You can start pansies from seed, but most gardeners purchase them in packs. When planting them outdoors, make sure they are hardened off. This means plants won't sustain damage from the cold temperatures and limited available sunlight that often accompany the spring and fall seasons in Colorado.
Growing compact, free-blooming pansies is easy. Just be sure to choose a site that receives some sun during the day. Pansies do best in loamy soil that is rich in organic matter, but they also do well in the heavier clay soils found in Colorado. Increase the organic matter in clay soils to improve drainage and aeration for the plants. Canadian sphagnum peat moss and well-rotted compost are good sources of organic matter. If possible, incorporate two to three inches of organic matter into six inches of soil.
Water plants thoroughly after transplanting and mulch lightly with leaf
mold or bark mulch. Pansies thrive when given a complete fertilizer such
as 5-6-5 analysis.
Adapted from: Colorado State University Cooperative Extension Sources, Credits and Copyright