Hello city. Couple questions for ya if you don't mind. My girls are 20 days from germination under a 400watt MH with temps between 75-80 during lights on and 68-72 lights off. 1. My humidity has been extremely low since the very beginning of my grow. When i say low i mean my RH reading literally says low! haha. I'm assuming it's not even able to register the airs moister level because there's next to non. Do you see any negative side effects to such a thing? 2. When running DWC you always have nutes in the water? Stupid question, I know, however i wanna make sure I'm doing it right. I've been maintaining a steady 300PPM for the following week and the ladies seem to be all over it. You only need to add back nutes when you notice you PPMs slowly starting to lower right?
I just had a similar discussion on another thread where the person was concerned about their humidity so they went and picked up a humidifier. They seemed to think that it helped. His concern was that he thought that it slowed the growth of his plants. However, my humidity level is about 20% which is pretty low, and i can't imagine my plants growing any faster. I have read where in flower, low humidity can actually increase trichome production. Humidifiers are pretty inexpensive, so the good thing is that you could pick one up and see if it makes things better. I almost always have nutes in my water. When I change the water out, I might not for a very short time (while filling, etc.) At the very end of the grow (the last week or two) most people seem to remove all the nutes. From what I have read, it can add harsh flavors. As far as adding back nutes, I think there can be many ways of doing it. I am using the Lucas formula. With it, you can add regular water until you have replaced your entire res, and then flush, refill, then start over. You can also get the ec/ppm of your nutes and add back an amount to keep it at your desired ppm. I keep mine around 1300. The formula is target/current-1*8ml*res gallons. So if I find that my ppm is 1000 and my res is 10gal, then I would add 24ml of GH Micro, and 48ml of GH Bloom.
This has got to be one of the most helpful responses to any of my posts. Thank you Sensi! Seriously man, that was awesome. I'll likely keep my system similar to yours, and i really like how you only change out your res once you've replenished the entire thing with top ups. That pretty handy, espectially considering I used distilled water and can't really afford to change up too often.
I am glad I could help you out. You might want to read this when you have time: Ask Lucas - Cannabis-World This is a thread by Lucas himself. It is long, but you don't have to read it all to get great information.
Plants breathe through tiny openings on the undersides of their leaves called stomata. Plants can (and do) open and close their stomata under certain conditions, for example if heat becomes excessive and causes a plant to start loosing more water than it can take up, the plant will close it's stomata to slow down the water loss. The ideal humidity range for healthy plant growth is 50% humidity, plus or minus 10%. Unfortunately, by closing the stomata and slowing evaporation the plant also has slowed down it's cooling mechanism. This causes heat to build up in the plant tissue, and in temperature too hot the plant actually cooks itself. It is important to understand the opening and closing of the stomata and how it, in turn, controls plant transpiration. Plant transpiration is how plants breath. Plants do not have lungs, however, so when molecules of gas and water vapor are released from the stomata they tend to just hang there in the absence of any breeze. That is why it is so important to have box fans or oscillating fans in a garden to circulate the air (in addition to exhaust fans). These fans are actually like the plant's lungs, and without them the plants would have no way of moving fresh CO2 molecules into contact with their plant tissue. The plants would slowly choke on their own transpired gasses and water vapor. As water evaporates from the surfaces of leaves, the surface tension of the water molecules tend to pull the next water molecule along behind it, up through the plant's veins. Water is pulled up through the plant stem, which is pulled from the plant's roots. This creates a negative water pressure in the root zone and allows the roots to suck moisture up out of the root zone like a straw. The process of water absorbing into the plant through the roots is known as osmosis Which brings me back to humidity. Water vapor is humidity. As a plant transpires, the humidity immediately surrounding the leaves will become saturated with water vapor. Now, the entire plant transpiration cycle is controlled by evaporation. When gasses surrounding a leaf become saturated with water vapor (100% humidity), there is no place for the next molecule of water vapor to evaporate to. The end result is that water vapor is not evaporating, so water is not being drawn up from the root zone...and neither are any nutrients. If nutrients are not being taken up, than developing fruits are not getting the food they need to be healthy. This is exactly why high humidity will cause blossom end rot in fruiting tomatoes just like a Calcium deficiency. It is another reason why it is so important to keep box fans and oscillating fans in the garden area to keep the air circulating. So, evaporation controls plant transpiration. High temperatures and low humidity therefor both cause fast transpiration. Fast transpiration means your plants will be taking up and using lots of water (and nutrients). This is fine, unless you were feeding your plants strong to begin with. Your plants can only handle so much fertilizer within a specific period of time. So if you now have warm temperatures, low humidity, and fast transpiration rates you may find your plants are using a little too much fertilizer a little too quickly. Leaf tip burn is usually a sign of this. Under these circumstances you can feed your plants with a weaker nutrient solution. Determining when to change res in veg is simple. Lets say it's a 10 gal res. Everyday the plants use 1 gal. In 10 days you will use 10 gallons thus. change res every 10 days. Simple. Hope it helps. ~HD
I have bits of this information in different places. However it is very nice to see the relationship between humidity, temperature, and nutrient uptake all in one place. Nice work, it is much appreciated. The information on the res change is just icing on the cake. I wonder if anyone else wishes they would have paid more attention in biology? Isn't life funny? One day you are bored to death listening to a lecture on plant physiology, then some time later you are trying to find the best way to grow trees in your basement, lol. This does leave me with two additional questions about the res change, if you don't mind. Would you do anything different for flower, and if so, why? Also, can you tell me what "happens" to the water that is fixed by a res change? Is it simply to reduce the likelihood of algae growth, or something else?
Well there you have it! haha. Thanks for the useful info. I've read Jorge Cervantes Growers Bible and remember reading a lot about stomata and how they play such a huge role with the plants well being. I think I'm going to head out and pick myself up a little humidifier. I Don't have a whole lot of room to work with so I'm hoping I can find something that will work with my space restraints. If I'm able to find a small enough unit should i run it 24 hours or would you recommend just letting it run during the light hours. During this time the warmth from the light will dry out any settled water and ensure mold and mildew are kept at bay. Also what are your views on spraying foliage during veg? I know it's a complete no no during flower but what about giving the leaves a light mist once in the morning?
Change out the res in flowering every 7 days. This ensures adequate nutrients available for the heavy growth needed. Also, wards off issues that may arise in the water it's self like algae or bacteria. I'm sorry but I don't understand the second question. ~HD
I maintain constant humidy levels in my rooms. 70% after a transplant then slowly ween down to 50% over two weeks. Late flowering I drop it to as low as 30% depending on how well they are growing. Lights off usually is when humidity wants to spike up. I go slightly lower at night to ward off moisture build up and stay around 45%. Get a digital dehumidifier so the machine can maintain the setting you choose. I prefer mechanical over digital. I hook them into a humidity monitoring device that has day/night settings. The key is to have one that auto-starts if you go the same route as me. I also install a bulk head union to the collection tray so I never have to worry about it filling up and stopping. I foliar during both veg and flower (not late flower stop after week 5). I like to use penetrator and 1/4 strength nutes with b-1 through out day to ward off deficiencies. I also use pure water (nutes, pure, nutes, pure) to help clean leafs. Stomata's don't work if they are clogged or dirty. Adding Azospirillum Brasilense to the foliar mix will help the plants perform nitrogen fixing. It creates a symbiotic relationship on leaf surface allowing plants to absorb nitrogen from the atmosphere like in nature. If using AB keep pH around 6.4 regardless of what pH is in root zone. This was taught to me by a Nobel Peace Prize Winner. The same group of scientist that discovered pH many moons ago.