Choose a small sunflower variety and the appropriate pot size to grow sunflowers in pots. The Pacino variety grows 24 to 30 inches tall. The Music Box variety grows 18 inches tall and produces flowers that are 6 inches in diameter. Other small sunflowers varieties suitable for growing in pots are the Big Smile and the Teddybear.
Use planters 10 to 12 inches in diameter for sunflower varieties that grow up to 2 feet. Varieties that grow up to 4 feet tall require 3- or 5-gallon planters.
Sunflowers need good drainage. Use plastic, clay or wood pots with at least one draining hole in the bottom. Place the pot on a tray to prevent spillage.
Fill the planter with sterilized general-purpose potting soil. Garden soil is not recommended because it compacts in the outer areas of the planter, preventing aeration. Mix vermiculite with the potting soil when using large pots.
Plant seeds 1 inch deep. Germination takes between five and 10 days, and the flower should reach full growth and bloom after three months.
Check the soil for dryness daily. Water the sunflower when the top 1 inch of soil is dry. Hot climates might require watering the plant more regularly.
Apply soluble high-phosphorus fertilizer when the sunflower begins to bloom.