Reading Seed Packets: What All Those Numbers Mean
Why Seed Packets Need Translation for Santa Cruz
Seed packets are packed with information, but if you're new to gardening, they can feel like reading a foreign language. Days to maturity, hardiness zones, spacing requirements, planting depth: what does it all mean, and how does it apply to Santa Cruz County?
Understanding seed packets helps you choose the right varieties, plant at the right time, and set realistic expectations for harvest. But here's the catch: most seed packets are written for a national audience. They assume distinct seasons (cold winters, hot summers, fall frost) that don't match our Mediterranean climate.
In Santa Cruz County, we garden year-round. Our cool, foggy coast differs dramatically from our warm inland valleys. Generic seed packet advice often misses the mark. This guide decodes seed packet terminology and shows you how to adapt those generic instructions for successful gardening here.
Anatomy of a Seed Packet
Most seed packets contain the same basic information, though the layout varies by company. Here's what you'll typically find and what it means for Santa Cruz gardeners.
Variety Name
The specific cultivar you're planting. For example, 'Cherokee Purple' tomato or 'Detroit Dark Red' beet.
Why it matters: Varieties perform differently in different climates. Some tomatoes are bred for fog tolerance (critical on the coast), while others need intense heat. Always note the variety so you can track what works in your specific microclimate. After a few seasons, you'll have a list of proven performers for your garden.
Days to Maturity
This number tells you how long from planting to harvest. But it's more complicated than it looks.
For transplants (tomatoes, peppers, brassicas): Days to maturity counts from when you transplant seedlings into the garden, not from seed starting. If a tomato says "70 days," that's 70 days after you plant a 6 to 8 week old seedling in the ground.
For direct-sown crops (beans, carrots, lettuce): Days to maturity counts from germination.
Santa Cruz translation: National seed companies assume consistent warm weather for summer crops. In coastal Santa Cruz, cool fog slows growth significantly. Add 10 to 20 days to maturity estimates for coastal areas (Aptos, Capitola, Live Oak, Santa Cruz beaches). Inland areas (Scotts Valley, San Lorenzo Valley sunny exposures, Watsonville) match published times more closely.
Example: A tomato listed as "75 days to maturity" might take 85 to 95 days on the coast but only 75 to 80 days inland.
Hardiness Zone
You'll often see "Zones 3-9" or similar. This refers to USDA Plant Hardiness Zones, based on average annual minimum winter temperatures.
Santa Cruz County falls in USDA Zones 9b and 10a, meaning our coldest winter temperatures average 25°F to 35°F.
Why this mostly doesn't matter for vegetables: Hardiness zones are designed for perennials (plants that survive multiple winters). Most vegetables are annuals grown in a single season, so hardiness zones are less relevant.
When it does matter:
Perennial vegetables (artichokes, asparagus, rhubarb)
Herbs (rosemary, thyme, sage)
Fruit trees and berries
For these, make sure the variety is hardy to at least Zone 9.
Better than USDA zones for Santa Cruz: Sunset Climate Zones. We're in Zones 15, 16, and 17 depending on location. Sunset zones account for heat, rainfall patterns, humidity, and growing season length, making them much more useful than USDA zones for our region. Look for varieties recommended for Sunset Zone 17 (coastal Santa Cruz) or Zones 15/16 (inland areas).
Planting Depth
How deep to plant seeds, usually given in inches or fractions of inches.
General rule: Plant seeds 2 to 3 times as deep as the seed is wide.
Tiny seeds (lettuce, carrots, herbs): Barely covered, just 1/8 to 1/4 inch deep
Medium seeds (beans, peas, beets): 1/2 to 1 inch deep
Large seeds (squash, cucumbers, corn): 1 to 2 inches deep
Santa Cruz consideration: Our soil stays cooler longer in spring, especially on the coast. If soil is cold and wet, seeds planted too deep may rot before germinating. When in doubt, plant on the shallow end of the recommended depth.
