Why do people cut back on feedings at night with hydro?

Discussion in 'Hydroponics / Aeroponics' started by Larry3215, May 26, 2018.


    Larry3215 Well-Known Member

    One of the earliest comments I got when I decided to use an auto siphon in my hydro setup was that I would be feeding/flooding too often - especially at night.

    It was suggested that the plants dont feed as much, or maybe not at all, during the night, so all you needed to do was keep the roots from drying out.

    However, I have been monitoring my rez water levels since I started this grow and just finished another day/night cycle with even closer checking. It turns out my plants drink almost exactly the same amount lights ON and lights OFF. As close as I can measure easily, they drank 1 gal during 12 hrs of lights ON and 1 gal during 12 hrs of lights OFF.

    I have three clones in a small tent running E/F. NFT, and Meniscus Membrane techniques. The auto siphon Im using in the E/F tote cycles the water about every 12-15 minutes or so 24/7. The other two totes also get the same flow rate 24/7.


    Someone on another forum posted some night time pics of their Ebb/Flood setup and the plants looked really droopy to me. Like they were very thirsty. My plants dont droop at night enough to notice. That made me think that it might be doing more harm than good to stop/reduce feedings at night.

    So, am I missing something? is there another reason to not feed or reduce feeding at night in hydro?

    eyderbuddy Well-Known Member

    Never heard of such thing. I suppose there's less respiration because they're not photosynthesizing, but nevertheless they're still alive and feeding...

    Larry3215 Well-Known Member

    Im surprised you havent run across that. Virtually every E/F grow I have seen, they reduce or even eliminate feedings at night. There are very few who feed the same 24/7.

    From my observations, there is no significant difference between day and night water usage.

    Maybe they do respire less at night, but they must be making up for it by drinking more?

    coreywebster Well-Known Member

    Depends on the set up, I used to run flood and drain pods with clay pebbles. I don't remember the amount of times day and night but it was a few less lights off. The only reason being the heat is lower and there is no radiant heat to dry out the medium. Last thing you want is dry roots.

    ttystikk Well-Known Member

    What is your temps and RH like overnight vs during the light cycle? If they're close then it's no wonder the plants keep drinking.

    PetFlora Well-Known Member

    I cut back from every hour to 4 hours

    Xs121 Well-Known Member

    Plants use water regardless of lights on or off. If the water potential difference during day/night remain or close to constant then the amount of water a plant uses is pretty much the same. Plants will continue to transpire through the night due to osmotic pressure (has nothing to do with photosynthesis). Wilting leaves at night is a sign that leaves are losing turgor pressure (plant doesn't sleep),

    I been saying this for a long time...that if you can maintain turgor pressure throughout (on and off), your plant will be more healthy, better growth, and better yield.

    But what do I know...when people insists that plant sleeps at night. :bigjoint:

    adower Well-Known Member

    I feed every two hours no matter day or night. However, I use hydroton only and net pots.

    Keesje Well-Known Member

    Could you explain this a bit more, please?

    Xs121 Well-Known Member

    Turgor pressure refers to the pressure inside the plant cells. When there is water inside the cell, the cell expands and stretch. Continous expansion and stretching of the cells wall promotes rapid plant growth.

    In nature, RH fluctuates between night and day. When the temperature drops (night), RH rises. Depending on RH at night, water potential difference between plant and environment reaches an equilibrium. Osmotic pressure (water potential difference) goes down, water movement inside the plant slows down almost to a stop. Cells start to lose their water (water is not moving) and the cells start to shrink and the entire leaves start to wilt or droop. And people assume that the plant is sleeping o_O

    But we grow indoor, we control our environment, if you can maintain your temperature and humidity then in essence you control the water movement within your plant. So even at night (lights off), if you have the same temp and humidity as during lights on (or close enough), water movement continues due to osmotic pressure therefore your plant cells hardly shrink at all.

    Larry3215 Well-Known Member

    I can verify that. I have read reports form several people that their plants droop at night, but mine do not droop at all as far as I can see. My small tent stays in pretty much the same temp range lights on or off. I have a heater that comes on when the temps drop and an exhaust fan that turns on when the heat gets too hi. RH might change some, but I dont log that so I cant say for sure. Ive taken pics during the middle of lights on and off and can see no significant difference.

