Winter Sowing: The Best Seed-Starting Technique You’ve Never Heard Of
Before you continue on reading this post, please be aware that the technique I’m about to share is very addictive. Proceed at your own risk!
For many gardeners, especially in cold winter zones like mine, February is a tough time. The days start to get longer, and we get those tantalizingly spring-like 40 degree days that give us seed-starting fever. However, unless you have a hoophouse or some sort of protective tunnel, it’s likely too early to be starting many of your seeds. We’ve all done it -- gotten over-excited, started seeds indoors too early, and ended up with leggy, rootbound, unhappy seedlings come May when there’s still snow on the ground here in Iowa.. I’m here to tell you that there is an answer to your February woes. It’s called winter sowing.
The basic idea of winter sowing is to create tiny “greenhouses” using milk jugs or other transparent plastic containers. The microclimates created in these little containers allows for earlier germination than direct seeding outside. If you have an indoor seed-starting setup, this technique will allow you to save valuable space under lights (or, possibly, eliminate your indoor setup altogether). This technique is also perfect for would-be gardeners who do not have space or equipment to start seeds indoors. It’s much much cheaper than buying plant starts!
So, here’s how it works (There are a ton of resources already out there on how to do this, so I’m going to do a brief overview and then offer links to other sites). First, collect your containers. The classic winter sowing container is a milk jug (cut in half with one part still connected to create a “hinge” near the jug handle), but I also really like to use clear plastic salad mix containers. I’ve also seen people use large rubbermaid tubs (they have to be transparent) or even Ziploc bags!
Next, put holes in your containers! I use a drill to make many holes in the bottoms (we want good drainage) and a few holes in the top (for air circulation, and also so moisture can enter). If you are using milk jugs, you do not need to drill any additional holes in the top -- the open mouth will be enough!
Then, put damp potting soil in your containers. A couple inches should be fine.
Finally, plant your seeds and label them. I like to stick to one variety per container. I highly recommend making labels to stick inside the containers, because if you write on the outside with Sharpie it will NOT last. (Pro-tip: the best label is made from cutting up an old plastic mini-blind, and writing the plant name on it with PENCIL - not permanent marker).
Now, close your containers. If you’re using salad containers, just put the tops on. If you have the milk jug setup, you’ll need to tape the top part to the bottom part, to create a somewhat closed system except for the open spout. I like to use blue painters tape, but duct tape also works. The taping is kind of a pain, which is why I gravitate more towards the salad mix containers.
Now, put your containers outside! You’ll want a full sun area, but somewhat protected so they won’t blow away. You also might want them up off the ground if possible, so little friends don’t come graze on them later in spring after you open the tops to vent them (my chickens decimated my kale one year!!).
Now you just let your seeds do their thing! When the weather starts to warm up, you’ll have to open the tops (which means untaping if you have milk jugs) to vent the containers on sunny days. But if the night temps are still low, you’ll want to close them up in late afternoon again to preserve some warmth overnight.
This method will not get you the earliest seedlings in the world. Starting things indoors is the best bet if you need really early plants (like some of my flower varieties that I plant out into low tunnels in March). However, winter sowing will provide you a massive number of seedlings in a small area. They will be incredibly tough and hardy (no need for hardening off) and healthy. When seedlings are about 1 inch tall or so, you can transplant directly into the garden!
Now, how do you decide what to plant and when? Most perennials work well with this method, because their seeds very often require a long cold period before germination. Also, any varieties that are labeled “hardy annuals” or “self-seeding annuals” will usually work well.
Here is a list (in no particular order) of things I’ve done very successfully, winter sowing in January through late February in northeast Iowa:
Ammi (False Queen Anne’s Lace)
Centaurea (Bachelor’s Buttons)
Calendula (Pot Marigold)
Salvia horminum (Clary Sage)
Rudbeckia hirta (Black-Eyed Susan)
Rudbeckia triloba (Brown-Eyed Susan)
Here are some new varieties I’m trying this year:
Orlaya (White Lace Flower)
Agrostemma (Corn Cockle)
Veronica longifolia (Speedwell)
Here are more resources on how to do this:
It’s not too late to get some winter sowing containers going this year. Enjoy!