Phosphorous deficiency, still flush?

I have a plant that is about 2 weeks from harvest, that has what I am pretty sure is phosphorous deficiency. I have the tell tale signs, including red stems. Should I still flush using only water, or should I keep giving her nutrients up til the end?

Here are some photos, though the 2nd two are from a plant 2 weeks behind, which has the same problem (I have the nutrients sorted now, so hopefully the 2nd will recover before flush time). My nutrient problem in case anyone was wondering, or has advice for: I bought the General Hydroponics trio of Micro/grow/bloom and am using it for soil at 50%. I originally thought that if I halved the water (smaller pots) I should halve the nutrients as well, but now I have signs of deficiency, so I am using the recommended amount in less water. Is this correct?

I think I see more N and Ca def. Maybe mix twice as much nutrients (half strength) for a semi-flush?

How much of the 3part are you mixing? Maybe go back toward a veg mix to get more N (and more micro)?

I used GH 3-part in soil and soilless (Pro-Mix HP with added perlite) and it worked well for me. But, I did have the kind of conditions you're having. It was too high in PK, not enough N.

It's not ideal to use hydro nutes in soil, IMO. But, it worked pretty good for my first grows. Yours look about as good as mine did at that stage.

You could add some AK Fish emulsion which would benefit the soil biology and increase N.

If you have a PPM pen, what is your runoff ppm? I found that's a good indicator of salt buildup and whether you should flush.

When you feed, how much runoff do you get? I like 20-30% to help avoid buildup.

az2000 said:

When you feed, how much runoff do you get? I like 20-30% to help avoid buildup.

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Unfortunately my drain dishes are a bit too small, both for size constraints and I skimped on the cost, so I can't afford much runoff. Definitely not 20-30% of the water I pour in, maybe 5-10% tops.

Also I didn't know these were hydro nutrients when I bought, they were just the only nutrients my local store had that weren't in gigantic expensive containers. I got a bit of nitrogen excess with claw tips when my first plant was vegging because I used a generic nutrient at too high of a strength and then that made me a little gun shy with nutrients.

You can use a wet-dry vac to suck it out. Or, lift the plant to another saucer, pour, transfer, pour. I made 4" deep saucers by cutting Home Depot buckets down with a hacksaw. (Mark 4" around the bucket, use tape to connect the dots as a guide, use a hacksaw to work around the edge of the tape cutting a groove. Keep cutting gradually around until it cuts through).

MistrBurrberry said:

Also I didn't know these were hydro nutrients when I bought, they were just the only nutrients my local store had that weren't in gigantic expensive containers. I got a bit of nitrogen excess with claw tips when my first plant was vegging because I used a generic nutrient at too high of a strength and then that made me a little gun shy with nutrients.

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I had N claw too. I used the so-called Useless schedule which runs between half and full strength. If you're doing half-strength of GH's "1-2-3" schedule, that's 2.5, 5 and 7.5 (ml/gal G, M, B, respectively). That's equivalent to a packaged product 2.1-2.6-3.3 (an NPK ratio of 1 - 1.28 - 1.59). That's a reasonable ratio. It's not a crazy high PK (like, if you added GH KoolBloom).

You could go 2.5 - 7.5 - 5 (ml/gal) and have a ratio of 1.62 - 1 - 1.55. That would give them a shot of N.

I don't want to make you feel like you did anything wrong using GH 3-part. It's good stuff and I liked the results I got (even though my plants were a bit rough in the end).

However, these multi-bottle boutique "lineups" are expensive compared to using ordinary products. I switched to Grow More Sea Grow and mix my stuff to get the ratios I want (1/2 tsp this, 1/2 tsp that). It costs about $1 per plant per grow. Many experienced growers here use JR Peters Jack's Classic. It's similar cost. Once you get your head around NPK ratios, it's pretty basic stuff. N, P, K is the same in any product. (Sources are different, chelation can make one product better. But, not worth most of the boutique mystery products.).

