The best survival garden is one that doesn't LOOK like a garden.

Any idiot can recognize a tomato... or a cucumber, green beans, corn, lettuce, cabbage or a watermelon. Any stranger looking for food would immediately know that those things are edible.

Most people wouldn't recognize radishes growing, or know what growing carrots look like. To 95% of people, it would look like random inedible weeds. They also don't know that radish leaves and stalks are really tasty and very nutritious. Most people don't know what Okra looks like. If you plant potatoes, people would just see it as a growing weed. They don't know what's underground. Same with onions. People know lettuce, but they wouldn't know Kale... or what Basil looks like, or mint.

The best survival garden is one where you know all of the edible plants... but starving strangers wouldn't know them even if they tripped over them. In fact, if the SHTF... I would take down any signs that it even was a garden (no stakes, no strings, no wire cages), maybe just use a few natural sticks from tree branches instead, and make it look as much NOT like a garden as possible... all the while knowing that I have a surplus of edible food there.

I am trying out the potato tower method where you let them grow inside of straw/compost mixture to allow for more room for growth and easy yield pickings. I have 2, 28" by 28" towers prepared and waiting on potato cuttings to day for a few more days before planting. I will also wrap plastic around the base for the next few weeks to avoid damage from an early spring frost.

turnips are a great food source too, and frow in all types of soils unlike potatoes.