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?!
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
18” – we grow in 4’ wide landscape fabric; 2 rows off-set
Every plant gets pinched at the third node; this promotes branching for a more stable plant and more blooms.
We install stakes on each side of the double-row, approx. 10’ apart and wind string (we use baling twine) about every foot or two of height along the aisles and insert a cross-wise string about every 6-8’ when the plants are about 2’ tall. (Staking every plant when you’re growing 2500 plants is not cost-effective.)
Take soil samples and amend according to the results.
Gotta have it! Or at least an accessible water source to hose ‘em if it gets dry. We use drip irrigation and turn it on when necessary. An inch/week is a good rule of thumb.
Not all farmers adhere to this practice as it is very time-consuming but we dis-bud; identify a good bloom and pinch all the laterals 18” down or more depending on where the next branch is. This allocates all that energy to the apical bud and wa-la! You have a phenomenal flower worth every penny!
Dahlias are notoriously short-lived cut-flowers BUT I believe this to be a misnomer. Our flowers easily look gorgeous for well over a week, sometimes even up to two weeks. Cut long stems (it’s okay to cut off other buds (potential flowers), trust me, they will produce more! Cut when the temps are cool – early morning or evening. We use a hydrator; all stems get a quick dip and then put into a holding solution. Then quickly off to the cooler (no more than 40 F).
Digging, Dividing & Storage
WoW! What a process! This is what separates the women from the girls! If you can get helpers, do it!
FIRST – label them BEFORE the first frost so you can tell what they are before the blossoms turn brown! We tie flagging tape around the base of the plant and use a permanent marker. This step occurs late September/early October.
Once the frost hits, you can adjust your schedule according to the weather and other obligations. Some folks wait a week or two to cut down the plants to allow for the nutrients to re-sorb into the tubers – I don’t. Cut the plants at the base, leaving a 4” stem for ease of handling (handy to have a handle).
We dig the clumps with either a shovel or digging fork – give yourself a wide berth as the clumps can easily be 18 – 24” in diameter, put them in bulb crates and transport them to the washing station. We do our best to clean all the soil off the clumps, the importance of this is so when we divide them, we can see the eyes. Try your best to clean out all the nooks-n-crannies; I try to remove all the worms, without killing them. Avoid using a super-high pressure stream as this can slough off the protective skin. Then they get put in a place that will allow them to dry.
Dividing tubers is an art and a science. And also can be dangerous – always wear gloves! Handy tools include pocket knives, old flower shears, and loppers to remove the large stems. Once cut, allow the cut surfaces to “cure” (dry) and then they get packed.
There are as many ways to store tubers as there are dahlia farmers. We line cardboard boxes with newspaper, fill the bottom with an inch or two of moistened peat – NOT TOO WET. (Tip: if you happen to have a cement-mixer, this will cut-down on time and more importantly, your exposure to the dust.) I ALWAYS wear a respirator mask and safety glasses during this process – this is a very dirty task. Layer the tubers on top of the peat in the box, add another layer of peat, a layer of tubers, peat, tubers, until the box is full, you’ve run out of that variety, or just BEFORE it’s too heavy to carry. Label the box with its contents. Now, they get put into their winter home; wire racks in a dirt basement. They must be kept at 40 – 50 F for optimal success.