Dahlias are grown from tubers, much like the flower bulbs of tulips, daffodils and crocuses. The tuber holds nutrients and moisture that feed the dahlia plant. Blooming in late summer and into fall, these delightful blooms bring back the feel of earlier months. Depending on the variety, dahlias come in many colors and sizes. You can find them in small border plants and tall landscape plants of up to 6 feet.
Choose a location that gets a full eight hours of sun per day. These sun lovers should be planted from mid-April to the end of May, depending on your location and the variety.
Prepare the soil for your dahlia tubers. These plants prefer a well-drained soil, on the sandy side. However, whether you have sand- or clay-based soil, a layer of compost will add nutrients. Dig up the soil in the planting area. Break up all dirt clods, while removing weeds, rocks and other debris. Pour on a 2-inch layer of compost. For extra hard clay soil, add a thin layer of sand. Work the soil until it is mixed thoroughly. Rake the area even.
Dig holes 4 to 6 inches deep, using a trowel, and 18 to 24 inches apart, depending on the variety. Always follow the manufacturer's recommendations. Lay the tubers sideways in the holes and push soil over the top. There is no need to water dahlias after planting, as the tubers have stored moisture.
Apply snail and slug bait around the planted area, right after planting. These are the primary dahlia pests. Continue to apply the bait, as directed by the manufacturer, throughout the growing season.
Water after the first dahlia sprouts are visible. The only time to water before this time is if your location is experiencing very dry, hot weather. Then you may lightly sprinkle the planted ground. After sprouting, water two to three times per week with a slow-running hose for approximately 30 minutes each time.
Stake your dahlia plant for those varieties that will grow to a maturity of 3 feet or more. Stick a stake into the ground next to the plant, careful not to injure the tuber. Use plant ties around the plant stem and the stake to hold the plant upright.
Fertilize your dahlia plants about two to four weeks after planting and then again three to four weeks later. Use a high-phosphorus and high-potassium fertilizer, such as 10-20-20. Phosphorus is always the second number and potassium always the third number on fertilizer packages. Most importantly, do not over-feed dahlias.
Pull weeds as they appear. Never use a herbicide for weed control, as it will kill the dahlia plants.