Spacing
Two numbers are usually given:
Spacing between plants (e.g., 12 inches apart)
Spacing between rows (e.g., 24 inches apart)
For intensive planting (raised beds, square-foot gardening): Use the "between plants" number in all directions. Ignore row spacing, which assumes you're planting in long rows with walking paths between them.
Santa Cruz consideration: Our long growing season and year-round planting mean succession planting matters more than cramming everything in at once. Give plants full spacing to reduce disease and improve air circulation, which is especially important in foggy coastal areas where fungal diseases thrive in damp, crowded conditions.
Sun Requirements
Usually listed as "Full Sun," "Partial Sun/Partial Shade," or "Shade."
Full sun: 6 to 8+ hours of direct sunlight
Partial sun: 4 to 6 hours of direct sunlight
Shade: Less than 4 hours, or dappled light all day
Santa Cruz translation:
Coastal areas often have less intense sun due to fog. A "full sun" crop on the coast needs every possible hour of light. Choose the sunniest spot available and don't compromise.
Inland areas have intense afternoon sun, especially in summer. "Full sun" crops thrive here. "Partial sun" crops (lettuce, greens) may actually benefit from afternoon shade during July and August.
Under redwoods: Even "partial shade" crops struggle in deep redwood shade. Focus on the most shade-tolerant options (lettuce, arugula, some herbs) and accept lower yields.
Germination Time
How many days until seeds sprout after planting.
Fast germinators (3 to 7 days): Beans, squash, cucumbers, radishes, lettuce
Medium germinators (7 to 14 days): Tomatoes, peppers, brassicas, carrots
Slow germinators (14 to 21+ days): Parsley, parsnips, celery
Santa Cruz consideration: Cool soil slows germination significantly. Warm-season seeds (tomatoes, peppers, squash, beans) won't germinate reliably until soil reaches 60°F to 70°F. On the coast, that might not happen until late May or June. Be patient and don't plant warm-season seeds too early.
Soil Temperature for Germination
Sometimes listed on packets, this is critical for successful direct seeding.
Cool-season crops germinate in soil as cool as 40°F to 50°F (lettuce, peas, spinach, brassicas)
Warm-season crops need soil at least 60°F, ideally 70°F+ (tomatoes, peppers, beans, squash, cucumbers)
How to check soil temperature: Use a soil thermometer (available at San Lorenzo Garden Center, Scarborough Gardens, or online). Push it 2 to 3 inches into the soil at 9am. Check for 3 consecutive days to get an average.
Santa Cruz timing:
Coastal soil warms slowly and may not reach 60°F until late May or June
Inland soil warms faster, usually reaching 60°F+ by early to mid-May
Don't rush. Seeds planted in cold soil rot instead of germinating. Patience in spring means healthier plants later.
Plant Height and Spread
Helps you plan spacing and support structures.
Determinate tomatoes: 3 to 4 feet tall, compact, need minimal staking
Indeterminate tomatoes: 6 to 8+ feet tall, need strong stakes or cages
Bush beans: 18 to 24 inches tall, no support needed
Pole beans: 6 to 8 feet tall, need trellis or poles
Santa Cruz consideration: Our long, mild growing season means indeterminate tomatoes grow LARGE here. Plan for 6-foot stakes minimum (8 feet is better), and provide sturdy support from planting day. Flimsy tomato cages collapse under the weight of a full-grown Santa Cruz tomato plant.
Common Seed Packet Terms Decoded
"Direct Sow"
Plant seeds directly in the garden where they'll grow. Don't start indoors.
Crops that prefer direct sowing: Carrots, radishes, beans, peas, lettuce, spinach, arugula, beets, turnips, corn, squash, cucumbers
Why: These either have delicate root systems (carrots, radishes) that don't transplant well, or they grow so fast that starting indoors isn't worth the trouble (beans, squash).
"Transplant"
Start seeds indoors, then move seedlings to the garden after 4 to 8 weeks.
