Growing Beautiful Dahlias

First, you need to learn about this unique plant. Dahlias are Tender Perennials – that means they are Annuals in Northern Climates, but they are perennials because you can over-winter the rootstock and they will re-sprout year after year. Dahlias are tuberous plants and produce what looks like a narrow, elongated potato. They were brought to Europe because it was believed to be a potentially viable food source, but as it turns out, although edible, they are not delicious.

You can dig them and store them in a root cellar or other location that remains at 40–50 degrees Fahrenheit, or you can just treat them like annuals and buy new stock every year. This method affords the opportunity to try new varieties and since there are thousands of varieties, why wouldn’t you?!

Planting Tubers

Dahlias are native to the highlands of Mexico; this means they like warm days and cool nights. They like a warm bed (soil) and are very susceptible to frost. Plant tubers when all danger of frost has past (you can push it a week early since they take about a week to sprout once planted); scientific evidence advises to plant when soil temps are at least 60 F. Dahlias like well-drained soil since they have a tendency to rot if the soil is too wet. Be careful when/if fertilizing; too much nitrogen will result in lots of foliar growth but not as many flowers as you would like.

Plant the tubers about 4” deep HORIZONTALLY; if you’re growing more than one in the same area, give them about 18” – 24” inches of growing space between/among them. To err on the side of caution, throw a little bone meal into the hole and maybe some compost if you don’t have great soil.

Caring For Your Growing Dahlias

Dahlias are very big plants on average. For the best quality blooms and a handsome landscape specimen they must be supported. The home gardener can use a single stake as they generally form a central stalk. Loosely tie up the main branch as it grows and you’ll be in good shape. Alternatively, tomato cages also work well.

Dahlias are hardy plants. Fertilize sparingly unless you have unusually poor soil. Water when they tell you – I water them when we have exceptionally dry  periods; when they wilt, I water them.  Otherwise, I just let them suck all the moisture out of the soil that they possibly can.

Dahlias are in the “cut-n-come-again” category; once they start blooming, they won’t stop until Jack Frost nips them. For the best performance, cut blooms for arrangements and if you plain have too many, remove the old flowers to direct the plant’s energy to new blossoms for more enjoyment.

If you do decide to keep your dahlia stock, you may want to label them if you are growing more than one variety. Once the frost hits let them dieback naturally; the tubers will resorb all the nutrients in the foliage priming them for a long winter’s nap. Two weeks or so after the first frost cut them at the base and compost the spent plant. Digging the tuber clumps is not for the faint-hearted. Depending on your soil type and the weather and soil condition, this may not be your most favorite thing to do. Wet clay soils make this a miserable task; if this is your first time, you will not believe how enormous and heavy these tubers have become over the growing season. We plant one tuber in the spring and dig up between 5-35 tubers/clump in the fall. Our tuber clumps can weigh as much as 25 pounds each!

To store dahlias, the home gardener can put the whole clump in a cardboard box in an environment that will not freeze nor get too warm; elevated temps will encourage fungal growth and the tubers will rot. If you are growing dahlias professionally or semi- professionally (are you a member of your local Dahlia Society?), you may choose to divide your tuber clumps into individual tubers.  Some folks divide tubers in the fall, some divide them in the spring, and some don’t divide them at all. Dahlias are versatile!

How to Grow Amazing Dahlias Professionally