Answer: Ideally you want to grow seedlings in such a way that they stay in vigorous growth throughout the process from seeding to hardening off to planting out in the garden. Tomatoes for example may only require 6 to 8 weeks, so it is important not to start too early. Timing is critical, since some seedlings grow very quickly and others much more slowly. In general, overly tall seedlings are caused by lack of light, and the warmer the temperature the more this will be accentuated. Most gardeners find it necessary to use supplemental lighting for 14 to 16 hours a day to produce good quality seedlings. Even with all those windows, your plants probably still could use more light. Temperatures closer to 60 or 65 degrees are also better for most seedlings and can help keep growth stocky. Some seeds sprout and grow so quickly that it really isn't necessary to start them indoors; some particularly cold tolerant plants (including lettuce, peas and spinach for example) can even be seeded directly in the garden before the last expected frost date. Lettuce is a particularly fast grower and can be ready to harvest in only three weeks, so you may want to keep this in mind while you plan your seed starting schedule.
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