Winter Sowing 101

Now that December is here it is time to plan for winter sowing. Winter sowing is a method of starting seeds outside in plastic containers in the winter so the seeds will have germinated by spring. In the spring, you transplant the seedlings to your garden bed. There are many advantages to winter sowing your seeds. You can:

• start seeds without indoor lights;
• start plants from seeds which is more economical;
• start plants from seeds so you can take advantage of a wider selection of plants;
• provide stratification (a cold period) or scarification (breaking the hard seed coat) for seeds that need it in order to break dormancy; and
• get a jump on the cool season plants so they are able to flower or thrive in the spring before the summer’s heat.

Winter sowing is ideal for perennials, hardy annuals, semi or half-hardy annuals, and the cool season greens, veggies and herbs. Hardy annuals can tolerate cold soil and weather down to the 30’s, such as light frost and moderate freezing. Most hardy annuals expire in the beginning of the summer – they do not like the heat. Examples of hardy annuals are calendula, cornflower, annual larkspur, and pansies. Semi or half-hardy annuals can tolerate cool temperatures and cool soil down to the 40’s; they are damaged by frost. They too do not like the summer’s heat. Examples are baby’s breath, bells of Ireland, blue sage, forget-me-knots, and strawflower.

Cool season veggies, greens, and herbs include lettuce, peas, beets, radishes, broccoli, spinach, parsley, cilantro, and chervil.  Usually, one does not winter sow the warm season veggies such as tomatoes and peppers.

Seed packets and catalogs will not mention winter sowing but if you read the descriptions, you will see clues as to what plant would benefit from winter sowing. Look for words such as:

• Hardy
• Withstands frost
• Self-sowing
• Colonizing
• Stratification required (cold period)
• Scarification required (nicking or soaking in water)
• Direct sow in early spring/late fall
• Sow as early as the ground can be worked

In the DC metro area, we start winter sowing on or after the winter solstice which is December 21 and any time through January. There is no need to count days or weeks from average last frost date like you would if you were to start annuals under lights indoors.

To start winter sowing, look for plastic containers that can hold 3 to 4 inches of soil with about 2 to 3 inches headroom for the seedlings. You will often see gallon milk jugs but there are other options:

• Clear, not opaque gallon milk, water, iced tea, juice, or apple cider jugs
• Large plastic container of pretzels or Twizzlers that come in bulk size for the office
• Coffee cans (cover with plastic)
• Plastic container used to sell a roasted chicken (has a high dome)
• 2-liter plastic soda bottles
• Large plastic ice cream containers

Assuming you are using a gallon milk jug, make sure it is clean first and throw away the cap (do not need to cover the top).

Create several drainage holes in the bottom with a knife, exacto knife, box cutter, electric drill, or a hot glue gun without the glue.

Using a blade or scissors, cut around and below the handle or about 4 inches from bottom. Do not cut all the way across; leave a hinge on the handle side.

Fill the jug with 3-4 inches of potting mix. Do not use seed starting mix. Do not use soil from the ground or compost pile and do not use bagged soil with “moisture control” or water storing crystals. PRO-MIX works well.

Water the soil so it is moist. Sow seeds of one variety per container. If they are very fine seeds, press down so is in contact with moist soil. If very large, like coriander, press down, cover with a thin layer of soil. Water again and make sure seed is in contact with moist soil.

Close up the jug with duct tape and label or mark it some way so you remember what you sowed. Sharpies will fade so try grease pencils, colored nail polish/paint, or different colored ribbons. I used old lanyards from conferences and old colored pipe cleaners from craft projects, tied around the handles. I then wrote down which one signified which seed. Always keep a record of what you have sowed and when on paper or on your computer.

Place the jugs outside in full sun where they can collect rain or snow. It is not necessary for it to snow in your area for this to work. Periodically check to make sure they are okay — dogs or foxes did not tip them over. You will have to make sure they have enough moisture. If it has not rained or snowed, you may have to add water through the opening. If you lift the jugs and they feel light, they will need water. If on a warm day you do not see any condensation in the jugs, you may want to add more water.

In the spring, you should see seedlings. When they are a few inches tall, or when they have two sets of real leaves, open up the containers and let the seedlings sit in full sun for a few days.

Depending on the plant’s preference for cool weather and the size, you may want to move the seedlings to a larger container to let them continue to grow or you may want to transfer to the garden bed. Also depending on the seedlings, you can either pick out individual seedings or take a hunk or chunk (like carving brownies). It really depends on the size/width of individual seedlings (i.e., if thin and fragile may want to take a chunk but if the stems are stout and strong, you can transfer each one). Needless to say, it also depends on your patience.

I have friends who stay in Florida for the winter, so they set their jugs out after Christmas and then come back to seedlings, ready to be transplanted into the garden. It is that easy. Try winter sowing this year, you still have plenty of time to get your containers, soil, and seeds.