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More light vs cooler temps

Posted by sue_ct z6 CT (My Page) on
Sun, Apr 7, 13 at 12:22

The room I have my seedlings in has a south facing window and a West facing window. I have the blinds closed to keep the room cooler. I usually have to deal with somewhat leggy seedlings even with the shop lights. I can increase the amount of light they get by opening the blinds on both windows, but it is a small room and this increases the temperature in there significantly. I keep the house at 68 degrees, but it does get warmer in there even with the blinds closed. Which is more important for healthy seedlings, more light or cooler temps? I suppose I could add ac into one south facing window but I hate the added electrical costs for seedlings. I could also open one window an inch away from the seedlings and keep the door closed, but I wouldn't want to do that when I am away at work day. What are ideal temps for seedlings?

This post was edited by sue_ct on Sun, Apr 7, 13 at 13:46


Follow-Up Postings:

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RE: More light vs cooler temps

Sue, this isn't exactly what you asked, but how many hours do you leave your lights on above the seedlings? How close are the lights? Unless the room is significantly warmer than 68°, I should think that the amount of light they're getting is more important than temps. But I'll be interested in hearing the responses you get. I usually leave the lights on about 17 hours per day; not sure whether that's optimal or not.


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RE: More light vs cooler temps

The ideal solution, but may not be possible, is to provide more fluorescent lights that won't add much heat and keep the room cooler.

It is balance that can be difficult to achieve but well worth the effort. With sunlight the ratio between lumens of light vs. heat degrees added is much higher than that between fluorescent light and degrees of heat. So you want to shoot for maximum lumens without added heat to try to keep the ambient air temp at 65 or a bit less if possible.

Ambient air temps can contribute just as much to leggy seedlings as insufficient light.

Dave


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RE: More light vs cooler temps

The more light the better. I can't think you could ever have too much light with fluorescent. Cool temps always helps keep things from getting leggy but still if you don't have enough light they will stretch. I've always have read the less light the cooler the temps but that will only help to an extent. Can you crack a window open? The shelves on my light stand are 24x48 and I have 6 four ft tubes on each one and still wish I could have more. I'm not using it now because there's no electricity now in the shed it's in, but when it is set up I won't even have any heat in there. Just the heat from the lights. In LA you can get away with that unless it gets really cold for a long time.


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RE: More light vs cooler temps

  • Posted by bets z6A ID (My Page) on
    Sun, Apr 7, 13 at 17:55

Sue,

You said "I usually have to deal with somewhat leggy seedlings even with the shop lights." Is that with or without the fan you mentioned in your other post? If you have not used a fan previously, I think you will find that using one helps keep the seedlings shorter and they will have stockier stems. That is the reason I rotate my trays when I water, because the ones furtherest from the fan tend to be less stocky.

Betsy <--- who is wondering if putting a celing fan in the room with my seedlings would help (that ceiling is pretty low.)


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RE: More light vs cooler temps

Ceiling fans!

[Okay, this is off-topic and not related to tomato seedlings.]

For years I've had a plan to grow tomatoes -- not seedlings but older plants and hopefully fruit! -- indoors in the winter. Yes, I am crazy. Yes, it probably won't work. Yes, I will eventually get around to trying it anyway.

I had never grown tomatoes in containers and wasn't sure about sizes (both container size and plant size), so last summer I experimented with dwarf and small tomatoes in containers outdoors. Other than the Late Blight, it was a positive experience.

The walk-out basement is partially heated and relatively warm, but might not be warm enough for the tomatoes to bear fruit. The house was sited and designed to keep the summer sun out (we may be in the mountains, but this is still The South). So the only south window is under the carport, the west windows are few and under deep eaves, and the east windows are teeny-tiny (definitely one-plant windows).

Maybe this year I'll get around to growing dwarf tomatoes in those east bedroom windows. And they'd surely be happier and healthier with the ceiling fans turned on occasionally....


