HELP! Leaves yellowing, brown spots / flowering stage

[bobix419]

Hi, problem started ca.4 days ago

Some leaves on a plant are affected with no apparent pattern (like from top / bottom). The rest looks fine.

Might be light burn? Ph problem?

This plant is 7.5 weeks old, 2. or 3. week in flower, grows in soil.
There are 2 other plants in veg next to it, they don't show any symptoms.
All plants were treated alike until this point, I suspect that could cause the problem. 1st time grower here btw.

Around a week ago I watered them once with ground coffee 'tea'.
2 days ago added dried ground banana peel to the soil.
All that I also did before in veg, with no problems.

The lighting was too dim before, so 1 week ago I changed lights to not ideal but brighter.
Now the top light is 50W LED grow light.
2 more lights between the plants, they were quite close to some of the affected leaves. I have already moved them away a bit.
These lights are:
20W LED bulb, 'full spectrum / grow' cool white light, propably better for veg stage than flowering.
30W LED purple light (blue + red)

Also, the plants were getting 24h of light for couple of last days. Yesterday I've switched back to 20/4.

The plant is untrimmed, got tall and skinny if that matters.

Thanks for looking, all suggestions appreciated!

[bigtoe]

What this mostly looks like is a magnesium deficiency. I could be wrong but it is exactly what it looks like. Try and spread some Epson salt on the top soil and water as normal. I hope this helps

[SoOrbudgal]

Best to mix epson salts into water

[Rwise]

If the coffee was not well washed it contains toxins not good for our girls.
a deficiency can be caused by PH being high or low.
Epsom salt can be mixed into the water at 1 Tablespoon per gallon.
Pics of the plant can help.

[Bluey]

Ground coffee tea that has not been fully composted will do 1 of 2 things
1. Kill your plants
2. Substantially reduce yields

I have tested ground coffee 'tea' and also solid on the soil and also mixed with soil and it does not produce good results unless completely composted as part of a composted soil mix....and even then questionable.

Coffee grinds mixed with soil will produce lower yields in all crops than the equivalent soil without coffee grinds...

[bobix419]

Bluey that's a valuable info, thank you. I don't have access to more specialized nutrients, so I was happy to use ground coffee. Guess I'll rinse the soil then.

Options I'm still willing to use are
– ground dried banana peels
– egg shells
– liquid artificial fertilizer for green plants with NPK ratio 10/2/5 – for veg stage (I got 2 more plants in veg)
– same but with NPK 5/2/5 – for flower (for the plant in question here)
Hope that's alright

[Bluey]

I have only ever grown in soil outdoors, never under lights. I suggest a conservative approach starting nutes. I'm no expert but did supplement my soil with a seaweed extract every week or 2. I'm not suggesting that. Try the above advice

[SoOrbudgal]

What maybe good for certain veggie plants is not always good for marijuana needs.

[Bluey]

Coffee grinds are no good for anything in the garden...oh. I forgot they can assist as a snail barrier when broken up and sprinkled on top of the soil. Snails hate the grinds..unfortunately so do plants

[AGH]

Snails also get the jitters from even the smallest amount of caffeine. Imagine a jittery snail crawling along a rock...so it's really the caffeine that they're avoiding which is why decaf coffee grounds don't work as snail barriers.

[AGH]

With lights like you have, it's not likely light burn.

Problems can often manifest when you flip to flower. You don't mention if they're autoflowers or photoperiods. If they're autoflowers, those can be finnicky in general. If they're photoperiod, issues often present themselves when they're flipped to flower. That includes their need for different nutrients. For example, in veg, they need lots of nitrogen since that aids in vegetative growth of leaves and stems. In flower, they need more phosphorous and potassium to help make healthy roots and fatty buds.

Good lights are essential. Afterall, it's actually light that is food for the plants, not the nutrients or amendments we put in the soil. When you have the opportunity, invest in a good grow light. There are some great articles on GWE that review different lights and there are some great ones in the budget category if that suits your needs better. Remember, when it comes to lighting, we're trying to replicate the sun.

The light schedule is concerning...you mentioned that they were in flowering for 2-3 weeks, but you have them on a veg light schedule. Unless they're autoflowers, not giving them at least 12 hours of dark is going to cause them to freak out, revert to veg, possibly herm, and overall hate their lives and do their best to make your life miserable as well. If they're autoflowers, ignore this paragraph.

Tall and skinny and untrimmed does matter. They're tall and skinny because they're searching for the light and yours aren't quite strong enough to keep them happy. Not too much you can do about this other than keep the light closer to the canopy. Untrimmed is exactly how they should stay until they're healthy and vigorous. If they bounce back and start growing strong, you can defoliate as necessary, but if they're tall and lanky, you probably won't need to do any defoliation.

Good luck!

[bobix419]

Thank you for detailed comment AGH !
The plant in question is autoflower.Yes, there is not too much light for now, I'm hoping to add some more soon.

[Bluey]

You do not need strong lights for autos, but that of course depends on your strategy.

If you are giving them light 24hrs that is continuous you only need half the light a plant would need if on a 12/12 schedule to obtain the same DLI....and that's what matters, the DLI. Look it up and understand what it means and why it is important to calculate what they need, then give that to them