Methodology
Where the numbers come from and how the ROI formula works.
Why This Page Exists
Every yield estimate, retail price, and ROI figure on this site is sourced from publicly available government and university data - not gardening folklore or editorial guesswork. This page names every dataset used, explains how the ROI formula works, and describes what "Low / Typical / High" variance means in practice.
If a number on a crop page looks wrong for your market or growing conditions, this page will help you understand where it came from and how to adjust it.
Retail Price Data
Retail prices used for ROI calculations come from two USDA sources. The primary source is used whenever data is available at the crop level; the secondary fills gaps for specialty or less-common crops.
USDA Economic Research Service (ERS) - Fruit and Vegetable Prices
The ERS Fruit and Vegetable Prices dataset reports average U.S. retail prices per pound (edible weight) for over 150 produce items, drawn from retail scanner data. This is the most widely cited consumer-level produce price dataset in the U.S. Prices reflect national averages and are updated annually.
ers.usda.gov - Fruit and Vegetable PricesUSDA Agricultural Marketing Service (AMS) - Market News
The AMS Market News program publishes weekly wholesale and retail price reports by commodity and region, including terminal market prices for specialty crops, herbs, and items not covered in the ERS dataset. Used for herbs, specialty greens, and items where ERS data is unavailable or stale.
ams.usda.gov - Market NewsLand-Grant University Extension Publications
For crops where USDA data is sparse (perennials, uncommon specialty crops), retail price estimates draw on cooperative extension budget sheets from Cornell Cooperative Extension, Penn State Extension, UC Davis ANR, and Purdue Extension. These publications include market price assumptions used in farm enterprise budgets.
All prices are national averages in USD. Local prices can vary 30-50% above or below the national average depending on market. See How to Find Local Produce Prices for how to substitute your actual market prices.
Yield Data
Yield figures (pounds per plant, or pounds per 10 row feet for crops planted by seed broadcast) come from controlled trial data published by land-grant university cooperative extension programs. These are trial-plot yields under research conditions - your results will vary based on soil quality, climate, variety, and management.
Cornell Cooperative Extension - Home Vegetable Gardening
Cornell's home vegetable gardening publications include expected yield ranges for major vegetable crops grown in typical home garden conditions. Used as the baseline for most vegetable yields.
gardening.cals.cornell.eduPurdue Extension - Vegetable Planting Guide
Purdue Extension publishes yield estimates per 100 row feet for most common vegetable and herb crops, which are converted to per-plant figures using standard in-row spacing recommendations.
extension.purdue.eduUSDA NASS Quick Stats
The USDA National Agricultural Statistics Service Quick Stats database provides commercial production yield data by crop and state. Used to cross-check extension yield figures and as a secondary source for crops with limited extension trial data.
quickstats.nass.usda.govYield ranges on crop pages show Low / Typical / High. "Typical" is the median reported yield from the primary source. "Low" is the 25th percentile (poor soil, suboptimal conditions). "High" is the 75th percentile (well-amended soil, experienced grower, favorable season). Outlier yields from trial plots are excluded.
The ROI Formula
The ROI calculation used across this site and in the Garden ROI app is deliberately simple. It answers one question: how much grocery value does this crop produce relative to what you spent to grow it?
Seed cost is the per-plant cost assuming a standard packet divided by typical seeds-per-packet figures from USDA and seed company data. For transplants, the transplant retail price is used.
What is not included: soil amendments, irrigation, fertilizer, infrastructure (beds, trellises), and labor. These are one-time or shared costs that vary too widely by gardener to include in a per-crop figure. The raised bed break-even article covers total cost accounting including infrastructure.
The seed ROI ratio (e.g., "107x") tells you how many times your seed investment returns in grocery value. The est. ROI dollar figure is the net grocery savings after seed cost - the number that shows up in the crops table.
Seed Cost Data
Seed costs per plant are calculated from retail packet prices and standard seeds-per-packet counts. Packet price data comes from major U.S. seed retailers (Baker Creek Heirloom Seeds, Johnny's Selected Seeds, Burpee) averaged across at least three sources. Seeds-per-packet counts use USDA Agricultural Research Service germination and seeding rate data where available, supplemented by seed company specifications.
Perennial crops (asparagus, rhubarb, artichoke, herbs) use crown or transplant cost for year-one figures, with a note that the amortized cost per year drops significantly after establishment.
Currency and Date Policy
Currency
All prices are in U.S. dollars (USD). The site does not convert to other currencies.
Price Year
Retail prices reflect the most recent USDA ERS annual data available at the time each crop page was written or last updated. The year is cited on each crop page. Prices are reviewed annually.
National Average
All prices are U.S. national averages unless otherwise noted. Regional variation is real - see How to Find Local Produce Prices.
Organic vs. Conventional
Default prices are conventional retail prices. Organic retail runs 30-100% higher depending on crop. If you grow without pesticides, your comparison price should be the organic retail price in your market.
Questions or Corrections
If you find a price or yield figure that looks wrong, check the cited source on the crop page first. USDA data is updated annually and prices shift. If the source has been updated since the page was written, the page may be stale.
For crop-specific breakdowns, see the full crop index or the ROI articles. For methodology questions, the Start Here page covers how to use these numbers in practice.