What's wrong little plant 2 weeks old

[Albertslund]

Hello friends. I am currently growing my first batch of 21 plants mix cbd/thc. All plants are autoflower and are grown outside. I use ph-meters for soil and water. Watering with 6,5-6,6 ph. Soil ph is around 6,8 on average. Humidity varies between 20-45%

The seedling (cbd/autoflower/non-feminized) in the picture started showing burn marks on the sides of the bottom leaves two days ago. Getting worse slowly. I can't find this exact problem on the internet. The tips are not burnt at all. But there are signs of some discoloration on tip-half of the leaf. Any ideas why? Medium consist only of plant mulch (a bit on the clay side), NPK: 1320. I know that it is too much, but I'm trying different stuff. All other plants are planted in cocopeats 40%, plant mulch 20%, leca balls 20%, fresh compost 20% and a bit of sand in the mix. Sand as top layer to minimalize evaporation from sun. Started using minimal dose of Canna Terra Vega in water after leaf-marks appeared.

 

[Nunyabiz]

Iam not sure what "plant soil" is but that's probably the likely culprit.
Soil could be a bit too hot or not enough oxygen (aeration)

 

[Old Salt]

to the forum...

We don`t have enough information to form an accurate diagnosis. Please see How to Ask for Grow Support.

It could be water focusing the light on the burnt areas, or something more sinister.

 

[Nunyabiz]

Oh, I just noticed this was an autoflower.
Its likely the soil could be too nutrient hot, some, maybe even most autoflowers need much less nutrients than photo periods especially the first couple weeks.
Here is my current autoflower at day 10 from planting the seed in ground and day 16.

 

[Albertslund]

That looks good mate. What do you use as medium and how many hours of light do you give the plants? And do you replant?

 

[Nunyabiz]

I use a Buildasoil Oly mountain modern mix 2 soil which is a good Clackamas Coots soil recipe.
Has lots of rice hulls, pumice and charged biochar for aeration.
20 hours of light per day.

And I never transplant, I plant right into the final pot.
Which for me is always fabric.

 

[Albertslund]

Okay, thanks for the advice. Even 20 hrs for seedlings? And is that a 3 or 4 gallon fabric pot?

 

[Nunyabiz]

Well this one is 4 gallon which is the smallest pot I've ever used and frankly I am hanging my head in shame that I used such a small pot.
But , and I will not do this again, l had to use this small of a pot because I tried to squeeze this autoflower in on a photo period grow.
I let it go like 4 weeks before I even planted my two photo periods that I have growing in my Living Organic No-till pots which are 25 gallon.
Thinking that in 4 weeks the autoflower should be gone and out of the way and I can let the photo period fill in that gap in the next 4 to 5 weeks of veg.

But the autoflower ended up growing over 3" a day for awhile there and got huge.
So it's kinda crowding out one of my other plants.
And it looks like it's going to be more like 10+ weeks instead the 8 weeks it claims.

Even though this auto is doing fairly good in this 4 gallon pot, I believe if I had it in my 25 gallon no-till that the buds would end up much better, stickier, bigger.
Personally if you have the room I wouldn't go with less than 7 gallon pots if you're bottle feeding and 25 gallon if 100% organic no-till.
And if you use plastic pots then add 30% to the size of the pot.
This is what she looks like now after 7 weeks.

 

[Albertslund]

That's a big pot and a beauty in 7 weeks! I will definitely take sizes more seriously next batch and when I replant current seedlings. My grow room gets really crowded in morning and evening since I only have 12 hours of sunlight here and 12 new seedlings. Only one Viraspectra LED V300
Thanks again mate