Crops typically transplanted: Tomatoes, peppers, eggplant, brassicas (broccoli, cabbage, cauliflower, kale)
Why: They need a long growing season and benefit from an indoor head start, or their seeds need consistently warm conditions to germinate (easier to provide indoors than in cool spring soil).
"Succession Plant"
Plant small amounts every 2 to 3 weeks for continuous harvest instead of one big harvest all at once.
Best crops for succession planting in Santa Cruz: Lettuce, radishes, beans, carrots, beets, cilantro, arugula
Example: Instead of planting 20 feet of lettuce in March, plant 5 feet every 2 weeks from March through May (and again September through November). You'll have fresh salad greens for months instead of more lettuce than you can eat for 2 weeks, then nothing.
"Bolt Resistant" or "Slow to Bolt"
Bolting means sending up a flower stalk and going to seed. Once plants bolt, leaves turn bitter and the harvest ends.
Cool-season crops (lettuce, spinach, cilantro, arugula) bolt when temperatures rise above 75°F to 80°F consistently.
Santa Cruz strategy:
Coastal areas: Bolt-resistant lettuce and greens can grow almost year-round because fog keeps temperatures cool. You have a significant advantage here.
Inland areas: Bolt resistance matters for spring plantings. Even bolt-resistant varieties struggle in July and August heat. Plant cool-season crops in September for the best fall and winter harvests.
"Determinate" vs "Indeterminate" (Tomatoes)
Determinate tomatoes grow to a set height (3 to 4 feet), produce fruit all at once over 2 to 3 weeks, then stop. Compact, good for containers, canning, or small spaces.
Indeterminate tomatoes grow continuously until frost kills them (which rarely happens here), reaching 6 to 8+ feet tall and producing fruit throughout the season (July through October or later). Need strong support.
Santa Cruz recommendation: Indeterminate varieties take full advantage of our long season. One plant produces for 3 to 4 months. Choose determinate only if space is very limited or you want a single large harvest for preserving.
"Hybrid" vs "Open-Pollinated" vs "Heirloom"
Hybrid (F1): Cross of two specific parent varieties. Uniform plants, often more disease-resistant and vigorous. Seeds saved from hybrids won't grow true to type (you'll get unpredictable results).
Open-pollinated: Pollinated naturally by wind, insects, or self-pollination. Seeds saved from these plants grow true to type. Includes heirlooms.
Heirloom: Open-pollinated varieties passed down for generations (usually 50+ years). Often have superior flavor but may be less disease-resistant than modern hybrids.
Santa Cruz consideration: Both work well here. Hybrids offer reliability and disease resistance, great for beginners. Heirlooms provide amazing flavors and connect you to gardening history. If you're interested in seed saving, grow open-pollinated and heirloom varieties so you can save seeds that will grow true.
"Treated" vs "Untreated" Seeds
Treated seeds have been coated with fungicides (and sometimes insecticides) to prevent rot and disease during germination. The coating is usually visible as a bright color (pink, blue, or green).
Untreated seeds have no chemical coating.
Consideration: If you're gardening organically, choose untreated seeds. Most local seed companies (including Renee's Garden in Felton) offer untreated and organic options.
How to Adjust Seed Packet Instructions for Santa Cruz
Most seed packets assume you're gardening somewhere with distinct seasons: cold winters, warm springs, hot summers, and fall frost that ends the growing season. That's not us.
Planting Dates
Generic advice: "Plant after last frost" or "Sow in early spring"
Santa Cruz translation:
Last frost varies by microclimate:
Coastal areas: Frost is rare, maybe late March in a cold year
Inland valleys (Scotts Valley): Mid-April
San Lorenzo Valley: Late April
But "after last frost" is often too early for warm-season crops here because soil is still cold.
Better approach:
Cool-season crops: September through March (yes, fall and winter are prime planting time)
Warm-season crops: May through June (later on coast, when soil has warmed)
Succession Planting
Generic advice: Often not mentioned or downplayed
Santa Cruz strategy: Critical for maximizing our year-round growing season. Plant lettuce, radishes, beans, carrots, and cilantro every 2 to 3 weeks throughout their appropriate seasons.
