"freezing temperatures"; "danger of frost"

After planting seeds last weekend I’ve been thinking a lot about how well they’ll do after we transfer them outside (under protection).  I am honestly not an expert on when and how frost forms or which plants can survive (or benefit!) from freezing temperature and which don’t…

Here’s some info on why frost forms (yes, I am this ignorant):

Frost is a crystalline deposit of small, thin ice crystals. This deposit forms on objects when the air directly above those objects reaches the frost point. The frost point is the temperature at which a given volume of air becomes saturated and thus can no longer hold water in the vapor state—provided that the air temperature is at or below freezing.

In the formation of frost, a layer of water initially freezes onto the surface. The layer of frost grows as water vapor from the air directly solidifies into ice without going through the liquid phase; this process is called deposition.

Usually frost forms on clear, calm nights, especially during early autumn when the air above the Earth is quite moist. A light frost generally damages only the most tender plants and vines, whereas a heavy frost (a heavy deposit of crystallized water) may kill even hearty (nonwoody) plants.

We’re going to be planting these very early seedlings under protection (not 100% decided on what kind) in the existing garden.  Planting in raised beds helps keep plants safe because they stay above the frost line – the garden doesn’t have raised beds per se, but the dirt is mounded up.

Something else I’ve been wondering about is that the average frost-free date for an area (ours is the end of April) is the time when there’s a 50/50 chance of frost.  No one else seems too concerned with this, so I’m just going to go with it…  Ha ha ha.   We’re assuming we have about 4 weeks to get the garden set up before the sprouts get too big and freak out.  Another thing I’m grappling with: “days to maturity” doesn’t include pre-transplant time?!  What if you are direct sowing?  Do any of the timelines take germination times into consideration, or they start counting from when the seed breaks the soil surface?  So many basic questions.  We’re going to learn a lot this year…