Proper heat, humidity and soil moisture are all vital when starting seeds indoors. These needs are rarely provided properly inside the home, but you can improve your seed-starting success with the aid of a miniature greenhouse and a seedling heat mat. The greenhouse can be as simple as a plastic bag over a pot or you can use a purchased tray with a clear plastic cover. Heat mats, readily available at nurseries and garden centers, keep the soil at the proper temperature for germination.
Sow the seeds in pots or a tray filled with a sterile seed-starting soil. Plant seeds at a depth that is twice their width then water the soil until it is evenly moist but not soggy.
Set the pots inside the greenhouse or cover them with a plastic bag, if applicable. Cover seed trays with the included plastic greenhouse cover.
Set the pots or trays on top of the seedling heat mat in an area that receives no direct sunlight. Set the temperature on the mat to between 75 and 80 F, depending on the requirements indicated on the seed packet for the specific plant variety.
Mist the surface of the soil with water from a spray bottle if the soil begins to dry before germination. The greenhouse cover usually retains moisture well enough that misting may not be necessary.
Vent the greenhouse cover once the seeds germinate and sprouts begin to appear and move the seedlings to a brightly location. Prop up one corner of the cover or plastic bag to provide air circulation to the plants and to prevent condensation from building up on the seedling foliage.
Remove the greenhouse cover completely once seedlings produce their second set of leaves or grow tall enough to touch the cover--whichever occurs first. Water the seedlings when the soil feels dry and continue to provide bottom heat until the seedlings are ready for transplanting.