Fall Planting
Generic advice: Often vague or missing entirely (national advice focuses on spring planting)
Santa Cruz strategy: September and October are prime planting months for brassicas, greens, and root vegetables. Fall planting is not emphasized on most seed packets but is essential for success here. Some of our best harvests come from fall-planted crops that grow through winter.
Variety Selection
Generic advice: Broad recommendations that work nationally
Santa Cruz refinement:
Coastal gardeners: Choose fog-tolerant, cool-adapted varieties. Look for descriptors like "performs in cool weather," "tolerates fog," "early maturing," or "coastal adapted."
Inland gardeners: Standard varieties work well. You have more heat units for warm-season crops and can grow varieties that need more warmth.
Under redwoods: Focus on shade-tolerant crops. Ignore anything requiring "full sun" and accept that some crops simply won't perform in deep shade.
Local Seed Sources That Understand Our Climate
Different seed companies specialize in different regions. Choose sources that understand maritime and Mediterranean climates.
Renee's Garden Seeds (Felton)
Based right here in Santa Cruz County. Varieties are tested in our conditions. If Renee's offers it, it grows well here.
Strengths: Regional testing, organic options, detailed growing guides, beautiful photography Where to buy: Local nurseries carry Renee's seed racks, or order online at reneesgarden.com
Territorial Seed Company
Based in Oregon, so varieties are selected for cool, maritime climates similar to coastal Santa Cruz.
Strengths: Cool-season crops, short-season varieties, fog-tolerant tomatoes Where to buy: Online at territorialseed.com
Kitazawa Seed Company
California-based, specializing in Asian vegetables perfectly suited to our climate.
Strengths: Asian greens, daikon radishes, unique varieties you won't find elsewhere Where to buy: Online at kitazawaseed.com, or seed racks at some local nurseries
Baker Creek Heirloom Seeds
Massive heirloom selection. Not region-specific, so read descriptions carefully for climate suitability.
Strengths: Heirloom varieties, beautiful catalog, seed-saving friendly Where to buy: Online at rareseeds.com
Botanical Interests
Colorado-based but offers detailed growing instructions and often notes regional adaptations.
Strengths: Organic options, exceptionally detailed packets, wide selection Where to buy: Seed racks at San Lorenzo Garden Center, Dig Gardens, Scarborough Gardens, or online at botanicalinterests.com
Johnny's Selected Seeds
Maine-based but widely respected for professional-quality seeds, especially cool-season crops.
Strengths: Professional quality, detailed growing information, disease resistance data Where to buy: Online at johnnyseeds.com
Local Resources for Seed Selection Help
Felton Seed Lending Library at Felton Branch Library (6121 Gushee Street) offers free seeds, many saved from local gardens. Borrow seeds, grow them, and return saved seeds if you can. santacruzpl.org
UC Master Gardeners of Monterey and Santa Cruz Counties can answer questions about variety selection for your specific microclimate. ucanr.edu/site/uc-master-gardeners-monterey-santa-cruz-counties
Farmers markets: Talk to growers at the Downtown Santa Cruz Farmers Market (Wednesdays at Cedar and Cathcart Streets) or other local markets. Ask what varieties they plant. They've figured out what thrives here through years of experience.
UCSC Farm and Garden: Notice what they plant during public tours. Their gardens are test cases for our exact climate, and their variety choices are well-considered.
Frequently Asked Questions About Reading Seed Packets
The seed packet says "plant after last frost," but when is that in Santa Cruz?
Last frost dates vary significantly across the county. Coastal areas rarely see frost at all, while inland valleys like Scotts Valley might have frost into mid-April, and higher elevations in the San Lorenzo Valley can frost into late April. However, "after last frost" is often too early for warm-season crops because soil is still cold. For tomatoes, peppers, and squash, wait until soil reaches 60°F (typically late May on the coast, mid-May inland) regardless of frost dates. For cool-season crops, you can plant earlier since they tolerate cold soil.
