When to Start Seeds Indoors: PNW Zone 8b Guide

Every February I convince myself I know when to start seeds indoors. Then I end up with tomato plants the size of small shrubs sitting in my garage in March because I jumped the gun by four weeks. Again. The hardening off process becomes this long awkward apology tour where I try to introduce my leggy overachievers to actual weather without killing them.

If you’re in zone 8b around the Redmond area, your average last frost lands somewhere around March 15th to March 25th. I use March 20th as my planning anchor. Write that date down. Everything else works backward from there.

The Countdown Method (Finally Made This Click for Me)

The seed packet says “start indoors 6-8 weeks before last frost.” Cool. Most of us read that, nod, and then start everything on the same day in late January because that felt right. That’s not how this works.

Different plants need different lead times. And since it’s already April, some of this is useful right now, and some is for next year when you’re smugly prepared. I’ll call that one out as we go.

What to Start When (Counting Back from March 20)

10-12 Weeks Before Last Frost (Early-to-Mid January)

This window is for peppers and eggplant. Both are slow germinators that want soil temps around 80-85 degrees to even think about sprouting. I use a seedling heat mat for these. Peppers especially will just sit there in cold soil looking stubborn until you give them warmth. Very on-brand for peppers.

8-10 Weeks Before Last Frost (Late January to Early February)

Tomatoes go in here. I know everyone starts tomatoes in January and I know why, but honestly, a tomato started February 1st and transplanted after last frost will catch up to a stressed leggy one started in December by mid-July. I’ve tested this. The later start wins.

Also in this window: celery, celeriac, and leeks. Leeks are worth starting from seed if you want to save money. They look like grass for weeks and you’ll wonder if anything is happening. Something is happening.

6-8 Weeks Before Last Frost (Early to Late February)

Broccoli, cauliflower, cabbage, and kale. These want cooler germination temps, around 65-70 degrees, so no heat mat needed. They grow fast once they get going. Start them too early and they get root-bound and sulky before you can get them outside. Brassicas hold a grudge.

This is also the window for herbs like basil (though basil really hates cold, so don’t rush it outside) and flowers like marigolds if you grow those to confuse the aphids. Which I do.

4-6 Weeks Before Last Frost (Early to Mid March)

Cucumbers, squash, and melons. Short lead time on purpose. These grow fast and do not want to be root-bound. I’ve learned this the hard way more than once. A cucumber seedling stuck in a too-small cell for too long will just decide it’s done with you.

Lettuces can also go in here for transplanting, though honestly lettuce is so easy to direct sow once the ground is workable that I rarely bother starting it inside. Up to you.

Direct Sow After Last Frost (After March 20, or Now)

Beans, peas (actually peas prefer earlier, direct sow as soon as soil hits 45 degrees), corn, carrots, beets, radishes, and chard all go straight in the ground. No indoor time needed. Carrots especially hate being transplanted. Don’t try it. I tried it once.

Since It’s April Right Now

Good news. You’re past last frost. You can still start cucumbers, squash, and melons indoors right now and transplant in a couple weeks. You can also direct sow a ton of stuff immediately if your soil has dried out enough to work, which in the PNW is always a hopeful question in April.

Tomatoes and peppers started indoors right now will still produce fine. You’ll just have a shorter window before our first fall frost, usually late October in zone 8b. Choose varieties with shorter days-to-maturity. Something like a Stupice tomato at 60 days beats a Brandywine at 90 days if you’re starting late.

One Tool That Actually Helps

I used to do all this math on a napkin and lose the napkin. Now I use a simple seed starting journal to track what went in when. Nothing fancy. You could use a piece of paper taped inside a cabinet door. The point is writing it down so March-you doesn’t have to guess what January-you was thinking.

You can also do this on graph paper with your frost date at the top and count backward in columns. Extremely nerdy. Works great. Free.

The Short Version

Peppers early, tomatoes not as early as you think, brassicas in the middle, cucumbers late, and everything else direct sow. That’s basically the whole guide. The hardest part isn’t knowing when to start seeds indoors. It’s not starting them three weeks too early just because you’re tired of winter.

I say that as someone who still has a flat of tomatoes on my heat mat right now that are definitely already too big. Growth mindset. (Gardening pun. Not sorry.)

Photo by Gigi on Unsplash