How to Winter Sow Seeds Outdoors Winter sowing

How to Winter Sow Seeds Outdoors
By Jerry Berry, MG 2008
Winter sowing is a method of starting seeds outdoors in winter. This is generally done
with seeds that require a period of cold and moist stratification. The method takes
advantage of natural temperatures, rather than artificially refrigerating seeds. Winter
sowing involves sowing seeds in a miniature greenhouse outside during winter, allowing
them to germinate in spring.
Stratification is a pre-germination technique designed to break the dormancy in seed and
to promote rapid, uniform germination. Seed dormancy is a condition of plant seeds that
can prevent germination unless certain environmental conditions are present. One
important function of most seeds is delayed germination, which allows time for dispersal
and prevents germination of all the seeds at same time. The staggering of germination
safeguards some seeds and seedlings from suffering damage or death from short periods
of bad weather or from transient herbivores; it also allows some seeds to germinate when
competition from other plants for light and water might be less intense.
Winter sowing helps to break seed dormancy through exposure to moist cold
temperatures. Most perennial flower seeds require cold and moist conditions before they
will germinate.
What you’ll need:
Soilless Seeding Medium
This is very important as soilless mediums are sterile and can prevent diseases like
“damping off” (a fungus that will kill seeds and seedlings).
Below are soilless starting mediums you can make.
2 parts Peat Moss
1 part Perlite (provides aeration)
OR
2 parts Peat Moss
1 part Vermiculite (holds moisture)
OR
You can go to a big box store or a local garden nursery and get a seed starting mix. Do
not use potting soil or dirt (soil) from your yard.
1
Containers
Ideally, pick a container with a clear top. Recycle any trays or containers you might have
at home, or go to a dollar store and buy some. You can use just about any container, and
if you don’t have a lid, just place it in a clear baggie.
Punch or drill holes in the bottom of each container for proper drainage. Punch a few
small holes in the tops and sides of each container for proper air circulation and
transpiration (without air circulation, you can literally “cook and kill” your seeds and/or
seedlings on a warm and bright sunny day).
Fill the container with your soil medium to about two
inches from the top. Water well and let it drain. The soil
medium should not be so moist that you can squeeze
water out of a handful. After the container has drained,
sow your seeds and pat them down or cover them,
whichever is required. Since you have “pre-moistened”
the seeding medium, there is no need to water after you
have planted the seeds. Be sure and label each container
with some sort of weatherproof label (something that
won’t wash off or fade in the elements).
Now just take it outside to somewhere it will be safe for the winter. Away from pets etc.
Just let Mother Nature do her work. Over the winter, your containers will freeze, and
thaw, and then freeze again, etc. This action of freezing and thawing helps loosen the
seed coat and breaks seed dormancy. From time to time, especially on an above freezing
day, check the moisture content in your containers, and if need be, add a little water.
Actually, some rain or melting snow will fall through the tiny openings in the lid, so this
step may not be necessary. It won’t hurt to check every so often though.
When winter is about to break, and you’re still getting nightly freezes, the first of your
containers will begin to germinate. Don’t worry. The seeds know when it’s safe to come
up; it’s part of their genetics.
When the seedlings have their first set of true leaves (the first leaves are not true leaves),
you can feed them with a liquid fertilizer, but only at about 5% strength. You can
increase the strength of the fertilizer as the weeks continue and your seedlings become
more robust.
Seeds
Seed packets will usually list stratification/ scarification requirements and there are many
books and resources available, where seed requirements can be found. The internet is an
excellent resource. Most seed catalogs will have some sort of information about a seed’s
germination requirements. For example, Park’s Seed Catalog has an excellent reference
section on the number of days it takes seeds germinate. Look for these terms: Needs
2
pre-chilling, freeze seeds, refrigerate seeds, stratify for x amount of days or weeks, needs
scarification, etc.
Some seeds need darkness to germinate
(cover with soil) and some seeds need light
to germinate (do not cover with soil). The
requirements for sowing depth can usually be
found on the individual seed packets. Try not
to crowd your seeds in each container as they
will have too much competition from other
seeds and will be more difficult to “thin out”
after they have germinated (about ¼” apart
is a good rule of thumb). With small seeds
this can be a tedious task, but it’s important
to give them the correct spacing.
When can I start?
Winter Sowing is done during the winter, but if you start too soon there’s the concern of a
late season warm spell that will stimulate some seeds to germinate prematurely. Take a
look outside. When the leaves have all fallen off the trees, we are probably into winter,
and you can start. Starting around Thanksgiving is probably OK as well.
Winter Sowing Glossary
Dormant seed: Alive but inactive, and in some
cases, incapable of growth until certain
conditions have been fulfilled (light, moisture,
temperature).
Perlite: Volcanic rock that has been heated to
expand.
Perlite is used in soil mixes to
provide aeration.
Scarification: The practice of scratching or
notching the seed coat so that moisture can
more easily penetrate the seed coat.
Stratification: Moist chilling of the seeds to
break dormancy and promote germination.
Many seeds need 30 to 90 days of this
treatment.
Transpiration:
The evaporation of internal
water from plant leaves.
3
Vermiculite: A form of heat expanded mica used in soil mixes to retain moisture.
Vernalization: The seeds ability to germinate, and then flower in the spring, following
prolonged exposure to winter elements.
Reference material:
The New Seed Starters Handbook by Nancy Bubel
Growing and Propagating Wild Flowers by Harry R. Phillips
The Plant Propagators Bible by Miranda Smith
Photo Credits:
Indiana Public Media Earth Eats, and the author’s own photo collection.
4