The price of a packaged good rarely changes between visits. The price of the same crop in the produce aisle can move substantially within a fortnight.
Perishable goods cannot wait for a better price
A harvested crop has a short usable life, so it must be sold within days regardless of what the market is paying that week.
Sellers with no ability to hold inventory have no ability to defend a price. Supply arriving at once must clear at once, and the price falls until it does.
Packaged goods have the opposite property. A canned or frozen equivalent can sit in a warehouse for months, letting the supplier release volume as demand allows.
Growing seasons concentrate supply
Most crops have a defined harvest window in each growing region, and the national supply is the overlap of those windows rather than a steady stream.
When several regions come into season together, volume arrives faster than demand grows and prices fall sharply. Between windows, supply narrows and prices climb.
Imports smooth this by drawing on the opposite hemisphere, but they add freight cost and transit time, which is why out-of-season produce carries both a higher price and a shorter shelf life.
Weather translates directly into price
A frost, a drought or an unusually wet harvest removes volume that cannot be replaced, because the growing cycle for the affected crop has already been spent.
The effect can persist across a whole season for tree crops, where damage affects yield well beyond the immediate harvest.
Processed equivalents absorb this more slowly. A cannery buying at elevated prices does not need to reprice inventory it packed the previous year.
Contract structures differ by category
Packaged goods are typically bought under supply agreements with fixed prices for a defined term, which is why their shelf prices step rather than drift.
A significant share of fresh produce moves on shorter arrangements or spot purchases, which pass current market conditions through to the shelf almost immediately.
Retailers also treat produce as a quality signal for the whole store, so they will accept thinner margins to keep displays full rather than let gaps appear.
Shrink is built into the price
Some proportion of fresh produce is never sold, lost to damage, spoilage and trimming, and that loss has to be covered by the units that do sell.
Expected shrink varies by item and by season, so the markup applied to a delicate crop in a difficult week is higher than the same crop at peak supply.
This is why price movements are asymmetric. Abundance lowers prices quickly, while scarcity raises them further than the shortfall alone would suggest.