The shit has hit the fan. The government has collapsed, a pandemic confines you to your homestead or the zombie appocalypse comes knocking on your front door; whatever the reason, Safeway isn't open and you're on your own. Where is your next meal coming from? If you plan on growing your own food, then you'd best be prepared for the realities of farming without: fertilizer, running water or any other external inputs and let me tell you, it is going to look quite a bit different from the intensive, raised bed, SFG garden your Old Lady grows salad greens in. You need a closed loop, no irrigation system that will feed you while the country collapses around you.
For starters," closing the loop" is requisite if you are cut off from external fertilizers and inputs and by “closing the loop” I mean utilizing the valuable fetilizer that is regularly coming out of your ass. You're already knee deep in shit. The world has gone down the toilet. It's a giant crap sandwich and you're gona have to take a bite, like it or not. All puns aside consider joining the Humanure Handbook t cult and hot compost your toilet, food scraps and garden weeds in a 5X5X 5 ft pile before tilling it straight into the garden. Aethetics aside, there is nothing wrong with this approach. If you cant stomach this approach, the next best thing would be to keep the pile underneath a large tree or in a bamboo grove and rake up the fallen leaves to mulch the garden with. The leaves will contain the nutrients that leak from the pile as it decomposes. If you have livestock, you might grow the animal food with humanure compost and the people food with animal manure compost in order to avoid the bad aethetics of “eating your own shit” (a common though highly innacurate and unrealistic observation). In either case, I hihgly recomend seperating the urine when practical (easier for the gentlemen than the ladies) to dillute and use as quick-release fertilizer. When Lowes stops selling giant bags of 10-10-10, you wont have much of a choice but to utilize that creamy, soft-squeeze, brown fertilizer so figure out a system you can live with and implement it yesterday! For humanure composting, I highly reccomend the Humanure Handbook by Joseph Jenkins which can be found here: http://humanurehandbook.com/contents.html
When running water is out so is intensive gardening and right spacing. Forget the "living mulch" paradigm. Leaves evaporate more moisture than bare soil and significantly more than mulched soil. How much extra elbow room the growies need is going to depend mostly on your local tempature, rainfall and soil structure but 4x the intensive gardening spacing is a good rule of thumb. That means that if the package recommends 1 square foot per plant, you are going to give it 4 (2X2 feet as opposed to 1X1). What does spacing have to do with water requirments? Its elementary, my dear Watson. Each plant takes up water, and the sun and wind evaporate that water through the plants leaves. If there are 4 plants dessicating a square foot of space, they will use up that water roughly 4x faster than 1 plant utilizing the same space. Because the feasability of “water wise gardening” and the requisite spacing is highly dependent on your location, climate and plant variety and breed, it is best to figure this out in peace time BEFORE Safeway is packed ass to pecker with zombies and you're forced to rely on your garden for 100% of your nutrition. Start a seperate, experiemental dry garden in addition to your already exisitng irrigated garden today so you arent caught flat footed when it hits the fan. For limited irrigation or irrigation free gardening, i highly recomend Gardening Without irrigation: or without much anyway by Steve Solomon which can be found here: https://librivox.org/gardening-without-irrigation-by-steve-solomon/
Feeding yourself is likely going to mean growing things you currently take for granted and foods you may have never eaten or even heard of. Harvesting the first tomato on the block may make your dick swell with pride, but after the shit hits the fan, the gardens job is first and foremost to feed you and your family. You may know how to grow a mean salad garden but unless you can live off of the salad, the whole salad and nothing but the salad, then God help you if you didnt grow some staples. We're talking: grains, roots and beans. What grows consistently well in your area? If you can grow porn star BBC sized potatoes 2 out of 3 years, but those tubers get waterlogged and die the other 1 out of three, then you are going to fuck yourself relying too heavily on potatoes when you could have done: cassava, camas or taro. Don't know what those are? If any of those happen to be what grows well in your area, then you'd best unfuck yourself and learn to grow and cook them. Maybe you're lucky and the crops that grow well on your land happen to be what you already like to eat. Otherwise, get ready to change your dietary habits. On that subject, just like a stock portfolio, diversity is key to security. Grow a bit of this and a bit of that and you might not find yourself up shit creek when one crop fails.
A final thought: dont put tall crops in between your home and the short crops. This makes it easy for the shorter crops to be stollen but more difficult for you to inflict sudden lead poisoning on the theif. Hungry humans aside, your garden may attract wild game that could add some protein and fat to your diet. That's a two for one deal, Son.
Growing a survival garden in a SHTF scenario is going to be vastly different from growing your favorite veggies in a fertilized, irrigated kitchen garden but that doesn't mean you cant feed yourself with some comon sense and second hand knowledge. Keep practical: fetilization, irrigation, species and varieties and defense in mind when growing your SHTF garden.