Yellowing is not neccessarily a lack of N.

MrFista · Sep 26, 2010

Hi all.

I'm on my second run with no fertiliser inputs and the plants are dark green and pumping away. The last run in flower showed senescence - leaves yellowing nearer the base of the plant and some dropping off eventually.

I have read here so many times than yellowing of leaves in flower signifies N is running low and the plant is using the N in the leaves, and not to top the N up as the plant is now in flower....

Ahem. Bullshit.

There is certainly no lack of N in my soil. I pulled those senescing plants out and planted some more 3 weeks later and they vegged really fast and now they're flipped to flower and are deep green.

The plant yellowing happened with plenty of N left in the soil. Senescence is not a symptom of lack of N when in flower, though a shortfall will provide conditions for more severe senescence.

Lorenzo · Sep 26, 2010

so the plant takes what it wants pretty much. sounds like you've got a nice healthy soil

thanks for the insight.

VerdantGreen · Sep 26, 2010

i agree that from mid - late flower many strains will yellow of their own accord. some dont at all though, and with these it's nice to get them to yellow from Nute def as it makes them smoke better imo (although a good cure can help too).

microbeman may know about this, but i wonder if a plant can only 'ask or encourage' the microbes for certain nutrients at one time, so once stretching and early flower is finished, it puts all of it's root exudate energy into garnering P and K. Because the plant has plenty of N in it;s lower leaves which it doesnt need so much for photosynthesis ( and older leaves are less efficient at photosynthesis anyway) so it uses the N from those instead.
also i guess there are two ways that N becomes available to the roots - some by root exudates and some will be available through normal microbial breakdown of ferts in the soil.

just rambling but would be interested to know peoples thoughts

VG

MrFista · Sep 26, 2010

I agree the plant is only taking what it requires and this seems to be evidence of that. I have had outdoor that are never quite as green but also are not in any way deficient. I think the microbial supply of N might become low in flower leading to scavenging of N from the plant itself, but the soil is not lacking it.

As you mention Verdant - the plants root system may have switched to priority transportation of things other than N which displays as a 'lack of N' around this time. Alternately, the transition to flower might create different conditions in the rhizosphere perhaps accelerating downward flow of photosynthates to feed rhizosphere inhabitants making the 'culling' of N containing organisms less overall.

I agree some very light feeding strains smoke might be improved by inducing a shortcoming in it's diet. There are a lot of plant responses that can be induced by humans. But - which are beneficial to growing better weed...

FoCo(No.Co) · Sep 26, 2010

Yellowing of lower leaves prior to the end of flower can also be a symptom of root pests.

Japanfreakier · Sep 26, 2010

MrFista said:
Ahem. Bullshit.

Usually when people give that advice they aren't talking about natural yellowing of the lower leafs so it's not really bullshit, it's just a misunderstanding.

MrFista · Sep 26, 2010

Yes it's cheeky.

Senescence in flower is (partially) the natural yellowing of lower leaves. The advice not to add N is sound, but it is not because the soil has no N, that is bullshit.

MrFista · Sep 26, 2010

I'll N test my soil late in flower when senescence is in full swing. That should settle it.

SilverSurfer_OG · Sep 27, 2010

Yeah i am sure the plants r smart enough to self regulate.

That being said if u r too generous wiv the N in liquid form they will suck it up!

captinknots · Sep 27, 2010

i have some yellowing and im 3 weeks in to flowering today. its been getting yellow for about a week now, and the past few days they have got pretty bad. they have little nickel size buds so far and i think stretch is over. would you add N with some P at this time in flower, with such sever yellowing? or just focus on the P? there was only 1 cup of bone in my soil, and i dont think that was enough...plus they were recovering from a pretty brutal clone sesh and ended up having to grow a lot of leaves the first couple weeks of flower.

not trying to highjack, seemed appropriate....

blancorasta · Sep 27, 2010

ive noticed N def symptoms in early to mid flower from being root bound.

peace

MrFista · Sep 27, 2010

I am being a bit provocative, I apologise for calling BS it was not my intention to say folks were talking BS just that the message was wrong - eg: BS. I have probably told people very similar stories about N being 'used up' by mid-late flower and so plants are scavenging leaves for it.

I don't believe this is the case anymore. For some there may be an N deficiency by flower, but senescence does not imply a lack of.

On N deficiency symptoms from being rootbound, that is a nice observation but doesn't apply in my case as I grow in a 16 sq ft bed. The 6 plants that senesced were not lacking root space, or N.

Captin - I think early onset senescence and the resultant display of 'N deficient' type symptoms may be an ailing plants overall effort to finish early which could be symptomatic of many things. The plant is going to finish anyway, but sometimes they finish faster (and smaller) than other times. But, you can't really say how a strain is doing unless you've grown it several times already and got to know how it handles in specific conditions. Some strains will senesce faster than others. Some strains I don't even bother trying to grow here, as they're problematic in my conditions, just too much effort compared to others of comparable quality and yield that like the local conditions. You can learn a lot about a strain online from other growers using that strain but the growers skill, local conditions and substrate play just as great a part in it as the genetics you are growing. I aint gonna answer adding fert questions, I'm over ferts hehe.

