Select a planting bed in full sunlight. Find a site away from any type of nighttime light source such as a street light or backyard floodlight. This is important for the mums to produce flowers.
Break up the soil to a depth of 12 inches and work in 4 inches of organic matter such as compost, peat or aged manure. Rake the planting bed level.
Dig holes the same depth as the lavender Belgium mum sits in its pot and space the transplants 1 1/2 to 2 feet apart.
Soak the plants to settle them in place. Continue to water the mums throughout the growing season, supplying an inch of water weekly.
Add a 2-inch layer of mulch around the lavender Belgium mums to prevent weeds and retain moisture.
Apply a balanced fertilizer as instructed around each of the plants every 30 days until August.
Allow the plants to remain through the winter before trimming off dead foliage. Cover the lavender Belgium mums with 4 to 6 inches of straw after the soil begins to freeze.