Keep doing what works for you. I used GH for awhile. But, if you start thinking in terms of soil (organic sources, not synthetic) it opens up a new world. Me and my friends noticed a very distinct taste difference when I switched to Sea Grow. It's a contentious topic. Hydro growers insist plants don't uptake "taste." But, we all noticed it. A more rich, smooth taste like tobacco. Not the sharp taste I associated with the GH 3-part nutes.

Not to overload you with info, but I made a spreadsheet to unwind those multi-bottle, schedule-driven products to see the resulting NPK ratio. Then, recreate it using other products. (That's how I got to my own Sea Grow mix.). If you play around with that it might help you see things in a different light (compared to MLs of bottles).

Back to your thing. I don't know why you're getting yellowing at what seems like a reasonable NPK ratio unless it's salt buildup. I think it could be good to feed with significant runoff (40%) and just let it run its course for now. My suggestion to give more N might be bad. Some people think N in flower makes the buds taste harsh. Maybe a mini flush and keep it where it's at. Or, if you revert back to more veg-like N, do less than I said above.

Wow, thanks for that writeup! Keep in mind that I only "fixed" my ratio about 3-4 days ago, before then I was using basically eighth strength for my smallest pot, and quarter for my normal pots. I also have the feeling they need a good flush with plain water since not only have I not been getting the right run-off percentage, but I'm ashamed to say I've been using a turkey baster to feed back the runoff to the plant. (this isn't newbie central for nothing!)

MistrBurrberry said:

Wow, thanks for that writeup! Keep in mind that I only "fixed" my ratio about 3-4 days ago, before then I was using basically eighth strength for my smallest pot, and quarter for my normal pots.

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Oh. They may just be hungry. Were they yellowing 3-4 days ago, or did it start after you increased from quarter- to half-strength?

MistrBurrberry said:

I also have the feeling they need a good flush with plain water since not only have I not been getting the right run-off percentage,

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Do you have a ppm meter? Flushing is over-rated, IMO. I doubt you need a flush if you were feeding 1/4 strength into flowering. If you are aware of your runoff ppms you can simply increase runoff of your nutes without doing a water-only flush (which, I think's more like an emergency).

MistrBurrberry said:

but I'm ashamed to say I've been using a turkey baster to feed back the runoff to the plant. (this isn't newbie central for nothing!)

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That might be a reason to push some salts out. Still, just a large volume of feed will do it, you don't have to do water unless you're concerned about the expense of wasting nutes (which gets to the other topic I mentioned). IMO, the problem with water flushing at this point is that you were underfeeding. Sounds like they need more nutes, not less. Even if you follow up with a feeding, that feeding will be diluted by the pure water you just poured into the container.

Considering everything you said, they look great. Don't wreck it now my doing too much.

az2000 said:

Oh. They may just be hungry. Were they yellowing 3-4 days ago, or did it start after you increased from quarter- to half-strength?

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Definitely before. I'd say at least 2 weeks ago. Is it that my soil had enough nutrients for a while, combined with the little I was adding, to have this issue take til week 8 to show up so strongly?

az2000 said:

Do you have a ppm meter? Flushing is over-rated, IMO. I doubt you need a flush if you were feeding 1/4 strength into flowering. If you are aware of your runoff ppms you can simply increase runoff of your nutes without doing a water-only flush (which, I think's more like an emergency).

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I don't have a PPM meter, I live in Iceland and the cheapest one I can find is about 80 bux for a pen, and amazon takes forever and has import tax making plenty of things cheaper to buy locally. I might just need to pony up and get one though.

I think based on what you said, I should just keep feeding the right amount, make sure I get the proper amount of runoff (and refrain from piping it back in) and see if the problem improves in a week or so. The only thing is that the oldest plant is about 2 weeks from harvest time, so not sure if I should continue with food til the end, or do any plain watering toward the final days.