JustinC · Sep 27, 2010

check your ph and ppms of your nuits, adjust acordingly...
some strains will freek if the ppms are to high
and if your ph is to low or to high, it will bind up your nuits

NUG-JUG · Sep 27, 2010

ppms are of no concern in living organic soil, and ph only matters if your water sucks or you didn't dolomite lime the soil. i agree with blancorasta, if you know your soil's good and the plant is yellowing too soon id guess rootbound.

compost · Sep 27, 2010

If you are growing in organic soil a N def near the end can sometimes be explained by the beneficials in the soil. As the plant gets farther into flowering the nitrogen fixating bacteria/fungi get crowded out by other beneficials vying for the same energy in the soil.

There may be a ton of N available in the soil but can almost be considered to be locked out since different beneficials are crowding the root zones.

Thats just my 2 cents.

Microbeman · Sep 27, 2010

compost said:
If you are growing in organic soil a N def near the end can sometimes be explained by the beneficials in the soil. As the plant gets farther into flowering the nitrogen fixating bacteria/fungi get crowded out by other beneficials vying for the same energy in the soil.

There may be a ton of N available in the soil but can almost be considered to be locked out since different beneficials are crowding the root zones.

Thats just my 2 cents.

Evidence?

Microbeman · Sep 27, 2010

JustinC said:
check your ph and ppms of your nuits, adjust acordingly...
some strains will freek if the ppms are to high
and if your ph is to low or to high, it will bind up your nuits

Poppycock! Does not apply to organic. I do not even believe the large amounts of dolomite lime used by many (most) growers are necessary. Try it without so much sometime and see if there is a difference.

Microbeman · Sep 27, 2010

VerdantGreen said:
i agree that from mid - late flower many strains will yellow of their own accord. some dont at all though, and with these it's nice to get them to yellow from Nute def as it makes them smoke better imo (although a good cure can help too).

microbeman may know about this, but i wonder if a plant can only 'ask or encourage' the microbes for certain nutrients at one time, so once stretching and early flower is finished, it puts all of it's root exudate energy into garnering P and K. Because the plant has plenty of N in it;s lower leaves which it doesnt need so much for photosynthesis ( and older leaves are less efficient at photosynthesis anyway) so it uses the N from those instead.

VG

That is my basic theory VG. Once the plant enters the flowering stage the molecular compounds are so structured so as to feed and stimulate mycorrhizal fungi and other microbial life forms which provide a greater degree of phosporous and other fruiting related (micro)nutrients to the root systems. Interestingly, a colleague recently sent me some papers indicating the roots produce exudates which mineralize a minor amount of nutrients in the absence of 'necessary' microbial life. I have yet to study this in detail so have not formed an opinion regarding the validity.

Whether the N is pulled from the leaves during flowering/death phase is something which I do not know but it would not surprise me. Ah! to be a full time student.

also i guess there are two ways that N becomes available to the roots - some by root exudates and some will be available through normal microbial breakdown of ferts in the soil.

I do not know what you mean by this. If you are discussing the aspect concerning the papers my colleague has sent me, this is a point of interest. If you are disassociating the interaction between root exudates and microbial delivery/processing of nutrients in the rhyzosphere, they are one and the same (AFAIK).

compost · Sep 27, 2010

Microbeman said:
Evidence?

No statistic evidence just logic... Logic that could be wrong....

As the plant gets heavy into flowering its needs change also. When the plant needs alot more P, the microbes in the soil that help with P production will "step up" and flourish. The microbes that assist in N uptake are gonna take a back seat as the plant sends down those signals that it needs more P and less N.

As the plant goes through the N stored in the leafs it runs into a problem. The low levels of the microbes for N will not change much as the plant is so far into flowering hormones will dictate the need for more flowering nutes rather then N.

What I am trying on my next run is to use Nitric acid for my ph adjustment in my RO water. I won't use much but that little kick for the first 75% of flowering should keep the plant from burning through its N reserves to quick. I did this on my first run(not on purpose) and didn't have the hardcore yellow leafs like I do now with straight organic the last 6-8 weeks of flowering.

Again this is just my opinion and people like yourself are more versed in the factual parts of the process.

Microbeman · Sep 27, 2010

You are correct that the needs of the plant change and the exudates change to promote fungal and other P delivering microbes, however this does not crowd out the other microbes which normally deliver N, they are just dormant.

I don't buy the pH manipulation nor the fact that the plant depletes the N reserves though. This was illustrated by Mr Fista being able to plant new seedlings into the same soil which promoted flower and death for the previous harvest if I understand correctly.

I have witnessed this myself on numerous occasions over a 7 year period outside and 5 inside.

Yellowing is not neccessarily a lack of N.

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