When are onions ready to harvest?

I have lots of onions planted, I think at least 3 squares full, and some seem like they may be getting ripe. Either they are almost ripe or I need to put more MM on top of them b/c the bulbs are starting to show through the soil. Unfortunately I don't recall what kind of onions they are, I think some sort of texas yellow maybe. They aren't supposed to be small, kind of medium sized I think. Any help will be appreciated!

I am new to onions this year. I do know that it is fine for onions to peek out of the soil. Mine are doing that and I have read that it is normal. I think you can pull an onion from the garden to use any time it is big enough. I remember my grandma letting the tops of her onions (the green part) fall over and turn brown before she would harvest them for storage.

Thanks! The next question is what is the best way to store them? Should I put them in the fridge? In the basement in a paper bag? I certainly can't make a special root cellar for them but want to be able to have them through the winter.

I know it was answered, but here is more on harvesting and storing onions...

"Pull green onions anytime after the tops are 6 inches tall. Green onions become stronger in flavor with age and increasing size. They may be used for cooking when they are too strong to eat raw. Though leaves are traditionally discarded, all parts above the roots are edible.
Remove any plants that have formed flower stalks and use immediately. They do not produce good bulbs for dry storage. Harvest in late July or early August, when most of the tops have fallen over. Allow the plants to mature and the tops to fall over naturally. Breaking over the tops early interrupts growth, causing smaller bulbs that do not keep as well in storage.
Pull the mature onions in the morning and allow the bulbs to air dry in the garden until late afternoon. On especially hot, bright, sunny days, the bulb may sunburn. On days when this is likely, remove onions to a shaded location and allow them to dry thoroughly. Then, before evening dew falls, place them under dry shelter on elevated slats or screens or hang them in small bunches. Tops may be braided or tied with string before hanging. Full air circulation for 2 to 3 weeks is necessary for complete drying and curing. Keep the dry wrapper scales as intact as possible on the bulbs, as they enhance the keeping ability.
After the bulbs dry, cut the tops 1 _ to 2 inches long (at or above the narrow spot where the stem bent over), and place the bulb in dry storage with good air circulation. Do not try to store bulbs that are bruised, cut or diseased, or those with green tops or thick necks. Store under cool, dry conditions. Dry onions may keep until late winter, but check them regularly and use or discard those that begin to soften or rot."

And,

"Onions are the single most important ingredient a cook can have on hand. What versatility– choose from sweet, sharp, mild, or pungent. Because the onion family is so diverse (chives, scallions, leeks, shallots, garlic, red onions, yellow onions, and white onions), this discussion will be limited to scallions, green garden onions and mature garden onions.
Scallions and Green Onions
Scallions can be harvested any time they look tall enough to use. Gently pull or dig well below the slender white portion when the leaves are 8 to 10 inches high. True scallions have no bulb. Select healthy bright green tops that look crisp.
Green onions or spring onions are a step above scallions although the terms are often used interchangeably. They have a 1-2 inch bulb with green tops. The smaller bulbs are sweet while the larger ones are more pungent. Left in the ground longer, the bulb will develop and become larger.
Scallions and green onions are best harvested as you use them. For longer storage, rinse soil from bulbs and dry, peeling away the first layer if necessary, trim roots and store in the refrigerator for up to a week in perforated plastic bags.
Mature Onions
Mature garden onions are ready for harvesting when the green top withers, falls over and starts to turn brown. This usually happens in mid to late summer. Be sure to harvest before the fall rains, mature onions will rot quickly in cool, wet soil.
Lay mature onions in a single layer on newspaper in a warm, well ventilated place to cure for a few days. Leave undisturbed until the outer skin becomes papery and crispy dry. Select unbruised onions, rub off the stringy roots, and braid the tops. Hang in bunches or place in mesh bags and hang away from moisture. If stored in a dry cool place (50 to 60 degrees), they will keep for months."

From my favorite resource... http://urbanext.illinois.edu/veggies/directory.cfm

Onions make them sing.

BBG quotes a source that says:

Green onions become stronger in flavor with age and increasing size. They may be used for cooking when they are too strong to eat raw. Though leaves are traditionally discarded, all parts above the roots are edible.

If they're talking about green onions/scallions (I still get confused with those two) and people usually discard the green leaves, man, are you ever missing something. Is it just a southern thing to use the greens as well as the small onion part? That's the way we've always used them in my family. If you've never tried the greens with the onions, try chopping some in scrambled eggs or an omelet. Man, that's delicious!