Our Guide to Growing Dahlias
Plant tubers whole, with the eyes facing up, about 6 to 8 inches deep. We space dahlias at least 12" apart. Dahlias will grow quite large and will require additional support (tomato cages or bamboo stakes work well).
Dahlias start blooming about 8 weeks after planting (usually in mid-July here in Massachusetts)
Choosing the right time to plant is the key to a successful dahlia crop. You can’t plant dahlias too early, when ground temps are still too cold. Dahlias prefer warm soil, at least 55-60 degrees. If the forecast is predicting a very damp, wet stretch, hold off on planting as newly planted tubers are prone to rot. In the Northeast, early to mid-May is typically the earliest we can plant.
Dahlias thrive in full sun and should be planted in a location that receives a minimum of 6 to 8 hours of sunlight a day. Dahlias planted in an area with less sunlight won’t yield as many blooms. Because dahlia tubers are prone to rot, it’s important to make sure that your soil isn’t too heavy. The soil should drain freely and easily; if not, amend it with peat or sand. Once you plant your tubers, wait to water until you see the first shoots emerge. If you are planting in a container, water well once at planting, then hold off on watering again until shoots emerge.
Once the dahlia plants are established (6-12" tall), water regularly and deeply 2-3 times a week for 30-60 minutes. In the heat of summer, dahlias will require more water especially if it is warm and dry.
We amend our soil with a general purpose (5-3-4) organic fertilizer at planting time. Once dahlias begin to bloom, we foliar feed every other week with a fish and seaweed formula (low nitrogen). Avoid high nitrogen fertilizers -- these will make your plants large and green but you will have small (or no) blooms with weak stems.
The best time to cut dahlias is in the cool of the morning. Using sharp pruners, cut the stem at a 45 degree angle just above a leaf node. (A good stem length is from the tip of your finger to the crook of your elbow.) The plant will branch from the cut and produce additional stems. Harvest dahlias when the flower is nearly or fully open (closed buds won't open after the stem is cut). Strip the stems of any foliage that may be beneath waterline in a vase. Place the stems in fresh water and add flower food as desired. Replace the water and recut stems daily for a vase life of 3-5 days (vase life of dahlias varies depending on variety and size).
Harvest dahlias regularly to promote additional flowering. Once flowers go to seed, the plants will slow down flower production.
Dahlia tubers are readily available from many growers online. Tubers are essentially the root stock of the dahlia plant and, once planted, will multiply in the ground every season. A dahlia plant grown from one tuber will yield multiple tubers once dug up in the fall. We sell our excess tuber stock in late winter/early spring. Join our mailing list to be notified when our dahlias will go on sale!
Storing Dahlia Tubers
In the Northeast, our winter temperatures are just too cold, and dahlias’ thin-skinned tubers will freeze if left in the ground over winter. Tubers can be pulled each fall, cleaned, and stored in a cool, dark room until next spring. It’s best to dig them up 2-3 weeks after a hard frost, when the plants have fully blackened and the tubers have hardened off. It's important to keep tubers clean and maintain a balanced level of humidity in storage over the winter. (These levels are dependent on your location and weather conditions; you will have to check on your tubers frequently. Tubers that have properly hardened off will maintain their firmness in storage.)
We have had success cleaning our tubers, dividing them, and storing loose (without any medium) in bulb crates in a climate-controlled room.