A pint of blueberries in July and a pint of blueberries in January are the same fruit at two very different prices. Most shoppers have noticed that much. Fewer have noticed that the January pint was probably picked in Peru or Chile in the middle of their summer, which means it was not out of season at all. It was in season somewhere else.
Seasonal eating gets sold as three things at once: cheaper food, better-tasting food, and a smaller carbon footprint. Two of those hold up well. The third comes apart as soon as you ask what the alternative would have been.
One number sets the scale. Between fiscal 2009 and fiscal 2019, inflation-adjusted US fresh fruit imports grew from $5.1 billion to $14.0 billion, according to USDA’s Economic Research Service. By fiscal 2019, fresh fruit had become the largest single category of American horticultural imports, at 21 percent of total value. Year-round produce is not a quirk at the edge of the grocery store.
This article covers what peak season genuinely delivers, which nutrients fade and which ones do not, why locally grown produce from a heated greenhouse can carry a bigger carbon footprint than the same vegetable shipped in from somewhere warm, and why the price tag is a better seasonality guide than any printed chart.
What peak season buys you
Start with the part you can verify yourself, because you verify it every week.
Produce gets cheap when a lot of it shows up at once. That is not a theory about food systems. That is what a surplus does to a price. USDA’s Economic Research Service maintains a data product covering average retail prices for more than 150 commonly consumed fresh and processed fruits and vegetables, reported per pound or per pint and also per edible cup equivalent, which is the unit federal dietary recommendations are written in. The current estimates draw on retail scanner data from 2013, 2016, 2020, 2022 and 2023. ERS warns that the figures should not be used to draw conclusions about price changes over time, so read them as snapshots rather than a trend line.
Quality is harder to measure and much easier to taste. A crop picked ripe and sold within days is a different product from the same crop picked early so it can survive a week of handling. Nobody needs a study to tell a July peach from a February one.
There is a reason price deserves top billing here rather than a footnote. CDC analyzed 2015 Behavioral Risk Factor Surveillance System data across all 50 states and the District of Columbia and found that 12.2 percent of adults met the federal fruit recommendation and 9.3 percent met the vegetable recommendation. Intake was low across every socioeconomic group the agency examined. CDC’s authors named cost and limited availability among the barriers worth addressing. Set against a shortfall that size, anything that makes vegetables cheaper matters more than any refinement in sourcing.
Some nutrients really do fade, and the list is shorter than you think
The claim that produce loses nutritional value in storage is true in part. The useful version of it is more specific than the headline.
Vitamin C is the fragile one. It oxidizes, it dissolves in water, and it responds to light and warmth. A 2015 study in the Journal of the Science of Food and Agriculture worked on babyleaf spinach and spinach beet and took as its starting point that leaf ascorbic acid commonly falls after harvest. The researchers found that deliberately restricting irrigation before harvest prevented that postharvest decline in spinach but did nothing for spinach beet. Treat that as preliminary research rather than settled practice: one trial, two species, a British growing system. What it does confirm is the direction of travel. Bagged greens lose vitamin C while they sit.
Now the part that gets left out. Minerals do not evaporate. A 2015 study from the University of California, Davis, published in the Journal of Agricultural and Food Chemistry, measured magnesium, calcium, iron, zinc and copper, plus fiber and total phenolic compounds, in corn, carrots, broccoli, spinach, peas, green beans, strawberries and blueberries. Retention varied by commodity, but for most of them the researchers found no statistically significant difference between refrigerated and frozen storage.
So the honest tiering looks like this. That some vitamins decline measurably with time, warmth and light after harvest is established. How much they decline in any particular shipment, and whether that difference changes anything for a person eating a varied diet, is not established and probably cannot be stated in general. Article 670 covers nutrient requirements and how to think about meeting them.
The greenhouse is the part that gets skipped
This is where the subject gets interesting, because the finding runs opposite to what most seasonal-eating advice implies.
In 2012, researchers at ETH Zurich published a life cycle assessment in Environmental Science and Technology covering 34 fruits and vegetables sold by a large Swiss retailer and drawn from 29 countries of origin. They modeled seedling production, fertilizer, pesticides, farm machinery, irrigation, greenhouse heating oil, cold storage and every transport leg, air freight included.
Two findings reorder the usual advice. The first matches intuition: air freight dominated the footprint of anything that flew, and asparagus flown in from Mexico or Peru carried 16 to 19 times the global warming potential of asparagus grown in Switzerland.
The second does not match intuition at all. For almost everything that did not fly, the biggest single driver of emissions was burning fossil fuel to heat a greenhouse out of season. Swiss cucumbers grown in a heated greenhouse carried more than ten times the global warming potential of cucumbers from an unheated one. Lettuce showed roughly the same factor of ten. Eggplant came in near six times, tomatoes and peppers near four. The authors reported that fossil-fuel greenhouse heating frequently mattered more than moving the produce by road, even across a distance as long as southern Spain to Switzerland.
