Leaves drying from the margins

[Kevin L]

Hi,

my plants are showing signs of stress, with some leaves drying from the margins and turning yellow. It is affecting mostly old leaves, but now it seems to be spreading to smaller/younger leaves too.

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• Kevin L
• Aug 4, 2018

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• Kevin L
• Aug 4, 2018

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• Kevin L
• Aug 4, 2018

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• Kevin L
• Aug 4, 2018

They are growing outdoors in hot weather. The soil is a mix of 60% generic potting soil, 35% of my own compost (made from organic kitchen scraps), 4% aged fine horse manure, 1% wood ash and perlite.
I water them with rain water when available, but lately I started using tap water.

Comparing with the images posted in the "Cannabis Plant and Pest Problem Solver" thread it could be a potassium deficiency, but it's difficult to tell.

Any help you can provide is very much appreciated.
Thank you very much.

 

[Blew Hiller]

Not looking good, especially since it is still in veg. How big is your pot? Hot weather shouldn't be an issue if they have enough soil and root structure...I routinely have plants in 95-100F. Have you grown in this soil mix before? If so, were there any issues? Lastly, what is the source of your tap water? If they were fine and this suddenly happened I would look at something that changed. If they are getting rootnound or running out of soil nutrients it might be time to consider up potting .

 

[Kevin L]

I used this kind of soil last year and one plant died before flowering. I was spraying colloidal silver on a couple of her lower branches and I thought that was the reason she had died. But now I start to suspect it has something to do with the soil.
Tap water is plain drinking water which I use for other plants too.
I up-potted them one month ago, in early July. Plants were fine until 10 days ago when I started to notice the first affected leaves. Pots are about 35 liters. I used these pots in the past with no issues. I'd love to use larger pots but I need to move them once a month and larger pots become too heavy for my back.

 

[Blew Hiller]

Hmmmm....someting needs to change...they are not looking good. I suspect more than P deficiency. Maybe someone else can add some ideas....

 

[LordofDanknis]

Have you done a flush yet?

This definitely looks like a K deficiency to me, but it's often caused by high salinity or "toxic salt buildup," which is super common in soil. I've had this problem, & doing a good flush, followed by a light feeding (with the proper PH) put her right back on track. If you have done the flush (recently) I'd ask if you are adding micro nutes (Cal, Mag, Mn, Zn, & Fe) because if those are deficient, it will also lock-out any K you have. (The heat doesn't help, so if you can get your temps down, the growth *rate* will return to optimal.)

Also, you shouldn't have to do a foliar spray, & if you do, I'd do it right before lights off. They benefit much more from added CO2, in my experience.

Hope this helps. Keep us posted!

 

[Kevin L]

Thanks all for your replies and encouragement.

I have no control over temperature as the plants are growing outdoors.

I haven't done any flush yet. I am not familiar with fertilizers and, if my understanding is correct, after a flush one needs to re-introduce nutrients to the soil with some form of fertilizer. I'd rather not go down that route as I have no experience and I fear I could mess things up even more.

Before noticing this issue with the leaves I watered the plants with some kelp (Ascophyllum nodosum) to add micro-nutrients, about 3 times in the space of 10 days.

In the attempt to supply some potassium to the plants, 3 days ago I put 3 banana peels in a blender and diluted the result in 6 Lt of water that I used to water the plants. I read that banana peels are an excellent natural source of K and they do not raise the PH like wood ash does. I am waiting to see the result, if any.

 

[Blew Hiller]

Before noticing this issue with the leaves I watered the plants with some kelp (Ascophyllum nodosum) to add micro-nutrients, about 3 times in the space of 10 days.

That was def worth mentioning in the first post...most likely you fried the plants with too many nutrients and now you are chasing a mis-diagnosis with more things...sometimes you just have to leave the plant do its thing, Live and learn....

 

[Kevin L]

Kelp only contains micro-nutrients and it's an algae, not a synthetic fertilizer. I doubt that it could fry the plants on its own and lock out other nutrients, since I used very little and diluted in many liters of water.

 

[bluter]

do you have a soil ph meter ? there is a good chart on this site showing which nutirents are available at different ph levels. when a defeciency occurs you can often check ph, which will indicate what is being locked out. alternately if your ph is fine you can rule out certain problems.

 

[Chris Scorpio]

I'd check the tap water pH as well, it could be way off, as well as the ppm of the water

For sure showing some nute issues

 

[Kevin L]

I don't have a soil ph meter but, as things stand now, I better get one quickly, thanks for asking. Do you have any to recommend? This one seems to be a decent choice, but I am no expert. I will also get a water ph meter and test my tap water. I shall post the results here as soon as I manage to test.

SONKIR Soil pH Meter, MS02 3-in-1 Soil Moisture/Light/pH Tester

 

[bluter]

that meter should do the trick. there are cheap soil testing kits you can buy to confirm the results as well. the meters can be off a fair bit sometime.

 

[Kevin L]

I managed to get hold of a digital PH pen meter, which I calibrated.
My tap water is 7.19.
I then diluted soil samples in distilled water.
The plant which is in worst shape gave a shocking 8.4.
The other one has 7.4.
A sample of my own compost gave 7.28.
What is the ideal PH? I guess nutrient uptake for the plant that has 8.4 is severely compromised.
Is there a way I can save these plants, maybe by re-potting them into acidic potting soil? They are still in veg state.
Thanks again for your help and advice.

 

[Chris Scorpio]

Id look at re potting for sure, without yer mix

Get some real Cannabis nutes, and move forward positive

Yer nutes and water pH should be around 6-6.5 in soil