MistrBurrberry said:

I don't have a PPM meter, I live in Iceland and the cheapest one I can find is about 80 bux for a pen, and amazon takes forever and has import tax making plenty of things cheaper to buy locally. I might just need to pony up and get one though.

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There's a way to use an electronic "multi-meter" (ohms, volts) to read EC. You don't need one. It's just handy to have. It helps me know if I'm overfeeding, getting salt buildup before it appears in the plant's condition (by measuring runoff ppm). (Also useful when trying a new nutrient to understand its strength.).

MistrBurrberry said:

and see if the problem improves in a week or so. The only thing is that the oldest plant is about 2 weeks from harvest time, so not sure if I should continue with food til the end, or do any plain watering toward the final days.

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When I used GH 3part I fed plain water the last couple times, letting the plant use what's left in the soil. I don't do that now, but I feed more organic ingredients and taste issues from synthetic ingredients isn't as much of an issue.

They don't look too bad for what I'm accustomed to using GH 3-part. Mine were N deficient due to raising K with KoolBloom. Following that "Useless" schedule, I cut the nutes in half and fed 1/4 tsp/gal KB a couple times. Also Liquid KB for 5-6 feedings leading up to it. I don't know if it helps. (I'm not recommending those products. All you need is an inexpensive product with a high proportion of P and K, if you were going to try "boosting" it. You don't need special, boutique products for Cannabis.).

I would feed with 50-100% runoff to flush and get fresh nutes in the soil (due to your recycling runoff. You shouldn't do that.). Feed normally. Water only the last couple times. I wouldn't worry about what happens the next two weeks. Growing is about learning. You've learned a lot. Don't keep messing with it or you could make it worse (and wreck your buds). Your next grow will be much better (not that this one is bad. It looks good to me.).

If I were you, I would start understanding nutrients and how to use inexpensive products to get your own custom NPK ratios. If you can find a product high in N, and another high in P, you can do your own "1-2-3" type of mix for a fraction of the cost. PM me with what you find and I can tell you how they would work. But, using that spreadsheet you can figure it out too. 1.5-1-1.7 (ratio) in veg. 1-1.5-1.7 in mid flower (end with 1-2-1.7, maybe go 1-3-1.7 once near the end as a "booster" if you want to see how that works). You'll learn to read your plants varying the ratios and seeing how things work. (And save *a lot* of money. You don't need cannabis-specific products.).

BTW: Are your nutrients labelled as % of weight or volume? In the US it's % of volume. I've heard other countries are % of volume. But, I haven't encountered a specific instance of this. My spreadsheet does % of weight. I've been thinking of adding a conversion of volume to weight. If that's an issue to you, let me know.

Well I was at the garden store today and they had a reasonably priced PH meter. It gave me all kinds of weird readings in the soil (it's a soil meter) in the same pot I read everything from 5.9 to 8.2. However if I measure cold tap water, it's right at 7, and if I measure the runoff I saved this morning, it's 6.6, so I think at least PH levels are not a problem.

I'm actually not sure what the percentages are. They are on the label, but no relation to how much they mean. Kind of strange.

I really appreciate your help with all of this. I have been thinking after these nutrients are finished of buying cheaper ones to make myself, as you are right about cost. Just the 3 bottles of the smallest size, .5L cost around 50 USD, though they are definitely lasting more than these 4 plants through one cycle. I'd estimate about 8 plants and possible more like 12 all the way through at the rate I'm using.

Inexpensive soil probes are inaccurate (pretty useless. I don't know if you can measure liquid with them.). I have $65 US Control Wizard Accurate 8 and it's pretty good.

6.6 is a bit high for runoff. Soil rises as it dries, so I liked to see my runoff around 5.6-5.8. Using my probe, that might mean 5.4-5.8 actual ph (because runoff is never accurate) and it would swing up to 6.4-6.8. What you're reading may be inaccurate due to the fact that it's a soil probe.

