The ROI numbers in this library are only as good as your harvest data. National averages for tomatoes or basil are a starting point, but your actual return depends on your soil, your climate, and what you planted. The only way to know your real numbers is to weigh what you pull out of the garden.
Most gardeners skip this step. They get a rough sense that a good summer means “a lot of tomatoes” and a bad summer means “not many.” That is not a number you can use.
Why measurement matters
A kitchen scale changes the ROI calculation from approximate to real. When you know you harvested 14 lb of cherry tomatoes from two plants over the season, and cherry tomatoes run $3.50/lb at your grocery store, you have a $49 harvest figure you can compare against your actual seed and input costs. Without the weight, you have nothing to calculate.
The Garden ROI app tracks this per crop, per season. Feed it real weights and it tells you which crops earned their bed space.
The kitchen scale method
This is the accurate approach. Every time you harvest, bring the produce directly to the kitchen, set a bowl on the scale, zero it, and add the harvest. Log the weight in the app before you wash or trim anything - you want the weight you actually grew, not the weight after you remove leaves and stems.
Common mistake: weighing after prep. Trimming lettuce, stripping basil stems, or cutting the tops off carrots loses 10-30% of the weight depending on the crop. Weigh first, trim after.
For herbs, weigh the full bunch or sprig before stripping leaves. A bunch of parsley might weigh 2.5 oz before you pull the stems; after stripping you have 1.2 oz of usable leaves. The USDA AMS tracks commodity weights before processing - that is the convention here. Weigh the whole harvest.
Average commodity weights per unit, for reference (USDA AMS Specialty Crop Market News, 2023):
- Slicing tomato: 6-8 oz per fruit
- Cherry tomato: 0.5-0.75 oz per fruit
- Bell pepper: 5-7 oz per fruit
- Cucumber (slicing): 8-12 oz per fruit
- Zucchini: 6-8 oz per fruit at harvest size
- Head lettuce: 12-16 oz per head
These are starting points, not targets. Your weights will vary by variety and growing conditions.
The estimating method
If you do not want to weigh every harvest, count and multiply. The USDA AMS average weights above give you a per-unit baseline. Count 12 cherry tomatoes harvested today, multiply by 0.6 oz average - that is 7.2 oz, or 0.45 lb. Close enough to be useful for tracking trends.
The count method works well for crops with consistent unit sizes: cucumbers, peppers, squash, melons. It works less well for herbs, salad greens, or anything harvested by the handful where individual weights vary widely. For those, weigh.
When estimating, round down. Optimism in harvest estimates is how gardeners convince themselves that a mediocre season was great.
Herbs: bunch weight vs. stem count
Fresh herbs are sold by the bunch or by weight - rarely by individual leaf. The USDA AMS tracks prices for cut herbs by the pound (fresh weight, trimmed to market condition). For home ROI purposes, weigh what you harvest at the stem, not after stripping.
A bunch of basil (roughly 1 oz fresh weight per standard grocery bunch, per USDA AMS data) at $2.99/bunch retail equals about $47/lb. That number only makes sense if you are weighing bunches - the same amount of loose picked leaves might look like more but weigh the same.
For perennial herbs like thyme, oregano, and sage: weigh each cutting. These plants produce continuously and the cumulative weight across a season adds up more than most people realize.
What to do with small harvests
Log them. A single cucumber, a handful of beans, four spears of asparagus - log it every time. Small harvests are where the season total comes from. Missing three or four pickings of beans because they seemed too small to bother logging can easily undercount your harvest by 20%.
The app makes this easy - one entry per session, weight optional if you are estimating. The habit matters more than perfect precision on any single harvest.
Related reading: Garlic ROI: The Per-Clove Math - a worked example of how accurate yield and price data produces a real ROI number