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Plant Moisture Stress - Symptoms and Solutions

Smokin Moose

Fallen Cannabis Warrior
Quite often I hear groans from folks having leaf problems - ?Help, my leaves are cupping and the leaf edges are turning brown!?, or, ?My plant's leaf tips are curling down and turning black ....what's wrong?? Unless insect damage has occurred or the plant is suffering from a severe case of calcium deficiency, the plant is trying to tell you that it is water stressed. It's hard to tell *exactly* what the culprit is, and unfortunately the ?solution? the grower chooses many times is not the right one. A mis-diagnosis only serves to make matters worse by promoting further decline. I?ll try to cover some of the more common causes that can induce these common symptoms and try to offer a few simple solutions. The ultimate and correct solution is in the hands of the grower.

1. Over-fertilizing - the most common cause of leaf cupping aka leaf margin rolling, leaf margin burn, and leaf tip curl/burn is the overzealous use of too much plant food in relationship to factors such as plant vigor and rate of growth. The first unit of a plant to show moisture stress is the leaf at its margins and/or tips, reflected by margin rolling (cupping) or burning. A hard, crispy feel to the leaf frequently occurs as well, as opposed to a soft and cool feel of a happy leaf. When you have a high concentration of salts in solution (or in the root medium) compared to lower salinity levels found in the plant?s tissue, water is actually drawn out of the plant across the root gradient in order to fix the ppm imbalance. IOW, this is a natural, osmotic response that serves to equalize salinity levels on both sides of the root?s epidermal gradient. Back off on the amount and/or frequency of plant food. Too much plant food can also burn the roots, especially the sensitive root tips, which then creates another set of problems. Note for the bio folks - as soil dries, the concentration of the remaining salts rises further exacerbating the problem.

2. High Heat - the plant is losing water via it?s leaves faster than what can be replaced by the root system. The leaf responds by leaf margin cupping or rolling (up or down) in order to conserve moisture. A good example is reflected by the appearance of broad-bladed turf grass on a hot summer day, high noon, with low soil moisture levels - the leaf blade will roll in and the grass will take on a dull, greyish-green appearance. Upon sunrise when moisture levels have returned to normal, the leaf blade will be flat. Lower the heat and concentrate on developing a large, robust root system by practicing sound plant culture. An efficient and effective root system will go a long way to prevent heat induced leaf dessication and leaf margin curling. One short episode of high heat is enough to permanently disable or destroy leaf tissue and cause a general decline in the leaves affected, which often occurs to leaves found at the top of the plant located near HID lamps. The damaged leaf (usually) does not fully recover, no matter what you do. Bummer in the summer. One can only look to new growth for indications that the problem has been corrected.

3. High Light - yes, it?s true, you can give our faves too much light. Cannabis does not receive full sun from sunrise to sunset in its natural state. It is shaded or given reduced light levels because of adjacent plant material, cloudy conditions, rain, dust, twilight periods of early morning and late afternoon, and light intensity changes caused by a change in the seasons. Too much light mainly serves to bleach out and destroy chlorophyll as opposed to causing leaf cupping, but it often goes hand-in-hand with high heat for indoor growers. Again, back off on the light and concentrate on developing/maintaining an efficient and robust root system.

4. Overwatering - this practice only serves to weaken the root system by depriving the roots of proper gas exchange. IOW, the roots are not getting enough oxygen which creates an anerobic condition causing root decline and root rot with the end result showing up as leaf stress, stunted growth, and in severe cases, death. Alot of times folks think the plant is not getting enough plant food (which it can't under such adverse conditions), they add more nutes for a "curative", and just add insult to injury.

5. Underwatering - not only is the plant now stressed due to a low supply of adequate moisture, but carbohydrate production has been greatly compromised (screwed up). Step up the watering frequency, and if need be, organic growers may need to water from the bottom up until moisture levels reach a norm throughout the medium. If the pot feels light to the lift - it?s time to water. Don?t wait until the soil pulls away from the sides of the pot or leaves droop before you water. And of course, leach once in a while to get rid of excess salts.

Happy gardening,

Author: Uncle Ben

Smoker Nick

New Member
:thanks:I had some one taking care of three of my girls then he tells me their not doing to good so i had him bring um back leafs were brown and cupping. Your advice here confirmed my thoughts about it and they are coming around not out of the water and into clear yet but they will be. So just like to say thanks for the advice and some solutions it was help full.


New Member
looks like u hit my problem right on the head.

im just gonna flush it this week incase its due to underwater or to much nutes. it shouldnt be light or heat because it did not occur last time (nothing has changed except no bugs this time). wish me luck:cheer:

Smoker Nick

New Member
:cheer:PhishyPhil. I wish you all the luck. Keep us posted on how their doing. Mine are doing better but I'm switching nutrients to fox farm don't like the chemical that they were on so hope fully they will thrive a gain :rollit::30:

Tyler Durden1

New Member
what might cause the actual white hairs to turn yellow and shrivel up. starts in the middle to lower regions of the plant and spreads across the table. kills the plants


New Member
I was looking all over on here for this bit of plant info & advice. I'm so glad you guys have a great forum to reference. For the Over-fertilizing I think I'm going to flush, then start again with the light nutrients. I was using 1/2 oz kelp & bloom (Old Age) and the plants were great. We then increased them to 1 oz, now I'm seeing the leaf issues as described.


fitzy monstar

New Member
hey noticed that the first two leaves that popped out of seeds have yellow spots and was wondering if this is due to the fact the first time under the lights they were to close as the plant itself is still growing good green leaves the p.h is 6.5 and the temp is at 80f any ideas???
Got some seedlings problems. Germinated in coconut seed starter fiber. Pop up ok but after 1st set of leaves seedlings are stalling and browning out a bit. Some seem to have stem rot( Possible over watering).Seems like there is something else going on besides stem rot. Using 600 watt full spectrum led about 2 foot above. In closet with reflective mylar on walls, good air flow, decent temperature, light 18 0n 6 off. My first post here so any info would help. Got some photos but not sure how to post just yet since I am new here. Thanks in advance.
spy smasherr
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