Community gardens passed a rare scientific test, so test the soil too

Key takeaways

• University of Colorado researchers ran what they called the first randomized trial of community gardening, giving plots to half of 291 Denver-area adults who had not gardened in two years¹.
• By fall, gardeners averaged about 1.4 more grams of fiber and about 6 more minutes of moderate-to-vigorous activity a day than the group still waiting for plots, in part because the waiting group’s numbers slipped¹.
• Stress and anxiety fell more for gardeners, especially those who started out more stressed, but the trial found no difference in weight, waist size or total fruit and vegetable intake¹.
• City soil can carry lead and other contaminants, and EPA says the bigger risk is swallowing soil rather than eating the vegetables, so test first and wash hands and produce⁴.
• Tetanus bacteria live in the environment and enter through broken skin; CDC says about 1 in 10 U.S. cases are fatal and lists falling behind on 10-year boosters as a risk⁹.

Most health studies of gardening share a built-in problem. People who choose to garden may already be healthier, calmer or better off than people who don’t. Comparing the two groups can’t show whether the garden did anything¹.

So researchers at the University of Colorado tried something rare. Between 2017 and 2019, they recruited adults from the waiting lists of community gardens in Denver and Aurora, Colorado, working with the local group Denver Urban Gardens¹. None had gardened in the past two years, and chance decided who got a plot that spring and who stayed on the list¹.

The new gardeners received a plot of about 10 square meters, roughly 108 square feet, plus seeds, seedlings and a beginner’s gardening course¹. The study covered their fees¹. The authors believe it was the first randomized controlled trial to test community gardening, meaning the first in which chance decided who would garden¹.

For people who value natural health, a community garden bundles a lot into one place: whole food, sunlight, movement, soil under your nails and neighbors who know your name. This article covers what the trial found, what it didn’t, how to keep soil from becoming a hazard, and how to get a plot.

The Colorado trial found real gains, and they were modest

The study enrolled 291 adults with an average age of about 41¹. Most participants (82%) were women, and about a third identified as Hispanic¹. Researchers measured diet with repeated food recalls and activity with a wearable sensor worn for 7 days¹.

By fall, the gardeners ate about 21.5 grams of fiber a day, compared with 20.1 grams in the waiting-list group¹. Both groups had started near 22 grams, which the authors noted is still below what U.S. health authorities recommend¹. Both ate a little less by fall, but the gardeners’ intake slipped far less¹.

Activity followed a similar path. Gardeners edged up to about 55 minutes a day of moderate-to-vigorous activity, while the comparison group dropped to about 49¹. That 5.8-minute daily difference adds up to roughly 40 minutes a week.

One technical point keeps this honest. The statistically significant result was in how the two groups changed over the season. The fall gap on its own, for both fiber and activity, was too small to rule out chance¹.

The mental health results stood out. Perceived stress and anxiety dropped more among gardeners than among controls from spring to fall¹. The drops were largest for people who started with higher stress or anxiety¹.

Just as important is what didn’t change. The trial found no significant difference in body mass index, waist size, sitting time, overall diet quality or combined fruit and vegetable intake¹.

The authors listed the study’s limits. Diet, stress and anxiety were self-reported, the COVID-19 pandemic cut off some data, the trial was too small to test effects in subgroups, and follow-up lasted only one year¹. Keep in mind, too, that the sample was mostly women, and about 9% of people offered a plot chose not to garden at all¹.

Funding came from the American Cancer Society, the National Institutes of Health, USDA and the University of Colorado¹. No seed or garden company appears among the funders, which matters when you weigh who benefits from a result.

Other research points the same way, with caveats

The Colorado trial adds rigor to a larger body of work. A meta-analysis, which pools results from many studies, examined 22 gardening studies published after 2001². Outcomes included depression, anxiety, body mass index, life satisfaction, quality of life and sense of community².

Overall, gardening showed a moderate positive effect on health, about 0.42 on a standard scale². After the authors adjusted for publication bias, the tendency for positive studies to get published more often, the effect shrank to 0.35 but stayed positive².

Two details matter for readers. Effects were larger in horticultural therapy, which is gardening guided by a trained therapist, and among patients². And the studies compared people before and after gardening, or gardeners with non-gardeners, so they can’t prove the garden caused the change².

A 2020 scoping review in BMJ Open, which mapped research from 1990 to 2019, linked gardens and gardening to better mental well-being, more physical activity and less social isolation³. That social contact may be the community garden’s quiet advantage over a backyard bed.

The physical side is easy to see. CDC lists general yard work as moderate-intensity activity and heavy digging or shoveling as vigorous¹¹. CDC’s talk test offers a quick check: during moderate activity, you can talk but not sing¹¹.

You may also have heard that a soil bacterium, Mycobacterium vaccae, works as a natural mood booster. A well-known 2007 study found that mice given killed M. vaccae showed activity in serotonin-producing brain cells and behavior researchers read as antidepressant-like¹⁴. That’s intriguing, but it wasn’t a study of gardening, and it wasn’t done in people.

