Knowing when to start seeds indoors can be tricky when you are a beginner gardener. Especially when you need to know what to start and when, and what applies to your growing zone! It can definitely feel overwhelming, I know it was for me when I first started. But I promise you once you get the hang of it, it will become second nature.

No matter what growing zone you are in, you can feel confident that you will know exactly what seeds you need to start indoors and when!

A seed starting setup with a tray of soil blocks with sprouts, a seed storage box, packets of seeds, and a soil blocker on a wooden surface.

Why You Should Start Seeds Indoors

The first question you may ask, is why do you need to start seeds indoors in the first place. There are many benefits to starting seeds indoors such as:

Extended Growing Season: In regions with short growing seasons due to cold climates, starting seeds indoors allows you to get a head start on the growing season. This is especially beneficial for plants that require a long growing period to reach maturity, such as tomatoes, peppers, and eggplants.

Protection from Weather Extremes: Young plants can be vulnerable to weather extremes, including frost, high winds, and heavy rain. Starting seeds indoors provides a controlled environment, protecting seedlings from harsh conditions until they are strong enough to withstand outdoor elements.

Improved Germination Rates: The controlled environment of an indoor setting (consistent temperature, humidity, and light) can lead to higher germination rates compared to direct sowing outdoors, where seeds are exposed to unstable conditions that might affect germination.

Selective Planting: By starting seeds indoors, you can select the healthiest and strongest seedlings for transplanting into their garden, resulting in a thriving plant and productive crop.

Save Money: Starting your own seeds indoors can be more cost-effective than purchasing mature plants from a nursery. A single packet of seeds can produce many seedlings at a fraction of the cost of buying the same number of plants.

Rare and Heirloom Varieties: If you are interested in growing unique, rare, or heirloom varieties you may find it difficult to purchase these as seedlings in garden centers. Starting from seeds allows access to a wider variety of plants that might not be available at your local local garden center.

A top view of a seed starting tray filled with soil blocks, each with small lettuce seedlings emerging.

Understanding Your Climate or Hardiness Zone

Understanding your climate zone is crucial for successful gardening, as it influences what plants you can grow and when you should plant them. Climate zones are defined by the average minimum winter temperatures of a region and help home gardeners determine the viability and timing for growing different types of plants.

Climate zones are categorized to help us understand the specific conditions of our local area, particularly focusing on temperature and the length of the growing season. These zones provide a guide for selecting plants that are most likely to thrive in a given location. For example, plants that are suited for a warm, tropical climate may not survive the winter in a colder, temperate zone without special care.

USDA Plant Hardiness Zone Map (United States): For those in the United States, the USDA Plant Hardiness Zone Map is the standard map where you can find which plants are most likely to thrive in your location. The map is divided into 10-degree F zones, based on the average annual minimum winter temperature.

Using The Old Farmer’s Almanac

The Old Farmer’s Almanac is my favorite resource for gardening information related to my specific region and hardiness zone. You can use The Old Farmer’s Almanac for many resources including:

Climate Zone Search: The Old Farmer’s Almanac provides tools to help you determine your climate zone. By entering your ZIP code or browsing through their regional gardening guides, you can find detailed information about your area’s climate zone, which is essential for selecting the right plants for your garden.

Frost Dates: Understanding the frost dates in your area is crucial for gardening success. The Almanac offers a Frost Dates Calculator, where you can enter your location to find out the average first and last frost dates. This information helps in planning when to start seeds indoors and when it’s safe to transplant seedlings outdoors.

Planting Calendars: The Almanac provides customized planting calendars based on your local climate zone. These calendars can guide you on when to sow seeds indoors, transplant seedlings, or sow seeds directly outdoors for various plants, ensuring optimal growth conditions.

