Let’s say you have a single pound of wheat — whole berries which can be planted as seed or eaten. Well, there is not much nutrition in only one pound of wheat. You could eat for a day or so. But if you plant that pound of wheat, with a decent yield, you could harvest about 30 pounds of wheat.
What’s a grow out? That’s when you grow those 30 pounds of wheat only for the purpose of replanting what you harvest. One pound of wheat seed gives you a rather small harvest. But 30 pounds of wheat seed can plant a third to one half of an acre. Then the yield is another 30-fold increase: 900 pounds. A grow out is when you plant seed in order to produce more seed for a second planting.
For survival purposes, you may want to plant more seed than is available from the most common gardening seed sources. And when the SHTF, those sources will, in all likelihood, dry up. You’ll be limited to whatever seed you have on hand. So a grow out is essential to increase your personal seed supply.
Now, what’s a grow out ratio? It is the ratio of the amount of seed a crop produces compared to the amount of seed planted for that crop. If you plant a pound of wheat and get 30 pounds in the harvest, the ratio is 30:1. If you plant 10 pounds of corn (maize) seed, you might harvest as much as 450 pounds of corn, a 45:1 ratio.
The plants with the highest grow out ratio have smaller seeds and/or more seeds harvested per plant. The highest grow out ratio of any crop, as far as I know, is amaranth. The seeding rate can be anywhere from 1/4 pound to one full pound per acre for a harvest of around a thousand pounds. That’s a grow out ratio of as much as 4000:1 and at least 1000:1. So if you have a small amount of amaranth, and you do a single grow out, you’ll have all the seed you need.
It’s a good idea to do a grow out for each type of food crop you will need for your survival garden. Then store those seeds safely. A vacuum sealer is good for that purpose. Include a packet of silica gel with the seeds to absorb moisture. Then store somewhere cool and dark. Basements can be too damp for seed storage. But with the vacuum seal, perhaps also inside a sealed 5-gallon bucket, they should be fine.