Starting Tomatoes from Seed in Santa Cruz County
Starting tomatoes from seed opens up a world that nursery starts can't match.
Those six-packs at the garden center offer maybe a dozen varieties, mostly the same hybrids year after year. Seed catalogs list hundreds of tomatoes bred for every climate and purpose imaginable: cool-tolerant varieties perfect for foggy coastal gardens, compact types for containers, heirlooms with flavors you've never experienced, and early producers that actually ripen in our shorter seasons.
The trade-off is timing. In Santa Cruz County, getting that timing right means understanding your specific microclimate and working backward from a realistic planting date. Start too early and you'll have leggy, root-bound seedlings waiting for soil that's still too cold. Start too late and you'll miss precious growing weeks in our already-short warm season.
This guide walks you through seed starting with Santa Cruz County's unique conditions in mind.
Why Start Tomatoes from Seed?
Before diving into technique, consider whether seed starting makes sense for your situation.
Variety Access
This is the compelling reason. Seed catalogs carry many short-season, cool-tolerant, and specialty tomatoes that rarely appear as starts locally. Varieties like 'Stupice,' 'San Francisco Fog,' 'Glacier,' and dozens of interesting heirlooms simply aren't available at most nurseries.
If you want to grow tomatoes specifically suited to coastal conditions, you'll likely need to start from seed.
Cost Savings
A packet of seeds costs $3-5 and contains enough for dozens of plants. Once you have a basic setup (lights, trays, soil mix), you can raise far more plants than you could afford to buy, with money left over for experimenting with new varieties.
Timing Control
Starting your own gives you control over exactly when seedlings are ready. You can stagger sowings for succession planting, time transplants precisely for your microclimate, and have backup plants if something goes wrong.
The Learning Curve
Seed starting does require some equipment, attention, and trial-and-error learning. If you're growing just a few plants of common varieties, buying starts may be simpler. But if you want variety access and volume, seed starting is worth mastering.
Understanding Your Planting Window
The key to successful seed starting is working backward from when you can safely transplant outdoors.
Why Soil Temperature Matters
Tomatoes struggle in cold soil. UC IPM notes that tomatoes grow poorly when soil temperatures are below 60°F. Cold soil stunts root development, slows growth, and makes plants vulnerable to disease. A tomato planted in warm soil in May will outperform one planted in cold soil in April, even with the later start.
Coastal Santa Cruz: Later Than You Think
UC Master Gardeners for coastal climates recommend waiting to plant tomatoes until nights consistently stay above about 55°F, which in foggy zones often means mid-May or later. This feels late compared to inland California, but planting into cold conditions just extends the stress period without speeding harvest.
For westside Santa Cruz, Live Oak near the coast, and other fog-influenced areas, plan for a mid-May to early June transplant window.
Warmer Inland Pockets: More Flexibility
Scotts Valley, sunny San Lorenzo Valley exposures, Soquel hills, and other warmer microclimates can often plant two to four weeks earlier. Once frost risk has passed and soil feels warm to the touch (not cold and clammy), you can transplant.
For these areas, late April to mid-May is typically realistic.
The 6-8 Week Rule
Standard guidance suggests starting tomato seeds 6-8 weeks before your target transplant date. This gives seedlings time to develop strong root systems and sturdy stems without becoming overgrown and root-bound.
Seed Starting Timeline for Santa Cruz County
Important: These are guidelines, not rigid rules. Observe your specific garden's conditions. If soil is still cold and wet, wait regardless of the calendar.
Seed Starting Setup
You don't need expensive equipment, but you do need adequate light and warmth.
Grow lights positioned 2-4 inches above seedlings. Raise as plants grow. Windows alone often produce leggy plants.
Use a heat mat in cool houses. After sprouting, 65-75°F is fine for growing.
Must have drainage holes. Start small, pot up as seedlings grow. Bury stems deeply when transplanting.
Not garden soil. Lightweight, well-draining, disease-free. Moisten before filling containers.
Light: The Critical Factor
Insufficient light is the most common seed-starting failure. Tomato seedlings need intense light to develop stocky, sturdy stems. Without it, they become leggy, weak, and prone to flopping over.
Options:
South-facing window: Can work if truly sunny and unobstructed, but even good windows often produce leggy seedlings. Supplementing with artificial light helps.
Grow lights: The reliable solution. LED shop lights positioned 2-4 inches above seedlings work well and are energy-efficient. Keep lights on 14-16 hours daily.
T5 fluorescent fixtures: Traditional choice, effective but being replaced by LEDs.
The key is keeping lights close to seedlings (2-4 inches) and raising them as plants grow. Distant lights produce leggy plants regardless of intensity.
Warmth for Germination
Tomato seeds germinate fastest in warm conditions, ideally 70-80°F soil temperature. In a cool house, germination may be slow and erratic.
Solutions:
Warm room: Top of refrigerator, near (not on) a heat register, or in the warmest room of your house.
