Starting seeds indoors only has one advantage over a greenhouse as far as I can see-- You don't have to pay for heating. At least that has been my experience. I don't think you can beat all around sunshine and the warmth that comes with the sun. My greenhouse is heated mostly by the sun, but I have a heater that is set above freezing. It may be 75F in the day and 40F at night and I do heat in the day if it is exceptionally cold and cloudy. Most days if it is just cloudy the sun will peep out enough to warm things up. I do start some things inside on my grow mat, but never let them grow long before I move them into the greenhouse. Impatiens is one of them and so are geraniums. I find I have better germination that way.I never leave them long enough to get leggy. I know many people use a grow light system successfully though. I guess it is like anything in gardening. There are many ways to do things and get the same results. You just have to experiment and find what works best for you.

I looked at your page to learn where you are growing. You should edit your post to show your zone, which will make a big difference in possible responses. As a zone nine gardener I would never offer any advice on when you should start your seedlings for your zone 3. You say your greenhouse is "indoors" with a fluctuation between 55 and 80 daily, your indoors must not be heated. The fluctuation should not be a problem, however. If you are able to get these temperatures without additional heat, why bother. Welcome to the GardenWeb and I will look for further postings. Al

I second the recommendation for Eliot Coleman's books. I think Winter Harvest gives more detailed information about each vegetable variety they grow and the critical timing. He does not heat his greenhouses but uses a system of high hoops and low tunnels. The low, fabric covered tunnels give additional protection. The current issue of Mother Earth News has some hoop house building instructions. Cost around $1,000 DIY. We are planning to build one next year. Understand that there will be little growth during the short days of winter. I heard people at the NOFA spring conference in NH talk about when you had to sow in order to get some growth before the short days. This year we started out with a single fabric covered low tunnel that would cover one bed. I planted a row of beans, a row of kale and a row of summer turnips in early May. The beans did fine despite a cold, wet spring. I heard other gardeners complain that their seed just rotted. Meanwhile, on Facebook our daughter-in-law's uncle was setting out his plants that he had started indoors. They were eating zucchini in June. He uses a system of plastic covered low tunnels. We recently put the fabric tunnel back into use to protect a late planted double row of string beans when temps got into the high 30s F at night. This past week it got hot and humid so we took the tunnel off. I was worried about air circulation/rust and pollination. The plants were in full bloom by mid-Sept. It looks like we have a nice batch of new yellow beans for supper tonight 9/26. It's going to get cold again by the end of the week. We'll watch the forecast and put the tunnel back on. We left some steel fence posts that held the pea fencing in the ground otherwise I probably could have tipped the tunnel off by myself. The bottom is a wood frame so the frame holds the hoops instead of putting the hoops into the ground. My plan is to start seed indoors where it is warmer and then put heat loving plants out under plastic low tunnels although I'm debating about fabric which doesn't need ventilation if it gets hot. But, I have the heaviest weight of Agribon. It was great for protecting our strawberry harvest from birds but in July it was too hot on young blueberry bushes. I've been debating the costs. Greenhouse plastic will need to be replaced about every 4 years. We will probably keep things simple and affordable but it will be "season extending" techniques for cool weather vegetables. We won't try to have tomatoes in January.

@esox07 they'll still flower and produce under fluros but you dont get as much production from them as you would say a HPS. MH = short and bushy HPS = flowering LED = can be both wave lengths Fluorescent = with multiple bulbs you can get both Induction = full spectrum( not much info on these as there fairly new to the grow industry, a lot of BS info saying there magical) so you can group MH/HPS together as most kits are switchable, decent price, high coverage area, effective, negative they cause a lot of heat(may need to vent) and will raise your electrical bill the most. LED Ive personally never had any experience with but they are comparable to Fluorescent with much longer bulb life. Fluorescent work great for starting seed/vegetative growth if you have the proper bulbs negatives, not that much coverage area, and bulbs dont last that long + expensive to replace Induction, these are fairly new(a few years) and from what Ive seen are pretty promising for seed starting/veg, I havent seen anyone flower with them yet nor do I care about indoor flowering, but the bulb life is way longer than the other, and the watts/coverage area is roughly half of a HPS/MH setup, big negative they are very expensive for an initial purchase Currently we have 3, 400 watt MH we start roughly 4000 plants under, we also have some fluro for other things this year were expanding a bit so we'll prob add couple of everything I plan on picking a induction to test mainly because the long term cost could save us a ton, if they work as advertised and what Ive seen my buddies test them at the hydro store. As only want them to veg/start seed so flowering/forcing flowering isnt a concern