September can be one of the best months at farmers markets in many parts of the country, and the reason goes beyond variety. Cool overnight temperatures can slow the process that burns sugars in certain ripening crops, and the fall harvest arriving right now has benefited from those conditions. In many temperate regions, September is also when late-summer crops and the first fall harvest are both available at once.
Fall crops arriving at September farmers markets each respond to temperature differently, and the effect depends on the plant, the region and the season. Plant scientists call the daily swing between daytime highs and overnight lows thermoperiod, and it affects photosynthesis, respiration and fruit development in ways that vary by crop. For apples and winter squash, cooler nights can help preserve sugars and encourage quality, while warm-season crops like tomatoes need temperatures to stay within a narrower range to ripen well.
Freshness is what produce shoppers say matters most
The shoppers most likely to care about these differences are already paying attention to produce quality. This year, 77% of consumers cited freshness as one of the most influential factors in where they shop for produce, tying with value for money and outranking discounts and promotions at 58%.
Seventy percent said health is one of the most important factors in their food decisions, and the share of consumers who say they try to eat organic whenever possible jumped from 46% in 2024 to 55% this year. If freshness and quality are driving more produce decisions than ever, knowing when specific crops reach their best becomes one of the most practical things a market shopper can act on.
What cool nights do to apples
Apples respond to cool nights more visibly than almost any other crop at the market, and September is when that response shows up on the table. Most varieties produce their highest-quality fruit when nighttime temperatures drop below 60 degrees Fahrenheit at harvest time, and apples grown under warmer conditions tend to be softer, less colorful and less flavorful. Apples grown with nighttime temperatures between 40 and 60 degrees tend to have better red color, firmer flesh, better storage characteristics and better flavor.
Cooler nights arriving this month are already improving color development in Minnesota orchards for varieties like Honeycrisp and Gala. Where cool nights have arrived, and fruit is nearing harvest, those conditions can support both color and quality.
Winter squash gets sweeter in the cold
Leaving crops like ripe winter squash on the vine during cool fall nights increases their sweetness because low temperatures reduce energy use and increase sugar storage. The first butternut squash of the season arrives at September markets with a sweetness that summer’s warm nights could not produce.
Cold exposure can also increase soluble sugars in root crops like carrots and parsnips as the plants convert some stored starch into sugar, a reaction that functions as a natural antifreeze for their cells. Parsnips often become sweetest after more sustained cold weather, which in many regions arrives later in fall or early winter.
Late-season tomatoes can benefit from cooler nights too
Tomatoes have a narrower comfort zone than apples or squash. Ripening is generally favored around 60 to 75 degrees Fahrenheit, and nights that drop below about 54 degrees can actually slow the process. The advantage of September in many regions is that overnight lows ease out of midsummer extremes without falling too low, giving tomatoes more hours in their ideal ripening range.
When late-summer heat subsides without nights becoming too cool, tomatoes can ripen more evenly than they do during periods of extreme heat. The flavor payoff depends on variety, sunlight, water and harvest timing, but the temperature window itself is a real advantage when it arrives.
September is when summer and fall produce share the same table
Beyond crop quality, September in many regions brings a stretch when late-summer crops and the first fall harvest are both available at once. USDA’s seasonal produce guide lists tomatoes, peppers, corn, eggplant and peaches as summer crops and apples, pears, Brussels sprouts and winter squash as fall crops. September is when both groups are available at many farmers markets.
That mix opens cooking combinations that are harder to find in July or October. For shoppers who plan around it, September can be one of the broadest periods of the market year in many temperate parts of the country.
This window is worth paying attention to
The increase in consumers who say they try to eat organic whenever possible, from 46% to 55% in two years, suggests growing interest in how produce is grown and sourced. Farmers markets give shoppers a direct way to ask growers about harvest timing, varieties and growing practices, and September is when many of those conversations are most relevant.
The market is doing its best work right now
The produce calendar works differently than most people assume heading into fall. Apples can be firmer, better colored and more flavorful because cool nights favor the conditions associated with higher fruit quality. Squash is richer because the vine held it through the season’s first cool stretch, and the tomatoes ripened at an even, unhurried pace their midsummer counterparts rarely get. For a few more weeks in much of the country, summer and fall produce are both available at once, and that window narrows fast.
Jennifer Allen is a retired professional chef and long-time writer. Her work appears in dozens of publications, including MSN, Yahoo, The Washington Post and The Seattle Times. These days, she’s busy in the kitchen developing recipes and traveling the world, and you can find all her best creations at Cook What You Love.
The post There is a scientific reason September produce tastes different, and it happens overnight appeared first on Food Drink Life.
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