Understanding Plants & Their Planting Requirements

an infographic of cold season crops

Cool-Season Crops

Cool-season crops are plants that thrive in cooler weather and can often withstand light frosts. They are planted in early spring or late summer/early fall and can be some of the first vegetables we look forward to to  plant in the garden. Many cool-season crops can even be started indoors and then transplanted outside well before the last frost date. Examples include:

  • Lettuce: Prefers temperatures between 60°F and 70°F and can often tolerate light frosts. It’s ideal for early spring or fall planting.
  • Kale: Known for its frost tolerance, kale’s flavor can improve with a touch of frost. It can be started indoors and transplanted outside in early spring or late summer.
  • Peas: Thrive in cooler temperatures and can be one of the first seeds sown directly into the garden in early spring, but starting them indoors can give them a head start.
An infographic of warm season crops

Warm-Season Crops

Warm-season crops require warmer soil and air temperatures and are sensitive to frost. These plants are started indoors in cooler climates to extend their growing season and are transplanted outside only after all danger of frost has passed. Examples include:

  • Tomatoes: Need warm temperatures to thrive and are usually started indoors 6-8 weeks before the last frost date, then transplanted after the soil has warmed.
  • Peppers: Similar to tomatoes, peppers need warm conditions and are often started indoors to ensure they have enough time to mature before the end of the growing season.
  • Cucumbers: While they can be direct-seeded outdoors, starting cucumbers indoors can be beneficial in cooler climates to get a head start on the growing season.

Annuals vs. Perennials in Indoor Seeding

The difference between annuals and perennials is also important when starting seeds indoors:

  • Annuals: Complete their life cycle in one year, going from seed to plant to seed again within a single growing season. Most vegetables, including many warm-season crops, are annuals. Starting annual seeds indoors is often done to extend the growing season, especially in regions with short summers. Since they need to be replanted each year, timing is crucial to ensure they reach maturity and produce a harvest within the season.
  • Perennials: Live for more than two years, often going dormant in the winter and returning in the spring. While not as commonly started from seed indoors (many are purchased as young plants or propagated from existing plants), some perennial herbs, flowers, and even some vegetables can be started this way. The advantage of perennials is their longevity, but they may take longer to mature and produce a harvest, making early indoor starts beneficial.

When starting seeds indoors, understanding whether your plants are cool-season or warm-season, and whether they are annuals or perennials, will help you plan the optimal starting time and care for your seedlings. This knowledge ensures that your plants are transplanted outdoors at the right time, maximizing their growth potential and yield.

A basket containing packets of seeds for tomatoes and spinach, with a seed storage box in the background.

Deciphering the Frost Date

Understanding frost dates is essential for us gardeners, as these dates significantly influence when to sow seeds, transplant seedlings, and harvest crops to avoid damage from cold temperatures.

What is the Frost Date?

Frost dates refer to the average dates of the first light frost in fall (first frost date) and the last light frost in spring (last frost date). These dates are very important for gardeners because most plants, especially warm-season crops, are susceptible to damage or death from frost. The period between the last frost date in spring and the first frost date in fall is known as the growing season.

Why Frost Dates are Critical for Gardeners:

  1. Planting Schedule: Frost dates guide gardeners on when it’s safe to plant frost-sensitive plants outdoors. Planting too early can lead to seedlings being killed by frost, while planting too late can shorten the growing season, affecting yields.
  2. Seed Starting: For regions with shorter growing seasons, starting seeds indoors based on frost dates can ensure that plants have a head start, allowing them to mature and produce before the end of the growing season.
  3. Harvest Timing: Knowing the first frost date in fall helps in planning the harvest, especially for crops that need to be harvested before frost for optimal taste and storage quality.

How to Find the Last Frost Date for Your Area:

As I mentioned above, The Almanac offers a Frost Dates Calculator, where you can enter your location to find out the average first and last frost dates. This information helps in planning when to start seeds indoors and when it’s safe to transplant seedlings outdoors.

Calculating Seed Starting Time Based on the Frost Date:

  1. Determine the Last Frost Date: Find the average last spring frost date for your area using the methods above.
  2. Check Seed Packet or Plant Information: Look at the seed packet or plant information for the recommended “sow indoors” time frame, usually expressed in weeks before the last frost date.
  3. Count Backwards: Count back from the last frost date the number of weeks recommended. This date is when you should start your seeds indoors. For example, if your last frost date is May 15 and your tomatoes require starting 6-8 weeks before the last frost, you should start your seeds indoors between March 20 and April 3.

Creating a Seed Starting Schedule

Creating a seed starting schedule is a productive way to stay organized on your gardening journey. Below are some tips to start your seed starting schedule:

  1. List Your Plants: Begin by listing all the plants you intend to grow. Include both cool-season and warm-season crops.
  2. Determine Last Frost Date: Find the last spring frost date for your area, as this is critical for scheduling.
  3. Refer to Seed Packets: Check each seed packet for specific recommendations on when to start seeds indoors relative to your last frost date.
  4. Schedule Seed Starting Dates: Count back from your last frost date to schedule when to start each type of seed indoors. Make a calendar or chart for easy reference.
A tray of seed starting soil blocks with small green flower seedlings sprouting.

