> 250 onion plants

That really sounds like you are getting into some serious onion farming.  How many onions does one get per onion plants, is it just one?

As I intrude with "Yes, unless you let them set for the two years/seasons to cast their own seed."

You should try sweet potatoes. They are real easy. You take one and put it in a glass of water so the top sticks out. Keep an eye on it and you will soon see it sprout out of the various eyes. When they grow little roots you carefully take them off and plant them.

Gunter,

Just one per plant.  Onions are new to me and I thought I'd try using plants, it's just a bit easier.  I planted some onion plants from a local supplier here last year and they didn't do well.  It was a dry season and the plants weren't the easiest to grow.  So this year I changed suppliers and ordered 3 different types of onion. http://tinyurl.com/jcfj5 You can start them from seed, maybe next year.

I've never tried growing sweet's, but I do love to eat them.  I'm running out of space and I'd rather grow a few "Long Island Cheese Pumpkin" plants. They make an outstanding pie....

The 1st of the 06 peas made it onto the dinner plate last evening along with a great heaping bowl of fresh  lettuce. I would have taken photos but everyone cleaned their plate before I could reach for the camera. The full crop of early peas will be in full picking this weekend....where's the butter?

Oh, this morning the 1st strawberries made it into the bowl along with Kashi 7 Grain Flakes.  Yummy!

Last evening we started the fall crop of broccoli, brussel sprouts, and a summer picking of lettuce.  The squash will be planted as soon as the peas hand over the last picking.

We're trying for dwarf strawberries on our window sill. 

I'm not optimistic ...

That should work just fine.  Keep in mind that it takes 1 yr for the transplants to start producing and you rotate fields (pots) every other year or so.

What you really ought to grow is chocolate.....