When you start your own seeds, the world of possibilities opens to new varieties not found in stores. Plus, you can do a little plant name dropping when talking to your neighbors. 
Carol O'Meara, Colorado State University Extension
Carol O’Meara, Colorado State University Extension

March brings with it dreams of spring and all the promise of a bountiful summer. After long, cold weeks, the time is here for gardeners to start seeds of their favorite plants. When you start your own seeds, the world of possibilities opens to new varieties not found in stores. Plus, you can do a little plant name dropping when talking to your neighbors. 

If you’ve never started your own seeds, don’t worry, it’s easy. Keep in mind some things don’t transplant well, such as beans, cucumbers, corn or squash, so leave those for directly sowing into the soil. Tomatoes, peppers, or cabbages are easy and pumpkins, melons or winter squash sprout quickly. The pumpkins, squash and melons need special handling when planting so roots aren’t disturbed.

Check the seed packet for timing on starting the seeds, but a good rule of thumb is six to eight weeks before planting out.   

You don’t need much to get started:  room to keep the plants, trays to hold pots, sterile seed starting media, seeds, labels and lights. Grow lights, daylight spectrum LEDs, or a combination of cool blue and warm daylight florescent bulbs work well. Make sure you have the lights on chains or cords to raise and lower them as the plants grow. A timer is worth the investment.

Prevent disease by using sterile containers and sterile planting media, a lightweight, soil-less mixture of peat, vermiculite or perlite, and compost. And trust me on this – labels are critical to reminding yourself what the plant is. Nothing is more annoying than asking a mute seedling whether they’re the hot jalapeno or sweet bell pepper.

To plant, mix the potting media with water in a large bowl, getting it damp but not soaked.  Fill tray cells or pots but don’t pack it down; leave it light and airy. Make a hole to a depth that is equal to three times the seed length, then pop seeds in and cover them up.  If the media is a bit on the dry side, sprinkle lightly with water.

Humidity and warmth are what seeds need at this point, so tent the tray with plastic to increase humidity during germination. Put the seeds in a warm room or use seedling mats that gently warm them. For most seeds, you don’t need light during germination, but once plants nose up through the media, lights are critical from then on. 

Just as seedlings emerge, remove the humidity tent slowly to avoid shocking them. Open the tent bit by bit, gradually exposing the seedlings to the air. Do this as soon as the seedling emerge to prevent mold from forming on the soil.

Set up lights to hang directly over the seed trays, making sure they’re kept at three to four inches above the plants at all times. Give plants 12 to 16 hours of light daily. Seedlings that are long, spindly and weak are stretching for light; it’s an indication that lights are too far away.

Water seedlings from the tray bottom, allowing water to be wicked up into tray cells or pots.  If this isn’t possible, carefully water seedlings from the surface using a gentle sprinkle.  

If more than one seed in a cell has germinated, select the strongest seedling and pinch off  – don’t pull – the others. Help seedling develop stronger stems by having a  small fan circulating air gently across them.

The first pair of leaves are cotyledons, not true leaves. The true leaves develop directly above the cotyledons. Pot up seedlings into the next size larger pot once they have two sets of true leaves. After transplanting, wait to fertilize until the roots touch the sides of the containers, usually about a week. Then fertilize at half strength once weekly.

By Carol O’Meara, CSU Extension. Colorado State University Extension, together with Boulder County Parks and Open Space, provides unbiased, research-based information about consumer and family issues, horticulture, natural resources, agriculture and 4-H youth development. For more information contact Colorado State University Extension at the Boulder County Fairgrounds, 9595 Nelson Rd., Box B, Longmont, 303.678.6238, e-mail [email protected] or visit ext.colostate.edu/boulder.