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When To Start Seeds Indoors

by | Jan 26, 2021 | Grow

If you want to get a head start on the garden season, then starting seeds indoors is the way to go. But how do you know when to start seeds? This post will be your new go-to guide for seed starting indoors.

Tiny plants in seed starting pots.

We are often asked, “When should I start my seeds?”, and we usually have to give one of our most common responses which is, “It depends!”.

Seed starting indoors is determined by your climate, the type of seeds you’re sowing, how long the seeds take to germinate, the time of year you’re planting, and your average first and last frost dates.

Why Start Seeds Indoors?

Seedlings growing in a seedling tray.

The most common reason for starting seeds indoors is due to a shorter growing season. Here in the very north panhandle of Idaho, we have a pretty short window for growing crops, so knowing how to start seeds is a must if we want a decent harvest.

A short growing season means the days to a mature harvest for an individual plant exceeds the amount of time between your last frost date in the spring, and your first frost date in the fall.

Seed starting gives you up to a 16 week head-start on these crops, that’s nearly a 4 month head start!

Benefits of Starting Seeds Indoors

A man adding water to a tray of seed starting pots.

Some plant varieties take a lot more care to germinate and need a bit of pampering when they’re seedlings. By starting them indoors you’re giving them a steady environment to thrive with stable temperatures and consistent watering.

Some examples of plants that are great to start indoors are your warm-weather loving plants like tomatoes, peppers, and cucumbers. Once they’re mature enough to handle the colder weather, you can learn how to transplant plants into the garden.

Do I Need to Seed Start Indoors?

In short, no! There are many seeds that do best when direct-sown into your garden. These are seeds that germinate well, are eager to grow and can do so in cooler temps, and are quick to mature.

Some examples of these would be lettuce, spinach and other brassicas. These seeds can actually be sown as soon as your soil is workable, and can handle frosts.

Other items like summer squash, sunflowers, and nasturtiums do better once the threat of frost is over.

First and Last Frost Dates

A man holding up a Clyde's Garden Planner.

Find the average first and last frost dates by going to the National Oceanic and Atmospheric Administration website (NOAA). Enter your zip code in the provided box and hit enter. You will then see your city, altitude, and first and last frost dates.

They also give you the number of days in your growing season. This can be very helpful for knowing whether a crop needs to be seed started in order to have enough time to produce a harvest.

NOAA is a great basic start to knowing your first and last frost dates, but most places have micro climates, so the best method is to talk to your neighbors, they will know best!

One of our favorite tools for knowing when to plant is to use Clyde’s Garden planner (photographed above – to purchase, use code “” for 10% off your order). You put in your average last frost date and the chart fills in all the rest! No counting backward, just follow the chart.

If you don’t have a garden planner (we recommend getting one!), you can count backward on your calendar to determine when to start your seeds. To know how long seeds should be started indoors, you can read the seed packet, or follow the chart below.

When to Start Seeds Indoors Chart (Vegetables)

Follow the list below for when to start your seeds indoors. Count back the number of weeks listed from your last frost date in the Spring.

For example, if your last frost date is May 16th, you would count backward 8 weeks to start your tomatoes indoors on March 24th.

Keep in mind you’ll want to harden your plants off about a week prior to planting them outside (see below for instructions on hardening off your plants).

  • 4 weeks before the last frost: Bitter Melon.
  • 6 weeks before the last frost: Asparagus, Basil, Chickpeas, Echinacea Root, Fennel, Ground Cherries, Melons, Okra, Onions, Peanuts, Rhubarb, Sesame, Shallots.
  • 8 weeks before the last frost: Amaranth, Anise Hyssop, Catnip, Chile Peppers, Chives, Lovage, Oregano, Paprika Peppers, Parsley, Sage, Savory, Sweet Peppers, St. John’s Wort, Thyme, Tomatillos, Tomatoes, Winged Bean.
  • 9 weeks before the last frost: Broccoli, Cabbage, Kohlrabi.
  • 10 weeks before the last frost: Eggplant, Jicama, Lavender, Lemongrass.
  • 11 weeks before the last frost: Artichokes, Cauliflower, Leeks.
  • 12 weeks before the last frost: Brussels Sprouts, Cardoons, Celeriac, Celery, Cutting Celery, Parsley Root, Roselles, Stevia.
  • 16 weeks before the last frost: Rosemary, Strawberries.

The times listed above are a very general guide line or rule of thumb. It’s a great starting point, but because every garden site is different, you can start here, take notes and then adjust over time with experience on your own site.

A mother and her children direct sowing seeds into the garden.

Vegetables That Can Be Direct Sown

The following are vegetables that don’t need to be started indoors, you can direct sow these after the last frost date (and some even before the threat of frost is over). Depending on your growing season, you may choose to start these indoors, but for many gardening zones, that’s unnecessary.

  • Arugula, Asian Greens, Beans, Beets, Belgian Endive, Borage, Broccoli Raab, Brown Mustard Seed, Carrots, Chamomile, Swiss Chard, Chervil, Chicories, Chinese Broccoli, Chinese Cabbage, Claytonia, Collard Greens, Coriander, Sweet Corn, Cress, Cucumbers, Daikon Radishes, Dandelion Greens, Dill, Edamame, Endive, Escarole, Fava Beans, Fennel, Kale, Kohlrabi, Lemon Balm, Lettuce, Lima Beans, Mache, Melons, Minutina, Mizuna, Mustard Greens, Orach, Pak Choi, Parsnips, Peas, Pumpkins, Purslane, Radicchio, Radishes, Rutabagas, Salad Greens, Salsify, Shelling Beans, Shiso, Sorrel, Spearmint, Spinach, Summer Squash, Winter Squash, Turnip Greens, and Turnips.

How to Harden Off Plants

Hands putting a tomato transplant into the ground.

Before transplanting your plant starts, you’ll want to acclimate them to the cooler temperatures by hardening them off.

This means you introduce your plants, slowly, to the colder weather.

  1. Day 1 – Take your plants outside on a sunny table or patio for a few hours, then bring them back inside for the remainder of the day.
  2. Day 2 – Take your plants outside on a sunny table or patio for 3 more hours than the previous day, then bring them back inside for the remainder of the day.
  3. Day 3-7 – Allow your plants to stay outside for 3 more hours each day, slowly building up to letting them stay outside all day and all night (as long as the threat of frost has past).

Take it Year by Year

Remember, learning to garden is a very individualized process based on your unique garden, climate, soil, etc. We’ll continue sharing all our helpful tips, but our biggest tip is to just get started and take notes year after year!

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