seed germination

iam wanting to start my carrot and radish seed in my garden I know my frost date but iam not really sure how far to count back to get my planting date please can you help me I have some spinach and lettuce to that I want to start in my garden from seed,

Googling gave me this for radishes:

Plant 4-6 weeks before the average date of last frost, after aged manure or organic fertilizer has been worked into soil.

Direct sow seeds ½ inch to an inch deep and one inch apart in rows 12 inches apart.

Thin to about 2-inch spacings. ...
Radishes need sun. ...
Practice three-year crop rotation.

However, some radishes , like Daikon radishes, prefer being planted in late summer for fall harvest. When I planted some in early spring, they put out lots of foliage and blooms, then lots of tasty padish pods! Then they dropped seed that keeps volunteering in my hard, hard clay "soil".

Hopefully the seed packet will warn you if you have the oddball "summer/fall" radishes.

Carrot seeds may take 2-3 weeks to germinate, but need to stay moist the whole time. They like cool weather, so plan for them to mature before summer gets too hot. Of course, when it does get hot, just harvest them all even if they are tiny, extra-tender and extra-sweet. They also like uniform moisture and fertility.

They need loose soil! You probably should be loosening the soil and adding compost (and even sand if needed) now, for next spring's crop.

Direct sow shallowly, maybe 1/4" deep.
I see several sources saying to plant carrots every 3 weeks, so I guess you can start around or shortly before your last frost and then repeat until you know that summer is going to be too hot for the adults.

But except for 1-2 crops of radishes, that's just "what I read online".

The Beginner Vegetable forum might have more practical advice for OK.
http://davesgarden.com/community/forums/f/b_veggies/all/

P.S. Ag extension co-ops always have good advice for their state and county. Consider looking at:

http://www.csrees.usda.gov/Extension/index.html (co-op finder)
http://countyext2.okstate.edu/ (OK)
http://www.oces.okstate.edu/ (OK extension service, find a list of counties here)
http://www.oces.okstate.edu/gardening-insects-pest-management (gardens)
http://www.oklahomagardening.okstate.edu/category/fv (garden videos)