There are several problems you might run into if you start seeds too early, and not a whole lot to gain if your plants are too big (overgrown), root bound or they are not strongly growing when set out into your garden. If snapdragon seedlings become root bound, they are notorious for not growing out of it unless you preform surgery on all of their root balls to loosen their roots a bit before planting out into their permanent place in the garden.

The longer you keep seedlings growing indoors - even under ideal conditions is that the bigger the seedlings are, the more space they take up and juggling them around to keep them healthy becomes more challenging. Snapdragon seedlings ideally like to grow at cool temperatures to produce strong stocky plants. The longer they spend growing indoors, the chance of something going wrong increases. Watering problems, insects and disease become more likely the longer they are inside. Younger strongly growing plants take off faster than ones that are overgrown once they are planted into the garden.

I work as the horticultural advisor for a commercial seed company and one of my jobs is to germinate and some times grow out to maturity any seeds that are causing the customers problems - last May I tested the germination on old (10 to 12 yrs old) Rocket Snapdragon seeds, the germination was very good, at least 90% and I took the four inch pot the 6 to 8 week old seedlings were growing in and divided it into several chunks of plants. The seedlings were planted out sometime in July, by August they were all in bloom and they kept blooming through November because the weather was so mild.

I have been growing plants from seeds for over 60 yrs, I would follow the established directions on how to grow plants from seeds and the time it takes to be successful with them rather than attempting a technique that hasn't been proven to work well. That is just my two cents from a lifetime of experience.

Good luck with your seedlings!

I think a major factor is that growlights are not nearly as strong as sunlight. Seedlings get etiolated. The temperature and dryness indoors is also a factor. Floral_uk gave me good advice about not starting parsley too early inside lest it bolt mid seaaon.

Many thanks for these comprehensive explanations, Jeb and kitasei2. Points well taken. One of the things I've always wondered about is that the seedlings I grow in my amateur home grow light system and then plant into my garden are invariably much smaller than most I buy at a nursery. Whoever has grown these plants that I see at nurseries clearly have professional growing equipment and techniques much different than mine, and I assume they therefore don't have to follow the "6-8 weeks before average last frost" advice that I need to follow. For those they grow from seed--I assume for many flower species they take cuttings instead--I'm sure they start those seeds much earlier than 6-8 weeks in order to produce the larger plants that one sees for sale at nurseries. My question: how do they do it? With what equipment and techniques?

But maybe I'm wrong: maybe they do start the seeds the standard recommended number of weeks before last frost, but then when the time comes they plant out into an outside pot rather than an outside garden as I do. And after that it does a great deal of its growing in its outside pot, not as I originally thought inside under grow lights.

Rick - I have worked as the head grower for several greenhouses and nurseries and the plants that are produced and sold commercially are started earlier than 6 to 8 weeks from seed. The reason for this is because the public will usually only buy plants that are in full bloom, or at least have a good amount of color showing. They seem to be attracted more to the flowers on a plant for sale than they are interested in the health of the plant. It is difficult to sell a perfectly healthy plant of the ideal (young) age to the public if it doesn't have a pretty little flower on it even if there is a flashy colored plant tag stuck in its pot! I have spent my whole horticultural career attempting to educate gardeners that a younger, stronger vigorously non - flowering vegetative plant will establish itself better and faster - and out preform a plant that is in full bloom when put into its permanent growing place. The general public is looking for instant gratification, so selling younger, stronger but not fully flowering plants has always been a challenge for me.

Most of the ornamental garden plants that are produced from cuttings commercially are started even earlier, many years ago I was in charge of the scheduling and production of rooted cuttings that were either sold wholesale to other greenhouses through the winter months as newly rooted plants, or grown on as retail 4 to 6" potted material and hanging baskets. I would start the cutting production in late December/early January so that the pots and baskets were planted up sometime in early February to be in bloom and for sale right before Mother's Day. One of the greenhouses I worked at offered "prefinished' pots of plants and baskets wholesale too, these were plants that were about a month away from being saleable (in bloom!) to other greenhouses and nurseries. They knew what they were buying and weren't afraid of purchasing plants that were green and growing without any flowers on them.

What kind of equipment is needed to commercially grow plants from seeds and cuttings? A heated greenhouse, a bottom heated mist bench for rooting cuttings, supplemental lighting to extend the daylength for some varieties - if you are a large grower automation is needed, a soil mixer, flat and pot filler, overhead water lines in the greenhouses to water hanging baskets, etc.,

If I wasn't a horticulturalist I would probably be a psychologist, because there is a good amount of psychology involved in selling plants to people. Some of it I understand from years of experience working with plants and people, and some of it will always be a mystery to me. The best I can do is try to educate those interested in gardening, some are more receptive than others!

Hope this helps - and hope you have the best garden you've ever had this season!

i also think most plants sold in the north are grown down south.