Pics and your climate/area?

I posted the pics after your comment. And I'm in Alabama, so its a hot and humid climate. But we had a lot of very cold days in Jan / Feb and same thing into early March.

It looks like your soil is holding too much water, which causes the roots to rot. You'll have better luck with a potting mix that drains well.

It looks like you have garden soil in the containers. If so, that's what's wrong.

Ditto what jean said.

Heavy garden soil and far too wet.

Ditto. You may have taken those pics right after watering, but you're sprouting in a whole slew of organisms (some hostile) with a soil that might stay too wet. Try using something from a commercial source that mentions "seeding" or "drainage"; something you might even run through a microwave oven first to kill off beasties (probably unnecessary but can't hurt, especially since you're troubleshooting).

If you do want to stick with garden soil, add lots of sand, sterilize it all, and be scant with the water.

Will need to be close to 100 percent sand in order to work in a container. Unfortunately, garden soil is unable to drain sufficiently when in containers.

To drain well, the potting media must be quite coarse. In fact, much more coarse than is garden soils.

And, no, coarse stuff in the bottom of the container won't improve drainage.

" using soil from what used to be a garden years ago on our property."

Wrong soil for containers. Garden soil holds too much moisture and causes plants to die from root rot. You need a soilless mix, potting soil, to grow things in containers.

kimmq is kimmsr

Thanks for all that great advice everyone! I'm going to be trying some new things with my container garden, which will include barely any actual soil and much much more potting mix and other things that will drain much better. This is my first ever container garden so I'm a total newbie haha.

Update on my chard. I now know that what was happening to my chard is called Damping Off and it's caused by a fungus attacking them. Makes sense, knowing what I know now about growing in containers.

I tried sand too though and it did not work. Water still isn't draining even with the sand. I suspect that the "sand" I used from my yard is actually still filled with clay and I just didn't know it...

I also tried 90% potting mix to 10% garden soil and that didn't work either.

Then I tried 100% potting mix and it still didn't work...plants died from Damping Off, but they were outdoors in water-holding pots and we got lots of heavy rain...I guess they need to be sheltered? These little guys are so delicate...the heavy rain really compacted the potting mix...

Been trying since...well, since Jan 2015...with little success.

"Then I tried 100% potting mix and it still didn't work...plants died
from Damping Off, but they were outdoors in water-holding pots and we
got lots of heavy rain."

You do have drainage holes in the pots, correct? If you do then you'll probably need more. If you don't then you definitely need to add some.

Rodney

Yes the pots do have drainage holes. We bought them from Lowes. They are, however, self watering pots so I suppose that means they are holding water in the bottom. I'm not exactly sure how self watering pots are supposed to work and I didn't much pay attention to that feature when buying them.

I believe I figured out what the issue was. I have been very suspicious for months now that something was wrong with the Miracle-Gro "organic" potting mix I was buying. Based on many other reviews of the same product on Lowes' website, I was right. The potting mix is infected with fungi and kills plants planted in it. It kept killing almost eveything I was planting, from carrots to kale to spinach to chard, and I thought it was my fault all along...didn't know any better, I'm a noob gardener...

I will be trying again with ingredients from the local plant nursery instead...