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Home › Marijuana Grow Guides › Troubleshooting › Nutrient Issues › Iron deficiency in marijuana plants

Iron deficiency in marijuana plants​

Updated: 19 April 2023Robert Bergmanhttps://www.ilovegrowinginvalid.com/wp-content/litespeed/avatar/1bbc20584a830bc2154d2c565fcc147d.jpg?ver=1714645345
11 min. read
Comments: 16
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Iron may just be a trace nutrient to the marijuana plants but a lack of it can lead to serious problems. In fact, it is one of the most common mineral deficiencies found in growing cannabis.
Information about iron deficiency in cannabis plants

Why is iron important for weed plants?​

What makes iron a crucial element is its role in the formation of chlorophyll. Essentially, this green pigment absorbs light, and together with carbon dioxide, converts it to plant food. Add to that, this element aids the uptake of nitrogen which triggers the rapid growth of leaves. Hence, not having enough iron compromises the plant’s ability to store energy and grow.
As a result, the plant becomes weak and malnourished which often leads to stunted growth and susceptibility to diseases. Ultimately, if nothing is done, this condition affects the yield and quality of the buds. Fortunately, there are many things we can do to stop this before it becomes severe.
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In this article, we will cover all there is we need to know about this problem including its causes and treatment. But most importantly, we will learn to properly diagnose it so we can immediately fix it. Through this information, we can easily manage the issue before it gets out of hand.

Iron deficiency in marijuana plants​

To grow healthy cannabis, it is vital for the plants to get all the nutrients they need at the right amount. In iron deficiency, the plants suffer from a host of problems that could be tricky to identify and treat. Hence, growers must learn how to tell if this condition is affecting their crop.

Signs​

The biggest challenge with this problem is that it can be tricky to correctly identify. As such, growers commonly confuse a lack of iron to other mineral problems such manganese, zinc, and nitrogen deficiencies. To avoid this mistake, learn the most common symptoms of a plant that craves iron.

Early signs​

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The earliest sign of iron deficiency in plants is chlorosis in which the young leaves turn pale yellow but the veins remain green. Left untreated, it later works down and inward to the older leaves.
To differentiate it from other nutrient problems, determine which part of the foliage turns yellow first. Again, a lack of iron first affects the newest and freshest growth which is on the top part of the plant. Whereas other mineral deficiencies target the leaves on the middle part or base of the plant.

Late signs​

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As the condition progresses, the pale-yellow color of young leaves will get brighter and spread on the whole leaf. Luckily, iron deficiency spreads very slowly. Hence, there is ample time to make the right diagnosis and provide the remedy.

Also read “Nutrient deficiencies in marijuana plants“

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However, if left to continue, the yellowing will occur in every new leaf which will give the plant no chance to manufacture enough food. Ultimately, the leaves will drop and the plant will stop growing. Expect to see minimal bud sites as well.

Causes​

To effectively treat the affected plants, we must first learn the root of the problem. By doing so, we not only get ideas on how to solve it, we also learn how to prevent it. Below are some of the most common reasons for iron deficiency in the marijuana crop.

Bad soil drainage​

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Growers who like to use soil as the grow medium should make sure that it has a good drainage. Otherwise, the water will pool and make the soil compact and choke the roots. This makes it difficult for the plant to absorb iron which is naturally present in soil but only in minute amounts.
Thus, when choosing a soil, it is best to avoid clay-based materials since this tends to hold water. Most growers use a potting mix since it drains well and has high-quality organic elements.

Excess of other minerals​

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Most of the time, the problem can be due to the excess amount of other nutrients such as manganese, phosphorous, zinc, calcium, or copper. Too much of these minerals can build up and block the uptake of iron in the soil.
Hence, we must find a way to balance the number of nutrients and work hard to maintain them.

Imbalance in the pH Level​

A neutral or alkaline pH level is the most common cause of iron deficiency in marijuana plants. Interestingly, this happens when we use too much fertilizers.
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To promote the absorption of iron, keep the soil’s pH between 6.5 to 6.7 by using a pH meter. The good news is, most nutrients also become more available for the plants when we maintain this pH value.

Overwatering​

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Like the effects of poor soil drainage, an overabundance of water limits the root from taking up iron. Therefore, it is best to know the correct watering practice to avoid this problem.

Using Coco Coir​

While iron deficiency in cannabis can occur in all grow medium, it occurs most frequently in coco coir.
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This is mostly because this medium lacks organic iron and naturally contains a high amount of salt, making iron less available for the roots.

