Yellowing leaves on plants are one indication of a nutrient deficiency and many people may tell you that this indicates a Nitrogen deficiency which is one of many of the deficiencies that yellowing leaves can indicate. Along with N would be Magnesium, Zinc, Iron, Sulfur, Boron, Copper, Manganese, and possibly Molybdenum, or the reason could be that the soil pH is not in the 6.2 to 6.8 range, or it could be an indication the soil is too cool, or it could also be an indication that the soil is too wet or too dry and the plants cannot uptake the necessary nutrients.
When was the last good, reliable soil test done?
What is the level of organic matter in that soil?
What is the tilth (workability) of that soil?
What does that soil smell like?
What kind of life is in that soil?

Sunny: Potting mix, rather than soil, is generally recommended for anything that's in a container. Potting mix contains no soil.

That said, yellowing leaves can be a symbol of so many things- among others too much water, too dry, lack of N or other nutes, burning with fertilizer, etc.

But those yellow leaves, since they're grown in garden soil put in a container, might be hard to diagnose. How big are the seedlings? Do they have true leaves yet? Generally a weak feeding is advised once they have true leaves. Have you fed them anything? Could they be too wet? Clay tends to hold a lot of water. Could they be too dry? Do you top or bottom water?

Like I said, lots of variables in your scenario. Have you tried seeding them directly in your garden bed and, if so, how did they do? I sometimes do that.

Karen

Thanks for helping, Kimmsr.

let's try to answer your questions.

When was the last good, reliable soil test done?

I haven't had a good, reliable one but, have had some crappy ones. Bought 2 of the DIY ones from store and they both read that pH was in "normal" range. It also checked for three other things but neither test showed any results. Don't know if that's because of the test themselves, I did in incorrectly, or there just wasn't any of that stuff in it. Also, got one of those $20.00 (waste of $) from Burpees that you stick in the dirt and it's supposed to give a reading. That thing didn't work at all.

What is the level of organic matter in that soil?

Not sure what you mean? How many inches? I mostly bury the stuff in the dirt year round. The ground rarely freezes here so I can do it all the time. I do spread some stuff on top depending what it is. Leaves, sometimes kitchen scraps, but I mostly bury it(scraps) about 2-3 inches. Keeps the critters out.

What is the tilth (workability) of that soil?

I can dig with my hands about 6 in. deep with little effort. The soil has sand ( I live close to the beach and it rains a lot) and also has a medium grey clay in it.

What does that soil smell like?

Uggg....like dirt? Doesn't have a bad odor if that's what your asking.

What kind of life is in that soil?

Right now, nothing. At least I don't think so. Just started getting worms for the first time a few months back. Before it started getting too cold.

Thanks Karen.

I was just experimenting to see if the soil was in better condition. I don't care if the flowers live or die. I just wanted to see if they would be healthy or not. Before I go crazy and plant all my wintersown flowers in there.

Sorry for repeating some of what Kimm said; I didn't see his post when I posted.

Sunny, are you talking about using your garden soil in your wintersowing containers, or about planting them in the garden after starting in potting mix? You should be using potting mix in your containers.

A good soil test would give you some answers. On the other hand, adding organic matter is a good thing to do to continually feed that soil and the food web. Attention to moisture levels, too. When I get yellow leaves, the cause has usually been too much or too little water. Yellow leaves is such a common symptom of plant distress that it's really tough to diagnose the cause.

Karen

I'm using store bought soil for w/sing. I was just trying out my backyard soil for when I plant out in the spring. I will admit though, the nasturtium I planted is in a very small pot and possibly didn't get enough water. It is about 6-7 inches tall and has a bunch of leaves.

I just thought that yellowing leaves meant that I had to add something in particular ( I spelled that word so wrong, spell check thought I was trying to spell particle board.LOL) to it. I had no idea that it could be caused by so many different things.