I live in the Tampa Bay area and planted onions and carrots the first week of March. The green leaves on the carrots and the chaves growing on the onions are very long and green I was wondering when do I harvest the carrots and onions?

Carrots are mature at around 2 ½ months and ½ inch in diameter. You may harvest whenever desired maturity is reached.
You may leave mature carrots in the soil for storage if the ground will not freeze.
To store freshly harvested carrots, twist off the tops, scrub off the dirt under cold running water, let dry and seal in airtight plastic bags, and refrigerate. If you simply put fresh carrots in the refrigerator, they'll go limp in a few hours.
Carrots can be stored in tubs of moist sand for winter use.

When onions start to mature, the tops become yellow and begin to fall over. At that point, bend the tops down or even stomp on them to speed the final ripening process.
Loosen the soil to encourage drying, and after a few days turn them up and let them cure on dry ground. Always handle them very carefully—the slightest bruise will encourage rot to set in.
When tops are brown, pull the onions.
Be sure to harvest in late summer, before cool weather. Mature onions may spoil in fall weather.
Allow onions to dry for several weeks before you store them in a root cellar or any other storage area. Spread them out on an open screen off the ground to dry.
Store at 40 to 50 degrees F (4 to 10 degrees C) in braids or with the stems broken off.
Mature, dry-skinned bulbs like it cool and dry, so don't store them with apples or potatoes.

Cindy that was wonderful information. Thank you )
I remember reading about when and how to harvest onions before but I was going to have to look the information up again but here you are with all your wisdom!!! )