Winter is a great time to plant for next year’s garden. Did you know that it can also be a great time to sow some seeds outdoors?
Winter seed sowing is a relatively new method of planting certain types of seeds for the following season. It greatly simplifies planting, and even improves germination rates of seeds that require cold stratification.
So, in this article, I’ll teach you the simple technique of winter seed sowing in milk jugs. I’ll cover which plants are good candidates for this planting method, when to start winter sowing, and how to do it, step by step. Let’s get started!
What is winter seed sowing?
At its most simple, winter sowing is the act of planting seeds during the winter months. Many seeds can endure harsh winter weather and will naturally germinate when the warmer weather arrives.
How it works
The basic principle of winter sowing is to create a miniature greenhouse in which seeds are planted. This enclosed space retains moisture, lessening the need to water your seeds through the winter.
During the winter months, the seeds will freeze and thaw, helping weaken the seed coating for germination in spring. This cold period also helps break dormancy in seeds that require cold stratification.
Winter sowing is amazing for its simplicity and allows us to save money, too. Starting plants from seed is much cheaper than buying pre-started plants from the nursery, and the process is more satisfying in the end.
Winter sowing may sound traumatic for a tiny seed, but this is not true. Many seeds are designed to go through winter before sprouting, so it can actually provide benefits!
- No need for grow lights
- Cold stratification helps germination rates
- Helps weaken seed coats
- Less frequent watering
- No more worrying about when to plant seeds – they sprout when they’re ready!
Which plants can be winter sown?
Seed dormancy is a complicated topic. Many seeds won’t sprout until they have first undergone a specific set of environmental circumstances.
The best example of this is cold stratification: Many perennial flower seeds and bulbs require a cold period to grow properly. Without enough time in the cold, the seeds may not germinate, or the resulting plants may not grow as desired.
With winter sowing, the seeds are exposed to repeated freezing and thawing, which aides in proper sprouting. However, even if a seed doesn’t require stratification, it may still be a good fit for winter sowing.
Flowers for winter sowing:
This is a mix of annual and perennial flowers that can all be winter sown. Click to find seeds for the listed species.
There are a large number of less common flowers that are cold hardy, making them a good fit for winter sowing. Look for native perennials or hardy annuals in your region and get experimenting!
Vegetables and herbs for winter sowing:
Cool weather vegetables and herbs are great candidates for winter sowing. Instead of trying to remember when to plant, the seed will “wake up” and sprout when the time is right.
While these plants are a great starting place for winter sowing options, there are many more. Both your climate and specific cultivars will dictate whether seeds are a good candidate for winter planting.
Other key phrases to look for on your seed packet:
- Perennial (in your zone)
- Cold or winter hardy
- Cold stratification or pre-chilling
- Cold period
- Native (in your region)
- Plant in late fall
- Direct or self sowing
If you see any of these terms on your seed packet, it is worth trying to winter sow them. While you may find that some work and others don’t, at least the process is quick and easy!
When to start winter sowing
So you’ve decided to give winter sowing in milk jugs a shot, but when should you begin? This is probably the most important thing to get right!
As a general rule of thumb, start winter sowing on or after the Winter solstice (December 21st). It is better to start later than earlier, so early to mid-January is a good time to shoot for.
Timing it right:
- Don’t start too early. If you plant your seeds too early, there is a chance of there being a late warm spell. This can initiate germination prematurely, and the seedling sprouts will be killed off once the real frost comes.
- Wait for the Winter solstice. The Winter solstice (Dec. 21st, or June 21st for Southern Hemisphere) is the shortest day of the year. From this date forward, the days lengthen and weather warms up very gradually.
Winter sowing seeds in milk jugs (steps)
Since milk jugs are a by-product of most staple diets, they make a very cheap option for winter sowing seeds. However, there are a number of other containers that can be used for winter seed sowing.
Alternate winter sowing containers:
- Propagation tray and humidity dome
- Food container with lid
- Clear 2 liter soda bottles
The right container should have a translucent or transparent covering, drainage holes, and some form of ventilation. Milk jugs are easy to modify for winter sowing, easy to move around, and re-usable.
