My only comment would be to work out when you will be able to plant them out (if they are not hardy) then work back from that time. You don't want them too big too early.

>> You don't want them too big too early So, I guess the question boils down to... 1) HOW big can I reasonably grow them before planting them? and 2) does it make any difference (i.e. will the smaller plant simply "catch up" in the long run)?

Using Zinnia's as an example. Could I reasonably start a 6-12" zinnia indoors or am I going to end up with a leggy plant that won't do as well, in the long run, as the 2-3" plant I might buy at my local garden center?

Part of me is saying... hey, I can go to the local walmart and buy flats for little (compared to time/lamps/seeds/elec). So, what do I really gain by starting my own (outside of the enjoyment of doing it)?

John
just for the fun of it visit winter sowing forum read FAQ and you will see totally different world of very inexpensive way of growing tons of plants for very little investment.
I am not sure what is my benefit of growing plants indoor- mostly I grow what I can not buy in my regular box stores and what will cost me arm and leg at expensive nurseries to buy.
I do easy count with annuals- many of them take 10-12 weeks to bloom. So count back 10-12 weeks give 1-2 weeks for germination and see when you need to start. Some annuals need 20-24 weeks to bloom. Perennials mostly won;t bloom first year so it does not matter.

It doesn't make sense to start seed of annuals too early indoors. Conditions are never as good as they are outdoors, and you wind up having problems with leggy, insect-infested plants. I'd stick fairly closely to the recommendations on the seed packets on when to plant.

I have a fair amount of light shelf space indoors, but it's not worth it to me to start seeds of common varieties available cheaply at the garden center. What I work with is seed of plants that are either unusual sorts or too expensive to buy in bulk as young plants.

Side note: I'm sure winter sowing is just absolutely wonderful, but why do its proponents constantly have to evangelize for it in unrelated discussions?

John, there's a growing-under-lights forum here at GW and they can answer your questions about the lights and lumens.

I don't think that starting a plant sooner indoors will gvie you a longer bloom period unless you deadhead it frequently, but even so a plant can become exhausted. Cold season annuals like sweetpeas are effected by heat and can reduce the amount of blooms they make or simply stop flowering. Some veggies, like lettuce will be stimulated to bloom and set seed by the warmer weather.

Bloom period will depend upon the species and the season.

Here is a link that might be useful: Growing Under Lights

Very often seedlings are kept too long indoors. As soon as possible I like to move them to a cool cold frame where they get more light and less heat. With a partially open cold frame the added air circulation helps grow a more robust plant that will do better when planted in the garden. Al

I started with just a few plants in the basement about three years ago. Last year with a four year old daughter helping and wanting her own flower bed out front, we went from a one light set-up to a three light set-up with a timer, and from strictly vegetables to both edible and beautiful to look at. Needless to say, we've both learned a lot along the way. As I write this, she has her nose in a catalog, and we invested in "The Gardener's A-Z Guide to growing flowers from Seed to Bloom" (Eileen Powell)
OK, back to the point. It's something that I tried just to see if I could do it. Now every seedling that goes into the ground is started "in house." If you have a little helper like I have, it's well worth however much it cost'.

I do it because I get unusual plants/exotic colors only catalog seeds can give me. I do it because I like doing it. Yes, you can get earlier bloom with some plants. With others (like cosmos and zinnia) I find they do best planted directly outside. You learn from experience.

Lately (after doing it for 30 years) it's become a bit of a chore so I stopped doing seeds that need to be started before March 1st and buy those plants in the nursery.

I use an 8 tray light setup with two shop lights next to each other on each level, each light with one ordinary 40 watt tube and one full spectrum tube.

Keep a list of when each plant needs to be started (by weeks before last frost), keep the lights no more than an inch from the plants, and always have a fan or slightly open window in the plant room to prevent fungus. Try to water from the bottom and without soaking the top of the soil.

Have as much fun with this and go nuts obsessing over whatever you feel comfortable with. Rewmember, it's for pleasure!