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RE: More light vs cooler temps

I have 3 four foot shop lights each with a single light, on chains from the ceiling. They are touching, so there is no space not covered by the light. This is a craft/sewing room that I put a counter top into for a work space, and the seedlings are on the counter with the shop lights hanging above them. I have the lights about 3-4 inches above the seedlings. For the past 2 days I have had lights on 24 hours because I forgot to shut them off, lol. Usually they go on at about 5:30-6 am and off about 10-11pm. That is on work days. Days off they may get an hour or so less. The counter they are on is right in front of a South facing window and the blinds are closed. Then there is a west facing window, about 6 feet away from them, also with blinds closed. The blinds do not completely keep out the heat. I may invest in more insulated custom shades soon, but that won't help right now. There are no curtains/drapes over the shades. I don't know if it is possible to provide more artificial light than that easily and inexpensively. I left the shades open today to see, which was mostly cloudy but some sun, temps 58-60 outside. I put a thermometer in room and it was 76. Obviously when the sun shines and temps go up, the room temp would easily be in the 80's. So I guess I know now I really have to keep the blinds down.

I have used a fan before, but didn't start this early and I think last year just used the ceiling fan, which doesn't help as much because it is above the lights (obviously) and doesn't even move the seedling underneath them.

An open window is only an option when I am home, but yes, I could do it then. Once temps outside get into the 70s or above that won't help, either. I could invest in an extra small AC for the window away from the seedlings, I have been wanting one for that room anyway. But I don't want to run it daily for 6-8 weeks just for seedlings. They would end up being some very expensive seedlings. :)

This post was edited by sue_ct on Sun, Apr 7, 13 at 21:03


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RE: More light vs cooler temps

Another thing I have done to lower the temp a bit not much though, is to reverse the photo period. Lights on at night when it is cooler and off during the day. Early in the year like right now nights are still cool so it helps a little. Of course here, cool nights don't last long. And like everyone, I use a fan too.


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RE: More light vs cooler temps

  • Posted by edie_h 5bNY (Finger Lakes) (My Page) on
    Mon, Apr 8, 13 at 18:57

Sue, can you lower the lights further? Or set the seedlings on something to raise them up? If you can get them 1" - 2" from the light instead of 3" - 4" that will help.

A timer that accepts a three prong plug will cost about $15, less if your hardware store has them on sale. You'll want the three-prong so you can plug a power strip into the timer, and run all the lights off one timer. And then you have one less thing to remember in the morning. :-)


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RE: More light vs cooler temps

First time, this year, I am leaving the lights on all the time. After three weeks they are doing great. Don't know how they will do in the long run. Another blogger said he had great results, so I am giving it a try. Anyone else try this?


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RE: More light vs cooler temps

When I used shop lights with 4-foot, 40 watt bulbs, I ran my lights 24-7 and kept them 1-2 inches above my seedlings. Growth was significantly better than when I had them on only 16 hours a day. My temperatures were probably close to 80, but I used a fan and they grew pretty well. Light is a lot more important than temperatures in my opinion. That's why I invested in a T5 light fixture.


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RE: More light vs cooler temps

I have 3 four foot shop lights each with a single light, on chains from the ceiling. They are touching, so there is no space not covered by the light. This is a craft/sewing room that I put a counter top into for a work space, and the seedlings are on the counter with the shop lights hanging above them. I have the lights about 3-4 inches above the seedlings.

Sorry I missed that before. 3 single tube fixtures isn't much light. Needs to be doubled at least for best results unless these are T5 bulbs. And 3-4" is hung too high.

Dave


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RE: More light vs cooler temps

Yep, 1-2" above the plants. And if I'm using T12s or T8s I don't worry if the plants touch the lights. The T5s run hot. Those I would worry about.

Leggy seedlings aren't the end of the world. Just plant them deep or trench them.


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RE: More light vs cooler temps

I would have to scrap the three single lights I have to buy double lights. Not sure it is worth it, but I might consider it for next year. As the plants grow they do sometimes touch the lights, esp. when they are growing fast. I haven't had any burn yet, but I like to keep them just a tiny bit above the plant. I plant deep during the first transplant and the leggyness is gone unless planting is delayed from the weather and then they can get a little leggy again. I then plant them deep at planting time. I will have to consider if it is worth replacing these lights that are only 1-2 yrs old right now.


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RE: More light vs cooler temps

Ooops, I was mistaken. I have 3 double lights over them, so 6 bulbs in all, 40 watts each. They are the larger cool bulbs, can't remember if they are T8, maybe? I will have to look another time if it is important, its bedtime. 5 am comes early. :)


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