Regarding percentages, a nursery or hydroponics store would know. In the UK, it's % of volume. That's why the famous Canna PK 13/14 is 10/11 in the US. It weighs more as a percentage of total weight than the volume it consumes.

That would throw off my spreadsheet's results if/when you fiddle with your own stuff. I'll create a supplemental spreadsheet to convert %v/v to %w/w.

MistrBurrberry said:

I have been thinking after these nutrients are finished of buying cheaper ones to make myself, as you are right about cost.

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I'm journaling a grow using MiracleGro Tomato ($6-7 US for enough to grow 100 plants.). The goal is just cheap, not perfect ratio. If I wanted a better ratio I would mix MG All Purpose which has higher N & K. In flower I would mix MG Bloom Booster product which is higher in P & K.

For the money, I like Grow More Sea Grow (or Jack's Classic). But, like you, some people can't get those. Or, they might be on an extreme budget and might only be able to buy one product. So, I wanted to see how it works. I've been curious about it.

It does say in the instructions that for the most accurate measurement to place some of the soil in water to measure, so while the probe is probably cheap, it is most likely more accurate when measuring the water. I might need to return it to get something more accurate though.

Well, found the probe I bought on amazon and according to the reviews it is absolute rubbish. Back it goes.

az2000 said:

I'm journaling a grow using MiracleGro Tomato ($6-7 US). The goal is just cheap, not perfect ratio. If I wanted a better ratio I would mix MG All Purpose which has higher N & K. In flower I would mix MG Bloom Booster product which is higher in P & K.

For the money, I like Grow More Sea Grow (or Jack's Classic). But, like you, some people can't get those. Or, they might be on an extreme budget and might only be able to buy one product. So, I wanted to see how it works. I've been curious about it.

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That's awesome! Will follow for sure.

IMO, ph in soil isn't that important. It's nice to have a ph pen to measure the liquids. But, I don't use mine anymore. After I stopped using calmag to replace minerals in my reverse-osmosis filtered water (because I began mixing tap water to RO to get a starting 150ppm), I just pour it into the soil the way it is. I'm using less salts (because the calmag has N, and the ph-up products have potassium). Less salts makes the liquid's ph less "potent" (for lack of a better word) compared to the soil's ph potency (gravity, buffering, whatever you want to call it.). But, I would try this without fortifying the soil with dolomite lime. This is lime that has calcium carbonate and magnesium carbonate in a 1.2 to 1 ratio. This means it has elmental Ca and Mg at 1.61 to 1. (Be careful not to use hydrated lime. It has no magnesium and consists of calcium oxides, not carbonates.).

When it comes to ph, I think a ppm/ec meter is better for measuring runoff and detecting salt buildup. I used to see my runoff ph drop and it didn't tell me why. I would raise the ph of my nutrients, adding more salts with more phup, etc. Add more calmag to fight the ca/mg def due to lockout (more salts again). If I had looked at the runoff ppm I would have seen it rising from 1200 ppm to 1600, to 1800, to 2000, and so on. By early flower it was 2400 and starting to have show in the plant's appearance.

A soil ph probe like the one I mentioned is good to have. I can dial my initial soils' ph in with a little hydrated lime (higher) or aluminum sulfate (lower). But, that's not something you should have to do with a balanced commercial soil, especially if you amend 1-2 Tbsp/gal of soil. I do 1-1.5.

The lime should be sand and powder texture. If it's chunks you should crush it.

I'll bet the pH of the soil sets to low...too!
N,Ca and Mg are effected that way by limited to blocked uptake under 6.5.
Water with a higher pH for your water/feedings, say like 7.0
You need to remember that soil will drop in pH when watered and rise back as it dries.....If it sits to low too long on average.....You get that look.
Salt buildup is another and that effects pH down too.
The last thing is that synthetic's give the living bio's in the soil a real hard smack and salt build-ups really kill them off.
The use of a "zyme" like product for soil helps a lot in keeping those alive for their work at what they do. Including helping the soil self pH like it should better.

