Growing & Dividing Dahlias

Dahlia Labyrinth

Dahlia Labyrinth

Dahlias love sun, and it is recommended that they receive at least 6-8 hours of sun per day. The more sun the more blooms.

Dahlias can be planted out in workable soil when the soil temperature has reached 60 F. Dig a hole that is 4-6 inches deep and lay the tuber horizontally in the hole. If the dahlias have shoots longer than 2-3” then pinch them back to one inch. It will encourage stronger stalks. It is also a good time to put in garden stakes if using them. Usually the May long weekend in Canada Zone 5b.

At this point your dahlias need little water, until sprouts have appeared above ground. But once they start growing they will require a deep watering twice a week and little more if very warm. If you are using. Fertilizer, use low nitrogen fertilizer. Stop using altogether in late August.

Hand weeding is the only way to control weeds around dahlias. If you are using mulch them apply it after sprouts have emerged, but keep it away from the base of the tuber to allow water to penetrate properly.

Topping or pinching to promote shorter bushier plants and more blooms, is always recommended. Pinch the centre shoot just above the third set leaves (plants are about 12-18 inches tall). Disbudding means getting rid of side buds leaving centre bud only

We sell only single division tubers, field grown, divided, stored and shipped to you. Tuber size has nothing to do with the size of the plant or bloom.

In the fall, after a true ‘killing frost’, wait 2 weeks or so, to help set the tuber, then begin digging them up. The stems and leaves will be black or brown at this point. The clump will have built up over the summer, and some can be quite large. Cut the stock to about 6” to give you a handle for the clump. I use a pitchfork or a spade and start about 12” or so away from the stalk. I carefully move around the clump to loosen the soil, then gently lift up the clump, then grab the stem to hold onto. Mark you variety at this time, so you know what you are dividing later.

Some schools of thought are to wash each clump, then dry them, in a protected area for at least 24 hours before dividing and/or storing for the winter. I prefer to leave some dirt on my clumps, but I do dry them for a few depending upon how wet they are (weather determinant).I do not split tubers till the spring, but I do trim back the stalks to around one inch or so. I label the clump and store them in milk/produce crates in a cool area that always remains between 40-50F (as long as they don’t freeze). I can say that I have reduced my winter losses by using this method, and in our climate , sometimes it is faster to get the clumps out of the ground and drying instead of worrying about dividing. My failures have been our to not allowing enough time for clumps to ‘cure’ sufficiently, and they are usually my last ones, because it is colder and wetter.

I do not recommend sealing plastic containers for tuber storage they hold in too much moisture, and are conducive to tuber rot. There are several potential mediums to use in whatever storage container you use such as Wood Shavings, Peat Moss, and Vermiculite, all are good.

Dividing clumps may seem like a daunting task, but not so much, just rather imperfect. I use very sharp garden shears and cut the clump into halves, then quarters if I cannot see eyes at the time that I start dividing. But a viable tuber MUST have one eye, and they are located near the centre stalk. I prefer individual tubers not clumps for planting out. The clumps run the risk of one or more tubers rotting and taking out the entire plant, even at 16” tall.


The bonus of Dahlias aside from long bloom time is the multiplication factor. One tuber becomes many quickly sometimes. But not all Dahlias are great tuber producers, and may only reap a couple per year vs. Ten or more from one tuber.

They are often a few things you should look for as your dahlias grow, which signal significant disease. If you see stunted, almost twisted plants, or pale curled leaves then your plant likely has a virus. Viruses are spread by blood sucking insects and nematodes (the bad ones). Unfortunately you will have to dig out your plant and destroy it - DO NOT COMPOST IT! Burning is actually best plan, if you can. Clean up in the garden of excess debris is very important. Sterilize you cutting tools before cutting anything else with them. I use a jar of Bleach for the job, just to prevent any cross contamination.