Starting Plants Indoors

Alaska’s climate is too cold to grow sweet corn the conventional way.  They do not have enough growing degree days to get corn to mature.  Bryan, my brother, and his corn growing mentor have grown sweet corn successfully for many years in Alaska.  How?  He starts sweet corn in a greenhouse about one month before it is time to transplant in the garden.  When temperatures are finally warm enough, he transplants into the garden.  The corn is given a better chance by planting through holes in plastic.  The plastic does warm the soil creating a warmer microclimate for the corn roots.  The last key is growing the shortest maturity varieties of corn available.

Plants best started indoors and easily transplanted are tomatoes, peppers, broccoli, cabbage, most flowers, watermelon and cantaloupe.  Plants best planted directly into the garden are peas, corn, beans, radishes, cucumbers, lettuce, carrots, beets, onions, leeks, and potatoes.  Are the terms seeding and planting interchangeable?  Seeding refers only to putting seeds into the ground.  Planting refers to putting plant parts, including seeds into the ground.

When is the right time to plant both seeds and plants?  Potatoes, peas, red beets, radishes, and onions grow great when seeded as early as the garden can be prepared to plant.  Broccoli, cabbage and other cole crops will survive very well in cold climates whether seeded or transplanted, as long as the indoor grown plants are hardened off before setting outside.  Corn, beans, cucumbers, melons, squash, tomatoes, and peppers should be delayed until all chances of frost are past and the soil is good and warm.  Lettuce, carrots, parsnips, and a few others are somewhat cold tolerant but shouldn’t be planted too early.

When starting seeds indoors make sure you use clean containers.  If you reuse old containers rinse in a mild bleach solution then rinse.  This is to control diseases.  Use a good potting mix.  The best potting mixes may not have the biggest name or cost the most.  Potting mixes with vermiculite, peat moss, and/or coir work very well.  Keep seeded pots moist but not overly wet.  If you have a cold location you may use a heat mat to keep soils in the 70 degree range.  When seeds are germinated and have true leaves, you may remove the heat mat.

The most important part of growing starter plants is to provide enough light to imitate sunlight.  Grow lights generally work.  Incandescent and fluorescent lights together provide a complete light spectrum.  Either alone provide an incomplete light spectrum.  If you have a greenhouse outside, natural light is the best, but due to the plastic intercepting some light rays and frequent cloudy late winter or spring days you should plan on supplementing with artificial light.  Plan to provide light for 14 hours.  Plants do need both light and dark.  Part of the photosynthesis process requires a dark period.  If plants don’t get enough light they get “leggy” which is spindly overly tall plants.  Professional growers often treat with a growth regulator to keep plants short.  Homeowners can’t easily buy these growth regulators and if you can they can be very tricky to use.

The time to plant varies based on where you live.  Still some items can be planted as soon as you can get into the garden, others after the frost free day which is often in May to late May in the northern US.  A good rule of thumb for many northerners is to plant frost sensitive plants on or after Memorial Day.

When in graduate school I transplanted some broccoli plants a couple of days before my second child was born.  That week end was a whirl wind weekend as well as a colder than normal weekend.  If the broccoli plants were hardened off they would have survivied but they froze.  The busy weekend meant I didn’t get them covered or pay attention to the low temperature forecast.

BONUS – Check out these designer pumpkins. 

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The Garden Doc