Seeds to Start Indoors 10–12 Weeks Before Your Last Frost

Learn which seeds to start indoors 10–12 weeks before your last frost date, including slow-growing vegetables and herbs that need an early head start for a successful garden.

If you’re itching to start seeds while winter is still lingering, you’re not alone. After a long winter, most of us are ready to dig into the soil again.

The 10–12 weeks before your last frost date mark the earliest window of the seed-starting season. This is the ideal time to sow slow-growing crops indoors under lights, giving them a head start and allowing them to mature before transplanting outdoors.

These crops are well suited to an early start because they grow at a steady pace and are less likely to outgrow their containers before it’s time to plant them outside.

In this guide, you’ll learn which seeds to start indoors during this early window, why these crops benefit from a long head start, and how to set yourself up for healthy, manageable seedlings as the season unfolds.

Start With Your Average Last Frost Date

All seed-starting schedules are based on one key piece of information: Your average last frost date.

This date tells you when it’s typically safe to plant tender crops outdoors in spring. To find yours, enter your ZIP code at PlantMaps.com or Garden.org, then count backward 10–12 weeks to determine when to start seeds indoors.

If it’s still a little early for your area, go ahead and save this post for reference. Timing varies by region, and this guide will be ready when you are.

For a step-by-step explanation of how frost dates work and how to build a complete planting plan, see: How to Create a Seed Starting Schedule Based on Your Last Frost Date.

Why These Seeds Are Started 10–12 Weeks Before Frost

This early seed-starting window is reserved for crops that need extra time and patience.

Seeds started during this period:

• Germinate slowly or grow slowly at first.
• Tolerate a long stay indoors under grow lights.
• Need a long growing season to reach maturity.

Starting these crops early ensures they are strong, well-established transplants by the time outdoor conditions are suitable. It also helps prevent rushed planting or underdeveloped plants later in the season.

Seeds to Start Indoors 10–12 Weeks Before Your Last Frost Date

The following crops are well suited to starting indoors during this early window. Each benefits from a protected environment while developing healthy roots and steady growth.

Alliums to Start Indoors

Alliums are some of the best crops to start early indoors. They grow slowly, don’t take up much space under lights, and transplant well into the garden.

Onions

Starting onions from seed allows you to grow a wider range of varieties than transplants and gives plants enough time to form full-sized bulbs by harvest

Leeks

Leeks require a long growing season. An early indoor start helps them develop strong stems and roots before transplanting.

Green Onions and Scallions

Green onions are easy to grow from seed and can be harvested young or allowed to mature longer. Early planting ensures steady growth once transplanted outdoors.

Slow-Growing Vegetables to Start Indoors

These crops either take a long time to germinate or grow slowly during their early stages, making early indoor sowing essential.

Celery

Celery seeds are tiny and slow to sprout. Starting them early gives plants enough time to mature before summer heat arrives.

Celeriac

Grown for its flavorful root, celeriac needs a long, consistent growing season. Early indoor sowing is key to producing well-developed roots.

Eggplant

Eggplants grow slowly at first and prefer warm conditions. Starting them early indoors helps ensure strong plants ready for summer heat.

Herbs to Start Indoors

Some woody and perennial herbs establish slowly and benefit from an early indoor start.

Rosemary

Rosemary seeds can take a long time to germinate. An early start allows plants to establish before being transplanted outdoors.

Thyme

Thyme grows slowly in its early stages. Starting it indoors early helps produce compact, sturdy plants for the garden.

Review the Seed Packet Before You Start

Your seed packet is one of the best resources for successful seed starting. Before planting, take a moment to review the information on the packet, including:

• Timing: When to sow seeds based on your last frost date.
• Planting Depth: How deep to plant seeds for proper germination.
• Germination Time: How long seeds typically take to sprout.
• Spacing: Helpful to know when potting up or transplanting.

Seed packets can vary by variety, so always follow the instructions provided whenever possible.

Tips for Starting Seeds Indoors Successfully

Because these seedlings will spend more time indoors than later starts, good growing conditions are especially important:

• Use bright grow lights positioned close to seedlings.
• Keep soil evenly moist, but not soggy.
• Provide gentle air circulation.
• Label everything, even if you think you’ll remember. Many seedlings look alike early on.

A simple grow light setup and consistent care go a long way toward producing sturdy plants.

Helpful resources:

• Using Grow Lights for Seedlings
• 10 Steps to Starting Seeds Indoors
• How to Harden Off Seedlings

Can These Seeds Be Started Earlier or Later?

There is some flexibility built into seed starting, especially with these early crops.

Many of the seeds in this group grow slowly and tolerate extended time indoors, making them good candidates for a slightly earlier start if you’re eager to begin. That said, strong light, good quality fertilizer, and careful watering are essential to prevent weak or leggy growth.

• Alliums, celery, and herbs can be started slightly earlier if you’re eager to begin.
• Eggplant is best started within this window or a little later to avoid oversized seedlings.
• Be ready to re-pot into larger containers as the seedling outgrow their starter pots.

If you’re unsure about timing, it’s usually better to wait until you’re closer to the 10–12 week window than to start too early without adequate light. These crops reward patience and steady conditions.

What to Start Next

Once these seeds are sown, there may be a short pause before the next wave of indoor seed starting begins.

Next in the seed sowing schedule: Seeds to Start Indoors 8–10 Weeks Before Your Last Frost (Coming Soon).

This window includes additional herbs and specialty crops that benefit from an early indoor start as spring approaches.

Starting seeds indoors is one of the most rewarding parts of gardening. Beginning with the right crops at the right time helps keep the season calm, organized, and enjoyable one tray at a time.

Good planning is key to a successful vegetable garden

Whether you are new to growing your own food or have been growing a vegetable garden for years, you will benefit from some planning each year. You will find everything you need to organize and plan your vegetable garden in my PDF eBook, Grow a Good Life Guide to Planning Your Vegetable Garden.