This method is also great for the environment because you reuse containers that you would usually just throw in the garbage. The containers act like little greenhouses where the seeds will germinate at their own pace when they are ready, much like in nature. It's great because you can take your time and work on sowing your containers all through the winter. But be careful because it's so easy that you end up with way more containers than you realize; and then when your seedlings are ready to be planted, you'll find that you don't have nearly enough space in your garden to plant them all. It's a good problem to have!
When I used to start my seeds indoors, I estimate my success rate was only about 25-50% of the seeds I sowed would germinate and survive being transplanted into the garden. Now with winter sowing, I estimate my success rate is about 75-100%!! It's crazy! Here is a picture of the containers that are currently sitting out by my deck...
For your flats, you can use any type of plastic container with a lid as long as the lid is clear and closes tightly. I have heard from other winter sowers that they prefer 2 liter bottles or milk jugs, I prefer the type of take out container you get a salad or sandwich in from a restaurant.
Experiment with different types of containers and see what you prefer. The shape and size of the container doesn't matter, but it must be deep enough to allow for 2-3 inches of dirt and at least a few inches of space between the dirt and the lid to allow room for the seedlings to grow. (Updated Jan-09-2011 - See my post about winter sowing containers for more information)
Here are the steps to get you started with winter sowing...
- Clean the container well and then poke holes in the bottom and top of the container. Heating a knife and melting the holes makes this task easier. (Use an old knife and not a good one because it will turn black over time and have plastic residue on it.) You don't want to poke too many holes, only enough for drainage but not so many that the water will run right through and allow the soil to dry out quickly. (note: If you're using a tall narrow container like a 2lt bottle or milk jug, you'll need to cut the container in half as well.)
- Add your potting soil to the container and sow the seeds like you normally would, according to the directions on the packet. I use the same type of potting soil in my winter sowing containers that I use when starting seeds indoors. I buy the seed starting soil mix that is specifically made for starting seeds. It's a little more expensive than other soil mixes. You could probably find a recipe online to mix your own seed starting mix and possibly save some money. Either way, you absolutely want to use fresh, sterile soil when starting any seeds; and never, never use soil from your garden in any of your containers.
- Mark the container. There are a few ways to do this. I have heard some people use masking or duct tape to label their containers. If you do this, make sure to put the tape on the bottom of the container or it will fade by Spring (even with permanent marker). I like to cut up old vinyl mini blinds and write on them with pencil and push the marker into the soil, these won't fade.
- Water them well. I like to use the sprayer in my kitchen sink and saturate the soil and let the excess water drain out.
- Put the lid on the container and put it outside in a protected spot that gets only morning sun. This part is crucial! Whatever you do, do not put them in full sun! This will just bake the seeds and they will not germinate. (I made this mistake with some of mine the first year). When I say morning sun I mean a location where they will be in the sun only until about 11am, and then they are in shade for the rest of the day. Remember that the sun changes as we move into Spring so check regularly to make sure the spot you chose in February doesn't suddenly become a full sun location in March or April. Also be careful to protect them from strong winds so they won't blow away.
- Now forget about them until about mid to late March.
- Once the weather starts to warm up and is consistantly above freezing during the days, check your containers regularly for any signs of growth. Cold weather plants will start to germinate first, things like broccoli, lettuce, spinach and spring blooming perennials.
- The only maintenance you have to do at this point is to make sure they stay out of the full sun and make sure the soil doesn't dry out. As they start to grow, I like to take the lids off during the day and put them in the sun (if they are full sun plants). Then I will cover them back up in the evening before it gets dark. This is optional though, you don't have to do this.
- Once the seedlings get tall enough where they are touching the top of the inside of the container, it's time to remove the lids for good. Once you remove the lids, you can move them into the full sun (if they are full sun plants). Check them at least once a day to make sure the soil hasn't dried out. They can dry out pretty quickly once you take the lids off. Also keep an eye on the weather report. If there is a chance of frost, cover the containers with a sheet or blanket over night.
- That's it, at this point the hard part is over!
So, when can you plant them into your garden? Well, for most plants you will need to wait until after the last frost date to be safe. Cold weather plants can be planted much earlier however. Here in Minnesota, we are in Zone4. That means that cold weather plants (which can handle frost exposure) can be planted as early as mid to late April. Our average last frost date is about May 15th so you'll need to wait to plant most of your seedlings until after the last frost. Every year is different though so keep an eye on the weather report.
Keep in mind that not all seeds will do well if you sow them very early in the winter (December-January). Start your cold weather veggies and any plants that are self sowing or require cold stratification first. Then, as you move in to late winter (February-March), start your warm weather plants like tomatoes, beans and peppers. I wait until late March into April before I start my tropical seeds and succulents. As I sow my seeds this year, I will share my list and more pictures.
Now, get busy collecting and preparing those containers and get some sowing done! Have fun and good luck! Feel free to ask me any questions you may have.