How to winter sow seeds
Preparing each milk just takes a matter of a few minutes. After that, all that is left to do is plant the seeds and set the container outdoors.
- Moist potting soil
- Razor blade
- Drill and 1/4″ drill bit
- Tape for labeling
- UV-proof clear tape
- Permanent marker (or gardener’s marker)
How to winter sow seeds in milk jugs
- Label the milk jug with seed variety.
I always recommend starting by labeling the containers with each seed variety. That way, you’ll avoid forgetting which seed was planted where. Use a UV resistant marker so the writing won’t fade outside.
- Drill drainage and aeration holes.
Drill several holes in the bottom of the milk jugs to allow for drainage. Use a 1/4-1/2″ bit and drill at the lowest points on the container. Also, drill a few holes towards the top for airflow.
- Slice the jug horizontally.
Start slicing at the base of the handle, and move horizontally around the whole jug until you reach the other side of the handle. Leave the handle intact so it acts as a hinge to open and close the “greenhouse” roof”
- Fill with moist potting soil.
Moisten the potting soil and mix thoroughly to ensure it is nice and damp, but not completely soaked. Seed starter mix works for this as well. Fill the bottom half of the milk jug to about 1/2″ from the top.
- Sow the seeds.
Plant your seeds according to the seed packet. Some seeds require light, while others should be completely buried. Tiny seeds are usually sprinkled and pressed into the soil’s surface, then misted.
How many seeds? I recommend planting many seeds in each container, to ensure enough sprout. Many seed packets will include germination rate, so you can get an idea of what percentage should sprout. As with any seed, some might not come up, and with each milk jug, you can potentially get dozens of seedlings to transplant.
- Mist the soil’s surface.
After planting, mist the surface of the soil to ensure good seed-to-soil contact.
- Close the “lid” and tape shut.
With your seeds sown, close the lid and use duct tape to keep it shut. If you haven’t yet, make sure your containers are labeled with the correct seed variety!
- Place the containers outdoors.
Find a location with partial shade or full shade. If you live in a warmer climate, full shade is best. If you have harsh, frigid winters, some sunlight can help warm up the containers to provide more freezing and thawing cycles.
- Check regularly for moisture levels.
After a day, you should start to see condensation forming on the inside of the milk jug. This is normal. After this, check every week or so to make sure the soil isn’t becoming dry. You want your seeds to remain moist during the entire winter until they sprout.
With the “hard” part done, all that is left to do is wait! Nature will take its course, and your seeds will sprout when the time is right (usually in early spring).
How to winter sow seeds (video):
When the seeds sprout…
As the weather begins warming up, you may need to open up the milk jug a bit to provide better airflow. Remember, this container is essentially a micro-greenhouse, and it will be much warmer inside than out!
You should also begin checking more frequently for sprouts in the early springtime. Once you see seedlings emerge, you should make sure the containers get plenty of morning sunlight.
Again, it is very important to provide more airflow as the weather warms up! The tiny seedlings will need a gradual transition from inside the “greenhouse” to out in the elements. Either cut the holes larger, or prop open the lid to avoid baking the young plants.
Most seedlings are ready for transplant when they have 1 or 2 sets of true leaves. Don’t wait too long to transplant, as you don’t want the different root systems to become too entangled.
Using a chopstick or spoon, scoop deeply around an individual seedling, trying your best not to break the roots. Pull the seedling out of the soil holding it gently by its leaves.
Then, move the rootball into a 3-5″ pot to continue growing on. Try to use soil that is similar or the same as the soil where they will grow permanently. I like to mix 50% potting soil and 50% native soil to adjust the seedlings.
Once the roots are developed in larger pots, they can be planted out into their final growing location for the season.
Top tips for winter sowing
If I had to offer my top 3 tips for successful winter sowing…
- Don’t start too early.
- Keep the seeds moist through winter.
- Try new seeds (even if they might not sprout)!
I hope this article inspires you to try winter sowing in milk jugs. The process couldn’t be more hands off, and it makes for a very exciting spring when sprouts appear. Happy growing!