These trace elements are to be mixed with N-P-K and Epsom salt (instructions included), and each 20-oz pack will make up two 5-gallon buckets of garden nutrition. Depending on what you are growing and the number of growing seasons for which your USDA zone allows, you will need approximately 1 bucket of fertilizer per adult feeding unit per year.
Therefore, if you wish to store up 5 years of nutrition for 4 adults, you would need 5 of these 20-oz packs. Additionally, you may wish to purchase a few extra to account for unforeseen circumstances, changes in garden plans or additional mouths you may be required to feed. These nutrients may be stored indefinitely; they do not go bad.