Example Schedules for Various Types of Plants

Assuming a last frost date of May 15th, here are example schedules for starting seeds indoors:

  • Tomatoes: Start 6-8 weeks before the last frost date. Seed Starting Date: March 20th – April 3rd.
  • Peppers: Start 8-10 weeks before the last frost date. Seed Starting Date: March 6th – March 20th.
  • Eggplants: Start 8-10 weeks before the last frost date. Seed Starting Date: March 6th – March 20th.
  • Broccoli: Start 6-8 weeks before the last frost date. Seed Starting Date: March 20th – April 3rd.
  • Cabbage: Start 6-8 weeks before the last frost date. Seed Starting Date: March 20th – April 3rd.
  • Lettuce: Start 4-6 weeks before the last frost date. Seed Starting Date: April 3rd – April 17th.
  • Kale: Start 6-8 weeks before the last frost date. Seed Starting Date: March 20th – April 3rd.

Seed Starting Planner Download

If you don’t want to worry about figuring out what you need to keep track of, or you just want a really easy way to organize your seed starting schedule, download my new and improved seed starting planner below! It make your seed starting organization a breeze.


Essential Materials for Starting Seeds Indoors

Over the years I have tried different method of seed starting, with many wins and fails. There are a few items that I would highly recommend for the success of your seed starting season. 

Seed Trays or Containers: You can use specialized seed starting plastic trays with individual cells for each seed, or individual containers like yogurt cups or egg cartons can work, provided they have drainage holes. I am trying my first year at soil blocking which is fairly close to the traditional peat pots, but without the mesh!

Potting Mix: Use a lightweight, seed-starting mix that’s designed for seed germination. This mix should be fine-textured and free-draining to prevent waterlogging, yet capable of retaining enough moisture to support seedling growth.

Seeds: Choose high-quality seeds from a reputable supplier. Consider the plant variety’s suitability for your climate and growing conditions.

Labels and Markers: Label each container or cell with the plant’s name and sowing date to keep track of what you’ve planted and when.

Watering Can or Spray Bottle: Gentle watering is crucial. A spray bottle can provide a fine mist that moistens the soil without displacing or burying the seeds further. As seedlings grow, switch to a small watering can with a fine rose to avoid disturbing the young plants.

Light Source: Natural light from a south-facing, sunny window may be sufficient, but most seedlings benefit from additional light. Grow lights provide consistent, suitable light intensity and can be adjusted as seedlings grow. Budget-friendly fluorescent lights or LEDS is good enough for your seed starting set up grow light.

Heat Mat (Optional): Many seeds germinate more effectively with bottom heat. A heating mat designed for seed starting can increase germination rates and speed up the process.

Plastic Covers or Domes (Optional): Covering seed trays with a clear plastic cover or wrap can help maintain high humidity levels, which is beneficial for seed germination. A DIY option for this would be to cover your cell packs with plastic wrap to encourage a greenhouse effect.

Tips for Creating the Best Environment for Seed Germination

Consistent Moisture: Keep the potting mix consistently moist but not waterlogged. Use a spray bottle for gentle watering initially, and never let the soil dry out completely.

Optimal Temperature: Most seeds germinate best at temperatures between 65°F and 75°F (18°C to 24°C). Heat mats can help maintain consistent soil temperatures, especially for warmth-loving plants.

Adequate Light: Place seedlings near a bright south-facing window or under grow lights for 14-16 hours per day. If using natural light, rotate the trays regularly to ensure even growth.

Ventilation: Good air circulation is important for preventing fungal diseases. If using plastic covers, remove them for a few hours daily or ensure there are ventilation holes to allow air exchange.

Thinning: Once your small seedlings develop their first true leaves, thin them out if they are too crowded. This ensures the remaining seedlings have enough space to grow strong and healthy.

Hardening Off: Gradually acclimate indoor-started seedlings to outdoor conditions by placing them outside in a sheltered spot for increasing periods each day over a week before transplanting them into the garden.

Tip: Check out my full guide for seed starting featuring my seed starting set-up and tips.

More Spring Gardening Tips:

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