Harvest, store and handle produce safely

Harvest signs for common crops, storage groups by temperature and humidity, curing, toxic plant parts, and food safety from manure to the kitchen sink.

1. Read the harvest signs Understand

A vegetable is ready when the part you eat has reached the stage you want, and that stage is different for every crop. Some crops are picked immature on purpose: a snap bean, a cucumber, a summer squash and an eggplant are all eaten long before their seeds ripen. Others are picked mature: a winter squash, an onion for storage and a potato for the cellar all need to finish growing first. Days to maturity on a seed packet tell you roughly when to start looking (Module 7). They do not tell you the day to pick, because weather, variety and spacing all move the date. The plant tells you, through size, color, firmness and the state of its leaves or stems.

That is why this module teaches signs, not dates. Convention The University of Minnesota Extension and New Mexico State University Extension each publish a harvest indicator for each common crop, and the table below sets the two side by side for the 21 crops in the course's crop guide. Where the two say different things, both are shown. Read the difference as information: Minnesota gives a beet range of 1 1/4 to 3 inches across and New Mexico gives 1 1/2 to 2 inches, which tells you the sign is a range of preference, not a line a beet crosses on a given morning.

A few general rules sit under every row. Physical principle Minnesota's harvesting guide points out that the less you handle a vegetable, the longer it lasts, and that a nicked or bruised one keeps poorly. It also says to harvest only produce of high quality for storage, because rotting produce does not keep and can spread decay to its neighbors. So pick with a knife or scissors where a crop has a tough stem (broccoli, cabbage, peppers, eggplant), set produce down rather than dropping it, and put anything damaged in the eat-first pile, not the storage pile.

Two harvest stages need names because the table uses them. Sweet corn is picked at the milk stage: the kernels are near full size and a kernel pierced with a thumbnail releases a milky liquid, according to both Minnesota and New Mexico. Past that stage the kernels turn doughy and starchy. Winter squash, by contrast, is picked when the rind resists a fingernail: New Mexico's test is that the rind is firm, glossy and does not dent when you press it with a nail, and that the patch that rested on the soil has turned cream to orange.

Harvest signs for the 21 crops in the crop guide

Sources: University of Minnesota Extension, "Harvesting and storing home garden vegetables" (UMN), and New Mexico State University Extension Guide H-216, "When to Harvest Vegetables" (NMSU); garlic from University of Illinois Extension's garlic sheet. Neither UMN nor NMSU lists kale or garlic on its own; NMSU groups kale with collards and mustard. Basil appears only in UMN. The storage column is UMN's group, explained in the next section. The figures are paraphrased; the pages give more detail.

Two rows show the sources disagreeing, and both disagreements are useful. For winter squash, Minnesota says to harvest before "a frost" and New Mexico before "a heavy frost." For onions, New Mexico's sign is tops falling over and Minnesota's is a tight neck and dry scales. Neither pair is a contradiction you need to resolve; they describe a stage from two sides. Where frost is the issue, the safer reading is the earlier one, because Physical principle a winter squash is a very tender crop (Colorado State University Extension's class, used in Module 6) and its fruit is damaged by cold the leaves did not survive.

Store by temperature and humidity

Physical principle A harvested vegetable is still alive. Minnesota's guide puts it plainly: harvested vegetables still breathe and need oxygen to keep their quality. Breathing uses up the sugars and water the vegetable stored, and it runs faster when the vegetable is warm. That is the reason cold storage works for most crops, and it is the reason Minnesota says that shelf life can shrink by up to 25 percent for every 10 °F above the ideal temperature. A carrot kept at 50 °F instead of 32 °F does not spoil overnight, but it keeps for noticeably less time.

Water loss is the second process. Relative humidity is how much water vapor the air holds, as a percentage of the most it could hold at that temperature. Dry air pulls water out of a root or a leaf, which is why a carrot left loose in a dry refrigerator goes limp. Air that is too wet, on the other hand, condenses on cold produce and feeds mold. Minnesota warns that unperforated plastic bags often create too much humidity for exactly that reason, while perforated bags give moist conditions for a moderate time.

Put the two factors together and you get a storage group: a set of crops that keep best under the same temperature and humidity. Minnesota names three long-term combinations and describes a fourth condition for warm-season fruits. Convention The temperatures and humidities are Minnesota's; other extension services publish similar groups with slightly different numbers.

Read the table against your own house before you trust it. Minnesota says 32 °F is the ideal for the cold groups and that it is not easy to reach in most homes. A refrigerator is the cold storage most people have, and its roughly 40 °F and 50 to 60 percent humidity make it a cold and dry space: good for cured onions and garlic, and, in Minnesota's words, "not much else" for the long term. Root crops in perforated bags in the crisper drawer get closer to cold and moist for a few weeks. A basement that holds 50 to 60 °F fits winter squash. Nothing in a typical house holds 55 °F and moist for long, so the warm-season fruits are short-keepers whatever you do.