Do I really need to add 10 to 20 days to maturity estimates on the coast?
Yes, often more. Coastal fog reduces both temperature and light intensity, slowing plant growth compared to inland areas. A tomato variety listed at 70 days might take 85 to 95 days in Aptos or Capitola. This matters for planning: if you want ripe tomatoes by August, you need to account for our slower coastal growing conditions when choosing varieties and planting dates.
What's the difference between USDA hardiness zones and Sunset climate zones?
USDA zones only measure average minimum winter temperatures, which is useful for knowing if perennials will survive winter but tells you nothing about summer heat, humidity, or growing season length. Sunset zones consider all these factors, making them far more useful for vegetable gardening in California. Santa Cruz County includes Sunset Zones 15, 16, and 17 depending on location. When seed catalogs mention Sunset zones, pay attention.
Should I buy hybrid or heirloom seeds?
Both work well in Santa Cruz. Hybrids offer reliability, disease resistance, and predictable performance, making them great for beginners or when you need consistent results. Heirlooms offer incredible flavor diversity and connect you to gardening traditions, but may be more susceptible to diseases. If you want to save seeds, choose open-pollinated varieties (including heirlooms) since hybrid seeds don't grow true to type.
The packet says "full sun" but my sunniest spot only gets 5 hours. Will it work?
It depends on the crop. Fruiting vegetables (tomatoes, peppers, squash) really do need 6+ hours and will produce poorly with less. Leafy greens and herbs are more forgiving and often produce acceptable harvests with 4 to 5 hours of sun. Root vegetables fall somewhere in between. Be honest about your light conditions and choose appropriate crops rather than fighting your site.
How important is soil temperature for germination?
Very important for warm-season crops. Beans, squash, cucumbers, tomatoes, and peppers won't germinate reliably in soil below 60°F, and seeds planted in cold, wet soil often rot before sprouting. A soil thermometer (around $10 to $15) is a worthwhile investment. Check soil temperature at 2 to 3 inches deep for several mornings before planting warm-season seeds directly.
What does "days to maturity" mean for crops I harvest continuously, like lettuce?
For lettuce and other cut-and-come-again crops, days to maturity usually indicates when you can start harvesting outer leaves (baby leaf stage is often earlier). The plant will continue producing for weeks or months after that initial harvest date if you harvest properly and conditions remain favorable. Think of it as "days to first harvest" rather than "days until done."
Can I trust the spacing recommendations on seed packets?
Generally yes, though you can often plant slightly closer in intensively managed raised beds with good soil. However, in coastal Santa Cruz where fog promotes fungal diseases, generous spacing improves air circulation and reduces disease pressure. Don't crowd plants in foggy areas, even if the packet suggests you could plant closer.
Free Seed Starting Resources
Download these guides to help you succeed with seeds:
Seed Starting Guide — Complete instructions for starting seeds indoors and out, including timing for Santa Cruz County.
Seasonal Planting Calendar — Month-by-month guide to what to plant when in Santa Cruz County.
Know Your Microclimate Worksheet — Identify your garden's specific growing conditions for better variety selection.
Vegetables by Season Chart — Quick reference for which vegetables grow in which seasons here.
Garden Troubleshooting Guide — Solutions for common problems, including germination failures.
Practice Makes Perfect
Reading seed packets gets easier with experience. Over time, you'll develop intuition for which varieties work in your specific microclimate and which instructions need Santa Cruz adjustments.
Start with a few trusted seed companies that understand our region (Renee's Garden is the obvious local choice). Keep notes on what you plant and how it performs. After a season or two, you'll be able to scan a seed packet and immediately know whether that variety belongs in your garden.
The most important skill is learning to question generic advice and adapt it to local conditions. That's what separates successful Santa Cruz gardeners from frustrated ones. Every seed packet is a starting point for conversation, not the final word.
