Help! Leaves Turning Brown/Yellow. Phosphorus Deficiency?

[morehawes]

Hi everyone, I would really appreciate some help on this.

Description of the Problem

All through veg the leaves start out well, but once they get big they start to go brown and crispy and eventually end up yellow/brown (photos attached). Nothing I do seems to change this. I cut off the dead leaves and try to fix the problem... and the cycle repeats. I am eager to flower, but wanted to resolve this before I do and am feeling somewhat lost.

I have been told that this looks like a Phosphorus deficiency, so I have been feeding them with 5-30-20 for a couple of weeks, but the issue persists.

The Project

After a few successful outdoor grows I decided it would be worth growing something in the “off” season. I live in a 240sqft house with my partner and we do not have any space “indoors”. We do however have a greenhouse, so I thought it would be a fun exercise to try and figure out how to grow something in there through a Canadian winter (Pacific Northwest).

Setup

• Strains: Kali Mist (left) Sour Diesel (right) – both feminised
• Age: Week 15 of veg
• Lighting schedule: Currently 24/0 (started out at 16/8)
• Medium: Mix of soil from my garden/perlite/mulch (same as previous outdoor grows)
• Nutrients: Reefertilizer grow 20-5-10. In the last two weeks I have been feeding with Reefertilizer Bloom (5-30-20) to try to boost Phosphorus, added to water as per instructions
• pH: Have only been monitoring for about 5 weeks. Around 6.5 when feeding and run-off around 6.5 also.
• Temperature: 18-22oC / 64-72oF
• Light: LED 18 inches from plant (MARS HYDRO TS 1000W)
• Humidity: 40-65
• Watering: Every 5-7 days, when top 1-2 inches of medium is dry

Challenges

• Environment consistency – the outside temperature and humidity varies a lot, including below freezing temperatures. It took a while to get things stable inside the box, so they definitely suffered some sub-optimal temperatures and humidity early on.
• Nutrient Balance – I started out very haphazard with my approach and simply made up a medium that worked outdoors and added the liquid nutrients as per the instructions. I did not monitor ph to begin with, but around 5 weeks ago flushed the soil with mild nutrient water (PH 7). The first time I did this the run-off from Kali Mist was around 6, from Sour Diesel 7.8. I gave it two weeks and did it again, this time the run-off was mid 6’s from both.

Thanks for taking the time to read this and for any suggestions.

[YYCannabis]

I’m not a dirt grower so I can’t speak to that part of pH and nutes, but looking at the pics your leaves look droopy. I don’t think it’s a phosphorous deficiency. From what I understand, P deficit is more in line with flowering stage vs veg growth stage.
Few things:
1- you’re at 15 weeks of veg? Seems like a long time, but I’m only experienced with autos. Maybe a photo grower can chime in on this.
2- reduce you’re electrical costs by switching lights to 18/6 or 16/8 if you are staying in veg.
3- check out the Plant Doctor on the main GWE website.

[morehawes]

I’m not a dirt grower so I can’t speak to that part of pH and nutes, but looking at the pics your leaves look droopy. I don’t think it’s a phosphorous deficiency. From what I understand, P deficit is more in line with flowering stage vs veg growth stage.

Thanks for your reply. I took the photo before watering, they definitely needed a drink.

1- you’re at 15 weeks of veg? Seems like a long time, but I’m only experienced with autos.

It's definitely been slow, mainly due to this issue from early on. I could have flowered them weeks ago, but I decided to wait until I got this issue sorted. In the mean time I have been experimenting with topping and LST, so they are getting bushy. Possibly too much for the 2x2 space.

I am wondering if the plants got shocked early on and never recovered, or the soil in my growing medium combined with my nutrients just isn't good for the plants. Flushing didn't help.

Instead of giving up on them I'm going to flower and see what happens.

2- reduce you’re electrical costs by switching lights to 18/6 or 16/8 if you are staying in veg.
3- check out the Plant Doctor on the main GWE website.

Thanks for the tips. Not too concerned about power, using LEDs and made everything as efficient as possible.

[YYCannabis]

I think what he is saying is that the plants closest to the air intake look to be in the worst shape. What temp air is coming in that intake?

[morehawes]

Ah I see, thanks. It has gone below freezing (-5C/23F) in the past, but for the last month the lowest it's been getting is about 5C/41F at night. The fan kicks on for 15 minutes every hour, so there is some temperature and humidity fluctuation as the air gets recycled.

[Mr.furley]

Your plants look wind brunt, cold air isn't good and could be your problem.

[morehawes]

Thanks for your suggestions. I moved the air intake fan inside the cabinet, so instead of blasting in cold air it is gently circulating air around the plants.

I left the air out fan as is, so fresh air will be drawn in through air leaks in the cabinet and hopefully a little less harsh than before. Probably still not ideal, but will see how it goes.

[morehawes]

Since making the change to the air intake the plants have been doing well, so it looks like windburn was indeed the issue. Thanks for the help!

[Mr.furley]

Good to hear.