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minimum light requirements

Posted by njitgrad 6A/6B New Jersey (My Page) on
Thu, Nov 7, 13 at 9:06

I have a 2 foot grow light and 4 foot workshop light.

Last season (my first growing from seed) wIth the combination of these two I was able to work a rotating schedule of providing 12-16 hours of light to a total of 6 flats (3 at a time) using timers, a round robin approach, and doing my best to keep track of how much light each tray got. It got pretty confusing after a while.

I am wondering for next season if 12 hour shifts would considered enough. This way I can rotate all three out and put the other three in every day on my lunch break.

If 12 hours are not enough, I welcome any advice on how to work a SANE rotating schedule. I just don't have the room for a third light in my garage.

I am growing tomatoes, peppers, eggplant, various herbs, leaf lettuce, cukes, and annual flowers.

Follow-Up Postings:

RE: minimum light requirements

Hi Nijtgrad,

Are you trying to grow these plants to maturity or just seedlings to plant out?


RE: minimum light requirements

The easy and best solution is just to buy more lights and make room somehow for them to fit and then don't have to rotate. At least replace the 2 footer with a 4 foot.

Better yet, convert all the lights to one HPS or multi-bulb T5 fixtures that give a bigger footprint and then don't worry about rotating. There are also multi-light shelving units available in many sizes and formats. They aren't cheap but if you plan to do years worth of seed starting they pay for themselves quickly.

Is 12 hours enough? No unless there is also lots of supplemental natural light as in a greenhouse for example.

You can also reduce the need for rotating by not starting all the seeds for all the crops at the same time and direct seeding when appropriate rather than using transplants. For example, peppers get started weeks before tomatoes and cukes and squash are best direct seeded. Then build a cheap plastic cold frame outside for the advanced plants and let the sun take care of them.


RE: minimum light requirements

Seedlings to plant out. Last year I had to rotate 6 trays of seedlings when I only had room for 3 trays. 2 trays were under a 4 foot Lowe's flourescent fixture, and 1 tray was under an actual 2 foot grow light).

I'm trying a way to add more fixtures without breaking the bank, unless 12 hours of light per tray would suffice.

RE: minimum light requirements

Digdirt provided a very informative post and I would follow his advice.

RE: minimum light requirements

I totally agree with Dave but the problem is the lack of space in my garage. Last year with the rotating, nearly all of my seedlings thrived. I gave them on average about 12-16 hours of light, rotating them between the cheap Lowe's fixture and the pricey grow light. My hope for the upcoming season was the to prevent myself from going nuts keeping track of schedules by getting away with 12 hour rotating schedules. Three trays on, three trays off, every day at noon.

RE: minimum light requirements

An analogy, You have two dogs but only have enough food to feed one well each day. So you split the food between them. Will they live, yep. Will they thrive, nope.

You have enough light to feed 3 trays well. If you want to raise another 3 trays and have them all on half rations they will grow but thats it.

Space is a problem for a lot of us. I have a 10'X12' room dedicated for growing and I still want more :)

Good luck.

*edit* FWIW, and I will get some opposition, the light setup you run is, IMHO, barely adequate at 16hrs a day. The plants on the sides will get leggy if not rotated.

This post was edited by SouthCountryGuy on Fri, Nov 15, 13 at 13:39

RE: minimum light requirements

SCG, love the analogy, made me chuckle. But all of my seedlings thrived last year with the amount of light I gave them. I had to cull a lot of them as they grew so I could keep the same amount of trays.

RE: minimum light requirements

I, personally, think that 12 hours of GOOD light should be enough. In most places out there in the natures seedlings do not get much more than 12 hours of sun/daylight. Having said that, switching back and forth just require some extra efforts and if you are willing to put up with it , it should be fine. Plants need certain amount of light , like moisture that hey really need and can use. Beyond that, the excess is not utilized. That is why they have found out that a shaded plant getting 40%(~~) light for 6 or 7 hours will do fine. This is just my general opinion in the absence of scientific laboratory experiment.

The other issue is that our indoor growing seedlings is a temporary thing, until we plant them out. So it is OK if they are slightly less than perfect.

RE: minimum light requirements

While I will agree that most plants outside don't get 12 hours of sunlight we run our lights longer to compensate for the lower intensity. Depending on lights, you may have to run them16hrs/day to make the equivalent of 6hrs of sunlight. While the OP has found results seemingly favourable, I have not found this to be the case running similar setups. YMMV

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