Answer: The best way to begin calculating is to find out when your average last spring frost date occurs. Your County Extension can help with this (666-8143) and may also be able to suggest the best varieties of vegetables for your area. The average is only a guide, but it is better than nothing. Over time you will discover if your garden's microclimate usually runs early or late or about the same.
Things like broccoli and cabbage can be started about 12 weeks before the frost date and planted out about 5 weeks before it. Cauliflower and onions, 10 weeks and 4 before. Lettuce and chard can be started about 7 weeks and planted out about 3 weeks before the frost date. Tomatoes can be started about 6 weeks ahead and planted out right after the frost date. Eggplants and peppers can be started 7 weeks before and planted out 2 weeks after the frost date. Squash, cucumbers and melons need warm soil so are usually set out or planted from seed about two weeks after the last frost.
Plants for direct sowing such as peas and spinach can be planted about 5 weeks ahead of the last frost, beets, radish, carrots, and chard about three weeks ahead, beans and corn at about the last frost date, and the cucurbits about a week or two later.
All of these dates are a rule of thumb; some years the soil will be cold later into the season than others, some springs will be gentler than others. You might want to look into some of the season extender methods such as using cold frames, floating row covers and so on as well as using black plastic and raised beds to try to warm the soil a bit faster in the spring.
Producing good healthy transplants at home is doable but not always easy. Timing of course is important, so are the growing conditions you can offer the plants. The most difficult to manage is usually providing adequate light, and after that the problem is usually one of not enough space to accommodate the plants as they grow!
Once they have germinated, most annual seedlings grow nicely at a temperature a bit cooler than the normal room, say 60 or 65 degrees. As they grow you will need to raise the light to keep it within just a few inches of the tops of the plants. Eventually you can move them to a cold frame to harden off or gradually acclimate them to being outdoors over the course of a week or so. When the weather begins to settle, somewhere around your last average frost date you can plant them outside. Keep an eye on them and be prepared to cover them at night if a cold snap hits.
Seed starting is lots of fun and part of the fun is in the experimentation -- gardeners learn something new all the time, so don't feel intimidated. You might find some of the following general (and detailed) information useful:
Seedstarting Made Easy at http://www.gardeners.com/gardeners/bgbseedstart.html
Seedling Savvy at http://22.214.171.124/nga/articledetails.taf?id=514&kwd=seed&A...
Finally, you can follow principles of successive cropping and even push for a fall crop -- to work out the finer points of this you might look at a few books. One I particularly like for its schedules and suggestions is "Square Foot Gardening" by Mel Bartholomew ISBN 0-87857-340-2 -- amny of the techniques and suggestions work as well in a large garden as in a small one.
Good luck with your garden!
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