Leek and Let Grow: Starting Onions and Leeks Indoors for Almost Nothing

I killed my first two batches of onion starts before I figured out what I was doing wrong. Actually, I killed three batches, but the third one I’m blaming on my youngest daughter watering them with an entire cup of juice “to help.” So. Two batches on me.

The thing about onions and leeks is they need a long head start. A really long one. We’re talking 10 to 12 weeks before transplant, which means if you want to put them in the ground around late March or early April here in Redmond, you should be starting seeds right now. December. While it’s grey and raining and you haven’t seen the sun in what feels like six weeks.

Good news is the setup costs almost nothing.

What You Actually Need

Forget the fancy seed starting trays with the little humidity dome that costs $14.99 at Sky Nursery. I use the plastic containers from the salad greens we buy at Costco. Deep enough for roots, already have drainage slots in the lid if you flip it over, and the clear top works as a humidity dome. Free, assuming you were already eating salad, which you should be anyway.

Fill them with a basic seed starting mix. I do 2 parts coconut coir to 1 part perlite, which I buy at the Home Depot on Aurora. Bag of coir runs about $8.47 and lasts forever. Perlite is maybe $9.12 for a big bag. Don’t use straight potting soil. It’s too dense and your seeds will sulk.

Onions and leeks germinate best around 70 to 75 degrees, which is a problem in December because my garage, where I keep my grow shelf, sits around 52 degrees right now. I put a seedling heat mat under the trays, an older one I grabbed off Craigslist for $6.00 a few years back. Without some bottom heat, germination gets slow and spotty and sad.

Light Is Where People Cheap Out Wrong

Here’s where I made dumb mistake number one, by the way. I tried growing onion seedlings on my windowsill. In December. In the Pacific Northwest. If you have done this you know exactly what happened. Pale, floppy little threads leaning desperately toward a window that offered roughly the same light as a mood lamp.

Onion seedlings need actual light. At least 1500 lumens, ideally more, for 14 to 16 hours a day. I run a cheap shop light with two 4000K LED bulbs I got for $18.76 total at Bi-Mart. Set a timer, forget about it. The bulbs hang about 2 to 3 inches above the tops of the seedlings and I raise the light as they grow.

The whole setup on the wire shelf in my garage cost me maybe $35 to build the first year, and I’ve been using it for four seasons now. Which works out to about $8.75 a year. That’s the kind of math I enjoy doing.

Sowing the Seeds

I scatter onion seeds pretty thickly, like really thickly, and then thin later. Onion seeds are tiny and my hands are not, and I have made peace with this. Aim for maybe a half inch apart if you’re feeling precise, but honestly just try to avoid dumping half the packet in one corner. I have done this.

Cover with about a quarter inch of mix, mist with a spray bottle, put the lid on, and set on the heat mat. Germination usually takes 7 to 10 days. Once they sprout and straighten up, pull the lid off and get them under the lights immediately. Don’t wait. They will flop toward whatever light exists and you’ll be straightening tiny onion grass for a week.

Leeks are basically the same process but even more laid back about it. They’re forgiving plants. A leek is the friend who shows up 20 minutes late but brings good snacks and nobody minds. Real low-key. Which, now that I think about it, is a solid way to go through life.

Varieties Worth Starting

For onions I grow Walla Walla sweet onions because we’re in the Pacific Northwest and it feels almost legally required. Long-day variety, which is what you want here. For leeks I’ve been growing King Richard for years. Good flavor, holds well in the garden through our wet fall.

Seeds from Territorial Seed Company are what I usually use. They’re based in Oregon, bred for our climate, and a packet runs $3.49 to $4.25 depending on the variety. Way cheaper than buying starts in April, which is what I did my first year before I knew any better.

Anyway. Salad container, coir and perlite mix, a heat mat, a shop light on a timer. That’s the whole setup. You probably already have most of it or can get it for close to nothing. And you’ll have onion starts in spring that cost you about $0.11 each instead of $1.79 at the nursery.

The thyme to start is now. (I’m not sorry about that one.)

Photo by Felix Erdmann on Unsplash