Treatments​

After confirming the problem and finding out what causes it, we can now confidently save the crop. This involves applying the three basic ways that ensure a quick and effective treatment.
Using the correct nutrients and plant protector will get you a long way and your plants will have less chance of getting sick, in addition of being less vulnerable for pests and diseases.
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Flush and add nutrients​

Essentially, we want the grow medium to have the right pH that will promote the absorption of iron. In effect, this method provides the fastest recovery to malnourished plants.
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To start, we must flush the grow medium using water that has a pH of 6. This cleansing process makes sure that there are no excess minerals that locks out iron.
The next step is to follow it up in the next watering with an all-around nutrient solution designed for marijuana. Furthermore, to avoid the development of another nutrient problem, we must regularly check the pH of the grow medium.

Spray with iron chelate​

Applying iron chelate on the affected leaves helps them regain chlorophyll so they can turn green again. But this is only a temporary remedy for iron deficiency.
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As such, it helps only the leaves that are present during the spraying. Thus, we need to repeat the application every time a new growth appears.

Use soil additives​

There are many products that are excellent sources of iron while also stabilizing the pH level of the soil. Hence, it’s up to the grower to select which one is the most convenient and suitable. But before starting any treatment, it is vital to flush the grow medium first so that it can facilitate iron absorption.

Compost​

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Adding compost decreases the pH value by 0.1 to 0.2. This helps stabilize the soil while also enriching it with iron. In addition, it also improves the drainage, helping the soil to readily take up trace minerals. To use, apply 3 to 4 inches of compost on the soil and work it up to 6 to 12 inches deep.

Elemental sulfur​

It usually takes months to see the positive effects of elemental sulfur but it is worth it. As such, it provides the longest-lasting cure for the problem, lowering the pH and making iron more readily available to the plants.
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To get the best results, work the sulfur 6 inches into the soil about a year before planting. This serves as the perfect prevention of iron deficiency in marijuana plants.

Fertilizers​

Another way to lower the pH level and make iron more accessible is to use nitrogen fertilizers. The ones that contain ammonium sulfate or urea work wonders in the soil. However, be careful to give only the amount that is recommended for the plant. For the sake of the plants, we want to avoid nutrient excess at all costs.
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Immediate treatment is key to fixing the problem​

As with all other nutrient problems, the only way to save the plant is by acting fast. While iron deficiency tends to occur gradually, it can spread and wreak havoc on the plant’s health. Moreover, a quick recovery is crucial for a perfect harvest.
As growers, our role is to monitor the nutrient status of the crop and make sure that they are in their optimal condition. Thus, having the patience to do this as well as the skills to spot the first sign of trouble can be very useful. Equally important is knowing what to do when such problem arises.
By learning all the information on iron deficiency, we increase our ability to take care of the plants. As a result, our crop flourishes and we have the guarantee of harvesting enjoyable buds.

FAQs about iron deficiency in cannabis plants​

What are some common signs of iron deficiency in marijuana plants?​

The most common sign you will notice in your plant is the yellowing of leaves. Eventually, the leaves will drop and the plant will stop growing. You’ll see minimal bud sites as well.

How can you treat iron deficiency in cannabis?​

Flushing and adding nutrients, spraying with iron chelate and using soil additives are some ways to treat iron deficiency in marijuana plants.

I don't believe it's iron, and iron deficiency would start at the top of the plant in the new growth, like this:



It's a mobile nutrient that's lacking, my guess would be magnesium, simple way to check is to give the plant a foliar spray of epsom salts. A mag deficiency looks like this:

When did you feed it last?

She just looks hungry, specifically PK.

What's your RH and PPFD?

It gets complicated. Looks like magnesium to me.

emma.dir said:

Hi guys,
My plant is 7 week old grand daddy purp autoflower in coast if maine strongington soil. At like week 5 some of her leaves started yellowing from the outside. leaves only on the bottom of the plant. i gave her flower feed early and a dose of cal mag. since then i have just been watering and gave liquid squid yesterday but only half the recommended dose bcuz i was unsure if it would help. i also turned my sf1000 light down to 80% cuz the plant is really close to the light my tents only 4 feet sadly and i wasnt sure if she was getting tm light.

i really dont know what the heck the issue is..please help!! im scared to feed her more

Click to expand...

I'm currently using Stonington blend, what's your watering pH?

Your soil pH is probably low,
recommend a simple slurry test (you can Google it online) and post the results

Stonington makes a couple different soils, one is 70/30 coco/perlite, the other is more of an organic supersoil. If you're doing the organic, unless the PH is very badly out of whack, soil PH should shouldn't be a big deal. Stonington soil is buffered (even the Coco/perlite)..

Is that color because of your LED or is it actually the true color?