    Keesje Well-Known Member

    Very interesting.
    3 questions.
    1) A lot of people have a lights-on temperature of 27 to 29 degrees Celsius (80 tot 84 degrees Fahrenheit)
    And during lights out a temperature of 20 to 24 degrees Celsius (68 tot 76 degrees Fahrenheit)
    Do you suggest that keeping your temperatures around for example 28 degrees (82/83 degrees Fahrenheit) both during lights-on and lights-off would be better?
    2) As you say that plants don't sleep, what is then the purpose of lights off?
    3) Did you ever do a saide by side test with Room A with a lower lights-off temperature and Room B with the same temperature during lights on and lights off?

    ttystikk Well-Known Member

    From an old friend and agriculture professor; plants grow just fine in the dark as long as their needs are met.
    Michael Huntherz and smokebros like this.

    Xs121 Well-Known Member

    Ideally yes. In some areas, growers have to use ac to cool their grow room during lights on, so during lights off their temp is pretty much at the same level 24/7. But if your are area is predominantly cold then you might have to use heater to up your temp at lights off.

    In a nutshell, without going into the nitty gritty of plant function. During the day, this is the time where plants gather their foods and for storing excess foods. Also, this is the time plant focusses its energy in acquiring food. At night time (which is actually grow time), this is the time where plants process and consume those stored foods (glucose). Yeap, plants still eat at night. This is also the time when plant focusses its energy in maintaining its overall health and growth.

    No I did not, at the beginning, I automatically assumed that everybody knows this. Agriculture 101
    Larry3215 likes this.

    dstroy Well-Known Member

    I think that since they transpire less at night that you can reduce the duration of feedings safely, but not the frequency that is working for your system. Generally, humidity is higher at night because of lower temperatures, and unless your space is tightly controlled the humidity drifts up a bit at night. With a higher humidity and lower temps, the vpd is lower and plants transpire less, so they don’t need as much feeding time as they would with the lights on, but they still need it as often as they would if the lights were on. Even with humidity controlled to +-1% the vpd will be lower due to lower temps most of the time, which the casual observer would translate to less feeding at night is needed.

    Larry3215 Well-Known Member

    That seems logical to me, but then why do my plants drink exactly the same amount of water at night as during the day?

    It seems to me they would cut back on how much they drink on their own if they needed less, but they dont cut back at all as near as I can tell.

    I dont think its possible to over water in hydro is it? Why not let the plants decide how much they will drink instead of forcing them to do without? Or am I missing something?

    My night time temps stay at least in the low-mid 70's with the heater on, and dont go over the mid to hi 70's with the lights on - unless its a really hot day.

    dstroy Well-Known Member

    It sounds like your environment is really tight, so in your case the vpd would be pretty similar during the day and night, which would mean that you would feed the same amount and duration day or night.

    The thing that you are missing is vpd, when it changes the feeding requirements can change. My vpd isn’t the same as your vpd, my feeding requirements are different from yours. You’ve just got to remember that everyone’s environment is different, so their vpd will be different, and can be change with lights on and off.

    Larry3215 Well-Known Member

    I understand the part about different environments, but it still seems to me you are (at least potentially) starving your plants by reducing feedings at night - unless you know in advance how much they are going to drink.

    What about guys who do DWC/RDWC, etc, where the plants always have the same amount of water/nutes 24/7? Im sure their environments vary as much as other peoples do. Why are those DWC plants not suffering from over watering?

    I guess what Im trying to say is, I see at least potential downsides to not watering at night, but what is the up-side to reducing watering at night?

    Please dont misunderstand me - Im not trying to pick a fight. Im a newbie trying to understand the logic behind why things are done the way they are.

    I just dont understand the mechanism/reasoning that would make you not feed at night in E/F when you feed 24/7 in other types of hydro - with no ill effects.
    Xs121 likes this.

    Xs121 Well-Known Member

    Water is not the culprit in the so called over-watering, its the lack of oxygen to the roots that kills the plant. When the root is fully submerged in the water for a long time then eventually it will deprive the root of oxygen. In the case of DWC, it solves this problem by aerating the water (dissolved oxygen), so even if the root is submerged or sitting in the water it still able to capture oxygen from the water.

    Hydro growers (DWC) with fluctuating environmental temp and humidity will experience different amount of feeding or water uptake by the plant as compared to the same type of growers with steady temp and humidity.
    coreywebster likes this.

    dstroy Well-Known Member

    DWC/RDWC the roots sit in water all the time, so food is constantly available. And they have an ample supply of oxygen at the roots.

    Ebb and flow you have to contend with not only feeding the plants, but with how saturated the medium is as well. The feed duration would be different at night when compared to day because the medium would not dry out as much as it needed to in some environments, oxygen in the root zone gets depleted and then they droop from overwatering.

    Some people who drip feed do it for not as long at night for the same reason, but they still feed as often as they would during the day, just less water each time.

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