Yellowing Leaves/Tips - Week 7

[dobbins52]

Hi all - hoping some of the more experienced growers could give me a little guidance here.

Problem: Leaf tips have been yellowing for a couple weeks now, but never moving too far up the leaf – literally just the tips. The last week or so, all of the leaf mass seems to be getting a bit pale – at first light green, and now getting more yellow.

Medium/grow method: Soil (Ocean Forest/Perlite); 3 gallon fabric pots.

Feed: I’ve been Fox Farm Grow Big every other watering since about week 4 (about 2 feeds a week). Usually about 1/2 the dose recommended by manufacturer – but I skipped the last feeding in light of what I thought was nute burn evidenced by the discolored tips, and the feed before that I only used a 1/4 dose for the same reason. I’m also supplemented with 1/2 dose of CalMag and Silica every other week (but have held off on that for a couple of weeks in light of leaf coloring issues). First tiger bloom feed this week - 1/4 dose with 1/4 dose of Grow Big. I was watering every 3 or 4 days for first 30-35 days; now I’m having to water every 1.5 to 2 days – very thirsty plant

water source: city water; runs a little acidic, so usually have to PH down to about 6.3-6.5.

Strain/age: Northern Lights Auto - ILGM. Just finished Week 7. Still not entirely sure what the difference is between “pre-flowering” and “flowering”, but she started throwing off pistils around Week 5. I didn’t get much of a stretch at all – she’s only about 24 inches tall from the floor (about 12 inches from the soil). I was holding off on starting the bloom ferts in the hope that I get a little vertical push, but it didn’t really materialize. Perhaps I waited too long to start bloom ferts and this is a potassium deficiency? Overall the plant has a nice little canopy. About 12 or so decent colas all with equal access to the light.

Light: HLG 260xl - about 18 inches at 250 Watts; 20/4 light schedule

Climate: Indoor Tent; running a Cloudline T6 inline exhaust fan with Carbon Filter; passive intake; couple desk fans pushing air around; Temps: 78-79 during the day; 69-70 at night; RH: 45-55.

Any ideas what I might be dealing with here? Is it worth running a sledgehammer flush at this point, or is that going to just create more problems for me? I’ve tried to look at some deficiency/toxicity diagrams/photos on the internet, and it’s tough for me to figure out exactly what’s going on. Any ideas?? Thanks so much!!

[Myfriendis410]

N deficiency I believe.

This could be due to a lockout. When did you last flush your media and what was the TDS of the runoff? I’m guessing salt buildup. FF calls for multiple flushes during the grow.

[PurpNGold74]

The flush is very very recommended if u havent.

Also im not seeing N shortage as much as a possible Mag issue

But of course pH lockout could throw all kinds of deficiencies.

[dobbins52]

Hey, thanks for taking a look. I haven’t flushed at all, but I’ll jump on that. I watered last night to about 10% runoff. Runoff was about 800 PPMs (my tap water runs at close 300) – my runoff is generally about 500 PPMs higher than whatever I’m feeding.

[dobbins52]

Thank you both for responding! No I haven’t flushed – I’ll do that right now actually. i do water to about 10-15% runoff every couple days, so I was hoping that would be enough to move salts through. Guess not. I have some clearex flushing agent I believe. So do you all think I should flush with about 2 or 3 times the normal watering amount? And then immediately thereafter feed a 50/50 dose of Grow Big/Tiger Bloom? And should add a serving of CalMag as well? Or do I wait for the pot to dry and then feed in a couple days and just hope the plant is ok with a nute-free medium until then? Thanks again!

[Nicky]

Ensure to water to 20% minimum run off to avoid salt build up when feed salt based nutrients (non organic)

Agree a flush, not exactly sure on what’s going on I’m sorta leaning on @PurpNGold74 side with it looking like mag but more of a lockout issue because, your in flower so nitrogen will be used less and the other most common deficiencies we see are cal, mag and PK which this looks most like mag in my brief viewing of what I can see.

The flush should help, I would put the plant in the sink or the tub and just run water though it for a while I did this when I was in soil as well.
Whike it’s flushing mix up a full feed for the week your in.
Read the ppm make sure it’s less than what the feed chart recommends dilute it to maybe 3/4 of the ppm recommendation is. Remeber fox farms is on the 700 scale and our tds meters are normally on the 500 scale (or vice versa I never Remeber)

So this is a converted chart with the math done if you have a normal ppm chart. Otherwise go by EC with fox farms to be certain.

[dobbins52]

Awesome - I had no clue that fox farm schedules were on a different scale! My tap water is pretty hard - runs about 200 ppms. You think that’s ok to run though it for the flush? Or should I head to the store and grab a bunch of gallons of distilled for the flush? If you think the tap is fine, should I be concerned about the pH being around 7.2-7.3? Obviously it would be much easier to stick it under the faucet, but I don’t mind taking a couple extra steps and pH’ing it if you think that’s the right move.

Also, are you suggesting that I flush the medium and then immediately feed? Or wait until the plant dries out in a few days before feeding again? Thanks so much!!

[Nicky]

Never used distilled water. If your tap water is less than 300 its fine.
But… Your tap water has chlorine in it, so you need an inline carbon filter or you need to let water sit out for like overnight/a day otherwise your pouring chlorine into your soil.

Flush then feed right away, might as well. your flushing the medium of salts and poor Ph.
Then feed (PH the feed) because the nutrients will be absorbed by the medium and the liquid won’t.
But you’ll get a proper nutrient ratio in the soil that’s the point of the whole process.

You don’t have to PH the flush but I prefer to myself because I run tap water. If I ran RO water then I woildnt.

[dobbins52]

Great - that’s the plan. Thank you!

[dobbins52]

Hey everyone - just wanted to say thanks for the flush suggestion. I flushed 3 days ago and the plants are already looking a lot better – and it didn’t appear to stunt them much at all. Smart pots were already very light today, and so I watered again at the runoff was perfect.

Also, I figured out that I was running my lights at a DLI of about 75 So I turned that waaay down. Live and learn I guess – thanks for the help with the learning!