Seed-starting in the classroom - without a greenhouse!
While not widely-known in most gardening circles, winter sowing is a way of seed-starting outdoors in winter that has quite the cult following, for many reasons. Some of those reasons include ease of sowing, use of recycled materials, reduced loss of seedlings due to damping-off, no need for fancy equipment, playing in the dirt in the middle of winter, the absence of seed flats placed precariously on endtables near the window, hovering over a beige carpet, waiting to be knocked over by a rambunctious child or two...
Okay, that last one was the reason that sold me personally on trying this method. The great results I had that first year were what keeps me at it ten years later. I would never bother to start another seed any other way. As I was contemplating the upcoming winter-sowing season, and thinking about what I would grow this year, I realized that this method could be adapted for use in the classroom.
So just what is winter sowing? It is a method of sowing seeds in containers, which are then placed outside in winter. Yes, outside. The containers act as miniature greenhouses, protecting the seed from adverse weather, from birds and other critters, and from being washed away; and while the container, by virtue of being covered, affords temperatures a bit warmer than outside for the seed to germinate, the resulting seedlings are hardier than indoor-started seedlings, and the problem of damping off is negated. Additionally, there is no need to harden off the seedlings, as they are completely acclimated to the outdoors. (This was yet another selling point for me, as I've lost I don't know how many seedlings because I would forget to bring them back inside at night!)
The winter sowing season officially starts on the winter solstice, and many gardeners will plant something symbolic on this day. The great thing is, winter sowing can be done any time from December through April or even May (which would technically make it spring sowing, but the method is the same!)
Before I get into details, let me add that the method I'll be describing was developed by Trudi Davidoff, who maintains a website, WinterSown.org. She was also instrumental in getting a Winter Sowing forum on GardenWeb.com. Both of these sites offer a wealth of information, and each provides a place to ask questions and discuss variations on the method, as well as thorough FAQs. Be sure to visit either site if you have further questions.
Winter sowing starts with a container. You can use many different containers, as long as they have a depth of at least two inches, preferably three. The potting mix in the container will compact over time, so you want to start off with a good depth. Your container should also be see-through or opaque. One way to easily check for both these requirements is The Rule of Thumb. First, can your thumb fit in it? The human thumb, from tip to palm, is over two inches long. If your thumb fits in the container, that tells you it is at least two inches deep. Secondly, can you see your thumb through the container? If so, that means light can get into the container.
A very popular choice of container is an opaque milk or water jug. I use these almost exclusively. The depth is perfect, the height (for seedlings to grow) is great, the cap removes for ventilation, there is no need to add a cover, and it has a handle for easy moving, lifting, etc. Other choices include:
Soda bottles - clear or green, 2-liter is better but smaller ones work as well.
Water bottles -smaller, but can be used for single plants.
Tubs from things such as ice cream, whipped topping, pudding, etc. - the larger the better
Large clear juice bottles - these are roomy and clear and sturdy, but I've found them quite difficult to cut into. However, if you use these, their sturdiness lends itself to reuse the next season.
Berry containers - I've had mixed results with these, due to too many openings. They also don't leave much headroom for seedlings. However, some of the holes can be taped off, and they have the convenience of an attached lid. You will need to remove the cover sooner than some other containers to allow for seedling growth. Larger containers, such as for strawberries, work better than smaller ones. Remember your depth.
Large trays from fruit platters/vegetable platters, and clear plastic-domed cake containers from the bakery - for both these items, recycle the black plastic bottom, turn the lid upside down, and use that as your container.
Large clear cups from Dunkin Donuts, etc., the ones with the domed lid with the hole - good for single plants.
Salad bar containers, bakery cookie containers, even containers from pre-cooked roasted chicken from the supermarket - just remember the Rule of Thumb when deciding.
Waxed cardboard juice and milk cartons, cut in half either horizontally or vertically. - these may work if your sowing is done later in the season and the exposure to weather is not as long. Otherwise, these can get soggy.
