Winter sowing in zip‑lock bags is simple, low‑cost, and surprisingly effective way to winter sow native milkweed and perennial seeds. It is also a low mess alternative to milk jugs. Ziplock bags act like mini cold frames, letting moisture, light, and fluctuating winter temperatures stratify seeds naturally. They’re lighter and easier to store than jugs, and they warm quickly on sunny days.
Here’s a clear, gardener‑friendly walkthrough to help you get started.
What You Need
- Quart or gallon freezer‑grade ziplock bags (sturdier = better)
- Seed‑starting mix (Not garden soil. I like using Organic Promix because it contains MYCOACTIVE to stimulate vigorous growth and greater resistance.
- Spray bottle with water.
- Permanent marker for labeling. I use Garden Markers because they are waterproof and will not fade.
- Seeds suited to winter sowing (Native milkweeds, perennials, hardy annuals)
Click here to Find Native milkweed seeds for your area.
Click here to find native perennial seeds for your area.
Prepare the Bag
- Cut two small drainage slits in the bottom corners.
- Add 4-5 inches of moist seed‑starting mix.
- The mix should feel like a wrung‑out sponge.
Sow the Seeds
- Sprinkle seeds on the surface.
- Press gently so they make contact with the soil.
- Cover lightly only if the species requires it (many natives need light to germinate).
Seal for Ventilation
- Zip the bag almost closed, leaving a ½‑inch gap for airflow.
- This prevents mold while still holding humidity.
“I started winter sowing today with 8 types of milkweed .
This was just before we hung the bags outside. I have many other bags to prep and hang outside. This was such a successful method for me last year! 
” Jennifer Zolinski Gezequel
Place Outdoors
- Set bags in a bright, open area that gets rain.
Jennifer Zolinski Gezequel hangs ziplock bags using stakes laying across raised beds.
Let Nature Work
- The freeze and thaw cycles stratify the seeds.
- Condensation inside the bag is normal and acts like a tiny greenhouse.
Monitor in Early Spring
- When seedlings appear, gradually open the bag wider over a week to acclimate them.
- Once they’re sturdy, transplant into pots or directly into the garden after the last frost in your area.