These are really good questions and make me re-examine my own preparedness!!
So, if the SHTF, how large of a garden would you need?
I could take the easy way out and say as big as possible, but I won't. If I had to rely on the garden alone, It would need to be 4-6 times what it is now or I believe we would starve. 200 x 200 feet would be minimum for 4 people and that is if done correctly. Some may say this is too much, but what if you get bacterial wilt, late blight, squash vine borers, and marauding animals / people all in one season? I think you'd have to grow the right things if you wanted to feed one person with a 10,000 square foot garden.
What plants would be part of your survival garden? Are there any that wouldn't be?
On a list of priorities, I think plant variety is one of the highest. Dried beans are great to store before hand, but it takes a bunch of space to grow a pound of dried beans. They just aren't practical for a survival garden until you have all bases covered. For example: This year, 60 feet of shell beans produced only 12 pounds of food (.2 pounds of food per linear foot). However, 40 feet of butternut squash produced 91 pounds of food (2.3 pounds per linear foot). Easily 10 times the yield. If you planted the squash among some dent corn, you could easily get 3 pounds per linear foot. Imagine getting 600 pounds of food from a 20 foot by 20 foot garden! Now imagine planting shell beans and getting 40 pounds. What you plant really can save you or starve you.
Why not grow a snap bean that seconds as a dried bean? There are many varieties that fit this description, but a few are: tongue of fire, borlotti, cranberry, roman, cherokee trail of tears, rattlesnake etc. You could can 200 quarts of snap beans and leave the rest to produce dry beans for seed and food. I picked 4 bushels of blue lake beans this year and then allowed them to go to seed. I got 2+ gallons of seed after getting 6 bushels of snap beans! With commercial fertilizer or some compost, this could easily be doubled.
According to Jackie Clay, you can grow enough wheat for 3 people for one year with an area of 50 x 50 feet. I'd agree with that, but wheat and oats are very labor intensive and should be considered only when high production plants are covered. Of course a variety of plants is always a good idea, but don't think you must have wheat when you could have much more food for your time and efforts. Buy wheat now and store it rather than trying to grow it when times are extremely bad.
Here are some high producing varieties that are storable and open pollinated:
Corn - Reid's Dent
Butternut Squash - Waltham
Pumpkins - Winter Luxury
Beans - Rattlesnake Pole Bean, Blue Lake (snap bean only)
Tomatoes - Roma VF, Super Beefsteak, Trip-L-Crop, Legend (for blight resistance)
Cucumbers - Homemade Pickles
What do you think there chances of having a sucsessful garden are?
If you have never gardened before, you won't be able to jump in and produce enough food to live unless you get lucky. If you don't have a way to till the ground, you will likely starve. I have the biggest tiller I could find and I have clocked 20 hours of steady tilling time on this years garden alone. If I'm lucky, my garden is one fourth the size it needs to be for us to grow all of our own food. I wouldn't even consider having a survival garden without a tiller, you would be better off using your energy to harvest native wild foods and meat. You can use black plastic to kill all ground cover, but this method just doesn't hold up to tilling and it's still way too hard to even plant. What is a tiller without gasoline and oil? What if you have every seed under the sun, but no gasoline to run the tiller? How will you water your garden without running water or electricity? What happens when the rain floods your garden and kills half or more of your plants? These are serious questions that should be considered before, rather than after they happen.
Bottom line is that it's easier to store food now than to grow it when you are hungry, even if you know exactly how and have all the resources. I like to grow my own long term storage foods because it gives me experience and food stores at the same time (and it's cheaper.) I started gardening as a hobby, but it has become more serious to me every year. I would totally freak out if I had to grow all of our food, and I am completely prepared to do so. It would be no easy task, even if it was a perfect growing season.
Some of the older varieties are like that, but the corn I grew this year (Reid's Yellow Dent) practically grows itself. I wanted a large seed stock and this is one of the highest rated corn varieties I could find. With 350-400 plants, I think I got my seed stock!!
