Yes, directly plant seeds outside. Plant seeds a couple of inches apart. Do not harvest any of the green leaves this year, as they will be too small. Allow them to produce greens and blossom clusters next year, and soon, you will have good clumps of garlic chives in about 2 years.

I planted my flat onion chives outsids in early march.

They germinated and grew real fast. Now they are abot 8 inches high. Chives first grow as tubular but as you cut them
(about half inch above ground)they'll grow flat leaves after a while.
I have already cut some to experiment. Once in a while after cuting, I have seen some people sprinkle fine soil (ash + soil + organic)over them to just barely fill around the stems. When they are fully stablished I will cut them with a sharp knife almost to bare ground and water them real good.
In a couple of weeks they will be 6 -8 inches high.
They grow just like grass. And I plant them relatively thick so that you can hardly count them and they cover the whole patch.

Of course some people have different method of planting and harvesting.

The leaves are usually thicker than regular grass leaves and have a bump running the whole length of them when mature. My nearby wild onions look almost the same as young garlic chives, but my garlic chives are slow to grow, and are only a few inches tall right now, while the wild onions are very big and grow thoughout the winter months. The wild onions I grow are identical to regular chives in appearance of the leaves, but the wild onions die out in the heat of summer and come back in fall through spring time, which is quite the opposite to regular chives. The bees go crazy for the garlic chive flowers which are white color.

My garlic chives are one of my favorite plants this year. Started from last year's "root clusters" that sat outdoors all winter and now have self seeded 2 babies. I also planted some cuttings from them which one of has sprouted! They are amazing plants, plus quite tasty. :) Keep them picked (any that hang down too far or look like they're dying, etc., yank off). Mine have survived 3 frosts so far this year, so plant them outside if that's what you want to do. Direct sow like ksrogers suggested. Don't feel like you can't eat/use in cooking some of the bigger ones you pull or cut the first year cuz I did and they were tasty. :)

I have had garlic chives for several years.They get wider every year. If you don;t cut them when about 6" tall, they will get tough, especially when it get hot. Even if I do not have immdeiate use for all of them, stil I cut them, chop them and freez them. They are very fast growing.
This year I got some Onion flat chives seed That I have planted.As I mentioned in my previous post, I cut some of them. They are up about 3" by now. When our lows gets to 50s I will cut all of them.
My experience with chives is that the more you cut them, the wider they get. They are much like grass.They get vigorous when cut.