Hi Calliope, I know what you mean, but those plants that can be planted before frost date usually can take frost easily. My nasturtiums, e.g. went through a few snow falls last year with their beautiful leaves and flowers before they finally yielded. I agree that one must know his area well and know how to estimate (though we cannot be 100% accurate). For some annuals, I wait 2 weeks after our formal frost dates, then check the forecast for the next 10 days, and if it looks good I can plant them. For tender annuals, I might wait a little longer or start indoor. For half-hardy or hardy annuals, I can start earlier.

Check with your state's Extension Service. Each county should have it's own Cooperative Extension Office which provides free publications and information for the asking. They will have valuable vegetable/gardening tables available specifically for your area determined by universities and horticultural research scientists who have collected data from growing those crops in your state. Your tax dollars are already paying for this service so you may as well get some use out of it. See how detailed these examples are: Vegetable Planting and Planning Calendar for Missouri (download the pdf) complete with spring and fall planting dates (underneath the spring planting dates for appropriate crops), how much to plant per person, etc. They can also tell you the average last frost date for your area and ideal planting times for specific crops and varieties in your area. Here is an excerpt:

Well some may give you flowers in September and some won't germinate in the heat of July and August and some may not flower at all. Is it too late--I'd say so, but if you want to try go ahead. If it were me I'd save them for next year and get a summers flowering from them. With the Calendula--direct sow in early spring. They do not freeze unless there is a hard frost and they are seedlings. They will drop their seeds and come up again and again.

What did you mean by Burpee? That was the brand of seed you used, or you used the Burpee seed starting system? I started plants from seeds for the first time this year. I used the Burpee seed starting kit (tray of 72 soil pellets on a capillary mat, with a water reservoir beneath, no heat lamp, just set next to a window) and had great luck with zinnia (of course), shasta daisy Alaska, and hollyhock. At first, I thought the kit was a huge disappointment, as I got great germination rates but it was almost impossible to remove the seedlings without killing them. What ended up happening, though, was that after mid-late spring, I ran out of steam planting stuff outside, and I just left my seed tray outside, watering regularly. The seedlings continued to grow. Then, I went on vacation for 10 days and so I set the seed tray on the ground in a sunny area where it would get watered by our sprinklers which were on a timer. The plants grew like wildfire! That was early July. I finally got up the energy to plant the plants - the hollyhock seedlings are huge (I never thought they'd finally get big), and I repotted each shasta daisy in a 6" plastic pot leftover from other perennials I bought at a garden center. I now have about 16 plants in such pots - they're growing rapidly and I will plant them in the ground in early August. No, I won't get blooms this year, but I should get them this year. Delayed gratification. The zinnia, it goes without saying, are doing fantastically - if only they were perennials. I've also just planted purple coneflower seeds directly in the ground per the seed packet instructions, and hope they will come up, as it's very warm out and I am keeping them moist. I know that my other experience won't help you this season, but it's an approach you might want to take next year. When I transplanted seedlings into the ground in spring when the were very small, almost none lived. Now that they are much larger they're thriving after transplant. I wouldn't have thought seedlings would do well growing for 3.5 months in a 1" cell, but they did. I've got over $100 worth of shasta daisies for about $1. Worth it? In the end, yes. Of course $100 isn't all that much and it might have been easier to just buy the plants, but now that the plants are larger and look like they'll survive just fine, I'm satisfied with the effort I put in. I think I'll try it next year. It's an ongoing process. I'm not basing my entire garden on seeds, but since I'm in it for a fairly long haul, I figure I can help fill out my garden cheaply doing some stuff from seed.