Hi Amy,
Michigan has hardiness zones 3 through 6.*
http://www.hort.purdue.edu/newcrop/c...ps/MIhardy.jpg
http://www.gardenweb.com/zones/zip.cgi
Here's a planting calendar for hardiness zone 5 you can use as a guide.
http://www.savvygardener.com/Feature..._calendar.html
For the sprouting of seeds it would be the soil temps that would determine when they would sprout.* If the seeds are in the ground for 3 weeks or more they probably won't sprout.* Your seed packet should tell you how long it takes for the seeds to sprout (germinate).
Newt
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.