Do I really need lights on potted up plants?

[ScottinAtlanta]

I have potted up 400 seedlings into their 8 ounce cups. Do I really need to put them under lights for the next phase? I have them in a south facing room with full windows, and they will get about 2-3 hours of good sunlight a day.

I know lights would accelerate growth somewhat, but are the lights essential for this phase?

[shelleybean]

I'm not sure why the size of the cup would be a factor at all? I give my seedlings a minimum of 8 hours of light a day to keep them from getting leggy. They stay under lights until they can get it outside in the real world. Thank goodness I don't have 400 of them to worry about! As we get closer to spring and the sun gets higher in the sky, that time should naturally increase though. I think they need at least six hours a day of full on sunlight.

[Worth1]

Yes they need supplemental light or they may get leggy.
You want a nice fat and healthy plant not some NBA basketball player.

Worth

[shelleybean]

Correction--my timer is set for the lights to be on 16 hours and off for 8 hours. If you have the space under your lights, I think this is best. Outside, they need 6-8 hours a day. Hope it goes well for you.

[Doug9345]

They will grow faster with lights. It also depends on how far the last cups are from the window. I've raised sturdy but small plants in windows but ended up shuffling them from window side rows to back rows to keep them from growing sideways.

[Cole_Robbie]

If you did all that work to pot them up, it's really worth the trouble to use lights.

And good air movement will help leggy seedlings have stronger stems.

[newatthiskat]

At my other house I had a bay window and put all the plants on my nook table and the sunlight was really good. I did not need to have lights then. now I am ina house with a big window but not the three sidded light I had. I had to buy lights. Now I need to get more lights. and a shelf :-(. Plants are already trying to get leggy and it is a good thing I have a good sunny day outside tomorrow to put them out in. Shaded of course

[ScottinAtlanta]

I am leaving the US for 4 weeks, and the seedlings will sit in tubs on the floor with air temp of around 50 degrees. I thought I might just let them grow slowly for those four weeks, then hit them with more heat and light when I return at end February. My caretaker can water them in two weeks (bottom watering in the tub). Plant out date in Georgia is 4th week of March, generally. If they survive with just sunlight, even though they grow slowly, that might be my safest bet. Good idea to put a fan on them - I will do that.

[bcday]

I don't think your plan will work. Even at 50 degrees they will stretch out, reaching for the window light. A month is a long time. Leaving them unattended under lights probably wouldn't work either though. To allow room for them to grow without hitting the bulbs, you would have to set the lights too high when you leave for your trip. I'm thinking the plants would just stretch out reaching for the lights anyway.
I hope you won't blame the caretaker if you come home to dead or sick-looking plants.
Can you contract with a local greenhouse for a month?

[Worth1]

If you do what you say your plan is you will come back to dead plants.

Worth

[Doug9345]

I think a lot of them will be alive. I also think that they will need to be in the plant hospital for a while after you get back. A two week watering cycle concerns me also. When you mentioned south facing windows I thought you meant putting them on the window sill. I've found big differences how a plant grow very near the glass and six inches from it.

I would NOT put a fan on them. Tomatoes in 8 oz cups are going to need every speck of water there is to survive for two weeks even with minimal growth. I assume that you plan on leaving water in the bottom of the tubs. Additionally the tubs will cast shadows on the plants and further reduce the light unless you've figured that in you 2 to 3 hour number.

I think I'd get some light on them even if it means laying brooms across chair seats and hanging shop lights from the broom handles 6 inches above the tomatoes. I also think that you if you leave them wet enough to last two weeks without being watered that you are going to have problems associated with wetness. You really need a plant sitter(s) and I realize that you are totally out of time to do something about it.

[Cole_Robbie]

The fan does speed evaporation.

Now is a good time to consider not just lights, but big lights! A 400 watt metal halide can be placed far enough away from the seedlings so that they don't grow into it. A 1000 watt not that much more expensive, if your room is big enough and also climate controlled so it doesn't get too hot.

I would put all of the plant cups in a kiddie pool and use that as your watering tray. If you want to get even more elaborate, you can build a flood & drain hydro system.

[ScottinAtlanta]

OK, folks, you convinced me. I hauled out my T12s, and now they are under 14 T12s and two shop lights. Thanks for your help on convincing me to do more work.

The water is bit more tricky since I have a non-gardener watching them who killed hundreds last year with over watering. Here is how I organized it: an 8 ounce Dixie cup filled with dry ProMix HP is 1.5 ounces. The same cup properly watered weighs 4.5 ounces. So I have a digital scale in the room. Every four days, my helper will weigh a random set of 3 cups from each tray. If the weight is below 2.5 ounces for any one from a tray, he will add 50 ounces of water in the bottom of the tray. Et voila!

[tlintx]

I think the real question is, what dirt do you have on your helper to get him to be so precise?

As soon as I figure out what "properly watered" actually is, I might steal your method! Works for baking pretty well, too.

[Doug9345]

I like your watering instructions provided you have it written down somewhere.