Every February the seed catalogs arrive and something happens to otherwise rational people. You order six tomato varieties because they all sounded good, three packets of summer squash, and exactly one packet of carrots because carrots are boring. By August you are giving zucchini to strangers in the parking lot and buying carrots at the store. This is not a discipline problem. It is an arithmetic problem, and it is fixable in about two hours with a notebook.

The math is not hard. What makes it feel hard is that nobody teaches it in the order that makes sense. Seed packets tell you spacing but not yield. Extension bulletins give you yield per acre, which is useless for a 30-foot bed. Garden books give you “plant 5 tomato plants per person,” which assumes a person you have never met with eating habits you do not share. Here is how to build the number yourself.

Start at the Wrong End: What Leaves the Garden

Plan backward from consumption, not forward from bed space. If you plant to fill space, you will fill it, and then you will have a distribution problem instead of a growing problem.

Write down, for each crop you care about, how much you actually use in a year. For a household, that means honest numbers: how many pounds of tomatoes do you eat fresh in a week during the season, and how many quarts do you can? For market growers, it is cleaner — pull last year’s sales by crop, or estimate from your customer count. A 40-member CSA taking a weekly share for 20 weeks needs roughly 800 units of any given “one item per share” crop, and that number does not care how nice your beds look.

Typical annual household use, as a starting point to argue with:

  • Fresh-eating tomatoes — 20–30 lb per person for the season, plus 20–25 lb per quart of sauce you want canned
  • Carrots — 15–25 lb per person if you eat them regularly and store some
  • Onions — 30–40 lb per person per year for a household that cooks most nights
  • Winter squash — 6–12 fruits per person, depending on whether you actually like squash in February
  • Salad greens — about 0.5 lb per person per week you want salad

The onion number surprises people every time. Most home gardens plant about a quarter of what the household will use, then wonder why they are buying onions in November.

The Four Numbers Every Crop Needs

For each crop, you need four figures before you can plan anything. Get these once, write them down, and reuse them forever.

  • Yield per plant or per bed foot — the output number. Determinate tomato: 8–15 lb per plant. Indeterminate: 15–30 lb with good support and a long season. Carrots: 1–1.5 lb per bed foot at 3-inch spacing in a 30-inch bed. Bush beans: 0.5 lb per foot of row per picking, 3–4 pickings. Head lettuce: one head per plant, obviously, but that means bed feet is the only unit that matters.
  • Spacing — in-row and between-row, which together give plants per bed foot. A 30-inch bed at 6-inch row spacing holds five rows; at 3-inch in-row spacing that is 20 plants per bed foot for carrots or radishes.
  • Days to maturity — and remember the packet number is from transplant for transplanted crops, from seeding for direct-sown. Add 10–14 days for fall plantings as day length shortens.
  • Harvest window — how long the crop yields once it starts. Radishes: about 5 days before they split. Bush beans: 2–3 weeks. Indeterminate tomatoes: 8–12 weeks. This number decides whether you plant once or six times.
The harvest window is the number everyone skips and everyone regrets skipping. A crop with a five-day window planted all at once is not a harvest, it is an emergency.

Convert to Bed Feet, Not Plant Counts

Plant counts lie to you because they hide spacing. Bed feet do not. Every planning decision should end in the same unit: linear feet of a standard bed. Pick your bed width — 30 inches is the common market-garden standard, 4 feet is common in home raised beds — and stick with it so the numbers stay comparable.

The formula is three steps:

  1. Target pounds ÷ yield per bed foot = bed feet needed. Want 60 lb of carrots at 1.2 lb per bed foot? That is 50 bed feet.
  2. Bed feet ÷ bed length = number of beds. On 50-foot beds, that is one bed of carrots. On 25-foot beds, two.
  3. Bed feet × plants per foot = seed or transplant count. Fifty bed feet of carrots at 20 plants per foot is 1,000 carrots, which is roughly one 1,000-seed packet with no margin — buy two.

Do this for every crop and total the bed feet at the end. This is the moment of truth: if your total exceeds the beds you have, you are not going to grow all of it, and it is far cheaper to find that out in February than in June. Keeping the per-crop yield figures somewhere you will actually find them next year matters more than the precision of any single number — a tool like CropsBook lets you log planting dates, bed assignments, and harvest weights per bed so the math gets more accurate every season instead of resetting each spring.

Build In the Losses Nobody Budgets For

Textbook yields assume everything germinates, nothing gets eaten, and every fruit is sellable. Plan on the real numbers instead.