Aluminum foil lasagna/roasting pans with clear lids - these can be filled with soil, or you can place individual peat pots in them and fill the pots with soil.
Yogurt cups - these are truly on the small side, both in depth and in height (for seedling growth) but for some classroom settings they may be easier to work with. Again, just remember the Rule of Thumb, which you can cheat on a bit if your containers will not be outside too long and your seedlings are planted out early.
Warning: If you try winter sowing, be aware that you will begin to salivate as you drive home on recycling night and see the bins in your neighborhood. Another side effect is the desire to stop your car and pick up trash-, er, uh, containers from the side of the road.
Once you've decided on your container, and it has been cleaned, you will need to make drainage holes, and depending on your lid, ventilation holes. This is one step that may have to be done by adults, depending on the age of the students, as it can be a bit dangerous.
Adequate drainage is essential to success. You will need drainage holes in the bottom of the container, and even consider putting them in the side, along the bottom, if your containers will be on asphalt or concrete. I put about 12 drainage holes in the bottom of a milk jug. If you are using some kind of clear lid, put your ventilation holes in it now as well (more on coverings later). Some winter-sowers just use slits, but I prefer holes; they don't clog as easily. Soda bottles and milk jugs need no ventilation holes; removing the cap is enough (but they do need drainage holes). A soldering iron makes quick work of hole-punching; just be sure to have adequate ventilation as it does give off odors. You can also use a steak knife, an ice pick, or a screwdriver heated in a flame. You get the idea why this step is not suitable for young children. Be careful. I've stabbed my palms and burned myself more than I care to admit.
If you are using berry containers, you may want to consider taping up some of the holes at this point. Small pieces of duct tape work well for this. Too many holes is almost as bad as too few. It will mean more watering for you down the road.
If you are using a container such as a soda bottle or milk/water jug, you will need to cut it now. Poke a hole in the side near the base of the handle (or use the soldering iron to make a hole) and using this as a starting point, cut around three-quarters of the milk jug, leaving a hinge. You can cut all the way through if you'd like but this will require a bit more work in closing the container. Soda bottles can be cut all the way through, with 2 or 3 vertical slits being cut in the top half.
Fill your containers with a good quality potting mix, at least 2 inches deep and 3 to 4 inches if possible. Wet soil thoroughly and let drain.
Sow Your Seeds
Place your seeds in the container. You may follow the depth recommendations on the seed packet. Sow thinly if you don't like to thin seedlings later.
Put a Label on It
You should label your container so in a few weeks or months you will know what is inside it. In my experience, a sharpie on the outside of a milk jug works fine. Others say it fades in the sun. Other options for labeling are a sharpie on a piece of duct tape on the bottom of the container (not just on the bottom half of the container, but underneath, on the literal bottom) or putting a label right inside the container - popsicle sticks, plastic knifes, etc. If your students are doing individual containers, they may want to put their names on them as well.
Close It Up
Depending on your container, there are different ways to close it. For the milk or water jugs, make sure the cap is off (you can discard it) and tape up the sides using duct tape. You can tape along the entire cut, or just put a piece vertically on each side. If your containers will be outside all winter, a bit more tape will keep it more secure. For soda bottles, after discarding the cap, you can tape them shut like the milk jugs, or you can take the tops with the slits which you cut earlier, squeeze this section and insert down inside of the bottom half. With this method, you can actually cut the top down to a shorter size, which will keep it more stable outside in the wind. And for either of these containers, instead of tape, you can punch more holes in the top and bottom on the container, directly across from each other, slip a twist tie through them, and close it up! If you used something with a clear lid (cookie tray, or berry or salad container) just snap shut. Remember to add ventilation holes if there are none. If you used a tub of some sort, you cannot use the lid, as it will not allow light. The same goes the for black plastic bottoms of cake trays and veggie platters, which, since you used the tops to sow in, would now appear to be the lid. However, you can cut out the center portion of the lid, cover the tub or tray-top with plastic wrap, and snap the lid/ring back on the tub to hold the wrap securely in place. Remember the holes in the plastic wrap. If you prefer, you can cover with plastic wrap and use an elastic band or duct tape to keep it on instead of the lid/ring. The same method (elastic/tape and plastic wrap) works for yogurt cups and other types of cups. If you are using waxed cardboard boxes, you can slip these into plastic bags (with holes!).
