February 7, 2026

When to start seeds indoors

Every year around January, gardeners get the itch. Seed catalogs arrive, the days start getting longer, and suddenly you're on your kitchen counter with a bag of potting mix and 14 varieties of pepper seeds. I've been there. More than once I've started seeds way too early, ended up with leggy, root-bound transplants, and had nowhere to put them because it was still snowing outside.

Timing indoor seed starting correctly is about counting backward from your last frost date. Each crop has a specific lead time, and getting that right makes the difference between strong transplants and sad, stretched-out stems.

The countdown method

Here's how it works. Find your average last frost date (you can look this up by ZIP code with our planting calendar). Then count backward based on the crop:

For example, if your last frost date is April 20 (typical for zone 6), you'd start tomato seeds around February 25 to March 10. Peppers would go in a week or two earlier. Cucumbers wouldn't start until late March or early April.

What you actually need

The internet will try to sell you a $200 seed starting setup with grow lights, humidity domes, heat mats, fan systems, and self-watering trays. You don't need all of that. Here's what actually matters:

Containers: Anything with drainage holes works. Cell trays from the garden center are cheap and reusable. Yogurt cups with holes punched in the bottom work too. I've used egg cartons, though they dry out fast.

Growing medium: Use a seed-starting mix, not garden soil. Garden soil is too dense, holds too much water, and can contain pathogens that kill seedlings (damping off). A basic peat or coco coir mix with perlite runs about $8 for a bag that fills dozens of cells.

Light: This is the one thing you can't skimp on. A south-facing window sounds romantic, but in February most windows don't provide enough light. Seedlings need 14 to 16 hours of direct light. A basic shop light with LED tubes, hung 2 to 3 inches above the plants, costs $25 and works fine. Fancy grow lights with purple LEDs are not necessary.

Heat mat: Optional but helpful for peppers, eggplant, and tomatoes. These crops germinate best at 75-85°F soil temperature. A seedling heat mat is about $20 and speeds up germination significantly. Once seeds sprout, you can turn it off.

The biggest mistake: starting too early

I know this sounds counterintuitive. More time should mean bigger plants, right? Nope. Seedlings that outgrow their containers before it's warm enough to transplant become root-bound and stressed. They get tall and floppy because they're reaching for inadequate light over too many weeks. By the time you plant them outside, they're weaker than a stocky transplant started at the right time.

Tomatoes are the worst offenders here. People start them in January for an April last frost, end up with 18-inch tall spindly plants by March, and wonder why they perform poorly. A tomato seed started six weeks before transplanting, with good light, will be a sturdy 6-inch plant ready to take off once it hits warm soil.

The second biggest mistake: not hardening off

Plants grown indoors under artificial light have never experienced wind, direct sun, or temperature swings. If you move them straight from your basement to the garden bed, they go into shock. Leaves get sunburned. Stems snap in the wind. Sometimes they just stop growing for two weeks while they recover.

Hardening off is boring but necessary. Starting about a week before your transplant date, set plants outside in a sheltered spot for a few hours. Bring them back in. Each day, increase the time and exposure. By day 6 or 7, leave them out overnight (assuming no frost). Then transplant.

Direct sow vs. indoor start

Not everything should be started indoors. Some crops resent transplanting because they have taproots (carrots, radishes, beets) or they grow so fast there's no advantage to an indoor start (beans, peas, corn). Here's a quick split:

Start indoors: tomatoes, peppers, eggplant, broccoli, cabbage, cauliflower, onions, leeks, celery, herbs.

Direct sow outside: beans, peas, corn, carrots, radishes, beets, turnips, squash (though indoor start is fine), cucumbers (same), spinach, arugula.

Some crops go either way. Lettuce transplants well but also direct sows easily. Swiss chard is the same. If you have a short growing season, starting these indoors buys you a few extra weeks of harvest.

Keeping track of it all

If you're growing more than a few crops, label everything. I cannot stress this enough. All pepper seedlings look identical at two weeks old. All tomato seedlings look identical. You will absolutely forget which is which unless you write it down.

Popsicle sticks and a Sharpie work. Plastic plant tags work. A piece of tape on the tray works. Just do something.

A simple spreadsheet or notebook with planting dates, germination dates, and transplant dates helps you plan better next year. After two or three seasons, you'll have your own data that's more useful than any generic guide, because it's calibrated to your house, your lights, and your local conditions.

The short version

Find your last frost date. Count backward by crop. Don't start too early. Use real lights, not a windowsill. Harden off before transplanting. Label everything. That's really the whole process. The plants do most of the work themselves.