Best Seeds to Start Indoors or Direct Sow

Planning your garden from seed gives you more control, better variety, and a deeper connection to the growing process. But before you open your first seed packet, it's important to know how and where to start each type of seed. Some seeds prefer to be sown directly into the soil, while others need a head start indoors under controlled conditions. Knowing the difference can make or break the success and timeliness of your season.

At Park Seed, we’ve been helping gardeners make smart, confident planting decisions since 1868. In this guide, you’ll learn which seeds to start indoors, which to direct sow, and how to choose the right method based on your USDA Hardiness Zone, plant type, and season length. We’ve also included practical tips from our horticultural team to help your garden get off to its healthiest start.

Learn more about direct sowing techniques.

Why Planting Method Matters for Seed Success

Choosing the right way to start each seed affects how strong your plants grow, how well they produce, and how quickly they mature. Starting seeds indoors gives some plants the extra time they need in shorter growing seasons. Direct sowing works better for others, especially those with delicate root systems that don’t like being transplanted.

Factors that influence your planting method include:

• The plant’s tolerance for cold
• How long it takes to mature
• The structure and sensitivity of its roots
• Average frost dates in your area
• The length of your growing season

“Some seeds simply won’t tolerate transplanting. Others benefit from the steady warmth and shelter of indoor growing. The key is understanding which is which for your climate,” says Shelby DeVore, horticultural writer for Park Seed.

General Rules of Thumb: Indoor vs. Outdoor Seed Starting

If you're unsure whether a particular seed should be started indoors or direct sown into the garden, there are some time-tested guidelines that can help. While every plant has its preferences, many sowing decisions come down to a few consistent characteristics like seed size, root sensitivity, and how long the plant takes to mature. Understanding these patterns gives you a helpful shortcut when you're scanning seed packets or mapping out your planting schedule.

Below are some reliable indicators to guide your decision:

1. Seed Size and Sensitivity

Smaller seeds are often started indoors, while larger seeds are usually direct sown outdoors.

• Start Indoors: Tiny seeds (like snapdragons, lettuce, or petunias) benefit from indoor starting because they are more vulnerable to environmental stress (wind, rain, temperature fluctuations).
• Direct Sow: Larger seeds (beans, corn, peas, squash, pumpkins) have enough stored energy to push through the soil quickly and establish without babying.

Why it works: Larger seeds have more internal food reserves, which help them germinate in unpredictable outdoor conditions.

3. Days to Maturity

Plants with a long growing season often need a head start indoors, especially in colder zones with short frost-free periods.

• Start Indoors: Peppers, tomatoes, eggplant—anything that takes over 90 days to mature.
• Direct Sow: Fast-maturing crops like radishes, lettuce, and bush beans can go straight into the garden.

Tip: Check the “Days to Maturity” on your Park Seed packet. If it's longer than your growing season, start it indoors.

4. Frost Sensitivity

Frost-tender plants are usually started indoors, while cold-hardy seeds can be direct sown early in the season.

• Start Indoors: Basil, tomatoes, melons, cucumbers, and marigolds need warm soil and air to thrive.
• Direct Sow: Peas, kale, spinach, chard, and poppies can handle chilly soil and air temperatures.

If you have spring or fall frosts, use your last frost date to guide planting time and method.

Direct Sow These Seeds Right into the Garden

Some seeds grow best when planted directly into outdoor soil, where their roots can develop without interruption. These seeds often germinate quickly, establish faster, and don’t transplant well. Root crops and many large-seeded vegetables fall into this category.

Here are vegetables best suited for direct sowing:

• Arugula
• Beans
• Beets
• Cantaloupe
• Carrots
• Collard or Mustard Greens
• Corn
• Kale
• Kohlrabi
• Okra
• Onions
• Parsnip
• Peas
• Potatoes
• Pumpkin
• Radishes
• Spinach
• Sweet Potatoes
• Swiss Chard
• Turnips
• Watermelon
• Winter squash

“Root vegetables like carrots, radishes, and parsnips should never be transplanted. Direct sowing helps them develop strong, straight roots and consistent size,” says Shelby DeVore.

