(Note: For more detail and demos, buy a ticket for Jenny’s how-to dahlia webinar on April 19).
When to Plant
Dahlias are long-season plants, so plant your tubers at the right time to get the longest flowering period possible in the late summer and fall. As a general rule, plant as soon as you’re sure the last frost date has passed and/or soil temperature is around 60 degrees.
Where to Plant
Find a sunny spot – the more sun, the more flowers! Well-drained soil is best (heavy, moist soil can rot tubers) and dahlias tend to like slightly acidic soil. Since tubers have to be planted fairly deep and have room to make nice roots and more tubers, well-worked garden soil makes them happy.
How to Plant
Plant tubers 6” deep and 18” – 24” apart. We put a scoop of compost or a handful of balanced fertilizer in the planting hole. Place your tuber horizontally in the hole, and cover. If the ground is dry, go ahead and water your newly planted tubers. Go light on the watering (only water if the soil is dry) until sprouts emerge or you could be risking tuber rot.
When Sprouts Emerge
Now is the time to start watering deeply. Dahlias are water hogs and a light spray won’t do the trick. Water has to reach down the full 6” to the tuber.
When plants start putting on some growth, we foliar feed with fish/kelp emulsion every 10 days or so until buds are initiated. Dahlias prefer low nitrogen – once plants begin flowering, we stop fertilizing. Too much nitrogen leads to big, bushy plants with few flowers.
Most varieties of dahlias need trellising. For home gardens, bamboo trellising works nicely, or if you’re growing a larger quantity consider the Florida weave or Hortonova netting.
Pinching does wonders to create bushy plants and long stems. This is a necessity if you’re planning to cut dahlias for the vase. When the plant is 12” or so tall, pinch down to three leaf sets. It can seem harsh, but it works!
Digging and Storing Tubers
In colder climates, tubers must be dug and stored over the winter. Once frost has killed your plant, cut the plant back to about 6”. Using a fork or shovel, loosen the soil around the clump and lift it out of the dirt, being careful not to break off the ends of the tuber clumps. Brush excess soil off the clumps and store them over winter in a cool, dark place that stays around 40 – 45 degrees.