When To Plant Tomatoes In Northern California

Getting your tomato timing right is the single biggest factor for a great harvest in Northern California. If you plant too early, a late frost can wipe out your seedlings; plant too late, and the heat might stop fruit from setting. This guide will walk you through exactly when to plant tomatoes in Northern California for optimal harvest timing.

Our unique climate, with its coastal fog, inland heat, and varied microclimates, makes timing a bit tricky. But with a few simple rules, you can have tomatoes ripening on your vine for months.

For most of Northern California, the best time to plant tomatoes is after the last spring frost date. The soil needs to be warm enough for them to thrive. A good general rule is to plant from late March through May, but this shifts depending on where you live.

Understanding Your Northern California Microclimate

Our region has three main gardening zones. Your planting date depends on witch one you’re in.

Coastal Areas (San Francisco, Monterey Bay): Cool summers with fog. Plant from late April through May. Wait for consistent warmth. Choose early-ripening and fog-tolerant varieties.
Inland Valleys (Sacramento, San Joaquin): Hot, dry summers. Plant from mid-March to late April. The goal is to get fruit set before extreme summer heat arrives in July.
Mountain & Foothill Areas: Shorter season with later frosts. Plant from late May to early June. Use short-season varieties and consider season extenders like Wall O’ Waters.

The Last Frost Date is Your Key Signal

Your average last spring frost date is the most important calendar mark. Tomatoes are very sensitive to frost and cold soil.

Sacramento Area: Around February 28.
San Francisco: Frost is rare, but cold soil persists; aim for April.
Santa Rosa: Around March 15.
San Jose: Around February 28.
Tip: Check with your local Master Gardener program for the most accurate date for your exact town.

Soil Temperature Matters More Than Air Temperature

Even if the air is warm, cold soil will shock tomato plants. They need soil consistently above 60°F, with 70°F being ideal for root growth.

Use a soil thermometer to check at a 4-inch depth.
If your soil is slow to warm, use black plastic mulch for 1-2 weeks before planting to trap heat.

A Step-by-Step Planting Timeline

Follow these steps for perfect timing from seed to harvest.

Step 1: Starting Seeds Indoors (6-8 Weeks Before Planting)

Start your seeds indoors. This gives you a head start on the season and access to more variety’s.

Count back 6-8 weeks from your planned outdoor planting date.
For inland areas, this means starting seeds in late January to February.
For coastal areas, start seeds in March.

Step 2: The “Hardening Off” Week (1 Week Before Planting)

Never move seedlings straight from indoors to the garden. They need to acclimate to sun and wind.

Start by placing plants in a shaded, sheltered spot for 2-3 hours.
Gradually increase their time outside and exposure to direct sun over 7 days.
Bring them in if nights are still below 50°F.

Step 3: Transplanting into the Garden

When frost danger is past and soil is warm, it’s time to plant.

Choose a cloudy afternoon or evening to reduce transplant shock.
Dig a deep hole or trench. Tomatoes can be planted deeply, as they develop roots all along their stems.
Mix compost into the planting hole and water deeply immediately after planting.

Step 4: Supporting and Early Care

Install cages or stakes right after planting to avoid damaging roots later. Water regularly to establish roots, but avoid wetting the leaves to prevent disease.

Choosing the Right Varieties for Your Season

Selecting types that match your microclimate ensures a better harvest.

Early Season (55-70 days): ‘Early Girl’, ‘Siberia’, ‘Stupice’. Great for coastal areas and getting a jump in inland valleys.
Mid-Season (70-80 days): ‘Celebrity’, ‘Better Boy’, ‘San Marzano’. Reliable performers for most areas.
Late Season (80+ days): ‘Brandywine’, ‘Cherokee Purple’. Best for hot inland valleys where you can plant early for a long growing season.
Coastal/Fog-Tolerant: ‘Juliet’, ‘Sun Gold’, ‘Legend’. Resist blight and set fruit in cooler weather.

Maximizing Your Harvest Window

To extend your harvest from early summer into fall, use these strategies.

Succession Planting for a Continuous Harvest

Don’t plant all your tomatoes at once. Make two plantings 2-4 weeks apart. This staggers your harvest and provides a backup if weather damages an early planting.

Planning for the “Fall Crop” in Hot Inland Areas

In the Sacramento and San Joaquin Valleys, you can plant a second crop in early July for a fall harvest. Use short-season varieties and provide afternoon shade for young seedlings during the hottest part of the summer.

Common Timing Mistakes to Avoid

Planting in Cold, Wet Soil: This stunts growth for the entire season and can cause root rot.
Rushing the Season: That one warm week in February is a trap. Wait for consistent warmth.
Missing the Heat Window Inland: If you plant too late in spring (e.g., June), fruit may not set during the peak summer heat above 90°F.
Not Accounting for Fog: In coastal areas, choosing a late-season variety that needs constant heat is a common error.

FAQ: Your Northern California Tomato Questions

Q: Can I plant tomatoes in early June in Northern California?
A: In coastal areas, yes, it’s a fine time. In inland valleys, it’s late for a main crop but perfect for a calculated fall harvest planting if you choose a 60-70 day variety.

Q: When is it too late to plant tomatoes?
A: A good rule is to plant so that your tomatoes have 6-8 weeks of good growing weather before nighttime temps consistently drop below 50°F in the fall. For many areas, planting after late June is risky for full-sized fruit.

Q: What if a late frost is forecasted after I’ve planted?
A> Be prepared to protect young plants with frost cloth, cloches, or even old bedsheets. Avoid plastic directly touching the foliage.

Q: How do I get an early harvest?
A> Use early-season varieties, warm the soil with plastic mulch, and use season-extending devices like hot caps or water wall teepees at transplant time.

By paying close attention to your local frost dates, soil temperature, and choosing the right varieties, you can master the schedule. The reward is a long, productive season full of homegrown tomatoes, perfectly timed from your Northern California garden.