These seedlings are separated and ready to plant into individual pots. (more instructions on transplanting below)
They like cool so you can set these outside during the day when its sunny and temperatures are in the forties.
You can transplant onions but I usually don't bother and just separate
them whenever I plant them in the garden.
Of course you can use any kind of container you want, as long as they have drainage holes. Here is a great article from a friend's blog that demonstrates how to make simple newspaper pots: http://www.keeperofthehomestead.com/1/post/2014/02/newspaper-seed-pots.html
I just fill my trays with the same potting soil I use for seed starting (see Pt. 1 of this series). If you moisten the soil just a little on top it makes transplanting easier. Wait to water thoroughly until seedlings are transplanted.
You can also mix organic granular fertilizer into the soil and your plants will feed off of it for about 6 weeks. This is an easy way to fertilize and your plants should do well, along with an occasional boost of Liquid fertilizer. Organic granular fertilizers are available at most garden centers like Lowes. Look for one that is suited for potted plants.
After transplanting, water seedlings with compost tea or Liquid Fish solution at full strength. If you mixed granular fertilizer into the soil, it is still good to water with compost tea or fish as it will help break down the dry fertilizer and make nutrients available faster. I like to give them a good boost right after transplanting to help them get over the shock/disturbance quickly. I just used my little hand pump sprayer to water.
Care after transplanting
I got this awesome little fan at Lowes and it works perfect to keep my window box ventilated. The air blowing over the seedlings will not only help prevent mold and disease but makes seedlings stronger.
When I first started growing plants in my greenhouse, I would take my watering wand and go back and forth over the whole table of trays. I felt good that I had 'done the watering for the day'. When my plants got bigger and I wanted to sell them, I noticed that they had very little roots and tended to break off when I tried to take them out of the cells. The problem was, plants almost never dry out evenly and if you just water everything you end up over watering. Lets just say I quickly learned to water only the cells/pots that were dry. This is fairly easy to do with a sprayer, and if just using water, a kitchen faucet on the spray setting with the pressure as low as possible works great.
When your seedlings get established again, they can handle life with a little less TLC and as always, love being outside in the warm sunshine. I work with my husband building cattle fences so we usually leave early in the morning and put in some long days. I try to make judgments in the morning what the weather will do during the day and care for my plants accordingly. I always water in the morning as seedlings don't like to go to bed with cold, wet tootsies. You learn with experience how much to water so they don't wilt during the day when you're not there to keep an eye on them. So far they have been doing just great!