Homestead Seed Vault Rotation Calculator

Keeping preparedness seed vaults on target

Homesteaders and preparedness-minded families rely on seed vaults to secure food independence. Seed viability declines over time, especially when stored in fluctuating temperatures or humid environments. This calculator models viability decay so you can schedule rotation cycles before germination rates fall below your comfort level. Enter the number of varieties, packets, and annual decay percentage to see how many years you have before seeds drop under your target germination rate. You can then plan resupply purchases, grow-out tests, or barter exchanges to keep your inventory fresh.

Conservative households who prize self-reliance often trade heirloom varieties with neighbors or church communities. Knowing the barter value of each packet and the number of extras produced during rotation helps you steward relationships without depleting your vault. The calculator also factors in testing percentages and emergency buffers, highlighting the number of packets you should retain for crisis scenarios versus those available for sale or trade.

Viability and cost formulas

The calculator applies exponential decay to germination rates. Each year, the germination percentage is reduced by the annual decay rate multiplied by any climate stress factor you enter. When the projected germination dips below your target, the tool flags that year as the rotation deadline. It also calculates annual replacement cost by multiplying the number of packets to be replaced by the average packet price. Barter surplus is estimated by applying the emergency buffer to the total inventory and subtracting the minimum reserve.

In the expression, $\mathrm{G\_\{0\}}$ is the initial germination, $d$ is the decay rate expressed as a decimal, $c$ is the climate multiplier, and $t$ is the number of years in storage. When $\mathrm{G\_\{t\}}$ falls below your target, rotation is recommended.

Worked example

Assume you store 24 varieties with five packets each, initial germination of 92 percent, and annual decay of 7 percent. You test 15 percent of packets annually and maintain a 25 percent emergency buffer. The climate multiplier is 1.1 because of high summer heat. The calculator reveals that viability will dip below a 75 percent target in about three years. Replacing the entire inventory would cost roughly $2,640 if packets average $22 each, but testing and barter exchanges free up 18 packets annually valued at $396 for trade.

Limitations

The model assumes decay is consistent each year. In reality, seeds may degrade faster if refrigeration fails or moisture spikes. Adjust the climate multiplier upward when storage conditions are less than ideal. Barter values are estimates; document local prices for accuracy. The calculator also treats all varieties as equal even though some seeds—like onions—decline faster than beans. Track high-risk varieties separately for best results.