How to Read a Seed Packet: The 8 Numbers and Terms Every New Gardener Must Understand

That tiny rectangle of cardboard contains everything you need to know to grow your crop successfully — but only if you know how to decode it. Across major seed companies like Seed Savers Exchange, Baker Creek Heirloom Seeds, and Johnny's Selected Seeds, every packet carries the same core set of numbers and terms, and misreading even one of them is one of the most common reasons first-year gardens fail.

Key takeaways:

• Days to Maturity: This number means different things for direct-sown crops vs. transplants — and most packets don't spell out which clock they're using ^[1].
• Germination Temperature: Soil temperature — not air temperature — determines whether your seeds sprout or rot. Tomatoes need 85°F soil; lettuce can sprout in 35°F ^[2].
• Germination Percentage: Federal law (CFR § 201.31) sets minimum germination standards for vegetable seeds sold commercially, and a number printed on the packet tells you exactly what to expect ^[3].
• Seed Variety Type: Terms like "heirloom," "open-pollinated," and "F1 hybrid" affect whether you can save seeds for next year — and your plants' consistency ^[4].
• Packed-For Date: Seed viability drops every year; older packets need more seeds per hole to compensate ^[5].
• Planting Depth & Spacing: Getting these wrong by even half an inch causes crowding, disease, and competition that stunts yields ^[5].

TL;DR: Eight numbers and terms on a seed packet — days to maturity, germination temperature, germination percentage, planting depth, spacing, days to germination, variety type, and packed-for date — hold the complete blueprint for a successful first garden season if you know how to read them.

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The Front of the Packet: Variety Names and What They're Actually Telling You

Before you flip to the data-dense back panel, the front of the packet carries critical information that filters which instructions apply to you.

Cultivar Name, Common Name, and Botanical Name

Every packet leads with the cultivar name — the specific variety, such as "Brandywine" or "Black Krim" for tomatoes. Many packets, especially from botanically rigorous companies, follow with the Latin botanical name ^[5]. This matters because common names vary by region (what one grower calls a "zucchini" another calls "courgette"), and the botanical name is unambiguous.

When shopping across Baker Creek, Seed Savers Exchange, or Johnny's, you'll notice Seed Savers in particular relies on dense text descriptions, while Baker Creek leans on vivid photography ^[4]. Neither approach is better, but knowing where to look saves time at the potting bench.

Heirloom, Open-Pollinated, and F1 Hybrid — This Isn't Just Marketing

The variety type designation is one of the most consequential things printed on a seed packet, and it's frequently misunderstood:

• Heirloom varieties are open-pollinated cultivars that have been passed down for at least 50 years (some definitions say pre-1951) ^[5]. Baker Creek Heirloom Seeds built its entire brand on this category — all its seeds are non-hybrid, open-pollinated varieties.
• Open-pollinated (OP) means the variety breeds true from saved seed — you can collect seeds this fall and grow the same plant next year ^[5].
• F1 Hybrid (often labeled simply "Hybrid") means the variety was created by crossing two distinct parent lines. Hybrids often show stronger early vigor and more uniform fruit, but seeds saved from an F1 plant will not grow true to type the following season ^[5]. Johnny's Selected Seeds is known for offering a wide range of commercial-grade F1 hybrids alongside open-pollinated options, clearly labeled on each packet.

"Many others, however, list only the days — which leaves you to wonder whether you start counting from the date you sowed the seed, the date the seed sprouted, or the date you set the transplant in the garden." — Garden Betty, Gardening Resource & Blog ^[1]

For a first-season gardener, the simplest rule: if seed saving interests you, choose open-pollinated or heirloom. If maximum early-season production from a short window is the goal, a labeled hybrid may serve you better.

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The Back Panel: The 6 Numbers That Make or Break Your Season

Number 1: Days to Maturity — The Most Misread Statistic in Gardening

Days to maturity (DTM) is the single most important number on the back of any vegetable seed packet — and the most misinterpreted one. It appears as a single number or range, like "65–75 days" for a tomato variety, and it looks simple. It is not ^[1].

The critical nuance: for crops that are direct-sown (planted as seeds straight into garden soil), like corn, beans, radishes, and carrots, the DTM clock starts at germination — the day the seed sprouts ^[6]. For crops typically started indoors and transplanted, like tomatoes, peppers, and eggplant, the DTM clock starts at the day you move the transplant into the garden, not the day you sowed the seed indoors ^[6].

So a "75-day tomato" from a Johnny's packet doesn't mean 75 days from when you put the seed in a tray in February. It means you can expect to harvest roughly 2.5 months after transplanting that seedling outdoors ^[6]. Factor in 6–8 weeks of indoor seed starting for tomatoes, and you're actually looking at 14–16 weeks from sow date to first tomato.

