by Dolly Foster, horticulturalist
Email: [email protected]
Instagram & Twitter: @Hort4U
Do you enjoy starting seeds? Do you need to start seeds for volunteer events like plant sales? Do you want to start seeds but you can’t accommodate shelves and lights to do it? Do you want to start seeds but you have cats that will decapitate your seedlings? Don’t want water marks ruining you dining room table? Then Winter Sowing is the method for you! Read on to learn about the easiest way to start seeds in the winter, outdoors.
What is Winter Sowing?
This method of starting seeds is done all outdoors during the winter. It is best for seeds that need to be stratified (a short cold period) to germinate outdoors. By winter sowing you are taking advantage of the natural temperatures and length of day to trigger germination. Germination rates are usually quite high. The advantages of winter sowing are many! You do not need seed trays, lights; treat your soil for damping-off disease or worry about your seedlings drying out.
(Editor’s note: Too late for winter sowing? Here’s a quick tip on jump-starting stratification.)
Start with milk jugs, clear water jugs or deep plastic food containers with clear lids. When you finish putting the container, soil and seeds together, you will in essence, have made a small greenhouse. The container does not matter as long as light can penetrate the plastic and it is deep enough for proper root development.
When to start?
For our area (Chicagoland), any seed that is perennial, a reseeding (hardy) annual or plants that need stratification can be sown from the beginning of winter (mid-December) until spring. Tender annuals and veggies should be sown a little closer to the beginning of spring. For example, I grow a huge variety of plants. I start my native perennials in January through February. Hardy annuals I start in March and towards the end of March and even into the first week of April, I start tender perennials.
Things you will need
Milk jugs or plastic containers that allow light to pass
Large (long) rubber band
Box cutter [or knife] Utility scissors
Potting soil (no fertilizer, no garden soil)
Garden marker (waterproof, UV proof), paint pens or grease pencil [Dolly recommends the Garden Marker.]
Clear poly tape or duct tape
Long-handled spoon (or similar device)
Plant labels [plastic cutlery works for this]
- Clean all of your containers with a 10% bleach solution and allow them to dry.
- Gather your supplies.
- Using a boxcutter or paring knife cut 4-6 1” long “V” shaped cuts in the bottom of the container for drainage.
- Mark 4” off the table on the side of your container. 4” will be your soil level and 4” is also your cutting line.
- Using your box knife, cut a starter slit along your 4” line. Use your utility scissors to cut the remaining line around the jug, leaving the area at the handle uncut; that is your hinge. It is very important to leave a hinge.
- Fill with dampened potting soil up to the 3.5” height. [Dolly recommends ProMix, supposed to be sold at Ace Hardware. Avoid potting mix, however. It dries out too quickly. Do not use potting soil with the water-absorbing crystals; your seedlings will die.] Most seedlings need a few inches to start strong deep roots. Use your fingers to tamp down the soil a little to get the air out and add a little more soil if necessary.
- Plant your seeds. How many seeds go into the container depends on how large they (the seeds) are and whether or not you want to thin them later on. Certainly, a whole package of any seed is too many in a milk jug. The larger the plant, the fewer seeds that should be planted. [Editor’s note: Commercial seed packets say how deep to plant your seeds. If you have gathered native seed and need more information, the Native Plant Network is a good place to check.]
- Label the container right away! Use your outdoor marker or paint pen on the outside of the container. Make a label for the inside too. At some point you will open the jug and discard the top. Therefore, labeling the inside is necessary.
- Time to close up your mini greenhouse! Using your poly tape or duct tape, cut a 2” long strip and attach vertically from the top of the jug to the bottom and close the gap so no air gets out. Now cut 2 8” long strips to tape around the seam.
- A spoon with a long handle is useful in smoothing the tape to the jug from the inside. Place your hand on the outside of the jug and stick the spoon handle in the jug, run the tip around the cut line and press from the outside at the same time. If you use duct tape, you probably don’t need to do this step.
- Do not place the cap on the jug. You do not need it. Take your jugs outside to a partly protected sunny area, e.g., the southeast corner of your house. Wait for germination. Be patient.
- Water the jug if the soil looks dry. This will be necessary on very sunny dry winter days above 30 degrees. This may be necessary later as the weather warms up and the soil dries out. The best way to do this is to make a water-bottle watering can. Look online for directions. [Directions can be found on Dolly’s Youtube video around the 40-minute mark.]
- When the plants are really big, during April, the top half of of your jug can be opened. On cold nights before planting out, the jugs should be closed up but not re-taped, to protect the plants from being nipped by frost. By May the top of the jug can be removed permanently.
- At the appropriate time for each type of plant, plant them in the ground or in pots to share.
The last word on your containers: they should be deep enough for proper root development. Shallow food containers will dry out faster as well as not allow for long root development. However, if you plan on transplanting quickly you can use whatever plastic containers you’d like to. Some containers can be used from year to year. That is great, but not necessary. You are reusing the jugs before you recycle them anyway. There will always be more containers. I like being able to cut that top off without worrying about keeping the jug from year to year. Just make sure that jug gets recycled and not thrown away.
Winter Sowing Forum On Facebook: Winter Sowers
The Seed site (germination rates)
Tom Clothier.hort.net (germination rates)
Wild Seed Project Autumn and Winter Sowing This is a different method for starting seeds outdoors that’s even easier, though the seedlings probably won’t be ready to transplant until fall.
Native Plant Network