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Sowing Seeds in Winter

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Sowing seeds in the wintertime sounds like a pretty crazy idea, but Northern Gardening hosts Diane Booth and Joan Farnam talk about this amazing trick with  Sue Schiess, U of M Master Gardener from Hennepin Count on this week's program. Later in the show, Jerry Starr and Peter Henrikson  discuss how they designed and built a solar greenhouse at Great Expectations School which has provided students with salad greens this year.

Note: if you want to learn more and/or want to start a vegetable garden this year, there will be a 2-hour workshop on how to start a vegetable garden at the Cook County Community Center from 1o a.m. to noon on Saturday, March, 26. Everyone is invited. For more information, call Diane at 387-301.

Winter Seed Sowing is a really old method of starting seeds during the winter time without starting your seeds or plants indoors under grow lights.

What  is Winter Seed Sowing?

  • An easy seed germination method that allows you to plant seeds in milk jugs or other containers, set them outside, and let ‘Mother Nature’ start these seeds when the timing is right for those particular seeds.
  • The temperature differences with freezing and thawing helps loosen up the seed coats and allows for germination at the correct time.

What kind of seeds would you use?

  •  Seeds that typically reseed themselves or self sow
  • Wildflowers / native seeds
  • Seeds that are considered to be hardy
  •  Seeds that can be directly sown early
  • Seedlings can withstand frost
  • Seeds that can be sown outdoors in Autumn, early Winter, early spring while nights are still cool
  •  Seeds that can be sown in early Spring while frosts may still occur, like spinach and lettuce.
  • Seeds that need to be pre-chilled, stratified, etc. to break their dormancy

How do you do it?

  • Save clear milk jugs, take out containers, strawberry containers – anything that can be used as a miniature greenhouse.
  • Make sure your containers are clean before using them.
  • You will need holes poked in the bottom for drainage and holes poked in the top for air circulation and for heat escape during warmer days.
  • Cut the milk jug nearly all the way around about 1/3 to 2/3rd of the way up on the jug.
  • Leave the handle part attached and bend it backwards.
  • Put about 3 inches of fairly good soil with some fertilizer in the bottom. Add another inch of germination mix to the soil for where your seeds will begin germination.
  • Make sure that the soil you add is already pre-moistened.
  • Plant your seeds to the correct depth.
  • Make sure you label your container with duck tape label on the bottom and /or a plastic label wrapped in tinfoil and placed inside the container. The tinfoil prevents the ink from breaking down. You can use a paint pen on a wooden stick as well.
  • Duck tape the milk jug back together.
  • Stick your containers outside where you can easily get to them.
  • Keep the cap on until the weather warms up.
  • Once the seedlings have their first set of true leaves, you can gradually open the top of the milk jug or cut more holes in the jug and expose them to more wind variations.
  • Eventually you transplant them into the garden or into larger pots and place them outside, protecting them at night if need be, until you can transplant them into the garden.

Why would people want to do this?

  • It allows you to start a lot of seeds very cheaply without having to purchase or make an indoor light setup.
  • If you have limited space in your home, this allows you to start a lot of seeds ahead of time outdoors.
  •  Gives you gardening projects to do during the off-season.
  • Recycle and reuse milk jugs, take out containers, anything you can turn into a miniature greenhouse, basically.
  •  Damping off is less likely to occur using this method. (Damping off is when young seedlings wither and seem to die at the soil line. It is usually caused by two fungi Rhizoctonia solani and Pythium species.
  • Rhyizoctonia usually causes stem lesions that girdle the stem. Pythium attacks underground root hairs and root tips either causing the seed to rot in the ground or to wither and die. Other fungi can also be associated with this like Botrytis cinerea, Sclerotina sclerotiorum, Alternaria species, Phytophthora
  • species, Fusarium species, etc.)
  • Stronger, hardier plants often result.
  •  Hardening off your plants is much easier. They are already used to temperature and light fluctuations and really only need the addition of being hardened off to wind.

