Dahlias: The Gift that Keeps Giving

Susie Rexius’s tips for growing the most amazing dahlias you’ve ever seen

One late-summer Tuesday afternoon, our co-president, Rusty Rexius and his wife, Susie, let us stroll through their garden — which is exactly as exquisite as you’d expect. We weren’t just there to casually absorb the beauty, however. We were there on a mission to glean expertise about dahlias.

“The cool thing about dahlias is, these are all dahlias,” Susie Rexius said as she gestured to a kaleidoscopic expanse of blooms in her breathtaking backyard. “There are dinnerplate dahlias, which are the really big ones (about 10 inches in diameter), and tiny, little [lollipop-style] balls — and they’re all dahlias! There are thousands upon thousands — you can’t even imagine how many different varieties exist of this type of flower.”

Dahlias 101

Dahlias are tuberous-rooted tender biennials, which means that their life cycle typically lasts two years, but they can behave like perennials. The best time to plant them is in the spring, after the ground has warmed up. They’re hardy to USDA Zone 8, which includes the Willamette Valley, but if you live in colder regions, you’ll need to dig up the tubers and store them for winter to preserve the plants.

“If you leave them in the ground [through milder winters], they will come back — if they don’t get soggy and rot. My very first dahlia, I didn’t know what to do with it. I left it in the ground for probably six years before I did anything with it, and it came back beautifully every single year.”

Flowers for Days (Like 90 Days)

“[Dahlias] are a wonderful late-summer bloomer because a lot of other flowers are kind of done when they really come on. They start blooming in mid-July, usually, and mid-August is when they’re [really spectacular]. Then they’ll go all the way up to [the first] frost, so probably mid-October. The really early bloomers will start to put out different kinds of flowers — they’re losing energy from the tuber, so their flowers change and they may not produce quite as much, but a lot of them will make flowers all the way up until we start getting temperatures below 35 (F).”

Dahlias don’t mind run-of-the-mill summer heat, but they don’t love extreme heat — especially when combined with humidity — so, they don’t do well in places like Florida or Texas. They thrive in Northwest coastal climates.

The Necessities

“They need really good drainage, but they do like a lot of water and they need at least six hours of sun each day. Staking is a huge deal, too, because you can see that they get really big and they have really heavy flowers; there’s a lot of weight on the plant, and so they fall over really easily and we’re out here wrangling them with twine and posts and pulls and… doing our best. [Laughs.] And the more you deadhead, the more they grow [and bloom].”

To Dig or Not to Dig?

“You don’t have to dig [dahlias] up every winter [where we live]; they don’t mind the cold, but they don’t like being really saturated with water because they’ll rot, just like a potato would.”

Divide and Conquer

“Dahlias can get really crowded [because of the way the tubers grow], so they’ll actually bloom better if you divide them. Every tuber that has eyes on its neck will grow a new plant, so if you dig one of these guys up and there’s a big, massive tuber, what you do is you dry it out and store it in a cool place for the winter, where it’s not going to get wet and it’s not going to dry out too much. When it starts to warm up, you can see the eyes kind of swelling and you can see where to cut around them. If you divide them up, you sometimes have like 20 tubers that you can give away — or you can plant more. They are the gift that keeps giving. It’s amazing!”

Pests and Pollinators

“Interestingly enough, we had a ton of bumblebees on [the dahlias] earlier this summer, and now, the honeybees have found them. They like them a lot. If [the bees] can get to the center (and the pollen), they just bury themselves in there and they’ll sleep all night on them. There are also a lot of bugs that like to eat dahlias — earwigs, cucumber beetles, slugs, and snails — but I’m really, super careful about anything that I use to deter those pests, because I want to be super careful of the pollinators.

“I use Sluggo for the slugs and snails at the beginning of the summer. Slugs and snails don’t like heat and dryness — and earwigs don’t, either — so, I don’t even really worry about them by about August 1. [The dahlias] do just fine… I do bring a lot of earwigs into the house, though.”

*Note: Sluggo® offers OMRI-listed products that are considered safe for organic gardening, pets, and wildlife.

“Deer will eat [the dahlias, too]. We are fenced in entirely (to prevent that).”

Final Words of Wisdom

“They’re really very easy, as long as you have the ingredients: the sun, water, and staking. Really, the big success story for us is that for the very first time, we tried [growing them] in our own Opus Grows soil, and it has outdone itself. Lots of growers all have different ideas about which compost and fertilizers to use. I’ve used organic liquid — basically, compost tea — but it really has been the Opus soil that’s been the difference maker. Apparently, dahlias are really picky about synthetic fertilizers, [and we were told to be very careful about which soil we used] so we were worried about whether the organic fertilizer would be a problem. Originally, [my husband and Rexius Co-President] Rusty was going to use the Opus Zero, [which doesn’t include any Bio-Tope] and it turns out that the dahlias like this kind, Opus Grows Mix 3