Cannabis Phosphorus Deficiency

Phosphorus Deficiency Cannabis
December 07, 2020

What Can Cause a Phosphorus Deficiency?

Many things can contribute to a phosphorus deficiency in cannabis. The most common for novice growers would be PH range issues. Whether they’re too high of PH or too low of PH. Being out of the proper PH ranges during your grow regardless of which medium you’re in can be detrimental to your cannabis plant or plants. Check out our Potcast on PH ranges to learn more about them. Cannabis grown in soilless grow mediums, hydroponics, or aeroponics will be affected by PH imbalances much more drastically than cannabis grown in soil medium. Now, exactly why does cannabis become more affected if it’s not in a soil medium? Soil acts as a buffer between the roots and the accessible or inaccessible nutrients stored within it. Microbes break down inaccessible nutrients creating chemical compounds that become accessible to your plant.

In the Potcast episode Microbes, Nutrients, and Grow Cycles, Kronic, and OrganiGrower cover what microbes do for nutrient accessibility, as well as how to feed or keep a healthy microbial life within your soil. Definitely give it a listen! In soilless grow mediums, hydroponics, or aeroponics your roots directly sit within the reservoir and are generally surrounded by nutrients that are already made accessible, not needing microbes to break them down. This means any PH imbalance will instantly shock your plants’ roots or cause your plant to completely be unable to consume food, drink, or develop any further. This is why generally when working with soilless grow mediums, hydroponics, or aeroponics we recommend using a reservoir size that’s 25 gallons or more. This will create more stability for your PH ranges to not fluctuate so dramatically. As with any smaller-sized reservoirs depending on how many plants you’re feeding within your system, you’ll notice when a plant feeds a lot in one day your PH will drastically shift. You’ll need to spend hours monitoring PH and adjusting to make sure your girls stay within the proper PH ranges, otherwise you can lose out on vital growth during those times your girls sit outside those zones. We’ll break into which PH zones are proper for the grow later in the article. 

The next most common cause of phosphorus deficiency would be lack of PK within your feed. If you’re using an organic blend or line, most of the time P (phosphorus) is found a lot less in abundance than K (potassium) is within the formulas. This is due to the low abundance of natural phosphorus found in nature. So always make sure whatever line or nutrients you use, you make sure to have several amendments high in phosphorus. One really great amendment we recommend is Bone Meal. Bone Meal is very high in phosphorus as well as having trace amounts of potassium, nitrogen, and other micronutrients.

The last common mistake that generally isn’t the issue, is overwatering. We say generally isn’t the issue as there is a pretty even split for soilless grow medium, hydroponic, and aeroponic growers to soil growers. Overwatering is really only an issue in soil mediums. For one, you can cause your plant to develop root rot issues. But for the issue of phosphorus deficiency, how does overwatering cause it? If you’re using soil, overwatering flushes your grow medium of excess nutrients or any nutrients within it. Overwatering causes your microbes to not be able to break down any nutrients in the soil fast enough to allow your cannabis plant to consume them. So what happens essentially, is you end up only feeding your girl water and wasting all your nutrients. This will cause deficiencies to appear, generally the most common is a calcium and magnesium deficiency. Which since calcium and phosphorus bind so closely with chemical reactions, generally their symptoms look the same as well as fixing one will usually fix the other. Now that’s not to say that will happen every time. 

However, if you do have a phosphorus deficiency that forms into a calcium and magnesium deficiency as well, you could just readjust your feeding for increased phosphorus and you should notice absorption of calcium acetate, carbonate, and tri-calcium phosphate should increase in your girl fixing both your phosphorus and calcium and magnesium deficiencies. 