What the evidence supports, claim by claim

Here is how the main claims stack up on our four-level evidence scale.

Claim	Evidence level	What the research shows
Gardening lowers stress and anxiety	Promising but early	One randomized trial and a 22-study meta-analysis point the same way12
Gardening keeps people more active through the season	Promising but early	About 6 more active minutes a day than controls by fall, in one trial1
Gardening helps people eat more fiber	Promising but early	Fiber held steadier than in controls, a 1.4-gram daily gap, in one trial1
Gardening makes you eat more fruits and vegetables	Not enough evidence	The only randomized trial found no significant difference1
One season of gardening leads to weight loss	Evidence says no, or unsafe	No difference in BMI or waist size in the only randomized trial1
Soil bacteria act as a natural antidepressant	Not enough evidence	Tested in mice, not in gardeners14
Community gardens reduce food insecurity	Not enough evidence	Not measured in the only randomized trial1

“Promising but early” is a fine place to be for something this low in cost and risk. Nobody needs a clinical trial to justify growing tomatoes.

If you live with depression or anxiety, though, treat a garden as support, not a substitute for care. Keep your clinician in the loop, and don’t stop a prescribed treatment because the garden is helping.

A plot can add food, but it isn’t a food-security plan

In 2024, 13.7% of U.S. households, about 18.3 million, were food insecure at some point in the year¹². Among households with children, the rate was 18.4%¹².

Community gardens are sometimes promoted as an answer. The honest picture is thinner. The Colorado trial didn’t measure food security or money saved, and it found no difference in total fruit and vegetable intake¹.

A small plot can still supplement a grocery budget, especially if you plan for it. Two tips help:

• SNAP benefits can buy seeds and plants that produce food for the household¹³. A few seed packets can turn into many meals.
• Grow what costs the most at the store and keeps producing: herbs, salad greens, cherry tomatoes, pole beans and summer squash.

Test the soil before you trust it

Soil is where the natural-health ideal meets city history. EPA lists lead, cadmium, arsenic, zinc and polycyclic aromatic hydrocarbons, chemicals formed when fuel, wood or trash burns, as common urban soil contaminants⁴. Old paint can leave lead behind, and treated lumber can leave arsenic, chromium and copper⁴.

This is the surprise. EPA says the biggest danger is swallowing tainted soil, through hand-to-mouth contact, unwashed produce or dust⁴. The agency says studies find little exposure from eating vegetables raised in that soil⁴.

Children face the most danger. CDC says researchers have not found any blood lead level in children that is known to be safe, and kids under 6 are more exposed because they put hands and objects in their mouths⁷. CDC lists soil near airports, highways and factories among lead sources⁷.

How much lead is too much? EPA’s cleanup guidance gives a rough yardstick, though it was written for Superfund cleanup sites, not gardens. In January 2024, EPA cut its residential soil screening level from 400 to 200 parts per million (ppm), or 100 ppm where other lead sources exist⁵.

That guidance has already changed. An October 2025 EPA directive replaced it, keeping the 200 ppm screening level and setting 600 ppm as the point to consider removing soil at cleanup sites⁶. Expect your test report to use its own categories.

To get a test, start with your local cooperative extension service. EPA says extension offices can help you interpret soil results and point you to labs that test for contaminants⁴. Ask the garden, too, whether its soil has been tested and when.

If results show lead or other contaminants, you don’t have to give up the plot. Here is EPA’s advice, grouped by what each step protects⁴:

• Your growing medium: Grow in raised beds or containers framed with untreated wood, with landscape fabric between old ground and new soil. Ask any soil supplier to prove the soil is clean, and work in compost at up to a 50:50 ratio.
• Your crop choices: Lean on plants that fruit above ground, like tomatoes, squash and berries. Carrots, potatoes, onions and other roots and tubers are the poorest picks.
• Your mouth: Cover bare paths with mulch or groundcover, garden in gloves, and wash up before you eat. Clean tools and shoes before they come indoors.
• Your kitchen: Discard outer leaves on greens, peel anything that grew underground, and rinse the harvest under running water.

Skip old pressure-treated wood for your beds. Manufacturers stopped making CCA-treated wood, which contains arsenic, for homeowner uses in December 2003, and EPA says it shouldn’t be reused as mulch or burned at home⁸.

Heat, tools and a tetanus shot: the safety basics

Tetanus comes from bacteria that are common in the environment, and they get in where skin is broken, most often by a wound⁹. Signs show up anywhere from 3 to 21 days later, and jaw spasms, known as lockjaw, are usually first⁹. In the United States, about 1 in 10 cases end in death, and CDC counts being behind on 10-year booster shots as a risk factor⁹.