Heat mat: Seedling heat mats provide consistent bottom warmth and significantly speed germination. Worth the investment if you start seeds regularly.
Once seedlings emerge, you can remove heat mats. Growing temperatures of 65-75°F are fine.
Containers and Soil
Containers: Cell trays, small pots, or recycled containers with drainage holes all work. Start in smaller cells and pot up as seedlings grow.
Soil mix: Use sterile seed-starting mix, not garden soil. Seed-starting mixes are lightweight, drain well, and are free of weed seeds and pathogens. Garden soil compacts, drains poorly, and may harbor disease.
Step-by-Step Seed Starting
1. Prepare Containers and Soil
Fill containers with moistened seed-starting mix. The mix should be damp but not soggy, squeeze a handful and it should hold together but not drip water.
2. Sow Seeds
Plant seeds 1/4 inch deep, two seeds per cell if you want insurance (thin to one later). Barely cover with mix and press gently to ensure good seed-to-soil contact.
3. Create Humidity
Cover trays with plastic dome lids, plastic wrap, or a clear plastic bag to hold humidity until germination. This prevents the soil surface from drying out.
4. Provide Warmth
Place trays in a warm location or on a heat mat. Check daily for moisture and germination.
5. Remove Covers at Germination
As soon as you see green emerging, remove humidity covers and move trays under lights. Leaving covers on after germination promotes damping-off disease.
6. Provide Strong Light
Position grow lights 2-4 inches above seedlings. Run lights 14-16 hours daily. Raise lights as plants grow to maintain the close distance.
7. Water Carefully
Water from below by setting containers in a tray of water and letting them wick up moisture. Or water gently from above, avoiding washing out seedlings. Keep soil consistently moist but not waterlogged.
8. Provide Air Circulation
A gentle fan improves air circulation, reducing disease risk and strengthening stems. Seedlings that experience gentle movement develop sturdier stems.
9. Pot Up When Ready
When seedlings develop their first true leaves (the second set, which look like tomato leaves rather than the smooth seed leaves), transplant to larger containers. This is usually 2-3 weeks after germination.
Bury stems deeply: Tomatoes can root along buried stems. If seedlings are leggy, bury the stem up to the lowest leaves when potting up. This produces stronger plants with more extensive root systems.
10. Begin Fertilizing
Once seedlings have true leaves, begin feeding with diluted liquid fertilizer (half strength) every week or two. Seed-starting mixes contain few nutrients, so growing seedlings need supplemental feeding.
Hardening Off: The Critical Transition
Seedlings grown indoors under lights are soft and unprepared for outdoor conditions. Direct transplanting from indoors to garden usually results in sunscald, windburn, and severe stress. Hardening off gradually acclimates plants to outdoor conditions.
- Place outdoors in sheltered, shaded spot
- 1-2 hours only, then bring inside
- Protect from wind
- Extend to 3-4 hours outdoors
- Introduce morning sun
- Still bring inside at night
- 5-6 hours with increasing sun
- Leave out during mild nights (above 50°F)
- Reduce wind protection
- Full days outdoors in planting conditions
- Overnight outdoors (protect from frost)
- Full sun exposure
The Process
Days 1-3: Place seedlings outdoors in a sheltered, shaded location for 1-2 hours. Bring inside.
Days 4-6: Increase outdoor time to 3-4 hours. Introduce some morning sun.
Days 7-10: Extend to 5-6 hours with increasing sun exposure. Leave out during mild nights if temperatures stay above 50°F.
Days 11-14: Full days outdoors in the conditions they'll experience in the garden. Bring in only if frost threatens.
After two weeks of hardening off, seedlings are ready for transplanting.
Hardening Off in Coastal Santa Cruz
Our coastal conditions add some nuance to hardening off:
Start earlier than transplanting: You can begin hardening off while waiting for soil to warm. This gives seedlings outdoor exposure even if planting is delayed.
Watch for wind: Coastal winds can be harsh on soft seedlings. Use cold frames, cloches, or sheltered spots during early hardening off.
Fog is your friend (sort of): Foggy days are gentle for hardening off; less intense sun and moderate temperatures. But don't let fog delay the process indefinitely.
Be patient: If conditions stay cold and wet, it's better to keep seedlings in larger pots, hardening off gradually, than to rush them into unsuitable garden conditions.
Hardening Off in Warmer Inland Areas
Inland microclimates often have more intense sun and less wind buffering:
Watch for sunscald: Strong midday sun can burn leaves that developed under indoor lights. Increase sun exposure gradually, starting with morning light.
Afternoon shade: Use afternoon shade during early hardening off to prevent heat and light stress.
Transition to full sun: By the end of two weeks, plants should handle full sun conditions in their planting location.
Troubleshooting Seed Starting Problems
Leggy Seedlings
Problem: Tall, thin, floppy stems that can't support themselves.
Cause: Insufficient light, or lights too far from seedlings.
Prevention: Use grow lights positioned 2-4 inches above seedlings. Increase light duration to 14-16 hours.
