Best Seeds to Start Indoors: Vegetables & Flowers That Benefit from an Early Start

Cool-Season Vegetables Started Indoors for Early Transplants

Indoor starting allows cool-season crops to be planted outdoors at the exact right moment for spring or fall harvest.

• Broccoli
• Cauliflower
• Cabbage
• Brussels sprouts
• Kale
• Kohlrabi
• Swiss chard
• Lettuce (for transplanting)
• Spinach (optional but often beneficial for early crops)

Why Start Certain Seeds Indoors?

Starting seeds indoors isn’t just about getting a jump on the season, it’s about giving certain plants the conditions they need to grow well. Many warm-season vegetables and long-germinating flowers depend on:

• Warm soil temperatures for sprouting
• Weeks of protected early growth
• Plenty of time to mature before first frost
• Consistent moisture and light

Growing indoors helps you support their earliest stages of growth. You can give a slow-germinating pepper the warmth it needs, encourage a long-season tomato to begin strong, or raise delicate flower seedlings without wind, pests, or cold spells interrupting their progress.

Popular Vegetables That Grow Best When Started Indoors

Below you’ll find the reasoning behind each recommendation so gardeners understand exactly why these plants appreciate an indoor beginning.

Tomatoes

Tomatoes thrive with an early start because they need both warm soil to germinate and a long growing season to reach full color and flavor. If sown outdoors, cool soil often slows germination and plants may not have enough time to mature before late-summer temperatures cool again.

Indoors, tomatoes grow at a steady pace, forming strong root systems and sturdy stems. By transplanting time, they’re well-prepared to settle into the garden and begin producing early in the season.

Start indoors: 6–8 weeks before last frost.

Peppers

Pepper seeds take their time to germinate and often sprout unevenly in cool soil. Indoors, they get the warmth they need—usually 75–80°F—to wake up and begin growing.

A healthy indoor start helps peppers reach transplant size before the soil warms outside. This is especially important for gardeners in cooler regions who want a full harvest.

Start indoors: 8–10 weeks before last frost.

Eggplant

Eggplant behaves similarly to peppers: the seeds love warmth, grow slowly at first, and need a long season to produce well. Indoors, they receive consistent conditions that help them form deep, reliable root systems.

Start indoors: 8–10 weeks before last frost.

Broccoli, Cauliflower & Cabbage

These brassicas prefer cool weather for maturing, not sprouting. Starting them indoors gives you the chance to raise sturdy seedlings and transplant them outdoors at just the right moment—early enough to enjoy cool spring weather, or timed for fall harvest.

A controlled start also prevents pests like flea beetles from damaging tender seedlings before they are established.

Start indoors: 4–6 weeks before last frost.

Onions (From Seed)

Onion seeds benefit from a very early start. They need months of growth to develop bulbs of good size, especially in northern climates.

Indoor sowing ensures onions reach transplant size before spring planting time, setting them up for a more reliable harvest.

Start indoors: 10–12 weeks before last frost.

Celery

Celery germinates slowly and grows gradually, often taking several weeks just to produce its first true leaves. Indoors, it gets the steady moisture and gentle warmth it needs.

A strong indoor beginning improves both flavor and productivity later in the season.

Start indoors: 10–12 weeks before last frost.

Favorite Flowers That Benefit from Indoor Seed Starting

Flowers with small seeds, long germination times, or delicate early growth appreciate the protected environment of indoor sowing. This leads to fuller beds, earlier blooms, and healthier transplants.

Petunias

Petunia seeds are tiny and need consistent light for germination. Indoor sowing gives them the time they need to develop a strong root system before moving outside.

Start indoors: 10–12 weeks before last frost.

Snapdragons

Snapdragons germinate slowly and enjoy cool conditions when maturing, not sprouting. Starting indoors ensures strong, early-season plants that handle spring weather well.

Start indoors: 8–10 weeks before last frost.

Coleus

Coleus grows slowly in cool conditions and responds beautifully to indoor warmth and light. A well-grown start leads to vibrant colors outdoors.

Start indoors: 8–10 weeks before last frost.

Impatiens

Impatiens germinate slowly and appreciate protected early growth. Indoor sowing helps you raise full, healthy plants ready to bloom early in the season.

Start indoors: 10–12 weeks before last frost.

Milkweed

Many milkweed varieties germinate slowly and benefit from warm, steady conditions indoors. Raising strong seedlings increases your chances of establishing plants that return year after year.

Start indoors: 8–10 weeks before last frost.

Echinacea

These perennials germinate slowly and need time to build a reliable root system. A head start indoors helps ensure they reach transplant size on schedule and establish well.

Start indoors: 8–10 weeks before last frost.

Timing Chart: When to Start Seeds Indoors

This chart helps you plan your seed-starting schedule based on your last frost date.

Crop	Start Indoors
Tomatoes	6–8 weeks before frost
Peppers	8–10 weeks before frost
Eggplant	8–10 weeks before frost
Broccoli / Cauliflower / Cabbage	4–6 weeks before frost
Onions (from seed)	10–12 weeks before frost
Celery	10–12 weeks before frost
Basil & most herbs	6–8 weeks before frost
Petunias	10–12 weeks before frost
Snapdragons	8–10 weeks before frost
Coleus	8–10 weeks before frost
Impatiens	10–12 weeks before frost
Milkweed	8–10 weeks before frost
Echinacea	8–10 weeks before frost

Your seed packets provide timing tailored to the specific variety and Park Seed includes detailed instructions for every seed we offer.