A quick post to share some fun info with you: Thomas Jefferson kept grow charts! (I don't know the correct term, but I call them grow charts.)
Our third President was interested in the same things we are: eating well, fresh veggies, and when will watermelons and asparagus be available?!
Check out the link above for the full blog post, entitled The President & the Parsnip, at the Library of Congress website.
For comparison purposes, here's a chart from the Virginia Cooperative Extension showing the same info.
BTW, the VCE is a great place to get lots more info about gardening, and they also have a help line if you've got a difficult question. The Master Gardeners of NoVA also have plant clinics at the farmer's markets in Alexandria & Arlington. For example, they'll be at the Del Ray Farmer's market starting 5/3/15 and will be there every Saturday through September.