Cheyenne Garden Gossip

Gardening on the high plains of southeastern Wyoming

Starting from Seed: Starting seeds indoors

lettuce under lights

Lettuce under lights

Published March 25, 2012, in the Wyoming Tribune Eagle, “Gone to seed: Planting and nurturing a garden from scratch can be one of the more rewarding aspects of the summer season. But keep a few tips in mind before turning over soil.”

By Barb Gorges

My eyes were bigger than my garden when I shopped the seed catalogs last month.

In my quest this summer to cultivate an early tomato from seed, as well as an annual (the dwarf cosmos), I now have 18 packets of seed sorted by when they need to be started indoors. By the way, it is now time to get those seeds started, if you haven’t already.

But some plants do best when seeded directly into the garden. I have five packets of sunflowers on standby, along with seeds for lettuce and radishes.

I’ve done the calculations (number of days to germination, plus two weeks to transplant size before May 24, the average last frost date), or used the information on the seed packet, and marked a spare calendar with the planting dates for each plant.

The earliest is Marine Heliotrope Peruvianum, very tiny seeds, which I started March 1. I’m not familiar with this annual – it showed up instead of a marigold I ordered, but I’m curious. I’m the gardener who lets things sprout in the perennial bed and waits to see what they are—if I don’t immediately recognize them as bindweed or thistle.

There are three factors important to seed starting success, says Shane Smith, director of the Cheyenne Botanic Gardens. They are: sterile pots; new, sterile soil and planting seeds to a depth twice the width of the seed.

Sterility

Pots need to be sterilized with a good scrub for ones being reused, plus a few swishes in a 10-percent bleach solution.

As for soil, you could bake your own at 250 degrees until it reaches 140 degrees for 30 minutes to sterilize it, but it smells. Instead of garden soil, buy fresh “soil-less” potting soil, which is light and fluffy and usually sterile. If you have time, leave it out in sub-freezing weather for a couple of weeks to kill everything.

You can make your own soil-less seedling mix: 3 parts milled sphagnum, 2 parts perlite and 1 part vermiculite.

For my pots, I’m trying a bag of “Seed Starting Jiffy-Mix.”  It’s very dry and needs to be mixed with water before putting it into the little seed-starting cells—otherwise it sheds any water I pour on it.

Depth

The rule of (the green) thumb is plant no deeper than twice the width of the seed (not the length or thickness), Smith says. Seeds have evolved to sprout with just heat and moisture (though a few actually need light, too), but if they don’t reach sunlight before they use up the energy stored within the seed, you’ll never see them.

Master Gardener Kathy Shreve demonstrated how to pick up a very tiny seed: Use the end of a dampened toothpick, and then brush the seed onto the surface of the growing medium.

Moisture

Pots need to have drainage holes in the bottom. While you are waiting for seeds to germinate, the growing medium can’t get too soggy or too dry.

I was particularly intrigued with Shreve’s Advanced Propagation System. It is a commercially available miniature, self-contained greenhouse, with a tray of planting cells, a clear plastic dome lid to keep moisture in and a water reservoir below that should only need filling every few days.

The ends of a porous mat hang down into the reservoir and capillary action brings moisture across the mat placed under the planting cells where the soilless planting medium wicks it up to the plants.

A less fancy method is to gently spritz the soil surface when necessary and lay plastic wrap over it until sprouts show. Verena Booth said she sprouts difficult seeds the way alfalfa is sprouted for salads, and then pots them. Or try folding seeds in a wet paper towel placed in a plastic bag. It worked for me.

Light  

The only sunny windowsill at our house is already full, so I’m using a 4-foot fluorescent shop light suspended over the workbench downstairs. Windowsills are rarely bright enough and ours would be a poor choice anyway since we have low-e glass which keeps out a part of the spectrum and makes my houseplants leggy.

However, Master Gardeners Shreve and Barb Sahl agree that cool white fluorescent bulbs work fine for starting plants. The blue spectrum is perfect for seedlings. Keep the light close to the seedlings, 1 to 2 inches above. If the height of the light isn’t easy to adjust, or you have plants of different sizes at the same time, add blocks of wood or something under the short plants’ pots to get them close enough. Shreve gives her seedlings light 16 hours a day. Sahl leaves her lights on 24/7.

Air

Damping off disease breaks a lot of hearts. One day the brave little seedlings are vigorously reaching for light and the next they are lying flat—rotted off at the soil surface. Sterile soil helps prevent this. Shreve and Sahl also use moving air, a preventive seeds started outdoors get naturally. But it’s too cold to open a window, so try a fan set on low and placed across the room.

The other benefit to subjecting seedlings to a breeze is stronger stems.

Heat

Heat, especially for plants of tropical origin—tomatoes and peppers—is necessary to germinate their seeds. The cost of plugging in a heat mat I bought through a garden supply store to put under a flat of seedlings is probably less than turning up our household thermostat to 80 degrees.

A week after planting, 30 percent of my heliotrope seeds had sprouted. Before April I plan to start the tomato and cosmos. If all goes well, I may be looking for ways to hang flats of seedlings under all of our fluorescent ceiling lights.

Clarification:

When sterilizing potting soil by baking it in your oven at 250 degrees, it must bake 30 minutes after the soil temperature reaches 140 degrees.

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