If you can’t remember your last tetanus shot, ask your clinician before planting season. Call promptly after a deep or dirty puncture wound.

Heat is the other big risk. CDC says adults 65 and older, people with heart disease, pregnant women and anyone working or exercising outside in the heat may need extra precautions¹⁰. Its advice: garden in the coolest hours, take breaks in the shade, and sip water all day¹⁰. Light yellow or clear urine usually means you’re drinking enough¹⁰.

CDC also warns against stopping or changing medicines without talking to a doctor, even in hot weather¹⁰. If someone in the heat becomes confused or faints, call 911.

A few more habits help. Kneel on a pad, lift with your legs, and switch tasks often to spare your back. The Colorado trial’s one garden-related adverse event was an allergic reaction¹, so bring your medicine if you have known allergies, such as to bee stings.

How to find a plot, or start a garden with neighbors

Waiting lists are common, and the Colorado trial recruited straight from them¹. Sign up in winter so you’re in line by spring.

Places to look:

• Your city or county parks department
• Local garden networks, like Denver Urban Gardens in the Colorado study¹
• Your county extension office⁴
• Libraries, schools, places of worship and neighborhood groups
• National groups such as the American Community Gardening Association

Before you sign up, ask these questions

• What does a plot cost, and can the fee be reduced or waived?
• Is water included, and how far is the nearest spigot?
• Has the soil been tested, and when?
• Are synthetic fertilizers or pesticides allowed?
• Are there raised beds for people who can’t kneel or who use a wheelchair?
• Are there required workdays or meetings?
• What happens if my plot gets weedy while I’m away?
• Is there a shared tool shed?

Starting a new garden takes a core group, land with written permission, water, simple rules and a soil test before anyone digs. EPA notes that some local governments can help assess a site, and federal brownfields grants are open to government agencies⁴. That makes your city a natural first call.

Questions readers ask

The bottom line

Community gardening has now been tested in a randomized trial. The trial found real but modest benefits for stress, activity and fiber, and no change in weight. That’s a solid reason to garden, as long as you expect a lift rather than a cure.

The garden’s biggest hidden risk is old soil, not the vegetables. Test before you plant, use raised beds when needed, keep kids from eating dirt, stay current on tetanus shots, and respect the heat. Then enjoy the food, the sun and the neighbors.

Related reading

• What a farmers market sign promises, and what you should ask
• A healthy month of groceries, priced by the government
• The preventive care that costs you nothing, and the exceptions
• The symptoms that mean call 911 now

Sources

1. Litt JS, Alaimo K, Harrall KK, et al. “Effects of a Community Gardening Intervention on Diet, Physical Activity, and Anthropometry Outcomes in the USA (CAPS): An Observer-Blind, Randomised Controlled Trial.” The Lancet Planetary Health, 2023. pmc.ncbi.nlm.nih.gov
2. Soga M, Gaston KJ, Yamaura Y. “Gardening Is Beneficial for Health: A Meta-Analysis.” Preventive Medicine Reports, 2016 (vol. 5, 2017). doi.org
3. Howarth M, Brettle A, Hardman M, Maden M. “What Is the Evidence for the Impact of Gardens and Gardening on Health and Well-Being: A Scoping Review and Evidence-Based Logic Model.” BMJ Open, 2020. doi.org
4. U.S. Environmental Protection Agency. “Reusing Potentially Contaminated Landscapes: Growing Gardens in Urban Soils.” EPA, 2011. epa.gov
5. U.S. Environmental Protection Agency. “Updated Soil Lead Guidance for CERCLA Sites and RCRA Corrective Action Facilities.” EPA, January 2024. semspub.epa.gov
6. U.S. Environmental Protection Agency. “Residential Soil Lead Directive for CERCLA Sites and RCRA Hazardous Waste Cleanup Facilities.” EPA, October 2025. epa.gov
7. Centers for Disease Control and Prevention. “About Childhood Lead Poisoning Prevention.” CDC, 2025. cdc.gov
8. U.S. Environmental Protection Agency. “Chromated Arsenicals (CCA).” EPA, 2025. epa.gov
9. Centers for Disease Control and Prevention. “About Tetanus.” CDC, 2026. cdc.gov
10. Centers for Disease Control and Prevention. “About Heat and Your Health.” CDC, 2026. cdc.gov
11. Centers for Disease Control and Prevention. “Measuring Physical Activity Intensity.” CDC, 2025. cdc.gov
12. USDA Economic Research Service. “Food Security in the U.S.: Key Statistics & Graphics.” USDA ERS, 2026. ers.usda.gov
13. USDA Food and Nutrition Service. “What Can SNAP Buy?” USDA FNS, 2025. fna.usda.gov
14. Lowry CA, Hollis JH, de Vries A, et al. “Identification of an Immune-Responsive Mesolimbocortical Serotonergic System: Potential Role in Regulation of Emotional Behavior.” Neuroscience, 2007. doi.org