Some packets are explicit — Seed Savers Exchange, for instance, sometimes specifies "days from transplant" directly in its description ^[4]. When a packet lists only a number with no context, the general convention is: direct-sown crops count from germination; transplanted crops count from transplanting ^[6]. When in doubt, check the crop category.

If your growing season is shorter than a variety's DTM, that variety will not produce a harvestable crop before frost. This is why understanding your USDA Hardiness Zone and frost dates is inseparable from reading your seed packet correctly.

Number 2: Days to Germination

This is the number of days you can expect between sowing a seed and seeing the first seedling emerge. Johnny's Selected Seeds is particularly thorough about including this figure — Seed Savers Exchange packets for lettuce, for example, list germination times of 5–7 days under ideal conditions ^[4].

This number is your indoor-start planner. If your last frost date is May 15 and you want to transplant tomato seedlings that need 6 weeks of indoor growth, count backward from May 15. Germination takes 7–14 days for tomatoes, then add 5–6 weeks of seedling growth — meaning your seed-starting date is early to mid-March.

Number 3: Germination Temperature — Soil Temperature, Not Air Temperature

Here is where an enormous number of first-year gardeners go wrong. The germination temperature listed on a seed packet refers to soil temperature, not the air temperature in your grow room or garden ^[2].

The gap between air and soil temperature can be significant — uncovered garden beds in early spring may barely reach 40°F in the top few inches even when daytime air temperatures are in the 60s ^[2].

Federal horticultural data makes the differences between crops dramatic ^[2]:

• Lettuce, spinach, peas: Can germinate in soil as cool as 35°–40°F ^[2]
• Tomatoes: Germinate best at an optimal soil temperature of 85°F ^[2]
• Peppers: Prefer a soil temperature range of 64°–95°F ^[2]
• Warm-season crops broadly (cucumbers, eggplant, melons): Need 65°–75°F soil to sprout reliably ^[2]

Planting warm-season crops into cold soil doesn't just slow germination — it frequently causes seeds to rot in the ground before they ever sprout ^[2]. A soil thermometer inserted 1–2 inches deep is a $10 investment that prevents the heartbreak of an entire seed packet wasted to cold-soil rot ^[2].

Many gardeners use heat mats under seed trays to maintain consistent soil temperature for warm-season crops started indoors. For tomatoes especially, the difference between a 68°F germination environment and an 85°F one can mean the gap between a 7-day emergence and a 14-day (or failed) one.

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Germination Percentage, Planting Depth, and Spacing: The Numbers That Determine Your Yield

Number 4: Germination Percentage and What Federal Law Requires

When a seed packet prints a germination percentage — say, "Germ: 88%" — that number has legal weight. Under 7 CFR § 201.31 of the Federal Seed Act, the U.S. government sets minimum germination standards for vegetable seeds sold in interstate commerce ^[3]. Packets for seeds that meet or exceed these minimums may omit the percentage from the label entirely, while packets for seeds below standard are legally required to print the percentage ^[3].

The practical meaning for you: an 88% germination rate means roughly 88 out of every 100 seeds you plant should sprout under ideal conditions. For newer gardeners whose conditions aren't always ideal, planning for a 10–15% buffer is wise — sow 2–3 seeds per cell when starting tomatoes or peppers indoors, then thin to the strongest seedling.

Critically, germination percentage drops as seeds age. A tomato seed packet from two seasons ago may perform significantly below its printed percentage. This is why Seed Savers Exchange includes both a packed-for date and a sell-by date on its packets — something the company does voluntarily, since the USDA does not require it ^[4].

Number 5: Planting Depth

Planting depth is printed as a fraction — typically something like ¼ inch, ½ inch, or 1 inch ^[4]. This number exists for a biological reason: seeds contain a finite amount of stored energy to push a sprout toward the surface. A seed planted too deep exhausts that energy before reaching light and never emerges. A seed planted too shallow dries out before it can root.

A common rule of thumb in horticulture is to plant a seed at a depth roughly two to three times its diameter — which is why tiny lettuce or carrot seeds are barely pressed into the surface, while large bean or squash seeds go an inch or more deep.

On Seed Savers Exchange packets, planting depth is clearly specified for direct-seeding — often listed alongside in-row spacing in a compact block of text ^[4]. Johnny's packets for the same crops are often more expansive, with separate depth instructions for direct seeding vs. transplanting.