Cold is not always better

Physical principle Warm-season crops are damaged by cold well above freezing. Minnesota lists the thresholds: tomatoes lose color, firmness and flavor below 40 °F; peppers pit below 45 °F; cucumbers pit and develop water-soaked patches below 40 °F; eggplant pits, bronzes and browns inside after long storage below 50 °F; summer squash should not stay in the refrigerator more than four days. Even snap beans, which Minnesota places in the cold and moist group, develop pitting below 40 °F. So the refrigerator is a short stop for these crops, not a store. Minnesota also says not to store cucumbers with apples or tomatoes.

The other half of the rule is light and company for potatoes. Potatoes go in the dark (the safety section explains why), and Poison Control's potato article says not to store them with onions, because gases from onions can speed sprouting. Minnesota adds a cooking note: potatoes meant for frying keep better at 40 to 50 °F, because colder storage turns some starch to sugar and the fries darken.

Know the toxic plant parts

Some plants in a vegetable garden have parts that are not food. Everyone who picks or eats from the garden, and especially children, needs to know which parts. The course names only what a fetched source supports, and two sources from the National Capital Poison Center cover the cases a beginner meets.

Potatoes. Physical principle Poison Control's potato article explains that every part of the potato plant contains glycoalkaloids, natural toxins (solanine and chaconine) that the plant makes. The highest concentrations are in the leaves, flowers, eyes, green skin and sprouts; the lowest is in the white flesh. Light and warm storage increase how much the tuber makes. Green color itself comes from chlorophyll, which is harmless, but the green is a sign that glycoalkaloids may have risen too. Poison Control is explicit that baking, boiling, frying and microwaving do not remove them, though peeling before cooking reduces them. The symptoms it lists are mostly digestive (vomiting, abdominal pain, diarrhea), sometimes with headache, flushing, confusion or fever, starting within a few hours and occasionally a day later.

Three garden habits follow from that page. Keep developing tubers covered with soil so light does not reach them. Cure and store potatoes in the dark. Sort the harvest: Poison Control's own advice for green or sprouted potatoes is that you are better off throwing them out, and its closing rule is "when in doubt, throw them out." The leaves and flowers of the potato plant are not food at all.

Rhubarb leaves. Rhubarb is not in this course's crop list, but it is common in home gardens. Poison Control's illustrated plant list names rhubarb leaves among poisonous plants. The stalks are the eaten part.

Bitter squash. The same Poison Control potato page links a note on what it calls toxic squash syndrome: squash that looks and smells normal but tastes very bitter can make people ill. If a squash tastes very bitter, stop eating it.

Poison Control's plant list also says that for some plants every part is poisonous and for others only certain parts, and that its lists are a guide, not a complete catalog. Do not extend the list by guessing. The course makes no claim about plant parts that the sources above do not cover; for any plant you are unsure about, identify it first and ask Poison Control.

Garden food safety, from manure to the sink

Produce from a home garden is eaten raw more often than anything else in a kitchen, so there is no cooking step to kill what it carries. UConn Extension's food-safe gardening sheet makes the point that the bacteria, viruses and parasites behind most produce-related illness are a natural part of the environment and are a concern in organic and conventional gardens alike. The practices below come from extension services and the FDA. Each one blocks a route by which something harmful reaches the food.

Manure and compost

Convention Iowa State University Extension says to apply manure at least 120 days before harvesting any crop whose edible part touches the soil (root crops, leafy greens, low-growing crops) and at least 90 days before harvesting crops that do not touch the soil, such as sweet corn and trellised tomatoes. University of Maine Cooperative Extension Bulletin 2510 gives the same figures for raw manure and ties them to the USDA National Organic Program standard. Call this gap the manure-to-harvest interval. Because most vegetables are harvested sooner than 90 to 120 days after spring planting, Iowa State says spring applications are not possible for most crops; its tactic is to apply manure in the fall, after harvest, and as a general rule not to apply manure after the garden is planted. Maine adds a firm rule: never side-dress growing plants with raw manure.

Composting lowers the risk but has its own threshold. Physical principle Heat kills many pathogens and weed seeds, but only when the pile gets hot enough for long enough. The sources give different targets: Iowa State says 131 °F or higher, Maine says 140 °F further reduces risk, and UConn's sheet asks for at least 131 °F for 15 days with the pile turned at least five times, checked with a compost thermometer. A cool backyard pile that never heats does not meet any of them. UConn's fallback is to apply compost in the fall, after harvest, if you are unsure about time and temperature.

