I live in a short season area and was raised to use transplants. I even grew bedding plants for sale in a
greenhouse for a number of years. I’ve since repented to some degree. If not for the short season I’d be glad to let things come up from seed in the ground. The volunteer tomatoes which came up this last year were very late to sprout.
During my greenhousing time I came up with an alternative method for annuals or perennials treated as annuals. I found my best results were to sprout tomatoes in the
greenhouse in containers which were narrow and deeper than the tomato
roots would grow before transplanting and let them grow to 2 true leaves (do not include the cotyledons or seed leaves in the count). Grow them very cool after the cotyledons emerge so they do not become leggy. Use cool or warm temperature to hold back or speed up their growth as needed depending on frosty nights having passed. Transplant them very young into the garden. Do not allow to get too many roots prior to transplanting. The key is young and already hardened off to cool temperatures. I’d plant them up to the cotyledons in depth. They required very small transplant holes and there was so little foliage and so few roots they would easily take off as if they were sown in place. This allowed for predictable placement and stand and some control over frosty nights.
I trialed seedlings planted out in this manner and seedlings then transplanted into larger containers for further growth in the greenhouse These were planted later
side by side in the garden with the small seedlings which had been transplanted earlier. Hands down the small seedlings were by far the more vigorous plants. Somehow they know when another tomato is near in the greenhouse and they adjust their growth to accommodate the nearness. Those small seedlings in the garden which had no tomatoes near immediately began a larger spread of both roots and leaves. I was stunned at the difference.