These spots started showing up on the leaves of my seedlings a day ago. I can’t tell if it’s a type of nute burn or if it is mildew. My humidity levels were extremely high but I lowered them and sprayed water with hydrogen peroxide and baking soda on the leaves today just in case if it is. Any thoughts?
Hmmm... A little hard for me to tell by looking at the picture. I definitely don't see nute burn. How is the air circulation in your grow space? I like 70%+ humidity for seedlings but I always make sure a fan is in the grow space moving the air around. Stagnant air greatly increases the chances of powdery mildew occurring.
My humidity has been at about 80-95 because of the dome. I took rockwool cubes and proped it open to lower humidity. I have no air circulation in my grow space at the moment but I will when they are transplanted into my 4x4 tent. Currently they are just in a seedling propagation tray coming up on week 2 after germination. The spots on the leaves kind of look like a brownish tan color to the naked eye and some spots are a little bit lighter colored.
This picture may be better. It started off as a lighter color, almost a light green and then got darker.
Ok, so not powdery mildew. That's good. When do you plant to put in the 4x4 tent and what's the humidity like in there? I personally only keep a dome on until a small root structure has been established. The plant has leaves then and will need fresh air (specifically CO2). What brand soil is that and have you fed it any nutrients?
The humidity is about 30-40% but I have a humidifier to help me control it it’s just turned off right now since the tent isn’t running currently. I’m using coco not soil and I have fed it blue planet nutrients easy weed, botanicare’s silica blast, and rhizo blast. I know that these are mainly made up of nitrogen and not much else. I fed a small amount of nutes but at a fairly high ppm since Im using tap water. My pH is about 5.5-6. Since it’s coming up on week 2 I feel like I need to increase nutrients so I really need to figure this out. I was thinking it could possibly be a phosphorous, magnesium, or calcium deficiency?
Got it. So you know what you're doing as far a nutes. Sweet. So the browning, slight dropping, curling symptoms that I see in the picture matches over-watering symptoms. See here for a pic of an over-watered seedling: https://www.growweedeasy.com/sites/growweedeasy.com/files/overwatered-seedling-looks-like-nutrient-deficiency.jpg I'm surprised to hear about it happening in coco since coco is more of an airy medium. Although, you had the seedling in a dome so it makes sense. Once you get the seedling out of the dome and the medium dries up a little then the plant will bounce back. The browning however will not go away. What PPM are you giving and/or targeting at this point?
I’m targeting around 400 ppm for week one and it’s week 2 right now so i’m shooting for 600 ish. I did keep the rockool cubes that the seedlings were in kind of at the surface of the medium on some of the plants which I feel like that could’ve affected it but probably not. I did water ~twice a day until now I guess I’ll do once a day from now on. Will the browning go away on future leaves if the plant becomes healthy again? Also later on when they are older would it be a bad idea to cut off the old brown leaves?
That's a pretty high PPM. I personally don't go over 250 PPM when the plant is a seedling. Yeah reducing to once every day or even once every-other day should help dry out the medium. Yes, new growth won't have browning leaves. If the plant continues to stay over-watered, slowed growth will occur and the browning will get worse. You could cut off the old leaves but I leave them on since there are nutrients still in those leaves that the plant can use. I only pick off leaves if it's 75% dead, i'm lollipopping, or defoliating.
Here are two other plants that started to show the same kind of thing on their leaves. Just thought i’d post em to get your opinion to confirm that it is overwatering.
The one on the Right, yes. The one on the left looks better.