What are some of the seeds work with the Winter Seed Sowing method?

Annual Flowers

1. Snapdragons ‘Magic Carpet’, ‘Tall Deluxe’, ‘Tetra Giants’
2. Artemesia
3. Aster chinensis ‘Crego Mix’, ‘Perser Mix’, ‘Powder Puff’
4. Brachycome iberidfolia Daisy – Swan river
5. Calendula officinalis ‘Double Mix’, ‘Indian Prince’
6. Calibrachoa Million Bells
7. Celosia cristata ‘Coral Garden’
8. Centaurea cyanus Bachelor Buttons
9. Clarkia elegans
10. Cleome hassleriana Cleome unspecified
11. Cosmos bipinnata ‘Sensation’
Larkspur ‘Imperial Giant’
12. Delphinium
13. Dianthus chinensis China pinks
14. Helianthus ‘Giant Russian’, ‘Earth Walker’, ‘Moulin Rouge’, ‘Valentine’, ‘Vanilla Ice’
15. Limonium sinuata Statice ‘Sunset Shades’, ‘Pacific’
16. Lobularia maritima Sweet Alyssum
17. Matthiola Stock ‘Mammoth Excelsior’ Night-scented
18. Mirabilis jalapa Four O-Clock
19. Molucella laevis Bells of Ireland
20. Nicotiana ‘Sensation Mix’
Love in a Mist
21. Nigella
22. Papaver Poppies
23. Petunia ‘Blue Wave’, ‘Misty Lilac Wave’, ‘Purple Wave’,
‘Dwarf Beauty’
24. Phlox drummondii
25. Portulaca ‘Sundial Mix’, ‘Margarita Rosita’
26. Scabiosa atropurpurea Pincushion Flower
27. Tagetes Marigold ‘Crackerjack’
28. Thunbergia alata Black Eyed Susan Vine
Nasturium ‘Jewel Mix’, ‘Cherry Pink’, Tall climbing
29. Tropaeolum
30. Viola tricolor Pansy ‘Helen Mount’
31. Zinnia haageana

Perennial Flowers
1. Achillea
2. Aconitum
3. Alcea rosea
Butterfly Weed
4. Asclepias tuberosa
American Bellflower & Creeping Bellfower
5. Campanula
6. Chelone glabra Turtlehead
7. Dianthus
8. Digitalis
9. Echinacea purpurea
‘Goblin’ ‘Burgundy’
10. Gaillardia
Baby’s Breath
11. Gypsophila
Day Lily
12. Hemerocallis
Dame’s Rocket
13. Hesperis matronalis
14. Lavendula angustifolia ‘Munstead’
15. Liatris
16. Lobelia cardinalis Cardinal Flower
17. Lychnis coronaria Rose Campion
18. Malva
19. Meconopsis x sheldonii Blue Poppy
Virginia Blue Bells
20. Mertensia
Bee Balm
21. Mondarda
Baby Blue Eyes
22. Nemophilia menseseii
23. Papaver
24. Penstemon hirsutus, strictus
Obedient Plant
25. Physostegia
Balloon Flower
26. Platycodon
Jacob’s Ladder
27. Polemonium
28. Rudbeckia hirta Black-eyed Susan
Painted Daisies
29. Tanacetum coccineum
30. Verbascum
Verbena on a stick
31. Verbena bonariensis

1. Alliums (onions, shallots, garlic, chives)
2. Beets
3. Brassicas (broccoli, brussel sprouts, cabbage, kale, cauliflower)
4. Chards
5. Corn – early types that can handle cold soils
6. Leafy greens, lettuces
7. Peas
8. Radishes
9. Spinach

Solar Greenhouses

What is a solar greenhouse and what makes it different than a regular greenhouse? All greenhouses collect solar energy, but solar greenhouses are designed to collect solar energy during sunny days and store the heat for use at night or during periods when it is cloudy.

