Brown spots on many leaves. Spreading fast!

Hello everyone,

2nd year growing a high CBD strain and one of my 3 plants have brown spots on the leaves and its spreading fast. The other 2 plants only have a few of the brown spots. Looked on the forums and don’t see anything identical but maybe I’m using the wrong terms.

Strain: CBDurban
Method: Soil (Pro-Mix)
Vessels: 5 Gal Buckets
PH of Water, Solution, runoff (if Applicable): PH 6.0 after using vinegar on tap water to bring it down
PPM/TDS or EC of nutrient solution if applicable: Not sure
Indoor or Outdoor: Outdoor
Light system:Sun
Temps; Day, Night: Day about 23 Celcius, night 12-15 Celcius
Humidity; Day, Night: Unsure
Ventilation system; Yes, No, Size: Wind
AC, Humidifier, De-humidifier,: NA
Co2: Nature
Ferts: ProMix Premium Organic Flower Boost 12-28-12
Size: Plants are in 4th or 5th week flowering, I topped them at about 5 feet tall.

Also of note, I have a bunch of tomato plants close that look like they have Leaf Septoria, but I can’t be sure of that one either. I thought maybe I could try some CalMag, but wanted your thoughts before giving that a try.

Thanks in advance

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Welcome @cbd4me!
This is a great group that will help you as much as possible. There are no stupid questions, and nobody is going to make you feel like a loser. Usually brown spots are from a calcium deficiency. But your plant almost looks like somethings been eating on it. I am going to tag a couple of more experienced growers to see what they think. I do not think this looks serious. To tag someone just do an “@” in front of their name, like @patchman. @Covertgrower and @Hellraiser could you assist this grower with their brown spot problem? Thanks!!
Good luck with your grow. Tag me if you need anything and good luck with your grow!! Here’s a chart on different nutrient excesses and deficiencies.


Is this in its own container? Check run off to verify it’s the same coming out. Or close. Cal-mag (mostly calcium) is definitely looking like that, it’s in the beginning stages.

You want the run off to be close to 5.8-6.0.


Thank you patchman, Seems like a great community. If its something eating it, it would have to be at night. I rarely see any bugs on these. The brown spots also are never all the way through.

I forgot to mention that I do have some lower leaves yellowing and as well leaves in the centre of the plants. I read that can happen when flowering starts so I really didn’t think twice about it.

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Thats a good idea Covertgrower to check the run off. I will do that tomorrow to see. And yes its in its own container.

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I found the worst leaf on the plant to give a better idea of how bad its getting.


@Covertgrower Just checked the run off. Going in it was 6.0. Coming out its 7.0. Should I drop the water down even further? Its soil.

I definitely would. Nitrogen is the first to be locked out. Flush would be good too.


@Covertgrower what PH should I put my water at after the flush?

This will will give a good indication of what the ph is all through the medium.

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I got the run off to be 6.2 yesterday. Today every leaf looks like the worst one above. So close and I’m not sure its going to make it.

Plant isn’t looking the greatest. Its being taken over by whatever the issue is. Every leaf is now like the worst one above. Any other thoughts on what it could possibly be? Anyone ever seen a disease that looks like this before? @patchman? @Hellraiser?

Appears to be a calcium deficiency, but being outdoor I wouldn’t rule out pests either, specially if happening to other plants as well. I’d treat for both, calmag and Capt Jacks Deadbug.

Thanks, already started with the calmag and will try to find some Capt Jacks Deadbug in Canada.

One other thought I had…the plants are in 5 Gal containers and the temperature at night has been going down to 5-6 degrees Celsius (43F) at night a couple times in the last 2 weeks. Could that have caused it directly to the leaves or could it have caused issues because the root temperature has been a lot lower than it should be? In general temp at night has been about 53f

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Mr cbd-
43 degrees is a little cool for some marijuana plants. You may need a warming pad or heater. I don’t think the brown spots are are weather related if that is what you are asking. You should start to see some improvement with the cal-mag on board. The key will be to look at the new growth. If it looks good then you are gling in the right direction. @Hellraiser and @Covertgrower can advise you a lot better than me. Good luck, and remember, these are very resilient plants!


Yeah 43F can be a problem and start causing deficiencies as well as the roots can’t uptake certain nutrients at that temp.

I have created a warming device for the roots outside for the next 3 weeks until flowering is done.

I’ve put the plants in an additional 5 gallon bucket without any drainage holes, then placed that into a large rubbermaid tote. Going to fill that with water and use an old aquarium heater and pump to keep the temperature around the root zone about 22-23 degrees Cel (73F). I’ve cut a hole in the lid of the tote that fits the 5 gallon bucket exactly and I will wrap everything in a comforter to insulate it a bit so the hydro doesn’t cost me a fortune.

I can’t do much about the temperature for the rest of the plant unless I build a greenhouse and that isn’t going to happen at this stage.

I’m hoping everything (PH adjustment, calmag, root zone temp increase) combined will have the plants bounce back for the last 3 weeks.

If its going to be getting that cold or colder there is one other thing you can do. You gave a good plan to bring heat to your roots. You can doctor up a trash bag to pull over the plant at night. That way the plant is protected from frost and the bag may help to hold some heat in to help the plant. Just popped into my head.

@patchman Thanks for the suggestion. I will have to try it tonight because we could get a really early frost tonight. Either that or I’m going to bring them close to the house and create a tent with ladders and blankets to my roof for the plants. The heat from the house with the blankets over top should keep it warm enough.

The root heating system surprisingly worked like a charm. Kept it a steady 24degs cel (75f) all night and the outside temp went down to 5c (41f) I might lower the root heating system to 23c (73f) tonight. I don’t want them getting too hot.

I have 5 autos planted directly into the medium at the same time, 2 are flowering one is pre flower and the other two still vegging all 5 are on day 43. I found a bunch of leafs with some yellow spots don’t know exactly what it is. Could someone share some light on this. All the other leafs look fine.