Plant Moisture Stress - Symptoms and Solutions

Uncle Ben said:

PLANT MOISTURE STRESS - symptoms and solutions (revised Jan. 12, 2009)

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 size, 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. Sometimes copper colored necrotic spots show in the leaf also. 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 and hairs, which then creates another set of problems such as nutrient deficiencies. A note for the bio folks - as soil dries, the concentration of the remaining salts rises further exacerbating the problem. Leach (flush) your pots once in a while to get rid of excess salts.

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 by supplying sufficient moisture for good plant health. One short episode of high heat is enough to permanently 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 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, debris and dust collection on the leaf surface, 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. Keep in mind that all but equatorial material receive less light during flowering than during the vegetative stage.

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. <gasp!> 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 soak the pot from the bottom up until moisture levels reach an even consistency throughout the medium especially with mixes that are heavy in peat. If severe, a little surfactant (liquid Ivory dish soap) added to the drench will help return the organics back to a normal moisture retentive state. 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.

Happy gardening,
Uncle Ben

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Erk said:

Soil: half FF ocean forest, half FF happy frog. Been giving FF Tiger Bloom 2-8-4 for 1 week, 3 teaspoons per gallon + 1 gallon of water in addition. Split between 4 plants. Feed only once a week. Followed by fresh water 2-3 days later. then Molasses 2-3 days later. then repeat. 600 watt light, fully vented, two fans on them. temps are 80 degrees with humidity now at 45-50%. humidity was at 65-75% entire time prior.

can you help?
thanks

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POLICEMATRIX said:

OK these have been in these 19 litre pots for just over 1 month and have been in 12/12 for about 5 days ,the are in plagron royalty mix which is said to have all the nutes needed through the whole life cycle , ok the last 3 days the temps went quite high so i gave plants more water than normal to try and compensate for the high temps , the last two days it has dropped to nice levels like 18 -22 c day and 12- 15 c at night , now 1 plant is the same growing normal as before but the other has wilting leaves , i have had leaves like this before but they wilted a lot more and a quick water fixed them these dont seem to wilt as much but defiantly are a bit, I am considering flushing or letting the soil dry out but i dont know what to do , i have tried watering this seems to have some slight improvement but the next day again they wilted, also i have noticed some low leaves have rust spots on them only a few and none on the top leaves , also i have about 4 leaf tips clawing under
this is how it looks now View attachment 1819309
this is how it did look about 5 days agoView attachment 1819310
now i know there isnt a great deal of difference but it is noticeable to me and i want to nip it in the bud (pardon the pun)
Like should i let it dry out abit or should i flush ,or am i overreacting =) thanks

ok more info about the soil
pH: 5,8 and 6,2
EC: 1.8 and 2.2
Plagron Royalty-mix contains a carefully selected combination of organic fertilizers which meet all the plant&#8217;s nutritional requirements throughout the complete cycle. These Plagron fertilizers are unique because they are only released exactly when the plant needs them.
ok says you should only add food after 6 weeks but i dont think lack of nutes is the problem from what i can ascertain it is too much fert or salts or too much water ,can plant really drown in these soils ?
heres some pics of the spots on lower leaves and the claw leaves View attachment 1819606 View attachment 1819607

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Uncle Ben said:

Stunting is usually related to a deficiency of N, IF, all things are in balance.

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Isisyogi said:

If you are in hydro and you are not supposed to feed seedlings anything, how to you increase N in order to increase vigor? My plants are a bit bigger than his, and I know they lack vigor from seed. I use RO, 18 ppm, 6.0 ph, sprout in either paper towel (no longer) or Root Shooters, place them under 2 T5, and I seem to get stretching and slow vigor. Happened with my first 2 rounds. Just germed 4 new in RS, haven't sprouted up yet, but I'd like to encourage vigor this round. I'm now using Dyna-gro 9-3-6 for veg, thanks to you. Would love your advice. Thanks.

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Isisyogi said:

If you are in hydro and you are not supposed to feed seedlings anything, how to you increase N in order to increase vigor?

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Uncle Ben said:

Huh? Plants need a complete elemental profile from start to finish. The 9-3-6 will work great, just gear the amount with the requirements of the plant which is determined by such factors as size (bulk) and vigor. Seedlings need food or they will die.

Tommycheese, time to replant and get a book on indoor plant culture.

UB

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Isisyogi said:

I was asking how you are supposed to encourage vigor in seedlings (by way of N) when you are not supposed to give them nutes until after several weeks?

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