Well rooted cuttings or vigorous divisions of overwintered clumps qualify as acceptable planting stock. Spring blooming mums from garden centers or florist shops that are typically popular around Mother's Day make poor selections for permanent garden plantings that will be productive in the fall. Mums are best planted after Mother's Day in the southern half of North Dakota, and after Memorial Day in the rest of the state. Be sure the plants purchased have been hardened off and that you are prepared to offer protection should a hard frost be predicted. Overwintered plants that are showing vigor may be divided and moved in mid-May, while the weaker ones can be moved once vigorous growth is apparent, generally after the Memorial Day weekend.
Mums do well in most well-drained and fertile garden soils.
If in doubt, add peat moss or compost. Where supplemental water will be lacking, a wider spacing is suggested. An important factor in good growth is to locate them where they can receive most of the day's direct sunlight. Mums are quite drought tolerant plants, often going through a growing season without supplemental watering. Be sure the soil is saturated completely to a depth of 4 to 6 inches.