The Right Place
Plant crocuses in the fall. September is best, but you can plant anytime as long as the soil has not frozen. Choose a sunny location. This may be under a tree because crocus blooms early enough in spring, before the leaves appear on the trees.
Plant crocuses in soil that drains well after it rains. Like most bulbous plants, crocuses do poorly in soggy, clayey soils. If necessary, build crocus beds higher than the surrounding soil surface, or add lots of organic matter to your soil such as chopped leaves, or peat moss to ensure good drainage. Soil that is slightly acidic (pH 6.0 to 6.5) is ideal.
Planting Nursery Stock
Prepare the planting site by digging the soil to loosen it. Remove any rocks or plant debris and break up large clumps. This is a good time to sprinkle some slow-acting bulb fertilizer on the soil so it will be mixed in as you plant. With a trowel or bulb planter dig holes 3 to 4 inches deep and 3 to 4 inches apart. Measure the depth from the bottom of the hole. Put a crocus corm in each hole, its pointed growing tip aimed upward, and its rounded bottom pressed gently into the soil. Use a slight twisting motion to ensure good soil contact for the root plate.
To plant a cluster of corms in one area, an alternative method is to dig a broad hole 4 or 5 inches deep and arrange all the corms at once in the bottom of the hole. Then fill it with soil, firming it gently over the buried crocus corms. Water well and add a layer of mulch. For visual effect, it's best to plant crocuses in clusters of 8 to 10. Or try "naturalizing" plantings by scattering the corms and planting them individually where they fall.