Seeds are easy yet complicated to germinate. In general, seeds need oxygen and moisture to sprout, followed by light and the right soil and temperature to grow.
Each type of seed has its own set of rules for germination. If you know something about the type of plant you're growing, you may be able to guess at its germination needs. For example, if the plants have origins in tropical climates, their seeds need warm temperatures and moisture to germinate. But if they're plants native to mountains, their seeds may need cold or freezing temperatures.
Moisture alone is often enough to break a seed's dormancy. Have you ever grown sprouts for salads or cooking? You've germinated seeds, using water and light.
However, some types of seeds are tough customers and need special treatment to germinate.
A chilling period with moisture is needed for some seeds, such as milkweeds (Asclepias spp.). This process is called stratification. (Side note: Vernalization is the term for a chilling period needed to promote blooms for some plants but doesn't involve seeds.) Other plants that need stratification for their seeds to germinate include columbines, daylilies, monkshood, primroses, and roses.
Other seeds, such as moonflowers (Ipomoea alba), need scarification. This scary term is a benign process that simply means using a knife or sandpaper to break open the tough outer seed coating. Other plants that need scarification include camellia, holly, tree peonies, and wisteria.
Every seed has its own optimal temperature for germination. Many need warm temperatures. Most need water to germinate.
Many experts suggest soaking perennial plant seeds overnight before planting. Avoid soaking the seeds longer than 24 hours; seeds left too long in water start to rot.
Vegetables easy to germinate: Beans, broccoli, Brussels sprouts, cabbage, cauliflower, celery, collards, eggplant, kale, kohlrabi, lettuce, onion, pepper, and tomato. Check your seed package for directions.
Herbs easy to germinate: Basil, chamomile, chives, cilantro, dill, fennel, oregano, sage, sorrel, and summer savory. Check your seed package for directions.
Annual flowers easy to germinate: Direct-sow or start the seeds indoors for these annual flowers: Calendulas, celosias, dianthus, marigolds, nasturtiums, pansy, petunias, salvias, snapdragon, sunflowers, sweet peas, vincas, and zinnias. Check your seed package for directions.
Perennial flowers easy to germinate: Columbines, coreopsis, purple coneflowers (Echinacea spp.), Shasta daisies, and violas. Check your seed package for directions.
For many plants, you can start seeds indoors and transplant the seedlings into garden soil or containers outdoors. Or sow seeds directly into garden soil or containers when the soil temperatures are warm enough. In both cases, you should read the seed packet to determine germination needs of the plants you're growing.