Just remember that your cover must be clear or opaque, must have holes for ventilation, and should be well-secured.
Get Out (Outside, That Is!)
Place your containers outside. Put them out and leave them out. It doesn't matter if they are in a sunny spot or shady spot at first. The only possible concern (other than safety of pedestrians, of course - you don't want all those containers in the way of people walking) is wind. If you are in an unusually windy spot, or if you are using smaller containers (single-serve water bottles, yogurt cups) you may want to have them in a location sheltered from the wind. However, average winds will not harm the containers; if they are larger, once they freeze, for the most part they are going nowhere.
Leave your containers alone! Don't worry about snow, rain, warm spells or freezes. Resist the urge to pamper your seeds or seedlings. Let it snow, let it rain, let the wind blow.
Spring into Action
As the weather warms up, you will need to monitor your containers more often. Check the moisture level, and water as needed. Determine if your containers are in too shady of a spot (or, if they seem to be drying out too often, perhaps they are in too sunny of a spot). You will usually not have to water till well into spring. When germination starts, you need to provide more ventilation. You can add more ventilation holes, or widen the holes you already have. Keep an eye on the forecast for unusually warm days; your seedlings could fry if they are not well-ventilated enough. (This is unlikely, but with the recent change in weather patterns, 90-degree days in April are not unheard of.) Soon you will be able to remove the covers completely.
Your seedlings may be smaller than seedlings sown indoors, but they will be hardier and healthier, and there is no need to "harden off". Your seedlings will quickly catch up in size to any greenhouse grown plants.
Some Thoughts on Seeds and Timing
As I mentioned before, winter sowing can be done any time from December through May. If you are planting flowers in your garden, one loose guideline to follow is perennials get sown first (especially those needing warm/cold stratification), then hardy annuals (poppies, bachelor's buttons, most early-spring-blooming annuals) and then the more tender annuals. The seeds themselves will germinate when ready; what is of concern is any hot or cold spells that may occur in spring which may damage the seedlings which have sprouted. To give a bit more guidance, I sow my perennials in January, then sow the hardy annuals in February and early March, and my other annuals any time from March through April.
If you are planting a vegetable garden, I have found that this method works well with everything except green beans, although others have successfully planted those. Your best bet with beans is to winter-sow them later in the season, although beans are so easy there is probably a better way to deal with them in the classroom. But winter sowing is great for most other vegetables - lettuce, spinach, onions, beets, eggplant, peppers, tomatoes, cucumbers, peas, carrots, radishes - and is also a great way to grow most herbs. I usually sow my vegetables and herbs a bit later, in late March into April.
Final Thoughts on Environmental Issues
Winter sowing is a not only a great way to garden, but also a great way to use re-use materials. Please keep the environment in mind when winter-sowing. While I have tried to show the various types of containers, and to show how adaptable this method is to each person, consider using containers that will not require additional resources such as plastic wrap or plastic bags. Find already-used containers before buying plastic cups to use. For labeling, find compostable or recyclable items such as wooden sticks or piece of plastic cut from milk jugs or soda bottles. Lastly, remember to recycle your containers when you are done, or better yet, reuse them. I've got some lasagna pans with clear lids that I used for five seasons before they fell apart.
Please visit the Winter Sowing Forum for loads more information. And feel free to contact me at email@example.com if you have any questions. I'm more than happy to share this great seed-starting method with anyone who is interested!