Three exclusions appear in every source. Never use cat, dog or pig manure in a vegetable garden or a compost pile; Iowa State and Maine both say parasites in these can survive and infect people. Keep pets out of the garden during the season (UConn and Maine). And note who is most at risk: Iowa State and Maine both name pregnant women, very young children and people with chronic illness as people who should be especially careful with uncooked vegetables from manured gardens.

Water

Maine's bulletin says to irrigate with water that meets drinking standards, and that this matters most within a month of harvest. If you use water that is not drinkable, such as water from a rain barrel, Maine recommends drip or trickle irrigation so the water reaches the soil without wetting leafy vegetables. Module 8 covers rain barrels; this is the food-safety reason for its soil-only rule.

Picking

UConn's sheet asks for clean, food-grade containers, meaning containers made to hold food. Garbage bags, trash cans and anything that once held cleaners, fertilizer or pesticides are not food-grade, however well rinsed. Pick with clean hands or clean gloves that have not been used for compost or weeding. Brush, shake or rub off soil outdoors before produce comes inside.

Storing and washing

Convention The FDA says to wash all produce under running water before preparing or eating it, home-grown included, and not to use soap, detergent or commercial produce wash. Its reasons: produce is porous and can absorb soap, and the safety and effectiveness of produce-wash residues have not been tested. Scrub firm produce such as melons and cucumbers with a clean brush. Wash even produce you will peel, so the knife does not carry surface dirt into the flesh. Dry with a clean cloth or paper towel. The FDA is direct that washing reduces bacteria but does not eliminate them. Start with hands washed for at least 20 seconds with soap and warm water, before and after.

UConn adds two details for garden produce. If you wash before storing, dry the produce thoroughly; otherwise store it unwashed after brushing off the soil. And when washing produce that is still warm from the garden, keep the rinse water no more than 10 °F colder than the produce. Refrigerated produce belongs at 40 °F or below (UConn and FDA), and a refrigerator thermometer is how you know yours is there.

The last route is the cutting board. Cross-contamination is the transfer of harmful organisms from a dirty surface, utensil, hand or food to a clean one. UConn says to wash hands, knife and board before preparing ready-to-eat food. The FDA adds to wash boards, dishes, utensils and counters with soap and hot water between raw meat, poultry or seafood and produce that will not be cooked.

After a lead result

If Module 3's soil test gave a lead result, the EPA's gardening page ties kitchen practices to it. Convention For preparing produce, EPA lists three steps: discard the outer leaves of leafy vegetables, wash all fruits and vegetables, and peel root crops such as carrots, beets, turnips and radishes. Its general practices for gardening where soil may contain lead add gloves, washing hands, tools and clothes after gardening, and taking shoes off at the door so soil does not travel indoors. Its tier list then adds more for higher results, starting with soil approaching 200 ppm. The EPA explains why: lead reaches people through soil left on produce and soil tracked into the house, not only through what a plant takes up. A raised bed of clean soil reduces the first route but not the others, so the washing practices still apply to a household whose yard tested high and whose beds did not. Module 3's lead section explains the tiers.

2. See it See it

• Harvesting and storing home garden vegetables (University of Minnesota Extension): the storage groups, the refrigerator figures, and harvest and storage notes for about 30 crops.
• When to Harvest Vegetables, Guide H-216 (New Mexico State University Extension): a one-page list of harvest indicators, with the most detail on melons, squash and peppers.
• Are sprouted potatoes safe to eat? (National Capital Poison Center): why green skin and sprouts matter, two short case reports, and how to store potatoes.
• Selecting and Serving Produce Safely (U.S. FDA): washing, drying, refrigeration and cross-contamination, in a short list.

3. Practice Practice

Minimum: Look up each crop's sign, pick and log one harvest, store it by group and write the household safety card; skip the thermometer readings and the curing setup. Time: about 45 minutes for the first harvest walk and storage setup, then a few minutes at each picking. Materials: a clean food-grade bowl or basket, a knife or scissors, a thermometer you can leave in the refrigerator, this page's harvest sign table (on screen or printed), and the harvest sheet in your garden notebook.

