Starting Plants Indoors from Seed Is All About Timing
Let me clarify two things before we get into figuring out when to start your seeds indoors.
First things first, starting seeds indoors—at least in a way that actually produces healthy seedlings ready to transplant out into the garden—is an advanced gardener skill. I'd already been gardening for several years before I ever even attempted to start my own seeds indoors, and it took me a while to get it right. So, if you've had some bumps or complete fails while trying to start your own seeds indoors, just know that you're in good company.
Second, you don't need to start seeds indoors for every single plant you'll grow in the garden. Lettuce plants, for instance, are short and small, meaning they don't take very long to grow to maturity, nor do they take up very much room in our gardens. For that reason, you'd typically just sow your lettuce seeds directly in the ground outdoors when the temperature is right.
It's really just the plants that I refer to as large and lengthy that need to be started from seed indoors.
Prioritize Certain Plants to Start by Seed Indoors
Some plants have very short windows of time during which they can be planted outdoors, grown to maturity, and harvested. That's because most of us don't live in a place where the temperature, sunlight, and setup are all just right to give those plants the full amount of time they need outdoors to complete their life cycles.
But if you start plants inside and give them as much of a head start as possible before moving them outdoors once the climate is right, you increase how much production and enjoyment you'll be able to get from those plants.
Plants that need more than 65, 75, or even 90 days in your garden before you can harvest from them—think plants like tomatoes, broccoli, cauliflower, kale, brussels sprouts, tomatillos, eggplants, peppers, melons, and okra—most likely need to be started indoors so that you have enough time to enjoy them in your garden under their optimal conditions.
Prioritize these plants that will spend a long time in your garden when starting seeds indoors so you can jumpstart your enjoyment of them and maximize their growing time outdoors.
Vegetable Seed Starting Indoors
Here are the veggies, fruiting plants, and leafy greens I prioritize starting indoors by season. (Use the temperature chart below if you're unfamiliar with your growing seasons.)
cool season
The plants I start indoors for the cool season include:
- broccoli
- cauliflower
- kale
- cabbages
- peas
warm season
The plants I start indoors for the warm season include:
- tomatoes
- peppers
- eggplants
- squash
- zucchini
- melons
- basil
hot season
The plants I start indoors for the hot season include:
- okra
- tomatillos
- large gourds
- large melons
Here are the simple steps you can follow to determine when to start your seeds indoors.
Warning: you're going to start many seeds way before it’s time to plant them in the garden, so don't be surprised if your calculations tell you to start a hot season plant in the spring.
Step One: Check the back of the seed packet
Most seeds will give you recommendations on the back for when to start your seeds indoors. Make sure you note how long the plants you want to grow take to harvest.
Step Two: Look up your predicted last frost date
You'll count back from your predicted last frost date to help you know when you can plant. Click here to find your last frost date in the US.
My last frost date in the Chicago area was around May 15, and it's early April now that I've moved to Nashville. For my Rooted Garden clients in Houston, TX, their last frost date is February 20.
Once you know that date, you can know what to start inside and when!
Step Three: Calculate your indoor seed starting dates
You'll use the date of your last expected frost to determine when to start seeds for each season.
cool season
To know when to start onions and leek seeds indoors, subtract 120 days from your last frost date. That would be early January in Chicago and mid November in Houston.
To know when to start the rest of your cool season plants indoors, subtract 100 days from your last frost date.
In Chicago, that's early February. In Houston, a much warmer climate, that's in early December. That means Houstonians will be starting plants like kale, broccoli, and cabbage inside before the holiday season, while Chicagoans can wait until around Valentine's Day.
Toward the end of your warmest season, it's time to think of cool season plants once more. Begin starting seeds indoors for your cool season 30 days or so before the end of your warmest season.
warm season
To know when to plant your large warm season plants indoors, subtract 45 days from your last frost date.
That means Chicagoans will be starting tomatoes, peppers, eggplant, and even some basil seeds indoors at the end of March, while my Houston peeps will start those in early January.
hot season
Not all of us will have a hot season. You won't count back from a frost date for this season. Instead, you'll subtract 45 days from the first month where your average high temperature exceeds 85 degrees. That's when you'll start your hot season plants indoors.
I don't have to plan an indoor planting day for large hot season plants because Nashville doesn't really have a hot season. My Houston friends, who most certainly experience a hot season, will start their hot season plants indoors around mid April.
Supplies for Starting Seeds Indoors
We rounded up all the supplies, including the best seed starting soil mix, trays, and LED lights, you'll need to start your own seeds indoors, plus budget options. Explore our picks for the best seed starting soil mixes, trays, and LED lights for indoors.
Don't worry if you don't have all of these supplies right now. Each season, you can add to your seed starting toolkit. Our number one priority with starting seeds indoors is to imitate nature indoors (sunlight, wind, water, etc.), and you can do that with all different kinds of supplies. Just make sure you do have some basic equipment ready to go before you order any seeds.
And speaking of seeds, here are links to some of my favorite seed companies:
Schedule Your Indoor Seed Starting Days
Final step: open your phone calendar app or grab your paper calendar and mark the dates you'll need start seeds indoors so you never miss a planting date again.
It's normal to get overwhelmed by seed starting at first, but just remember that you can always start small. Just one tray of seedlings can grow into enough large plants to fill an entire raised garden bed in the months to come. So, don’t wait till you can go big to start... start small and grow from there.
Now, no more paying $15 for a tomato plant at the store!
Happy seed starting!