Number 6: Plant Spacing and Row Spacing

Spacing appears in two forms: in-row spacing (the distance between individual plants) and between-row spacing (the distance between rows). These numbers are not arbitrary aesthetics — they're calculated to ensure each plant receives adequate light, airflow, and root-zone space to reach the yield potential described on the packet ^[5].

Crowding is one of the most avoidable causes of first-year disappointment. Two lettuce plants set 2 inches apart instead of the recommended 6 inches don't produce twice as much lettuce — they produce stunted, disease-prone plants that bolt early. Understanding spacing requirements is one reason the raised bed vs. in-ground vs. container gardening decision matters: container gardens impose hard limits on how many plants realistically fit, regardless of what the packet says.

Seed Savers Exchange packets for lettuce, for example, specify a direct-seeding spacing of 1 inch apart with thinning to 1–6 inches as seedlings mature ^[4]. Johnny's Selected Seeds often goes further, providing separate spacing recommendations for single-row, wide-row, and bed-system planting.

"Vegetable seeds in containers of 1 pound or less which have a germination percentage equal to or better than the standard set forth in § 201.31 need not be labeled to show the percentage of germination and date of test." — Electronic Code of Federal Regulations, 7 CFR Part 201 ^[3]

Number 7: Sun Requirements

Almost every seed packet categorizes light needs as "Full Sun" (6+ hours of direct sunlight), "Part Sun/Part Shade" (3–6 hours), or "Full Shade" (<3 hours) ^[5]. For vegetable gardeners, the realistic baseline is this: virtually all fruiting vegetables — tomatoes, peppers, cucumbers, squash — require full sun to produce. Leafy greens and root vegetables tolerate and sometimes prefer partial shade, especially in hot climates.

Planting a tomato in a spot that gets 4 hours of sun will produce a plant — it just won't produce many tomatoes. This is a direct reason so many first-year gardens underperform even when watering and fertilizing are correct. Misreading or ignoring the sun requirement is a root cause explored in detail in our guide to why first vegetable gardens fail.

Number 8: The Packed-For Date

This is the only number on the packet that tells you about the seed's past, not its future behavior in your garden. A packed-for date or sell-by date indicates the season for which the seeds were processed and tested ^[4]. Seed viability — the percentage of seeds capable of germinating — declines over time, with the rate of decline varying significantly by species.

Short-lived seeds (onions, parsnips, corn) may lose viability in 1–2 years. Longer-lived seeds (tomatoes, cucumbers) can remain viable for 4–6 years under ideal storage conditions — cool, dark, and dry. If you're planting from a packet purchased two or three seasons ago, consider doing a simple germination test: place 10 seeds between moist paper towels, keep them at the crop's required soil temperature, and count how many sprout in the listed germination window. If 6 out of 10 sprout, you have a 60% germination rate — plant more seeds per hole and expect thinner stands.

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Putting It All Together: A Real-World Packet Reading Workflow

The 90-Second Packet Check Before You Buy

Before a seed packet goes into your cart — physical or digital — spend 90 seconds running through these eight data points in order:

1. Variety type — Heirloom/OP or Hybrid? Decide based on your seed-saving goals.
2. Days to maturity — Does it fit your frost-to-frost growing season?
3. Packed-for date — Is this packet from the current or last season?
4. Germination percentage — Is it printed? If so, plan your sowing quantity around it.
5. Germination temperature — Do you have the equipment (heat mat, grow light, warm space) to meet it indoors?
6. Days to germination — Count backward from your transplant date to set your indoor start date.
7. Planting depth — Have it memorized before you're at the potting bench.
8. Spacing — Does this variety actually fit your available bed or container space?

Why "Hardening Off" Connects Back to the Packet

One task the seed packet describes (but doesn't always explain) is the transition from indoor germination to outdoor planting. When a packet says "transplant after last frost," it assumes you know that seedlings started indoors need a 7–10 day hardening-off period — a gradual exposure to outdoor conditions — before they can survive full outdoor sun and wind. Skipping this step can kill seedlings overnight even in mild conditions. The full biology of this process is covered in our guide to what hardening off means and what happens if you skip it.

Let Technology Handle the Math

Calculating all eight data points for an entire garden — across five, ten, or fifteen different varieties with different frost dates, zone requirements, and sow schedules — is where new gardeners get genuinely overwhelmed. This is exactly the problem GardenStarter was designed to solve. Input your USDA hardiness zone and space constraints, and GardenStarter generates a curated plant list with a week-by-week task checklist that translates every packet number into a specific action on a specific day — including when to sow indoors, when to start hardening off, and when to expect your first harvest.

Reading a seed packet is a learnable skill. Building and managing a full first-season garden calendar shouldn't have to be.