1. Find your rows. In the harvest sign table, find each crop you grow. If a crop is not one of the 21, look it up on Minnesota's or New Mexico's page, or ask your extension office. Note the storage group for each crop next to its name.
2. Go deeper Measure your storage spaces. Put the thermometer in the refrigerator for a day and read it. If you have a basement, garage or cool closet you might use, read a thermometer there in the morning and the evening for a few days. Write the readings down. Now you know which of Minnesota's groups your house can provide and which it cannot.
3. Walk the garden against the signs. For every crop that has started to produce, check the sign: size against the table's measurements, color, firmness, the fingernail test for squash, the thumbnail test for corn, the state of the leaves for onions, garlic and potatoes. Pick what is ready with clean hands into the clean container. Leave what is not.
4. Log the picking. In the harvest sheet, add a row for each crop: the date, the crop, the amount in whatever unit suits it (count, pounds, ounces, bunches) and a quality note ("firm", "a bit big", "two split"). Use one unit per crop all season so the totals add up; the review in Module 12 reads this sheet.
5. Store by group. Brush off soil outdoors. Put each crop where its group says, or as close as your house allows. Cold and moist crops go in perforated bags in the refrigerator; tomatoes stay out; basil goes in water.
6. Go deeper Set up curing if you need it. If you grow onions, garlic or potatoes, choose the curing spot now, before harvest: dry and ventilated for onions and garlic, dark for potatoes. Put a thermometer there.
7. Write the household rules. On one card for the kitchen: the toxic parts in your garden (if any), Poison Control's number, wash produce under running water with no soap, hands for 20 seconds, and, if you have a lead result, peel roots and discard outer leaves. If anyone else picks, show them the card.

4. Your garden Your garden

5. Check your work Check your work

Criteria

• For each crop you grow, can you name its harvest sign and say which source it came from?
• Do you know the temperature of your refrigerator and of any other storage space you use, from a thermometer rather than a guess?
• Can you name which of your crops should not go in the refrigerator for long, and why?
• If you grow onions, garlic or potatoes, do you have a curing spot chosen and a curing time written down with its source?
• Does everyone who picks know the toxic parts in your garden and the Poison Control number?
• Does your harvest sheet have a row for every picking so far, with one unit per crop and a quality note?
• If you used manure, can you show the manure-to-harvest interval was met for every crop it touched?

Worked example

Plot 14 is a 200-square-foot community garden plot shared by Dale Whitcomb and Ruth Asante (fictional; the frost dates are invented: first fall frost October 1). They grow potato, onion, bush bean, winter squash, garlic and kale. Checked against the criteria: their harvest signs come from the table, with garlic from Illinois. Their storage is a refrigerator Dale measured at 38 °F and an unheated cellar Ruth measured at 52 to 58 °F over a week, so winter squash goes to Ruth's cellar and cured onions to Dale's refrigerator. Curing is split: garlic on a screen in Ruth's garage for 4 to 6 weeks (Illinois), onions for 2 to 4 weeks at room temperature (Minnesota), potatoes in a dark box for 14 days (Minnesota), with the choice noted. The toxic-parts criterion matters here because they grow potatoes in a shared garden where other gardeners' children walk past: they keep the developing tubers covered with soil, keep the potato leaves and flowers out of anyone's salad, and discard green or sprouted tubers. The harvest log meets the criterion except for one gap: beans picked on two days in August were not logged. They write in the quality notes that those entries are reconstructed from memory, so the Module 12 review treats them as estimates. Ruth finds kneeling hard, so they dig potatoes and onions together, with Dale on the fork and Ruth sorting at bench height.

Common mistakes

• Refrigerating tomatoes. Minnesota says tomatoes lose color, firmness and flavor below 40 °F. If your tomatoes taste flat, check where they were stored before blaming the variety.
• Sealed plastic bags. Minnesota warns that unperforated bags trap humidity, which leads to condensation and mold. Use perforated bags, or poke holes in the bag.
• Storing produce with damage. One rotting potato or cracked squash shortens the life of those around it. Sort at harvest; eat the damaged ones first.
• Leaving potatoes in the light. A week on a sunny porch greens the skin. Cure and store in the dark, and discard tubers that turned green or sprouted, as Poison Control advises.
• Treating a cool pile as hot compost. Unless the pile reached the sources' temperatures for long enough, treat compost made with manure as carrying the same interval rule as raw manure, and apply it in fall.
• Washing with soap or bleach. The FDA and UConn both say not to. Running water and a brush for firm produce are the method.
• Waiting for one more day on squash and beans. The table's signs are early on purpose. An oversized zucchini is still edible, but it is past the sign Minnesota and New Mexico give; pick on schedule.

What is still unresolved

Your storage spaces. Minnesota's groups name ideal conditions, and few homes hit them. How long your carrots keep in your refrigerator, or your squash in your basement, is something only a season of notes can answer; the harvest log's quality column is where those notes go, and Module 12's review reads them. Preserving is unresolved by design: USDA and extension preservation guidance settles it, not this course. Anything about health, from a lead result to symptoms after a meal, belongs to a health department, a physician or Poison Control.

6. Knowledge check and scenario

Before you move on

• I found the harvest sign and storage group for each crop I grow.
• I measured my refrigerator, and any other storage space, with a thermometer. (Go deeper; optional)
• I chose a curing spot and time, with the source, for any onions, garlic or potatoes. (Go deeper; optional)
• Everyone who picks knows the toxic parts in our garden and the Poison Control number.
• My harvest sheet has a row for each picking, one unit per crop.
• I checked any manure or compost use against the 120 and 90-day intervals.