The ETH Zurich team’s own summary of the work states it plainly: “Sourcing fruits and vegetables locally is only a good strategy to reduce the carbon footprint if no greenhouse heating with fossil fuels is involved.”
Four caveats, because this is one study and the details decide the answer. It was built for a Swiss retailer using 2007 sales data and European energy assumptions, so the numbers do not transfer to a US supply chain unchanged. Greenhouses heated with waste heat or geothermal water change the result entirely, and the authors point to operating examples. The alternative matters as much as the method: the same paper found that holding local apples and kiwifruit in cold storage still beat shipping them in from New Zealand. And there is a real trade-off in the other direction, which the authors raise themselves, that sourcing winter vegetables from southern countries can shift the burden onto regions where irrigation water is already scarce.
US-specific work puts the whole argument in proportion. A 2008 analysis by Carnegie Mellon researchers in the same journal broke down the average American household’s 8.1 metric tons of annual food-related greenhouse gas emissions and found 83 percent of it arose in the production phase. All transportation together accounted for 11 percent, and the final leg from producer to retailer came to 4 percent, even though the average food item travelled 1,640 kilometers for delivery and 6,760 kilometers across its full supply chain. Article 739 covers local food systems and article 741 covers the emissions hierarchy, which is where the full ranking belongs.
None of this makes seasonal eating pointless. It means the carbon case depends on what the alternative was, and sometimes the alternative was a boat.
“In season” depends on which hemisphere you are counting
A January blueberry is in season. The season is simply happening a few thousand miles to the south.
USDA’s Economic Research Service traced where the growth in US fresh fruit imports came from between fiscal 2009 and fiscal 2019. Mexico grew the most in dollar terms, with avocados accounting for 89 percent of its $5.3 billion increase. Peru added $1.1 billion, led by a $0.4 billion rise in blueberries. Chile added $0.7 billion, mostly citrus and blueberries. Guatemala added $0.8 billion, nearly all of it bananas. Costa Rica added $0.4 billion, split between bananas and pineapples. By fiscal 2019, the top five fresh fruit products made up 75 percent of all fresh fruit imports. ERS credits part of this pattern to the alternate growing seasons of supplier countries, which it says help assure a year-round supply of many types of fresh produce.
Peru and Chile sit in the Southern Hemisphere. Their harvest is the North American winter. That is not a loophole in seasonal eating. It is what the phrase means once you stop assuming the calendar is local.
The scale of domestic production is worth knowing alongside it. ERS reports that US vegetable and pulse farm cash receipts, potatoes and mushrooms included, averaged $24.2 billion from 2020 through 2024, roughly 10 percent of all US crop cash receipts, grown on about 2 percent of harvested acreage. Per capita vegetable availability over the same period averaged 386 pounds, about 1 percent below the 389 pounds of a decade earlier.
One more wrinkle, and USDA supplies it against itself. The department’s own seasonal produce guide lists bananas, pineapples, mangos and plantains under summer. None of those grow in season anywhere in the continental United States. The same guide notes that seasonal produce in your area will vary by growing conditions and weather, which is an honest admission that a national chart cannot tell you what is in season where you live.
Frozen and canned were picked at peak
For most households, most of the year, this is the practical answer, and the research supports it better than the reputation does.
A 2015 UC Davis study in the Journal of Agricultural and Food Chemistry split eight crops at harvest and held half of each refrigerated and half frozen. The authors concluded that the vitamin content of frozen produce is comparable to fresh and sometimes higher, with beta carotene the one clear exception. Article 814 reports the nutrient-by-nutrient results in full, next to what each form costs per cup.
The mechanism is not mysterious. Produce headed for the freezer is usually blanched first, meaning briefly scalded in boiling water or steam. The National Center for Home Food Preservation at the University of Georgia explains the reason: “Blanching slows or stops the action of enzymes which cause loss of flavor, color and texture.” The center adds that blanching also helps slow vitamin loss, and it names the limit of the whole process, which is that freezing sterilizes nothing. Extreme cold slows microbial growth rather than ending it, which is why a thawed bag still has a clock running.
Canning works on the same logic of catching a crop at peak and stopping the clock, with trade-offs you read off the Nutrition Facts panel rather than guess at: vegetables are often packed with added salt, and fruit is sometimes packed in syrup. USDA’s MyPlate guidance is blunt about the category question, stating that vegetables count whether they are raw or cooked and whether they are fresh, frozen, canned or dried.
Frozen also solves a problem fresh produce creates, which is that a bag of spinach has about four days of patience in it. Article 746 covers food waste.
One seasonal swing worth raising with a clinician
If you take warfarin or another vitamin K antagonist, a sudden seasonal change in how much leafy green you eat is worth mentioning at your next appointment. Not a reason to stop eating greens.
The background is worth knowing, because the folk advice is partly wrong. A 2016 systematic review in Medicine gathered two dietary intervention trials and nine observational studies on whether dietary vitamin K interferes with anticoagulation. The findings conflicted. Some studies found a negative association with INR, the blood test used to monitor these drugs, and others suggested a baseline amount of vitamin K is needed to hold anticoagulation steady at all. Any detectable effect showed up only at intakes above roughly 150 micrograms a day.
