now is the time to switch your nutrients to a higher phosphorus mix to stimulate bud growth. High nitrogen levels will only continue to promote leaf growth at this stage, robbing energy away from flower production. Begin flowering phase with ¼ strength nutrients, and gradually increase to ½ strength in the later weeks of flowering.

Nutrient Burn

A sign of too many nutrients that manifests through yellow leaves, nutrient burn should be treated by flushing the substrate with water, then continue feeding with the correct dose of fertiliser for your substrate.

autoflower leaves turning yellow

Temperature can cause leaves to turn Yellow

Among the lengthy list of potential causes of yellowing leaves is the weather. Cold weather and hot weather are both capable of causing your plants stress, and in either case, your plant will show its disapproval for extremes of climate through yellowing leaves.


If your plants grow outdoors, you may have to think about bringing them inside in the evening to protect them from temperature drops. Otherwise, not only will you see yellowing of the leaves, those leaves will start to drop off and die. It should be a simple case of nudging the thermostat up a notch or adding a few extra lights if you grow indoors.


Heat has the same effect on your plants – stress. Your plant leaves will yellow and die just the same with excess heat as with cold. This is why balancing the temperature day and night is key. Indoor remedies include turning up the air conditioning or adding fans to your grow room or tent, but you can also back your lights off too.

Outdoor growers have it a little more complicated here; if you’re experiencing a heatwave, you can construct a shaded area in your grow space to keep your plants from overheating, but there are not many other options. The good news is, you’re growing autos, so they will have added resilience – more if you’ve chosen a strain suited to your area’s climate.

Pests and Bugs

If nature’s villains are chomping upon your crop, the plants will soon offer yellow leaves as a sign of discontent. Inspect your crops, and know your enemy. There are different ways to deal with pests, so remove them immediately once you’ve identified your invaders.

Leaf Septoria

Leaf Septoria is a fungal disease; its first signs will present as black or brown spots on your plant’s foliage. If left unchecked, the leaves will be yellow, brown, droop or wilt and drop off. A particularly nasty pathogen, leaf septoria spreads by wind and rain and is most likely during the early stages of flowering. At best, you’ll have stunted plants and smaller yields.

If you see signs of leaf septoria, you must immediately remove the plant’s affected foliage. Clean your scissors or shears after every clip to avoid spreading the spores to the rest of your plant. After removing affected foliage, spray your remaining healthy leaves with neem oil to kill off traces of the septoria. This will help prevent future spreads. You’ll then clean out your soil base and add a new layer of mulch to cover any remaining spores.

Yellow Leaves are not the End of the World

Cannabis cultivation brings many challenges, some easier to resolve than others. Think of yellow marijuana leaves like a yellow traffic light. It’s a sign to exercise caution. Don’t panic because your plant is simply communicating that something is wrong. Most of the things it’s signalling are fixable.

The key is quickly identifying why your autoflower leaves are turning yellow and then taking the appropriate action. Some of the reasons listed here seem scary, but the bottom line is that most of these are relatively straightforward regarding the necessary action to remedy them. Once you’ve nailed the cause of the yellowing leaves, follow the plan for the specific culprit, and it won’t be long until your autos are back on track.

Cultivation information, and media is given for those of our clients who live in countries where cannabis cultivation is decriminalised or legal, or to those that operate within a licensed model. We encourage all readers to be aware of their local laws and to ensure they do not break them.

Duncan Mathers