How to Grow Dahlias Like a Professional (Or Not)

I’m a professional grower. At least that’s the image I like to portray. To be fair, I’ve been part of growing millions of plants over the years. Hundreds of varieties of trees, thousands of varieties of perennials, and more annuals than I can count. As I’ve mentioned in previous newsletters, I’ve killed more plants than most people grow. I’ve seen every issue that could come up (although a new one seemed to pop up every year). Soil conditions, pH, temperatures, watering problems, and of course bugs. We didn’t have GPT back then, and for much of the time, not even decent search results. Answers came from phone calls to other growers or experts and plain old books. Remember those?

So when I retired, I got a little cocky. I always have some new plant I want to try, and it’s never just one to see what happens. I buy $500–$1,000 worth and give it a go. This year it was dahlias. We’ve grown tens of thousands of dahlias and they’re pretty easy. What I ordered were dinnerplate dahlias, which come in tubers, something I do have experience with. Normally we would place them in a 14-inch pot with a built-in cage, trim early, and they would come out nice. I put exactly none of this experience into practice.

Here is an Instagram post describing my purchase and installation. I realize how much weight I’ve lost this summer training in Colorado, but that’s for a different newsletter

botany

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What I Did Right

Nothing. Absolutely nothing.
Well, I take that back. I labeled them well and drew a map on a sheet of paper that was accurate. I also planted them at the right depth. Have to be positive here.

What I Did Wrong

Watering at planting
It’s very important to not let tubers rot. That’s true of any tubers, not just dahlias. The difference is dahlias are more delicate and rot out quicker than peonies or iris. So it’s important not to water them in deeply when you plant them. Naturally, I watered them in deeply when I planted them. Then it poured rain after that. I can’t control that, but I certainly didn’t help by already having them soaked. Fortunately, my soil was decent and I had added peat moss and compost for drainage. I didn’t lose any to rotting, which was a miracle.

Watering in general
Because my annuals needed watering every day, I watered these every day once they had green showing. A dumb routine but a routine. Literally the opposite of what you want. You need to soak them thoroughly every other day. I know enough to realize wilting is usually just the heat and not a real lack of water, but they looked so tired I gave in. That shallow watering forced shallow roots, which makes them fall over. They didn’t fall over because I had them well staked. I guess I should add staking to the “did right” list. I’m hard on myself.

Trimming
When dahlias first come up, once they get to about a foot high, you need to pinch them back so they get thicker and put up more shoots. I didn’t. I don’t know why, but I didn’t, and by the time I realized it, they were three feet tall. I didn’t want to start over. It probably would have worked out, but now most of my dahlias are one giant stalk. Big mistake. It’s going to cost me 20 flowers or more on each plant.

Fertilizing
Roots, foliage, and flowers. That’s what you’re trying to balance. I used a general fertilizer to start and slow-release after that. The problem was the slow-release was heavy in nitrogen. That’s fine for the first half of the season, but you need to cut nitrogen later because you want roots and flowers, not more foliage. I didn’t do that. Now I’ve got nice long stalks, but smaller blooms than I should. A few plants have full-size flowers, but again, it’s one stalk, so there won’t be many overall.

Starting the tubers
I put them straight into the ground. In hindsight, I should have started them in pots to get them going quicker. I should have sweated them out like I do roses—get the tubers warmer and trick them into thinking it’s spring. Then put them in pots, trim them, and then go to the ground. If I followed this method my plants would be four times the size. When we grew them in pots before, we started in March in a humid, warm greenhouse. By the end of May those plants were three feet tall and three feet wide. Mine in May were one foot tall and six inches wide. Which reminds me I need a greenhouse in my backyard.

Harvesting
Harvesting promotes more growth and more flowers. I didn’t do much of it because I barely had flowers to cut. But I did take a few, and immediately saw new stalks and flowers appear. That’s going to be part of my regular practice from now on. Cut them, enjoy them, and let new ones come.

So What Did I Learn?

Everything I just mentioned and a few other things. I need to get my tubers planted a whole month earlier to give them a head start. I’ll have to figure out the greenhouse situation, maybe steal a tiny bit of space at the nursery.

I also learned that I absolutely love dahlias. As pretty of a flower as there is. Before this, peonies were my favorite flower and coleus my favorite annual. Now I’m adding dahlias to the list. And I say this after only a handful of blooms. If I end up with hundreds, who knows, maybe I’ll go into the dahlia business.

Here are a few pictures of the dahlias I’ve gotten so far. Check the Instagram account for the other varieties as they come on. Zero editing on these pics

It's Go Time For Dividing These Plants

If you want to divide plants this year, now is the time to divide your peony, iris, hosta, and daylily. You've probably been told you need the top to die back to get the energy for next year. That's more for your tulips and daffodils. Iris and peony have stored plenty of energy. Don't let the green tops fool you. You should thank them. That lush top was sending back food and energy all summer long. They are ready

What you want to do is dig them up, getting the entire root system, and shake off the dirt. Then cut the tops down to 2–3 inches in length for all of them. Reducing the foliage makes it easier for the plant to grow roots. The cutting tells it: go down, not grow up.

You should easily be able to see the tubers in the iris to divide. Just break them apart into sizes of one or two fans. For peonies, I like to get them to three or five eyes. You may need a serrated knife or a sharp shovel to divide. There might be a little slicing at the base, but it will be fine. Same with the daylilies and hosta—a little cutting may be in order, but I like to get them to three or five fans or leaves.

Of course if you have any great peony divisions, feel free to send them to me. I’ll give you an address

A Picture is Worth a Hundred Words

If you enjoyed the newsletter please share with your friends. I always love comments or ideas so feel free to hit reply and say hello. Have a great weekend and send some pics of your plants




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