Starting seeds indoors lengthens your growing season and allows you to grow heirloom and uncommon varieties that may not be easy to find as transplants. Seeds need four things to start successfully: a growing medium, water, light, and a way to control the humidity around the seeds.
1. If you are using pots or other containers you have used before, it is a good idea to soak them in a solution of one part bleach to nine parts water for at least ten minutes before use. Rinse well, then fill them with your choice of growing medium.
2. One of the most important things to successful seed starting is the growing medium. There are many different types of growing mediums ranging from simple topsoil to soilless potting mix. Make sure whatever you use has been sterilized or pasteurized before you use it. This kills weed seeds and any harmful organisms such as mold or fungus spores that may threaten the seedlings.
If you are reusing growing medium or using topsoil from your yard, you will need to sterilize it yourself. This is easily done by spreading it in a layer on a cookie sheet, then cooking it at 200 degrees F for at least 30 minutes. This level of heat will kill weed seeds and microorganisms without damaging the rest of the soil.
3. Fill your containers approximately two thirds full of soil. If you are using expandable pellets, soak them to expand them according to label directions. Plant your seeds at the recommended depth for each seed. You will need to water in you seeds. Instead of watering from the top, set the pots in a shallow pan with an inch or two of water in it. As the water is absorbed into the pots, add more water to the pan. When the soil is saturated, drain off the remaining water in the pan.
4. Place plastic wrap over the top of the pots to seal in the moisture and place in a warm place for a few days. Check each day and remove the plastic wrap as soon as you see the seedlings appear. You may have to water the soil by setting the container in a shallow pan with an inch or so of water if it takes longer than three days to germinate the seedlings. You want the soil to remain damp but not squishy.
5. Once the seedlings are up, you will need to provide light for them to continue to grow. The best light is a grow light, available from nurseries or home improvement stores. It contains a bulb that has a full spectrum of wavelengths so the plant thinks it is sunlight. You can also purchase full spectrum light bulbs to fit most lamps so can use that, as well.
The light source should be adjustable. You want to keep it directly above the seedlings and only two or three inches above the top of the plant. As the plant grows, you will have to raise the light. If the light is not directly above the seedlings, they will turn and grow toward it. If it is too far above them, the seedlings will be leggy and spindly.
Seedlings need a lot of water. It is best to water them from below, as doing so avoids splashing soil, and any mold or fungal spores in the soil, on them. Even though the soil started out sterile, mold and fungus spores are in the air and might settle on the plants or soil. Watering by setting the pots in a shallow dish with an inch or so of water will allow the soil to draw up the moisture without getting the plant leaves damp. Damp leaves are an ideal environment for diseases. Keep the soil moist but not squishy during the entire time the plants are growing.
When you are ready to plant your seedlings outdoors, you will have to harden them off or they will die. This process is taking a week or so and gradually acclimating the seedlings to the outdoors. One nice days, set the seedlings in the sun, out of the wind, for several hours. Gradually increase the amount of time the seedlings are outside until they are spending the entire day outside by the end of the week.
When you plant the seedling, do so early in the morning so they are able to adjust to the new environment during the day. Water them in well so they do not dry out. If necessary, use a wind break to protect them from wind for the first week or so until their roots are established enough to hold them in the soil.