@az2000
If you run Organic it's far less a problem if when the soil is built - the amending for pH stability is done properly!
If not quite ,, You can get the low pH problems like I listed above.
I always water with 7-8 pH in my organics. Just cover my ass if I made a mistake in my liming agent.

Learning so much. I definitely think I'll do organic next. They sell BioBizz at reasonable prices here, so now I just need to find a nicer soil than generic flower potting soil. I have a compost bin that's been going for over 2 years, but not sure if it's the cold of Iceland but the very bottom is still completely recognizable objects, so not sure if I should mix any of that in when the time comes. I do have access to lots of rabbit poop though!

I'm fairly certain now from the reading I've done, and the great advice you two have given me, that it was a combination of underfeeding, and salt lock from too low of runoff, and feeding that runoff back in. I'm going to use plain tap water every third time, and start making sure I get proper runoff to flush out any salt buildup.

MistrBurrberry said:

I'm going to use plain tap water every third time, and start making sure I get proper runoff to flush out any salt buildup.

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Unless you're feeding organic goodies, I don't see a reason to do alternating feed/water schedules. Instead of feeding strong/strong/none, I would reduce the strength by 1/3 and feed that constantly.

From what I've gathered, alternating water-only is just to give the soil microbes a break from the synthetic nutrients. People usually do something beneficial to the microbes in that water-only feeding too, like a mild tea or "innoculants." I'm not into organic as much as I should be. I don't know what constitutes "inocculants." But, the idea is that the water-only feeding is to keep those away from the synthetic nutrients which are harmful to the soil biology.

You could get better info about that in the organic section. I'm just saying, all things being equal, I don't see any difference between supplying your plants a total amount of nutrients spread across 2 or 3 feedings. It's just a question of whether it's spread across, or 2 feedings made stronger. I've never understood the rationale for 2 strong, 1 empty unless it was to supply organic stuff in the empty slot. Without that, it seems like it would be the same thing to supply weaker nutes across 3 feedings. In either case, it would be the runoff that improves what I think you would be trying to improve with a water-only feeding.

Dr. Who said:

@az2000
If you run Organic it's far less a problem if when the soil is built - the amending for pH stability is done properly!
If not quite ,, You can get the low pH problems like I listed above.
I always water with 7-8 pH in my organics. Just cover my ass if I made a mistake in my liming agent.

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I'd like to do organic, but I don't have the time/motivation to properly prepare a living soil. I live in both worlds using Grow More Sea Grow. It's not entirely synthetic. I try to adjust my NPK ratios using organic supplements (Fish emulsion in veg to raise N; bat guano in flower to raise P; AK Kelp as a bloom hardener late in flower.).

It works well. I monitored my runoff PPMs to find a strength of feed (and runoff volume) that avoids salt buildup. As long as I avoid buildup the soil doesn't acidify -- even without ph'ing my nutrient mix. (But, I do fortify the soil with 1-1.5 Tbsp dolomite lime.).

I like organics. I notice a taste difference when I began using GM Sea Grow. I just can't get motivated to do the full "cooking" soil for 3 months. But, I should get into teas and "innoculants" and do a water-only application of those things occasionally.

The GH manual suggests a water flush ever 2-3 feeds to "flush excess mineral accumulation" which I'm pretty sure I have some of.

My point is: if you have excess mineral accumulation, reduce the minerals supplied instead of accumulating them and then giving none at all. Just spread less over more time (instead of more twice, then none). With hefty runoff, it should be the same thing instead of rewetting the soil to let the plant eat what has accumulated.