How To Spot a Phosphorus Deficiency in Cannabis

There are several ways to spot a phosphorus deficiency within cannabis plants. Phosphorus deficiencies, however, can and will show symptoms that are signs of other deficiencies as well, or just completely nothing at all. What we mean by that, is that phosphorus can cause stems of cannabis to become red or purple in color, in some circumstances, whereas if that is the only indicator that can be a genetic variation of that strain, excess of nitrogen, or a number of other reasons. So when looking to diagnose a phosphorus deficiency cannabis shows signs of, the best ways to tell if your girl is seeking phosphorus is to also look for a calcium deficiency. We’ll dive into why calcium and phosphorus go together here shortly, however, the signs you’re looking for are leaves that are greying out, or otherwise turning a bluish tone. Cannabis leaves that show fading, shininess, curling, or chlorotic spots that will decay into a brown like tone. Heavy indicator calcium is a part of this problem as well. You will also on occasion get very purple or red stems, as stated earlier, but this symptom is not one to rely on as many factors can play a role in coloring stems red or purple tones. You will also notice a halt on new growth or growth overall, new leaves will become small and undeveloped. Older growth will show heavier signs of affliction from the phosphorus deficiency as they’ve had more time to feel the effects. Generally, with any phosphorus like symptoms or problems with novice growers, it’s commonly more of a calcium deficiency. Considering if you’re lacking calcium your girl won’t be accessing phosphorus either. 

What Does Phosphorus Do For Cannabis? 

Phosphorus is directly associated with root development, strengthening stems, creating a vital resistance to many diseases cannabis potentially faces, how nutrients uptake, the formation of flowers, as well as your overall yield. Now, what other massively important functions does phosphorus serve cannabis? Let’s look at a list of them all! 

  • Phosphorus acts as a catalyst in biochemical reactions for growth; Photosynthesis
  • Phosphorus is vital for maintaining cannabis plants genetic makeup
  • Phosphorus is a primary component of deoxyribonucleic acid, or DNA, which is directly responsible for instructions to a cannabis plant on development and reproduction
  • Phosphorus also is a primary component of ribonucleic acid, or RNA, which is directly linked to reading DNA, otherwise translating the instructions in DNA for the cannabis plant to be able to form vital structural components, growth development, and reproductive compounds
  • Phosphorus deficiency can cause the plant to be unable to uptake other nutrients such as calcium, which is what generally is affected when there is a phosphorus deficiency 
phosphorus deficiency weed

Phosphorus is considered a low abundance macronutrient, however, being low abundance does not make it any less vital! We mentioned calcium earlier and let’s go back to that. Phosphorus directly reacts with the calcium in alkaline soils to create insoluble compounds. Now in fertilizer, this chemical reaction that occurs turns calcium carbonate to di-calcium phosphate which keeps reacting and turns into tri-calcium phosphate which keeps becoming more insoluble, up to 1000 times more insoluble than fresh tri-calcium phosphate.

These internal chemical reactions are vital to producing soluble and insoluble nutrients or compounds for your plant to consume as well as put back into your microbial life inside of your soil. These compounds include nitrogens, calcium phosphates, acetates, carbonates, and many more. Phosphorus plays a key role in many photosynthetic biochemical reactions cannabis needs for growth, flower development, and reproduction. One thing to remember, natural phosphates will always be broken down more quickly and produce fewer salt buildups. Inorganic, par-synthetic, or synthetic blends will always produce salts from phosphates which can potentially cause buildups within your grow medium.

How To Treat Phosphorus Deficiency in Soil?

If you’re a soil grower treating phosphorus deficiency will be relatively easy. It does take a little more time than balancing any soilless grow medium, hydroponic, or aeroponic setup. First and foremost you should absolutely make sure it’s a phosphorus deficiency before overdosing your plant on a nutrient she isn’t craving. Phosphorus deficiency acts like calcium and magnesium deficiency quite often. We recommend giving your girl an increased calcium and magnesium feeding if you start to notice those chlorotic spots or random splotching with color fading. Once you’ve fed, if you notice the spotting, fading, and other symptoms still persisting then it’s time to amend some phosphorus. 

