When To Plant Tomatoes In Delaware

If you’re planning your Delaware garden, knowing when to plant tomatoes is the first step to a great harvest. Getting the timing right protects your tender plants from late frosts and gives them the longest possible growing season. This guide will walk you through the optimal dates, how to prepare, and tips for success in the First State’s unique climate.

Our springs can be unpredictable, with warm days followed by surprise chills. Planting too early is a common mistake that can set your garden back. By following the local schedule and watching the weather, you’ll give your tomatoes the strong start they need.

For most of Delaware, the safe window for planting tomatoes outdoors falls between May 1st and May 15th. This targets the period after the average last spring frost. The date shifts slightly depending on where you are in the state.

Northern Delaware (New Castle County): Aim for May 10th to May 15th. Frosts tend to linger a bit longer here.
Central & Southern Delaware (Kent & Sussex Counties): You can often plant a little earlier, from May 1st to May 10th, thanks to milder coastal influence.

Remember, these are averages. Always check your local 10-day forcast before you put plants in the ground.

Why This Timing Matters

Tomatoes are tropical plants that thrive in warm soil and air. Planting them outside too early exposes them to several risks:

Frost Damage: A single night below 32°F can kill or severely damage young plants.
Stunted Growth: Cold soil (below 60°F) shocks roots and halts growth, even if the air feels warm.
Disease Pressure: Cool, wet conditions promote soil-borne fungal diseases.

The “Soil Temperature” Rule

A more reliable method than calendar dates is checking soil temperature. Invest in a simple soil thermometer. Your tomatoes are ready for transplant when the soil at a 4-inch depth consistently reads 60°F or warmer in the morning. This usually coincides with those mid-May dates.

Starting Seeds Indoors

To have robust plants ready for that May planting window, you need to start seeds indoors much earlier.

Count Backwards: Take your target outdoor planting date (e.g., May 10).
Subtract 6-8 Weeks: This is your seed-starting date. For a May 10 transplant, start seeds between March 15 and March 29.
Use a Good Setup: Plant seeds in sterile seed-starting mix under grow lights. Keep them warm (70-75°F) until they germinate.

Starting seeds to late is a common error that leaves you with small plants at transplant time.

Preparing for Planting Day

Success starts long before you put a plant in the ground. Proper preparation makes all the difference.

Choosing the Right Tomato Varieties

Delaware’s humid summers favor disease-resistant varieties. Look for codes like VFN on plant tags, which indicate resistance to common issues.

For Early Harvests: Try ‘Early Girl’, ‘Celebrity’, or ‘Sungold’ (cherry).
For Disease Resistance: ‘Mountain Merit’, ‘Defiant’, or ‘Better Boy’ are excellent choices.
Heirloom Favorites: ‘Brandywine’ and ‘Cherokee Purple’ perform well but may need extra care against fungus.

Hardening Off Your Plants

Never move indoor-started seedlings directly into the garden. They need a 7-10 day transition period called “hardening off.”

Day 1-3: Place plants in a shaded, sheltered spot outside for just 2-3 hours.
Day 4-6: Gradually increase their time outside to 6 hours, introducing a bit of morning sun.
Day 7-10: Leave them out all day, and finally, overnight if no frost is expected.

This process toughens their stems and leaves, preventing sunscald and shock.

Site and Soil Preparation

Tomatoes demand full sun—at least 8 hours of direct light daily. Prepare the soil in early spring.

Amend the Soil: Work in 3-4 inches of compost or well-rotted manure to improve drainage and fertility.
Check pH: Tomatoes prefer a slightly acidic soil pH of 6.2 to 6.8. A simple home test kit can tell you if you need to adjust it.
Consider Raised Beds: They warm up faster in spring and offer superior drainage, a big advantage in wet years.

The Planting Process: Step-by-Step

When your date arrives and plants are hardened off, it’s time to plant.

Pick a Cloudy Day: Transplant in the late afternoon or on a cloudy day to reduce wilting.
Dig Deep Holes: Tomato stems can grow roots. Dig a hole deep enough to bury 2/3 of the plant’s stem. Remove the lower leaves.
Add a Balanced Starter: Mix a handful of organic tomato fertilizer or a phosphorus-rich starter into the planting hole.
Plant and Water: Set the plant in, backfill with soil, and water deeply to settle the roots and eliminate air pockets.
Provide Support Immediately: Install cages or stakes right away to avoid damaging roots later.
Mulch: Apply 2-3 inches of straw or shredded leaf mulch around the base to conserve moisture and suppress weeds. Wait until the soil is fully warm, usually early June.

What If You Plant Too Early (or Too Late)?

Mistakes happen. Here’s how to handle off-schedule planting.

Early Planting Risks & Fixes

If you’ve planted and a late frost is predicted, you must protect your plants. Cover them with frost cloth, old sheets, or even cardboard boxes. Avoid using plastic directly on the foliage, as it can transfer cold. If plants get a bit chilled and look purple-ish, they often recover once true warmth returns, but their growth will be delayed.

Late Planting Considerations

Planting in early June is still feasible, especially with fast-maturing varieties like cherry tomatoes or ‘Early Girl’. The main risk is that fruit may not ripen fully before the first fall frost in October. You might need to harvest green tomatoes and rippen them indoors if you get a late start.

Season Extension Tips

To get a jump on spring or protect plants in fall, try these methods.

Wall of Water: These plastic teepees surround plants and create a mini-greenhouse, allowing planting 2-3 weeks earlier.
Cold Frames: Great for hardening off plants or sheltering early transplants.
Row Covers: Lightweight fabric draped over hoops protects from light frost and pests.

In the fall, similar covers can protect late-season fruit from early light frosts, extending your harvest by weeks.

FAQ: Delaware Tomato Planting

What is the last date to plant tomatoes in Delaware?

You can plant through mid-June, but for full-sized varieties, aim no later than June 10th to ensure a harvest before frost.

Can I plant tomatoes in April in Delaware?

It’s generally to risky for unprotected plants. If you use season-extension tools like Walls of Water, you might succeed with an April 20th+ planting.

When should I start tomato seeds in Delaware?

Start seeds indoors 6-8 weeks before your planned outdoor transplant date. For a May 10 planting, start seeds between March 15 and March 29.

How do I protect young tomatoes from Delaware’s cool spring winds?

Use a physical windbreak, like a section of fence or a row cover, on the prevailing windy side. Staking plants securely also helps prevent damage.

What about planting tomatoes in pots in Delaware?

Container planting follows the same frost-free schedule. Use a large pot (at least 5 gallons) and high-quality potting mix. Pots can be moved into shelter if a late frost threatens.

Following this local timing guide gives your Delaware tomato garden the foundation for a productive season. Paying attention to soil warmth, hardening off plants properly, and being ready to protect them from a late chill are the keys to a summer full of homegrown flavor.