  • Germination — assume 75–85% field emergence even for fresh seed rated at 95%. Direct-sown small seed in a dry week can drop to 50%.
  • Transplant loss — 5–10% between seeding flats and established plants, more if you are new to hardening off.
  • Pest and disease — 10–20% on a normal year for most crops, and 100% on the one crop that gets hit hard. Diversity is the insurance policy.
  • Cull rate — for market sales, 15–25% of tomatoes and 30%+ of a first-year carrot crop will not be pack-out quality. Home growers can eat the ugly ones; market growers cannot sell them at full price.

The practical shortcut: multiply your calculated planting by 1.25 for home use and 1.4 for market. If you hit your target exactly, you have surplus to give away or preserve. If you plan to exactly your need and the flea beetles find your brassicas, you have nothing.

Ready to put this into practice? Download CropsBook on the App Store — it’s free and works offline.

Fresh Eating and Storage Are Two Different Plans

The single biggest source of over- and under-planting is treating “how much do I want” as one number when it is really two. Fresh consumption is a weekly rate over a limited window. Storage is a one-time volume that has to survive months.

Run them separately. A household eating 3 lb of tomatoes a week across a 12-week season needs 36 lb fresh — two or three indeterminate plants. The same household canning 30 quarts of sauce needs another 650–750 lb, which is 25–35 paste-tomato plants. Those are wildly different plantings, and they want different varieties, different bed space, and a different harvest rhythm. Same with onions: your fresh-eating sweet onions and your storage keepers are separate calculations with separate varieties, because sweet onions rot by October.

If a crop has a storage version and a fresh version, plan them as two crops. They almost never share a variety, a planting date, or a bed.

Split the Season Before You Split the Beds

One bed is not one crop. It is a bed-year, and most beds can carry two or three plantings in a season. When you total your bed feet, count capacity as beds × turns, not just beds.

A 50-foot bed in a zone with a 180-day season can realistically do: spring spinach seeded in March and cleared in May, main-season bush beans in through August, then a fall radish or arugula planting. That is 150 bed feet of production from 50 feet of ground. Fast crops — radishes at 28 days, arugula at 30, baby lettuce at 35 — are what make the turns work; the long-season crops like winter squash, tomatoes, and leeks occupy their bed for the whole year and should be budgeted as such.

Where growers get burned is forgetting the reset time between crops. Budget 7–14 days between clearing and replanting for residue breakdown, amendment, and bed prep. Three turns on paper often becomes two in the field because nobody accounted for the three weeks of clean-up.

Make Next Year’s Numbers Yours

Every yield figure in this article is a regional average with a wide error bar. Your soil, your season length, your irrigation, and your variety choices will move them 30% in either direction. The only numbers worth trusting are the ones from your own beds.

So weigh things. Not everything, not forever — but pick five crops this season and record harvest weight by bed with the date. A kitchen scale and 30 seconds per harvest gets you a yield-per-bed-foot number that beats any published table. Do it for three seasons and your seed order stops being a guess. This is the same logic that applies across any production operation: ranchers running Barnsbook track weight gain and feed conversion per animal for exactly this reason, and beekeepers using HiveBook log honey pulls per hive to know which colonies are earning their space. The unit changes; the discipline does not.

Record three things per planting and you have enough: date seeded or transplanted, bed feet used, and total harvest weight with the harvest window dates. That is it. CropsBook handles this offline in the field, which matters because the harvest data you write down at the wash station is the data that actually gets recorded — the notes you plan to enter later tonight never happen.

A Worked Example, Start to Finish

Say you want 40 quarts of tomato sauce and enough fresh slicers for a family of four.

  • Sauce — 40 quarts × 22 lb per quart = 880 lb of paste tomatoes. At 12 lb per plant for a determinate paste type, that is 74 plants. Add 25% for loss: 92 plants. At 18-inch spacing in a single row, that is 138 bed feet, or roughly three 50-foot beds.
  • Fresh — 4 people × 25 lb = 100 lb. At 20 lb per indeterminate plant, 5 plants, plus loss margin makes 7. At 24-inch spacing, 14 bed feet.
  • Total — about 152 bed feet of tomatoes, 99 plants, needing roughly 120 seedlings started to account for flat losses.

Now look at that number honestly. Three beds of paste tomatoes is a real commitment in trellising, pruning, and a solid week of processing in late August. If that does not fit your life, cut the sauce target to 20 quarts and free up a bed and a half for something else. That decision — made in February with a number in front of you — is the entire point of the exercise.

Garden math will not make you a better grower. It will make you a grower who plants what they meant to plant, which turns out to be most of the difference between a season that feeds you and a season that mostly produces zucchini and regret. Spend the two hours. Write the numbers down. Then go weigh things all summer so next February’s two hours are even better spent.