Starting From Seed in a Greenhouse

Starting from the seed allows you to choose exactly what you want to grow.
Germinating in a greenhouse makes this goal easier to achieve.

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In the outdoors, seeds and plants are subject to constantly changing weather
conditions and temperatures. Growing them in in a greenhouse allows you
to control every element in the plant’s environment. A greenhouse allows
you to sow seeds at almost any time of year, depending on the winter
temperatures in your climate zone. Later on, greenhouse-grown flowers,
fruits and vegetables can be prepared (hardened off) for easy transition
to your garden.

Photo courtesy of Phil Maltz, UK who uses a Harmony 6x4 greenhouses (and so does his mom!)
Photo courtesy of Phil Maltz, UK who uses a Harmony 6x4 greenhouses (and so does his mom!)

Obtaining Seeds

After deciding what plants you intend to grow, you can order specific seeds accordingly.
You have the liberty to choose special seeds, for example organic non-GMO seeds.
Follow the planting directions carefully with attention to details such as temperature,
planting depth, and extended care.

Precautions: To prevent your seedlings from experiencing fungal disease, which can
weaken and kill them soon after germination, use sterile seed-starting trays and soil.
To further keep your greenhouse sanitary, you can regularly disinfect it with diluted bleach.

Photo courtesy of Gerry Leigh, USA who uses a Victory Garden Chalet greenhouse
Photo courtesy of Gerry Leigh, USA who uses a Victory Garden Chalet greenhouse

Sowing the Seeds

Soak large seeds, such as beans or tree seeds, in a bowl of warm water overnight
before planting them.
Fill seed-starting trays with moist potting soil. Sow one large seed per tray cell.
If the seeds are very small, pinch a few between your thumb and forefinger.
Spread them across the surface of the soil and tamp them down with your fingers.
Sprinkle a very thin layer of sphagnum moss or vermiculite over the surface of the soil,
if desired. Do not do this, however, when your seeds need light to germinate.
Examples include petunia and lettuce seeds, as well as many small herb seeds.

Mist the surface of the soil with a spray bottle. When seeds require high humidity
or constant moisture, put the tray in a clear plastic bag until germination occurs.

Put seed trays on a heating mat to encourage faster germination. Ideally, use a mat
with a thermostat so the soil does not get too hot. Many seeds prefer a soil temperature
between 70 and 85 degrees Fahrenheit.

Provide water as necessary to keep the soil moist before germination and during the seedling stage.

Dilute seedlings to one healthy plant per tray cell. When seedlings have at least two true leaves,
transplant them into larger individual containers.

Photo courtesy of Gerry Leigh, USA who uses a Victory Garden Chalet greenhouse
Photo courtesy of Gerry Leigh, USA who uses a Victory Garden Chalet greenhouse

Maintaining heat in winter: It is important to keep greenhouse temperatures
around 10°C (50°F) at night and around 21°C (70°F) in the daytime.
You can use a heater when necessary to raise the temperature;
provide additional ventilation by opening a window or door.

Maintaining illumination: Put seed trays under hanging fluorescent lights
when your greenhouse receives less than 16 hours of sun per day.
Keep the lights about 6 inches above the trays.

Maintain air flow: Spread out the containers in the greenhouse.
Avoid pushing containers close together. Doing so prevents adequate air flow.
Keep a fan blowing gently at all times to simulate the wind that normally helps
plants grow thick, strong stems.

Fertilize: Give seedlings a half-strength application of all-purpose, soluble fertilizer
when the first true leaves appear.

Photo Courtesy of Vicki Brower Andrade, USA who use a Snap & Grow 8x12 greenhouse
Photo Courtesy of Vicki Brower Andrade, USA who use a Snap & Grow 8x12 greenhouse

Transplanting

Plan to sow seeds in your greenhouse at any time of the year. When you want
to transplant your seedlings into the garden in spring, sow seeds in the greenhouse
about six to eight weeks before your area’s last frost date.

Begin hardening off plants two weeks before transition to the garden, in early spring
or after last frost date in your climatic zone. Move the plants outside to a shady spot
for several hours each day. Gradually increase the hours per day the plant spends
outside over the two-week period. Transplant the plants into their permanent locations
in the garden when hardening off is complete. Some plants do not transplant well,
such as melon, cucumber and dill. Consider sowing these seeds directly in the garden
or in a large container in the greenhouse.