It's not a problem if you do water only. I just never understand the premise for it except as I described previously (keeping synthetic nutrients away from organic goodies some people supply occasionally, or on a weekly basis). I think GH adds that instruction as a footnote just to cover their bases. If someone has salt build up, they can say "we told you to..." That sells more bottles than instructing people to use less.

az2000 said:

I'd like to do organic, but I don't have the time/motivation to properly prepare a living soil. I live in both worlds using Grow More Sea Grow. It's not entirely synthetic. I try to adjust my NPK ratios using organic supplements (Fish emulsion in veg to raise N; bat guano in flower to raise P; AK Kelp as a bloom hardener late in flower.).

It works well. I monitored my runoff PPMs to find a strength of feed (and runoff volume) that avoids salt buildup. As long as I avoid buildup the soil doesn't acidify -- even without ph'ing my nutrient mix. (But, I do fortify the soil with 1-1.5 Tbsp dolomite lime.).

I like organics. I notice a taste difference when I began using GM Sea Grow. I just can't get motivated to do the full "cooking" soil for 3 months. But, I should get into teas and "innoculants" and do a water-only application of those things occasionally.

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I've been mixing my own soils for the last year or so. I started with the most popular recipe floating around the organics section -- 1/3 compost, 1/3 aeration, 1/3 peat or coco, 1/2 a cup per cubic foot base of alfalfa meal, neem meal, kelp meal etc. etc. I let it cook for a couple months and it worked decently. Like you though, I wanted something a little easier/less time consuming.

The past couple grows I've been using this recipe:

Base mix:

• 50% Sunshine Adv. Mix #4 - e.g. 4 gallons
• ~25% Coco coir - e.g. 2 gallons
• ~25% compost or castings - e.g. 2 gallons
• Calcitic/dolomitic lime - 1 cup (~ 16 tbsp)

Amended with 6 tablespoons of Epsoma Plant, Tomato, or Garden Tone (the Garden and Tomato have extra calcium) per 1 gallon (#1 container) of base or 3 cups per 8 gallons.

The first time I mixed this recipe I used a compost from lowes that had some manure in it and the mix heated a little initially but it cooled after a couple days and I planted (clones) five days after mixing. The second time I mixed with a different compost from Lowes minus the manure, there was no heating, and I planted after only two days.

It carries me through two months of veg. to around four weeks of flower in a #7 container for my heavier feeders at which point I just feed some fish hydrolysate or kelp/alfalfa tea here and there until harvest -- it gets me through the entire cycle for more finicky strains. The yields are pretty darn impressive for organics but more importantly (for me anyway) it's easy to mix (no aeration needed -- plenty in the ss4), the ingredients are readily available almost everywhere, there's no cooking (or very little) and it's water only.

Espoma has some good stuff -- it's very alive; here's the mix after four days:


Just some food for thought I guess -- water only organics don't have to be all that difficult.

unwine99 said:

The past couple grows I've been using this recipe:

Base mix:

• 50% Sunshine Adv. Mix #4 - e.g. 4 gallons
• ~25% Coco coir - e.g. 2 gallons
• ~25% compost or castings - e.g. 2 gallons
• Calcitic/dolomitic lime - 1 cup (~ 16 tbsp)

Amended with 6 tablespoons of Epsoma Plant, Tomato, or Garden Tone (the Garden and Tomato have extra calcium) per 1 gallon (#1 container) of base or 3 cups per 8 gallons.

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Sounds good. The soil is similar to what I do.


You're doing 2tbsp dolmote. I do 1-1.5. (I did 2 and thought I got some ca/mg issues in the first 2-3 weeks.).

I feed Grow More Sea Grow every 2-3 days. I like the idea of amending food into the soil like you do. The lower maintenance feeding is appealing. But, I'd be afraid of burning the plant with something that doesn't "cook" for a long time. Or, not having control over what's reaching the plant. I know the idea of amending nutrients into the soil is that the plant takes what it wants as it needs it. But, without cooking I wonder if that's still the case. Apparently you don't notice a problem this way?