There are actually several ways to do this organically. One way is purchasing an organic liquid PK nutrient that has high traces of phosphorus and potassium. Another way is amending bone meal in powder form on top of your soil. Bone meal is high in PK, particularly phosphorus, along with nitrogen and other trace minerals. Potash is a term you’ll see if you’re searching for dry amendments or liquid nutrients that just means any potassium that’s been bonded with another chemical compound, mainly used in fertilizers. So you could seek out an inorganic potash high fertilizer if you’re using par-synthetic, synthetic, or solvent-based blends. One more organic method would be to purchase a foliar spray that is high in PK such as Bloom Yellow Bottles Froigen, Nectar of the Gods Bloom Khaos, or any organic PK foliar spray will work. This way you canfoliar feed cannabis plants excess PK by spraying and allowing absorption by osmosis.

If you notice none of these tactics have worked then you most likely are out of PH range and need to rebalance your grow medium so your girl can access the correct PH range for the most efficient and effective phosphorus uptake. To rebalance PH you’ll need to feed water for several days back to back PHed at 5.6 to readjust your soils PH. After your runoff reads 5.6 to 6.5 (within that range), you can allow your soil to dry for 3 to 5 days. Once your soil is completely dry you can give an adjusted feeding with an increased amount of PK so your girl can access what she needs. Make sure your feeding is in the correct PH range. We recommend for soil growers to stay within these PH ranges. 

  • Seedling to Mid Veg – 5.6 to 5.9 
  • Mid Veg to Flower Swap – 5.9 to 6.1
  • Flower to Harvest – 6.1 to 6.3 and as close to 6.3 as you can (soil has a higher buffer zone and can handle PH ranges up to 6.5 but we don’t recommend that high of a zone)
phosphorus deficiency in veg

How To Treat Phosphorus Deficiency in Soilless Grow Mediums, Hydroponics, or Aeroponics?

If you are a grower and you grow using soilless grow mediums, hydroponics, or aeroponics diagnosing or fixing a phosphorus deficiency weed shows signs of will be incredibly easy compared to soil growers. Phosphorus for cannabis in soilless grow mediums, hydroponics, or aeroponics can be accessed in several ways. First, and probably the easiest way to add PK to your reservoir every time, would be to use natural acids to adjust your PH. When working in soilless grow mediums, hydroponics, or aeroponics adjusting PH will be a regular day to day task unless you’re working with larger reservoirs over 25 gallons.

So realistically if you’re using natural acids for PH adjustments you should NEVER face a phosphorus or potassium deficiency. Now, why is that? Natural acids used for PH adjusting such as potassium hydroxide for PH up and phosphoric acid for PH down, contain heavier amounts of PK than inorganic or synthetic PH adjusters. So when in soilless grow mediums, hydroponics, or aeroponics the easiest way to maintain PK to prevent any phosphorus deficiency in the vegetative stage or flowering stage is to adjust ph with natural acids. Please use caution though, these are real acids that can seriously burn your skin or cause damage to your eyes. Wear protective gloves and eye coverings when working with them.

Now, if you don’t work with natural acids or you are and you’re still facing a phosphorus deficiency, then first we recommend adding additional calcium and magnesium to your reservoir to make sure what you’re seeing aren’t symptoms of that deficiency. If the deficiency persists and more phosphorus symptoms appear, you’ll want to empty your reservoir and rebalance your solution by making a new mix of nutrients increasing the PK, specifically the P you’re offering to your plant. Once your girls have had access to a proper reservoir dosage they’ll eat it right up! 

If you’re still having trouble after all of that, the last thing to do is check your PH. PH ranges in soil, soilless grow mediums, hydroponics, and aeroponics all can affect which deficiency you’re facing. Make sure to adjust your PH to the proper ranges by either using natural acids or synthetic PH up or down. We recommend using these PH ranges for a guideline.

  • For Seedlings to Mid Veg – 5.5 to 5.8 PH
  • For Mid Veg to Flower Swap – 5.9 to 6.1 PH
  • For Flower to Harvest – 6.1 to 6.3 and as close to 6.3 as you can

We hope you enjoyed this article on phosphorus deficiency in cannabis plants. We have many articles you can read, access, or browse over on one of our many platforms! During your growing journey you’ll be facing many obstacles, headaches, or problems you’ll need solutions to and over at Homegrown Cannabis Co. we have the answers! We have our Homegrown forum with a plethora of information from articles, to videos, to grow threads, and more!