Sorry for the long post but I was bored and you asked, I hope it helps and I hope more people consider getting a green house. Even if it's just to extend your fall tamato growing with a few plants, I'll be having fresh homegrown tomatoes for Christmas and after the 1st it's time to start peppers and eggplants for next year. Enjoy!!
Getting a GH is great and will extend your season in Spring and Fall. I would say
IF you're a gardener and garden all year every year then you need to get one bigger than you think. I started with a 7'x7'x15' and it seemed like it would be plenty big enough but it filled up quick with a dutch bucket hydro system with 8 plants and then when seed starting came it got full with plants every where and I also used it to over winter plants.
Here's the 1st GH
You can see I used 2"x4"'s cut in half and cemented in the ground for supports and used EMT straps to secure the GH to the wood and built a plant shelf.
I just checked the price for a friend and they're cheaper than it was 3 years ago, $91 with free shipping. The plastic will last about 1.5 years so plan on replacing it with good stuff in the future.
https://www.ebay.com/itm/Large-15x7x7-Wa ... SwoydWlgH6
OK, this is how full it gets
As you can see, it fills up in no time. I just built a bigger one for this year and now I have 2 to fill up again.
This was 3 weeks ago
and now
over wintered peppers under the shelves
a few other tender plants I want to keep going through winter
As you can see,
IF you garden all year get a bigger GH now instead of having to buy another one in the future.
On the seed starting: You don't need an elaborate system or area to start thousands of seeds. You'll need space to put them when you transplant and that's where the GH comes in handy using a small heater to keep temps at about 50-60 at night. The key is to time your seed starting so you don't have too many nights with cold temps so you won't have to run a heater, sometimes we can't predict the weather so it's a guessing game. You can also just start your seeds about 9 weeks before your last frost date and that will give you a 3 week head start but remember the plants will be bigger so you might need to transplant them again. You also need to be aware that even older plants that are too close together will get leggy too so make sure you give enough space between plants so all of the leaves recieve sunlight.
I use a small area to start seeds with only 2 24" grow lights from Wally World and once they have the 1st true leaves I put them in the GH and transplant into either a 4" pot or 16oz Styrofoam cups. What ever container you use make sure it has drainage holes and don't water until the soil is dry and always bottom water.
I start seeds in a community container to reduce the space I need for seed starting.
There's 16 different types of tomatoes in that tray and more than I needed but I gave many away after I chose the best plants after transplanting.
I used the back patio before the GH and Gumbo should recognize that custom made crawfish table.
I use a seed heat mat to start the seeds and this is the cheapest I found that works. I ordered 4 and shipping was $11 so the price for each one came to to about $12.
https://www.zenhydro.com/ipower-seedling ... wAodbNQP6g
I didn't invent the system I use but instead take parts from experienced growers and adapt it to my growing methods/conditions and have had success.
This was taken out of the book "Greenhouse Tomatoes, Lettuce & Cucumbers" by S.H. Wittwer & S. Honma where they recommend 'Cold Treatment' for hardening off tomato seedlings and grow healthy, stocky plants.
The cold treatment should be started just as the first true leaves emerge, whether the seedlings are still in seed rows or pricked-off. Air and soil temperatures should be lowered to 52 to 56 deg F for ten days to three weeks. A ten to twelve day cold treatment is adequate during periods of good sunlight. Three weeks are usually necessary in the fall and early winter when most of the days are cloudy and plant growth is slow. The amount of cold during the ten-day to three week period is more important than the time of day in which it is given. Cold exposure during either the day or night, or both, is effective. Night temperatures of 52 to 56 deg F are recommended when the days are sunny and partly cloudy.
Following the cold treatment, night temperatures should be raised to 58 to 62 deg F. Cool daytime temperatures (60 to 62 deg F) should be maintained in cloudy dull weather. On bright sunny or partly cloudy days, temperatures of 65 to 75 deg F accompanied by good ventilation are suggested.
Tomato plants properly exposed to a cold treatment develop large cotyledons and thick stems, with fewer leaves formed before the first flower cluster, up to double the number of flowers in the first, and often the second clusters, and higher early and total yields.
Basically this cold treatment is used to give healthier, more stocky seedlings that will give increased yields and earlier harvests. In regards to light intensity and duration they had this to say.
The tomato is a facultative short day plant which flowers and fruits earliest if the day is not extended beyond 12 hours by artificial light. Young tomato plants do not need the light intensities of full sunlight. Where there is no overlapping of leaves, light saturation is reached at intensities from 2000 to 3000 foot candles, or about one-fifth to one-third the intensity of direct sunlight at high noon. If artificial lights are used, an intensity of at least 500 foot candles should be provided at the leaf surface. Tests with fluorescent fixtures reveal that Wide Spectrum Gro Lux is slightly superior to cool white.
Hope this helps.
And CRAIG LEHOULLIER has great videos showing you all aspects of growing tomatoes from seed starting to pruning.
https://www.craiglehoullier.com/resources/
MHPgardener's video about transplanting
https://www.youtube.com/watch?v=u_YYEUcr45M