The reviewers concluded that the available evidence does not support telling patients to change their diets when starting these drugs, and that keeping eating habits stable while avoiding wide swings in vitamin K intake is the more relevant goal. A reader who suddenly eats far more kale and collards because they are cheap in October is making exactly the kind of swing worth flagging. That belongs in a conversation with the clinician managing the dose. This article gives no dose, no target and no instruction to change anything.
How to eat seasonally without making it a project
Skip the chart. Four questions do the same work in less time, and they are specific to your store rather than to a national average.
What is stacked high and cheap this week? Retailers advertise what they bought in volume, and they bought it in volume because a lot of it was harvested. USDA’s Agricultural Marketing Service issues thousands of market reports a year covering wholesale, retail and shipping data, including a section on grocery store features. You will never read it. You are already seeing its output in the weekly circular.
Is this one of the crops that travels badly? Berries, sweet corn, tomatoes, stone fruit and asparagus lose the most between the field and the shelf. Apples, citrus, cabbage, carrots, onions and winter squash hold for months in storage, which is part of why they cost roughly the same in February as in September.
Is there a version that was processed at peak? For anything you plan to cook rather than eat raw, frozen is usually the better buy out of season, and the vitamin research above is the reason why, not a marketing claim.
Will I eat it before it dies? The most expensive produce is the produce that gets thrown out. Three pounds of in-season peaches you do not finish is a worse outcome than one pound of imported ones you do.
Price is the seasonality chart
Peak-season produce is usually cheaper and usually better, and some vitamins genuinely fade on the way to you. Those parts hold. The carbon case is the weak link, because local and seasonal only lower emissions when the alternative was something worse, and a heated winter greenhouse down the road is frequently the something worse.
None of that requires looking anything up. Price already encodes the harvest. When a crop is abundant it is cheap, and when it is cheap it is in season somewhere that matters to your grocery store. That signal updates weekly, costs nothing, and does not require you to know which hemisphere your blueberries came from.
Sources
- U.S. Department of Agriculture, Economic Research Service. “Fruit and Vegetable Prices.” ers.usda.gov
- U.S. Department of Agriculture, Economic Research Service. “Amber Waves: U.S. Fruit Imports Grew By $8.9 Billion Over the Last Decade to Meet Rising Demand.” ers.usda.gov
- U.S. Department of Agriculture, Economic Research Service. “Vegetables and Pulses.” ers.usda.gov
- U.S. Department of Agriculture, SNAP-Ed Connection. “Seasonal Produce Guide.”
- U.S. Department of Agriculture, MyPlate. “Vegetables.” myplate.gov
- U.S. Department of Agriculture, Agricultural Marketing Service. “Market News.” ams.usda.gov
- National Center for Home Food Preservation, University of Georgia. “Freezing.” nchfp.uga.edu
- Centers for Disease Control and Prevention. “Lee-Kwan SH et al. "Disparities in State-Specific Adult Fruit and Vegetable Consumption, United States, 2015." MMWR Morbidity and Mortality Weekly Report, 2017. PubMed. DOI: 10.15585/mmwr.mm6645a1.” doi.org
- PubMed. “Stoessel F, Juraske R, Pfister S, Hellweg S. "Life cycle inventory and carbon and water FoodPrint of fruits and vegetables: application to a Swiss retailer." Environmental Science & Technology, 2012. PubMed. DOI: 10.1021/es2030577.” doi.org
- PubMed. “Weber CL, Matthews HS. "Food-miles and the relative climate impacts of food choices in the United States." Environmental Science & Technology, 2008. PubMed. DOI: 10.1021/es702969f.” doi.org
- PubMed. “Bouzari A, Holstege D, Barrett DM. "Vitamin retention in eight fruits and vegetables: a comparison of refrigerated and frozen storage." Journal of Agricultural and Food Chemistry, 2015. PubMed. DOI: 10.1021/jf5058793.” doi.org
- PubMed. “Bouzari A, Holstege D, Barrett DM. "Mineral, fiber, and total phenolic retention in eight fruits and vegetables: a comparison of refrigerated and frozen storage." Journal of Agricultural and Food Chemistry, 2015. PubMed. DOI: 10.1021/jf504890k.” doi.org
- PubMed. “Mogren LM, Beacham AM, Reade JPH, Monaghan JM. "Moderate water stress prevents the postharvest decline of ascorbic acid in spinach (Spinacia oleracea L.) but not in spinach beet (Beta vulgaris L.)." Journal of the Science of Food and Agriculture, 2015. PubMed. DOI: 10.1002/jsfa.7464.” doi.org
- PubMed. “Violi F, Lip GYH, Pignatelli P, Pastori D. "Interaction Between Dietary Vitamin K Intake and Anticoagulation by Vitamin K Antagonists: Is It Really True? A Systematic Review." Medicine, 2016. PubMed. DOI: 10.1097/MD.0000000000002895.” doi.org