A lot of people are getting more excited about the use of solar greenhouses. This is not a new concept. It was used during the time of the Romans and in this country was readily discussed in the 1970’s and 1980’s.
The Romans improved on Greek solar architecture by covering south-facing windows with clear materials such as mica or glass. They also passed sun-right laws that forbade other builders from blocking a solar-designed structure's access to the winter sun.
The ancient Romans not only used window coverings to hold in solar heat for their homes but also relied on solar heat traps for horticulture so that plants would mature quicker, produce fruits and vegetables out of season, and allow for the cultivation at home of exotic plants from hotter climates. With the fall of the Roman Empire, so to came the collapse of glass for either buildings or greenhouses.

Basic Principles of Solar Greenhouse Design (Passive and Active)
• They have glazing materials oriented to receive maximum solar heat during the winter.
• Use heat storing materials to retain solar heat.
• Have large amounts of insulation where there is little or no direct sunlight.
• Use glazing materials and glazing installation methods that minimize heat loss.
• Rely primarily on natural ventilation for summer cooling.
• Should be twice as long as it is wide to offset the effect of shade from the east and west walls.
• The peak should be made about as high as the building is wide.
How has the Great Expectations school greenhouse been designed and built using those principles?
• Shed type solar greenhouse with orientation of the long axis running east to west.
• South facing wall is glazed to collect the optimum amount of solar energy.
• North facing wall is insulated to prevent heat loss. R-22 for roof and walls
• North wall is covered with reflective material to reduce the effects of poor light distribution in an east-
west oriented greenhouse.
• 45 degree south roof glazing? (site latitude 47 + 10-15 = 57 -62 degrees)
• What type of glazing material was used?
• Part of end walls glazed for additional light.
• Earth thermal storage (ETS) collection of solar heat beneath the floor with pipes and rock flooring 3 times the volume of rocks for heat storage than water storage due to their lower value for heat storage
• Active solar was used where 4” black corrugated sewer pipe is in a bed of ? - 1 ?” rocks under the greenhouse. (Divide the square feet of the greenhouse by 2 to get the number of feet of 4” pipe you will need.) Pipes go up at each end of the greenhouse where small fans force the warm, heated air at the top of the greenhouse down into the pipes, heating up the floor area of the greenhouse. This heat then is
given off when the temperatures of the greenhouse decline such as in the evening. Is one pipe higher
than the other, giving a circular flow?
• Sand covered polyethylene sheet over the top of the rocks to prevent an air gap if the rocks settle.

How to select glazing materials?
• Lifespan
• Resistance to damage from hail or rocks
• Ability to support your snowload
• Resistance to condensation
• Sheet size and distance required between supports
• Fire-resistance
• Ease of installation

Glazing materials have a National Fenestration Rating Council Sticker that lists the following factors:
1. The SHGC (Solar Heat Gain Coefficient) is a measure of the amount of sunlight that passes through a
glazing material. A number of 0.60 or higher is desired.
2. The U-Factor is a measure of heat that is lost to the outside through a glazing material. A number of
0.35 BTU/hr –ft2-F or less is desired.
3. VT or visible transmittance refers to the amount of visible light that enters through a glazing material. A
number of 0.70 or greater is desired.
4. PAR or photosynthetically active radiation is the amount of sunlight in the wavelengths critical for
photosynthesis and healthy plant growth. PAR wavelength range is 400 – 700 namometers.

Active Solar Storage

Year round growing – 5 gallons of water storage per square foot of glazing.
Season extension – 3 gallons of water storage per square foot of glazing
Small sized containers like glass bottles provide more heat storage than large 55 gallon drums.


If you are looking for a garden space this year, there are several spaces available in our community gardens and private backyards through the GardenShare program. For more information please contact Joan Farnam at 370-9794.

Our next program will be on Thursday, April 14 from 4 – 5 p.m. on WTIP. Please call 387-3015 for future program topics or guest ideas you have!