Phyto said:

Stonington makes a couple different soils, one is 70/30 coco/perlite, the other is more of an organic supersoil. If you're doing the organic, unless the PH is very badly out of whack, soil PH should shouldn't be a big deal. Stonington soil is buffered (even the Coco/perlite)..

Click to expand...

Super soils require certain size pots to work as such.

Coast of Maine recommends a 15 gallon pot for its Stonington blend

OP is using a much smaller pots, and unless I missed it I don't see on my bag or their website where it says it's buffered, so what's to prevent the soil pH from dropping?

Beachbumm said:

Super soils require certain size pots to work as such.

Coast of Maine recommends a 15 gallon pot for its Stonington blend

OP is using a much smaller pots, and unless I missed it I don't see on my bag or their website where it says it's buffered, so what's to prevent the soil pH from dropping?

Click to expand...

I’d check the ph of the runoff, if anything. COM is supposed to have a ph of 6.5. Almost all muni water supplies are slightly alkaline, and other than calmag and organic liquid squid, the op didn’t mention any additional nutes. I thought I saw that it was buffered, but I can’t find it now, so I may be wrong.

Beachbumm said:

Super soils require certain size pots to work as such.

Coast of Maine recommends a 15 gallon pot for its Stonington blend.

OP is using a much smaller pots, and unless I missed it I don't see on my bag or their website where it says it's buffered, so what's to prevent the soil pH from dropping?

Click to expand...

You are correct. Makes wonder....are they attempting to balance pH by their ratio of peat and coir? That just doesnt make sense to me. It has some really great stuff in it but I don't see how this could meet the calcium needs of the plant. He may need some seabird quano or rock phospate when bloom comes. I would guess the potash is also coming from the organic inputs but again I have to question if it is enough for a high yield. Also if his calcium levels are on the low side then sulfur likely us not enough for hood cannabinoid/terpene development. Some azosperillum would be helpful growing indoors. Organic inputs are only useful if you have a sufficient bacterial population to decompose it. Plants can't absorb organic nutrients. They need bacteria to convert it into those "evil" inorganic nutrients the plant can use. IMO azos is best suited to limited vertical space. Unlike the other commonly used bacteria like subtilis, licheniformis, pumilis, megaterium, etc., it doesn't make Gibberellin so it should help tighten up node spacing. It can fix nitrogen and solubilize P, K and S just fine.

Idk just thinkng on the page....

I’m thinking that the buffer is coming from the Calcium carbonate in lobster and crab shells, decent Ca and Mg supply if you’ve got the microbes!

I believe it’s magnesium. I would do a foliar spray (top n bottom of leaves) 1 tbl Epsom salts/gallon every 3 days for 9 days. The 4th spray should be just water to wash excess off the leaves. I recently had this and the treatment works. You need to watch the new growth on the plant to see if it’s fixed. The old leaves may or may not improve. Also, your light intensity is pretty high.

It light stress, folks stop with the ph stuff
It mag deficiency.
Caused by having your lights output waaaay too high. 1000/100 par lamps are strong.
With leds it happens all the time.
So, turn your light down, allllllll the way back to 40% (come with me if you want to live) yes 40% take those manufacturers instructions and set them on fire, bc that’s what they are getting you to do to that plant with their terrible instruction.

Set the lamp 30inches above your plant, and 40% output.
My veg space is set at that. I have also used most brands of lights of all sizes and performance. I never veg over 40% and definitely not an auto,

Or spend more loot on shit too don’t need.

Phyto said:

Stonington makes a couple different soils, one is 70/30 coco/perlite, the other is more of an organic supersoil. If you're doing the organic, unless the PH is very badly out of whack, soil PH should shouldn't be a big deal. Stonington soil is buffered (even the Coco/perlite)..

Click to expand...

My bad I'm using Bar Harbor blend, thought it was Stonington. I'm in freaking Maine you'd almost think I'd know the difference!

emma.dir said:

Hi guys,
My plant is 7 week old grand daddy purp autoflower in coast if maine strongington soil. At like week 5 some of her leaves started yellowing from the outside. leaves only on the bottom of the plant. i gave her flower feed early and a dose of cal mag. since then i have just been watering and gave liquid squid yesterday but only half the recommended dose bcuz i was unsure if it would help. i also turned my sf1000 light down to 80% cuz the plant is really close to the light my tents only 4 feet sadly and i wasnt sure if she was getting tm light.

i really dont know what the heck the issue is..please help!! im scared to feed her more

Click to expand...

Here’s some mag def I run into on the reg.
Hell anyone led does. These are moderate at most, but this look familiar? Pic 1 zoom into the light plant.