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.
Harvest Weight Loss Table: Why Pre-Trim Weighing Matters
When you weigh after trimming, you’re measuring less than you grew. This matters for ROI calculations because yield data from USDA extension services and USDA AMS commodity reports uses pre-processing weight - the same weight standard you should use when calculating what your garden returned.
Here are the trim losses for 8 common crops, expressed as percent of fresh-harvested weight lost during typical kitchen prep. Source: USDA AMS commodity grading standards define commercial trim-to-market standards; these home kitchen estimates are consistent with those figures.
| Crop | Typical prep | Trim loss (% of harvest weight) | Pre-trim vs. post-trim weight (1 lb example) |
|---|---|---|---|
| Tomato (slicing) | Core removal | 3-5% | 1.00 lb → 0.95-0.97 lb |
| Basil | Stem removal | 30-40% | 1.00 lb → 0.60-0.70 lb |
| Lettuce (head) | Outer leaves, core | 15-25% | 1.00 lb → 0.75-0.85 lb |
| Carrot | Tops, peel | 10-15% | 1.00 lb → 0.85-0.90 lb |
| Cucumber | Ends trim | 2-5% | 1.00 lb → 0.95-0.98 lb |
| Green beans | Tip removal | 5-8% | 1.00 lb → 0.92-0.95 lb |
| Kale | Stem removal | 25-35% | 1.00 lb → 0.65-0.75 lb |
| Garlic | Papery skin | 3-6% | 1.00 lb → 0.94-0.97 lb |
Basil and kale are where the difference is largest. If you’re weighing basil after stripping leaves from stems, you’re recording 60-70% of what you actually grew. That understates your yield by 30-40% and makes your ROI look worse than it is. Weigh the stems before stripping.
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.
Season Totals and Extension Benchmarks
Tracking weekly harvests only pays off when you add them up. At the end of the season, your total yield per crop compared against extension service averages tells you whether you’re getting what the crop should produce.
Benchmarks from Penn State Extension (Vegetable Production Guide) and Purdue Extension vegetable guides:
| Crop | Expected yield (home garden) | Per plant or per row | Notes |
|---|---|---|---|
| Indeterminate tomato | 10-15 lb/plant | Per plant | Full season Zone 5-6 |
| Cherry tomato | 8-12 lb/plant | Per plant | From first fruit to frost |
| Basil | 0.5-1 lb/plant | Per plant | 5-month season, regular harvest |
| Lettuce (cut-and-come) | 0.5-0.75 lb/week | Per 4 sq ft | While productive |
| Bush beans | 1.5-2 lb | Per 10-foot row | One planting |
| Cucumber | 8-10 lb/plant | Per plant | Indeterminate type |
| Kale | 1.5-2 lb/plant | Per plant | Full season |
| Garlic | 0.25-0.4 lb/head | Per clove planted | Average head weight at harvest |
If your cherry tomatoes returned 5 lb per plant, you’re getting roughly half of what a productive plant should yield. That’s diagnostic. Possible causes: too much shade, inconsistent watering, not enough fertilizer, variety selection, or pest damage. Without a total harvest number, you can’t see the gap. With it, you have something to investigate.
If your basil returned 1.5 lb per plant, that’s well above average - you’re harvesting correctly and keeping it from flowering.
Management Style Comparison: What Succession Does to Your Numbers
Single-wave planting and succession planting return different total yields from the same bed space. This is only visible if you’re tracking per-crop totals.
Lettuce, single wave (10 plants planted May 1, Zone 6):
- Productive period: 3 weeks before bolt pressure begins in June heat
- Total harvest: approximately 1.5-2 lb
- Grocery equivalent at $4/lb: $6-8
Lettuce, 5-wave succession (every 2 weeks from April 15 through June 1, plus fall replanting in August):
- Productive period: April through June, then September through October
- Total harvest: 6-8 lb across all plantings
- Grocery equivalent at $4/lb: $24-32
Same bed, same amendment costs, same tools. The only difference is five seed packets instead of one ($2.49 each × 5 = $12.45 total), and five planting dates instead of one. The return is 4x higher.
Tracking makes this visible. If you track your lettuce by planting wave, you can see which waves produced and which were cut short by heat. That data tells you exactly how many succession waves actually make sense in your specific climate.
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.
Interpreting Your Data at Season’s End
Three questions to ask when you total up your harvest log:
Which crop returned the highest value per square foot? Divide your total dollar value for each crop by the square footage it occupied. If cherry tomatoes returned $120 from 16 sq ft, that’s $7.50/sq ft. If beans returned $18 from 16 sq ft, that’s $1.13/sq ft. This comparison tells you where your bed space is working hardest. Next season, you might give tomatoes more space and beans less - or grow beans only if you have leftover space.
Which crops underperformed their extension benchmarks? If your tomatoes returned 6 lb per plant against a 10-15 lb expectation, there’s a problem to find. Go through the variables: did they get 8+ hours of sun? Consistent watering? One side-dress of fertilizer at flowering? If all those were met, it was probably a variety or disease issue. Next year: change the variety, or move the bed to a sunnier spot.
What was your net value per dollar of input? Total dollar value of harvest divided by total seed, transplant, and amendment costs gives you a ratio. A ratio of 5:1 or better means your garden is working. Below 3:1, something - crop selection, yield, or price assumptions - is off. The ratio won’t be exact because you can’t fully price your time, but it gives you directional feedback.
The season-end review takes 20 minutes. It’s what converts harvest data into better planning decisions.
One more check worth doing: compare your total logged weight against your rough end-of-season estimate of what you think you grew. Most gardeners who estimate without a scale understate their real yield by 25-40%. The gap between “feels like a lot” and an actual weight surprises most people the first time they see it.
Related reading: Garlic ROI: The Per-Clove Math - a worked example of how accurate yield and price data produces a real ROI number; How to Find Local Prices - the other half of the ROI equation once you have yield data
Related crops: Tomato, Lettuce, Kale, Green Bean