While most herbs can be started indoors, a few do especially well when sown directly into the garden. These include fast-growing varieties that don’t transplant easily.

Top herbs for direct sowing:

• Basil
• Chives
• Cilantro
• Dill
• Thyme

SHOP FOR HERB SEEDS

Certain annual flowers are also better direct sown, especially if they self-seed naturally or dislike root disturbance. These flowers thrive when sown directly after the risk of frost has passed.

Recommended direct sow flowers:

• Amaranth
• Black Eyed Susan
• Calendula
• Coneflower
• Poppy
• Sunflower
• Sweet Pea
• Verbena
• Wildflowers

Know Your USDA Hardiness Zone Before You Plant

Your Hardiness Zone determines how long your growing season lasts and how early or late you can plant. This impacts which seeds need to be started indoors and which can go straight into the garden.

You can find your zone on the USDA Plant Hardiness Zone Map.

Here are general planting guidelines by zone:

Zones 3–5: Short Season, Cold Winters

These regions have a shorter frost-free growing window. Most warm-season crops and flowering annuals need to be started indoors to give them time to mature before the first fall frost.

Start Indoors in Zones 3–5:

• Tomatoes, Peppers, Eggplant
• Squash, Melon, Corn
• Okra, Zucchini, Pumpkin
• Most flowers and herbs

Direct Sow in Zones 3–5:

• Cold-tolerant greens (spinach, kale, mustard)
• Peas, Chives, Garlic
• Carrots, Radishes, Beets
• Brussels Sprouts, Cabbage, Onions

Zones 6–11: Longer Growing Season

Warmer climates with extended frost-free periods give you more flexibility to sow seeds directly in the garden.

Start Indoors in Zones 6–11:

• Broccoli, Cabbage, Cauliflower
• Tomatoes, Peppers, Eggplant
• Petunias, Poppy, Coleus
• Oregano, Lemon Balm

Direct Sow in Zones 6–11:

• Beans, Cucumbers, Melon, Corn
• Radishes, Kale, Carrots, Spinach
• Nasturtium, Sunflower, Calendula
• Wildflowers, Zinnias, Black-Eyed Susan

Smart Sowing Techniques for Better Results

Once you've decided whether to start seeds indoors or direct sow, follow these planting tips for stronger, healthier seedlings:

1. Follow proper spacing and depth.
Check your Park Seed packet for spacing and planting depth. If you're unsure, plant seeds at a depth roughly twice their size.

2. Thin seedlings carefully.
When direct sowing, plant two seeds per spot. After sprouting, snip the weaker seedling at the soil line. Avoid pulling it up, which can damage the roots of the plant you want to keep.

3. Harden off indoor seedlings before transplanting.
Gradually expose seedlings to outdoor temperatures, sunlight, and wind over 7–14 days. Begin with an hour in shaded conditions, increasing exposure each day.

“Hardening off is a step many gardeners skip, but it’s critical to success. A sudden move outside can shock young plants and stunt their growth,” advises Shelby.

FAQs: Seed Starting Tips

Can I start all seeds indoors to get a jump on the season?
Not always. Root crops and certain large-seeded vegetables do not transplant well and should always be direct sown.

How do I know when to direct sow?
Wait until soil temperatures are warm enough for germination and the last frost has passed. Check seed packets for ideal conditions.

What if I don’t have a sunny window for seed starting?
Use grow lights with a timer to provide consistent light and prevent seedlings from becoming leggy or weak.

Do I need a heat mat?
Heat mats are helpful for heat-loving plants like peppers and tomatoes. They speed up germination and promote healthier roots.

What is the best seed starting mix?
Use a sterile, lightweight seed starting mix. Avoid regular garden soil, which can be too dense and introduce pathogens.

Every planting decision starts with the seed, but success comes from knowing how and when to sow it. At Park Seed, you’ll find proven varieties, reliable growing guidance, and the kind of practical knowledge that helps every crop reach its full potential.

This post was written by Shelby DeVore, the founder of Farminence and the host of the Backyard Vegetable Gardener’s Summit. Shelby is a passionate gardener with 20+ years of experience gardening and growing food at home. She recently moved to north Texas with her husband and three children where she’s excited to explore a new gardening zone and build a new farm.