Plants don't like my small veg cupboard? I don't know why?

[Spider Crab]

Hello all,

I have a small cupboard i am using for a veg cabinet.
I have a 110w PL-L fluro light and a computer fan to circulate air.

The only ventilation i have is a hole in the back of the cupboard to allow light and fan cords in, and, the gaps around the doors.

It isn't light proof but it doesn't have to be, no one sees it and i leave the lights on 24/7.

I thought the gaps around the doors would be enough ventilation, with the fan, but it is the only thing i can think of as being why the plants don't seem to like it?

I upgraded my desk fan to a slightly more powerful computer fan and the plants seemed to perk up and look brighter but then after a week started to lose some color and get some yellowing and blotches and just look unhappy.

Does anyone have any advice?

Thanks.

 

[Spider Crab]

Well, i'm going to make the hole for the cords a bit bigger and point the fan towards the hole rather than at the plants and see if that makes any difference.

 

[DoubleDDsNuggs]

the larger watt flouros produce a lot more heat than two of the equivelant wattage. Philips makes a daylight cfl bulb with 6500K and 800 lumens but only 13 watts. I grew in hydro with those. I had four Y outlets coming out of a 3-4 ft power strip with two bulbs on each outlet. didn't warm up much at all and had to heat the small tent with a heater next to the intake passive vent. each plant had two bulbs with lots of mylar for reflectivity. they could grow within a inch or two with no burning or bleaching. the other option is to get two fans. one for intake and one for exhaust. small cabinets will heat up quick! a grow tent is surprising cheap on Costco's website. I picked up a 4x8 for $300 and they had a 4x4 for $150. I love my tent!

 

[Spider Crab]

It's definitely not heat, it is a 2 x 55w fixture.

All i can think of is it must be not enough fresh air circulation, with the unusual symptoms i mentioned.

I have a larger tent, i might have to see if i can find a really small one.

More opinions are welcome.

Thanks.

 

[DoubleDDsNuggs]

how often are you watering and how big are your pots and what medium? sounds like it may be dampening off. I don't think its not enough air because the fan will pull air through every crack in the cupboard creating a negative pressure. air is important and a plant can survive just fine in a stagnant room. it just will grow very very slow if at all.

 

[RB56]

You're not getting any meaningful ventilation through those small openings with the fan inside the box like that. There's no pressure differential to either push or pull fresh air from outside the box into the box. You might want to cut a hole in the box and mount the fan over it. I'd probably exhaust the inside air through the hole so you aren't blowing directly onto the plants.

Your problem might also be that you have the fan blowing directly on the plants?

 

[Spider Crab]

Thanks for the help.

I have cut the hole in the back so that it is roughly the same size as the fan now, so there is a lot more ventilation.

This should be enough (i think) to at least let me know if that is all that is wrong.

 

[pappy masonjar]

Whats wrong with fans blowing directly on plants?

Ive always done that. Makes the branches strong.
Plants dont seem to mind.
Am I missing something?

 

[RB56]

Whats wrong with fans blowing directly on plants?

Ive always done that. Makes the branches strong.
Plants dont seem to mind.
Am I missing something?

I always did that too and thought the same. Then I changed things around so that one plant was hit by one fan continuously. Not violently but continuously. Took several weeks for me to really notice but that plant was pretty stunted compared to her twins. It turns out that too much airflow over the leaves messes with respiration. I don't remember the exact details but there are threads about it here.

I pointed all of the fans away from the plants so they never blow directly on the plants but move exactly the same amount of air around the room. None of the bad things that giving them breeze was supposed to prevent have happened and the plants are healthier without it. My biggest concern was that not having the leaves in frequent motion might cause them to spend too much time in contact with each other allowing nasty things to happen between them. Hasn't been a problem.

 

[hush]

It's definitely not heat, it is a 2 x 55w fixture.

That is your problem right there, friend. You have setup a cabinet under the false impression that your light doesn't put out any heat, and then you built your cabinet around this premise. Your problem is heat. I couldn't help but notice you didn't give us a temperature reading from inside the cab?

You have no airflow other than a circulating fan. So what you are doing is circulating hot air. I'm not sure how or why people ever got the impression that fluorescents don't put out heat, but they do. Lots of it. Plants can get closer to the tubes, because that heat is spread out over a 2-foot length instead of a point of source... but the heat from the exothermic reaction is still there, building up in a small space. So you are generating heat, and it has nowhere to go. You need to have an exhaust hole that blows hot air out of the cabinet, and it needs to be placed somewhere up toward the top of the growing space (because heat rises). You don't need to have fans blowing air in, but you do need to have holes where fresh air comes in to replace the heated air that's being blown out. The standard rule of thumb is your intake hole should equal about twice the size of your exhaust hole.

But that's your problem, man. I assure you. I've been growing in cabinets for going on 20 years now. I speak from experience.

 

[Spider Crab]

Thanks Hush.

I am having trouble accepting that it is simply heat, as the cupboard doesn't get hot at all, and plants grow outside in the heat very well....

However, circulating the warm dry air, does seem more plausible.

Either way, increasing the exhaust hole seems to be the answer.

I appreciate your input.

 

[RB56]

Really helpful to have a thermometer/hygrometer mounted near the canopy. I've got a bunch of Acurite digitals that show current temps and RH plus max and min values. Inexpensive. Accurate enough to show you when you're getting into trouble.

 

[Spider Crab]

I will have a look into it.

 

[gaiusmarius]

what materials is the cabinet made of? do you have any cheap plastic in there from china? there is a phenomenon called off gassing, you will not find much info, but for a while some grow tents were made of this plastic and no one could grow anything in there as it reacts with the lights and poisons the plants some how. probably not the problem, but just in case.

i have noticed vegging plants can live with very little air when under cfls so i doubt they would get those symptoms from that, specially if it's not hot in the cab. look for any pests or eggs very thoroughly with a microscope ideally.

 

[hush]

I am having trouble accepting that it is simply heat, as the cupboard doesn't get hot at all...However, circulating the warm dry air, does seem more plausible.

That's the same thing, but okay.

and plants grow outside in the heat very well....

Of course they do, they aren't confined to a small cabinet when they are outside. They are getting constant supply of fresh air.

Either way, increasing the exhaust hole seems to be the answer.

That, and actually turning that hole into an exhaust hole, by attaching an exhaust fan to it. Otherwise, it's just a hole you have cords going through.


By the way, what temperature is your thermometer reading in there?

 

[heatherlonglee]

It's to hot in the cabinet. Also you need to turn out the lights for about 4 hours a day. (My veg plants like lights off, a few hours a day) 110 watts will put off signifigant amount of heat. The on and off cycle will help with the heat problem, it may take 18-19 hours before the cabinet gets to a point that's to hot for the plant.

 

[gaiusmarius]

yeah light off phase helps the plants, they regenarate. 4 hours off time is the minimum i do with veg plants.

 

[pinkus]

too hot, closed off so likely low CO2 as well. Mount a fan to pull air out of the cab AT THE TOP!!!! heat rises...It wouldn't hurt to have an intake at the bottom either.

Good Luck

 

[Dropped Cat]

Wax on, wax off.

 

[Spider Crab]

I know i am asking for help, but i think the light hours/ need a rest thing is a myth.