Growing in a greenhouse

Hi, I am brand new at this and have been reading all I can to learn. Most of the grow info here refers to either indoor or outdoor growing. I have a greenhouse at the farm, 10’ X 14’ that I keep some vegetables growing through the winter. I can keep it at at least 65F on very cold nights and the thermostats on the heaters are set at 68F. The greenhouse has 4 automatic overhead vents and door and or large window on each end. Even during the winter on a sunny day, the temps can get above 90F inside. I am ready to “learn” with a few seeds but I guess I am mostly confused with the light schedule for the plants. Unfortunately we have a security light behind and above the greenhouse, so it is never totally dark. I have ordered a 1000W LED grow light and wondering how to incorporate that with the sunlight throughout the day and the lack of total darkness a few hours every day based on what I read here.

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Id run my light a few hours in the morning and a few hrs at night to get the total 18hrs of “sun light” that would be a summer day for veg. Or you could do it at the end of the day, that part would be up to you. The light from the security light will be a problem when you get ready to flip to 12/12… I’d say you’ll have to move inside to flower because our days are getting longer.


Thank you, yes I may have to either rig something in the greenhouse for darkness or move inside as you suggest Right now I am getting just over 9 hours of light, so what you are saying is to supplement with the grow light to achieve 18 hours total, either all at once or in separate periods? Iots to learn.

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You may want to look at some auto flowering plants. Their flowering cycle isn’t typically light sensitive. If you grow photos the security light could potentially interfere with plants dark period, and the stress of that could cause flowering plants to hermaphrodite.


You must be a mind reader, lol. I was just reading up on them, great idea, specially for a first grow I think.
Thank You


@dbrn32 suggestion of auto flowers makes sense and I’m sure is the most prudent course of action.

I also want to point out that I have read and experienced that outdoor plants are less prone to issues from light pollution than indoor plants. I believe it has to do with the intensity of the sun.

You might benefit from testing this hypothesis with a few photos mixed in with your autos.

I mention this because I think autos are genetically inferior to photos.

I am thinking the Autos are easier to hide. I will have veggies outside and around the greenhouse, but this year I will keep some in grow bags in the greenhouse for cover. So you are saying that the outdoor photos may do ok and switch to flowering on their own schedule without my help? I see I will need an electric fan running to keep the temps down a bit, as it can get quite warm during the summer.


I’m saying the photos “might” not be affected by the light pollution from the security light. All depends on how bright and how close.

You also need to be mindful of your natural daylight hours and when you plant to avoid a reveg situation.

If you really want to maximize your growth cycle and keep size down starting mother plants indoors and then transplanting established clones in the greenhouse would be killer. I’m in so cal and can get at least 4 harvests a year outdoors with clones.

Here is a planting schedule:

So cal outdoor grow schedule

Jan 1st = Harvest, Set out clones, Take cuts for next set of clones

March 15th = Repeat

June 1st = Repeat

Oct 15th. = Repeat


Thank You, the greenhouse polycarbonate panels are not clear, so it is a dim light inside. I am in Eastern NC, so we do get cold, although today it is 80F, very strange but nice. It has been a warm winter but we should be in the 50’s for highs and 30-40’s in the evening. Sometimes it gets much colder but usually not for long. Could I not start the seed in the greenhouse? I do have an LED grow light on the way, along with two heat mats I use for starting the veggies, and then put them in their final grow bags once I learn when to transplant them.

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Yes you can. My thought was to have a separate veg area that is always on 18 hours where you start plants then start putting them in the greenhouse. More of a perpetual grow.

If you are lust looking for one harvest you can start in the greenhouse with the light then sync the light with daylight cycle when you want to flower.

Just seems like a greenhouse would be perfect for year round crops and having a separate veg area would be ideal.

I see what you mean and it does make a lot of sense. I will say we travel a bit, typically 3 week long trips throughout the year, sometimes a fourth lol, so planning is even more important. I don’t see me leaving them alone for a week, or can I?. The grow light arrives today, and I will set it up and practice with tomato and pepper seeds.

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You can leave them alone for 2 weeks. As long as your watering situation is handled.

I know you have climate control so you will need to keep humidity down in flowering.

I can set up a simple drip system. The humidity might be a different animal. It is raining outside today, and with the greenhouse closed up, the humidity is at 80%. I am sure I will have to run a fan once temps warm up in late spring.

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You will definitely need a fan. High humidity + dense buds= bud rot.

Thanks I will. grow light set up, very neat. The Manual says to start at 24-28" above with young seedlings. Sure looks kind of high. Also says to start with the veg setting at 40% and bloom at 15% for 2-3 days to acclimate the plants

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I would start there then adjust a little closer every few days to see how the plants like it. Also depends on if you have reflective side walls or the light is just escaping on all sides.

No reflective side walls, just hanging in the open. it is bright though, greenhouse looks lit up from the outside

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Cool. Got any pics to share? Be cool to see your set up

Would love to, just haven’t figured how to upload pictures, lol.

In the process of hanging the light I managed to bend two of my little tomato seedlings. One looked pretty bad, the other one not so bad. I ran the lights at 40/15% all night. One of them is almost straight up already. The second one is still bent, but it is not flopping over any longer. Yesterday it was hanging on the side of the pot.