Old-fashioned favourites, dahlias are regaining popularity with home gardeners. Native to Mexico, dahlias are an ideal flower for growers who love bright colour and seemingly endless variety; there are thousands of dahlia varieties and new hybrids are introduced every year. Dahlias require light, fertile soil and warm weather but even growers with poor soil or little gardening space can have success with these beauties since they grow just as well in pots as they do in the ground.
Drill drainage holes in bottoms of pots or enlarge existing holes if drainage is poor with a drill. Clean and dry each pot.
Line the bottom of each pot with biodegradable coffee filters. Cover drainage holes with filters to keep soil in and insects out without slowing pot's drainage. Fill the pot 1/3 full with a coarse, moistened soilless potting mix.
Lay the dahlia tuber on top of the soil horizontally, position the eye of the tuber in the centre of the pot if possible. If the eye has already sprouted, the sprouts should point upward. Add enough moist potting mix to cover the tuber but don't fill the pot entirely.
Place the pot in full sun and continue adding soil to the pot gradually as the tuber sprouts, leaving only the top leaves uncovered; water every time more soil is added.
Insert a 4-foot bamboo or metal plant stake into the pot. Stake the dahlia stem with plant ties once it has grown higher than the top of the container. Add plant ties every 12 inches of growth.
Pinch out the tip of the stalk when the plant has developed four sets of leaves; this encourages dense, bushy plants.
Feed dahlia plants with a low-nitrogen fertiliser, such as 10-20-20 or 5-10-10, every three to four weeks during the growing season.
To grow the largest dahlia flowers possible, remove the two side buds from every trio of buds, leaving the centre bud to grow.
Dahlia tubers are highly susceptible to rot so take care not to overwater the pots or let the soil become soggy.