Watering:
When you water your young seedlings you need to be as gentle as possible. I recommend picking up a typical spray bottle, of course do not reuse one that has had cleaning products or any chemicals as this will probably kill your plants no matter how much you have cleaned it out. Set the sprayer to a mist and gently apply the water to the plants in such a gentle manner that you don’t “blow” the plants over with a heavy spray. I apply a good soaking via misting daily when they are young. If you are using a heat mat to help the germination phase the soil can dry very quickly and the seedling can die very quickly. Keep the soil moist at all times at this stage. If you start to notice any mold or fungus then it is ok to let the soil dry a bit, but keep a good eye on the seedlings, it can turn ugly very quickly.
Thinning:
If you have chosen the safer, but more expensive approach of planting more than one seed per cell in your seed trays, you will soon reach the time of making a difficult decision. That decision would be to thin your seedlings to the strongest, healthiest one. Our ultimate goal here is to encourage more root growth and to give our strongest seedling the most nutrients possible that is remaining in the soil. To thin your seedlings down to one per cell, take a pair of small scissors and clip the weaker seedlings at the base, as close to the soil line as possible.
Do not pull them out of the soil as the roots might and probably are inter-twined with the good seedling and you could kill it very easily
Another method is to simply us your fingernails and give it a pinch near the base. It is very important to not disturb the young seedlings that you
Transplanting:
I am going to do a whole article on transplanting but I have seen a few questions in the comments wondering when the best time is to transplant. It is time to transplant when your seedling has outgrown the container it is in. I wouldn’t recommend transplanting until you start to see roots growing out of the bottom of the container through those little holes. You never want to disturb the plant until you have too and you never want to try to move a very young seedling as the process can kill it.
–Jay