Fix: Bury stems deeply when potting up. Tomatoes root along buried stems, and this strengthens leggy plants.
Damping Off
Problem: Seedlings suddenly collapse at soil level, often with a pinched, water-soaked stem.
Cause: Fungal disease promoted by wet conditions, poor air circulation, and contaminated soil.
Prevention: Use sterile seed-starting mix. Avoid overwatering. Provide air circulation. Remove humidity covers promptly after germination.
Fix: Once damping off occurs, affected seedlings can't be saved. Start fresh with clean materials and better conditions.
Slow or No Germination
Problem: Seeds don't emerge, or emergence is very slow and erratic.
Cause: Cold soil temperatures, old seed, or seeds planted too deeply.
Prevention: Use heat mats or warm locations for germination. Check seed packet dates. Plant seeds only 1/4 inch deep.
Fix: If nothing emerges after 14 days in warm conditions, start over with fresh seed.
Purple Leaves
Problem: Leaves develop purple coloration, especially on undersides.
Cause: Phosphorus deficiency, often because cold soil prevents phosphorus uptake even when present.
Prevention: Maintain warm growing temperatures. Use balanced fertilizer.
Fix: Mild purpling often resolves when plants are transplanted into warm garden soil. Severe cases may indicate ongoing cold stress.
Recommended Varieties to Start from Seed
These varieties are worth seeking out in seed catalogs for Santa Cruz County conditions:
Cool-Tolerant Varieties (Coastal Gardens)
'Stupice' (Czech heirloom, 55-60 days, excellent cold tolerance)
'San Francisco Fog' (bred for coastal conditions)
'Oregon Spring' (sets fruit in cool weather, parthenocarpic)
'Glacier' (extremely early, 55 days, compact plants)
'Legend' (disease resistant, sets in cool conditions)
Early Cherry Types (Reliable Everywhere)
'Sungold' (sweet orange, benchmark flavor)
'Matt's Wild Cherry' (prolific, intense flavor)
'Black Cherry' (complex flavor, dusky color)
'Juliet' (grape tomato, crack resistant)
For Warmer Microclimates
'Cherokee Purple' (heirloom, complex flavor, needs heat)
'Brandywine' (classic heirloom, late maturing)
'Costoluto Genovese' (Italian heirloom, great for sauce)
'Paul Robeson' (black tomato, rich flavor)
Seed Sources
Renee's Garden Seeds (Felton-based, excellent variety selection)
Johnny's Selected Seeds (wide selection, detailed variety information)
Territorial Seed Company (Pacific Northwest focus, good for cool climates)
Baker Creek Heirloom Seeds (huge heirloom selection)
From Seed to Garden
Starting tomatoes from seed connects you to the full cycle of growing and opens possibilities that buying starts can't match. Yes, it requires some equipment and attention. But once you've tasted a perfectly ripe 'Stupice' or 'Cherokee Purple' grown from seed you started yourself, you'll understand why so many gardeners consider it essential.
Start with a few varieties your first year. Learn your setup's quirks. Adjust timing based on your specific microclimate. Each season, you'll refine your approach until seed starting becomes second nature and you'll wonder how you ever settled for whatever the nursery happened to stock.
Frequently Asked Questions
When should I start tomato seeds in Santa Cruz?
Work backward from your transplant date: late March to mid-April for coastal areas (transplanting mid-May to June), late February to mid-March for warmer inland areas (transplanting late April to mid-May).
Can I start seeds in a sunny window?
Possibly, but most windows don't provide enough light for stocky seedlings. Even south-facing windows often produce leggy plants. Supplementing with grow lights is recommended.
How do I know if my seedlings are getting enough light?
Stocky, sturdy stems with short distances between leaf sets indicate adequate light. Tall, thin, leaning stems indicate insufficient light.
My seedlings are leggy. Can I save them?
Yes. When potting up, bury the stem up to the lowest healthy leaves. Tomatoes root along buried stems, and this strengthens leggy plants considerably.
How long can I keep seedlings in pots if weather delays planting?
Several weeks if necessary. Pot up to larger containers, continue feeding, and harden off gradually. Plants may become slightly root-bound but will recover after transplanting.
Do I need a heat mat?
It's not strictly necessary but significantly speeds germination, especially in cool houses. If your home stays warm (70°F+), you can skip it. In cooler homes, it's worth the investment.
Free Gardening Resources
Know Your Microclimate Worksheet: Understand your specific Santa Cruz County growing conditions
Seasonal Planting Calendar: Month-by-month guidance for Santa Cruz County
Seed Starting Guide: General seed starting tips
Related Tomato Articles
Growing Tomatoes in Santa Cruz County
Growing Tomatoes in Containers
Heirloom Tomatoes for Santa Cruz
Determinate vs Indeterminate Tomatoes
Watering Tomatoes in Santa Cruz
Tomato Fertilizing + Soil Prep
Tomato Problems + Troubleshooting
