Staking Dahlias: Why Loose Ties Grow Stronger Plants

One of the first things everyone warns you about when you start growing dahlias is their floppy stems — especially the dinner plate varieties.

Every book and article seems to say the same thing: dahlias need to be staked or corralled, or they'll fall over in the first heavy rain or summer windstorm.

So people stake their dahlias snugly, because they want to be certain they're protected. The thinking goes: the less they move, the safer they are.

But when the instructions only speak to staking, a big part of the story gets missed. Like the childhood game of telephone, something gets lost as advice passes from one gardener to another. In this case, what's lost is the nature and biology of the plant.

A dahlia's hollow stem does look like an obvious weakness. Add the considerable weight of a dinner plate flower (if that's what you're planting), and it's easy to imagine the whole plant toppling in wind or rain. 

But a snugly tied dahlia ignores its nature, and that creates its own problem. When a strong wind arrives, a tightly bound stem has no room to flex. The tie acts like a tourniquet, and that rigidity is what causes the stem to snap — right at the point where we thought we were protecting it.

Swaying actually helps a plant ride out a storm instead of fighting it. The plant senses the stress of wind and rain and responds to it. The process is called thigmomorphogenesis — the way a plant changes its growth in response to repeated mechanical stimulation, thickening and strengthening its stem over time. The stem isn't just enduring the weather, it's responding to the conditions it's being asked to grow in.

That's part of why a dahlia grown in an open field isn't quite the same plant as one raised in a greenhouse. Outdoors, it's continually responding to wind, rain, and the shifting weight of its own flowers. Those forces help shape the plant. There's more science behind it than that, but it's part of why we've always chosen to grow our dahlias outside.

Wiggle room is a nice place to be. When you tie a stem, leave it loose enough to allow space and movement. (Master growers often use a figure-eight knot.) A loose loop also gives the stem room to thicken as the season goes on; a tight tie that fit in June can turn restrictive by August.

The same goes for corralling. Don't pull the twine so tight that the plants are held rigidly together. Leave enough room for the stems to move before the corral catches them. A little leaning isn't failure. The plants will be fine.

At Bear Creek Farm, we no longer stake our individual dahlias, partly because we want to move quickly through the rows at harvest. We hill them instead, drawing soil up high around the base of each plant. Hilling braces the crown and lower stem and keeps the whole plant from loosening or toppling. It also buries weeds, so we're not spending time with that task. The mounded soil also acts like a mulch. Unlike a tie, it leaves the upper growth completely free to move with the weather.

So next time you're staking, think about all of it. A dahlia doesn't need to be held still. It needs room to move — just like the rest of us do, out here in the weather.