Six Years and Hundreds of Dahlias Taught Me the Same Three Lessons on Repeat

By Stephanie from West Seattle Flower Farm

People overcomplicate dahlias. 

I overcomplicate dahlias.

I've aggressively grown dahlias in my small urban lot in Seattle for the past six years — expanding from 40 plants my first year to about 300 last year.

I’ve grown a lot of flowers while simultaneously failing to grow a lot of flowers. 

Every dahlia-related bellyflop, however, has come down to three things: sun, water, or food. Yes, there are other details that can affect growth and success, like pests and disease, but most big issues can be solved with the basics.

Dahlia varieties: Chewy, Crichton Honey, Cornel Bronze and Ivanetti.

Instagram will tell you that you need perfect soil composition, perfect feeding schedules and that this one simple trick will guarantee you loads of blooms. (Full disclosure: I am a sucker for all the one simple trick Instagram reels. They'll always get a like and a save from me… right before they join the graveyard of flower hacks that is my saved folder.)

But six years and hundreds of dahlias have taught me the same three lessons on repeat: if your dahlias aren't growing well, start with sun, water and food before you go down the Instagram rabbit hole.

Sun: Your Dahlias Want A Lot of It

One of the hardest things about gardening in an urban space is understanding how much sun your dahlias ACTUALLY get. 

The city has a lot of obstacles to contend with: Your house, your neighbor’s tree that they never trim and the fence you built to keep your neighbor’s house, with it bath-towels-instead-of-curtains and dandelion-filled yard, out of sight.

If your dahlias aren’t blooming well (or at all) observe throughout the day how much sun your dahlias REALLY get.

Dahlia varieties: Summertime Merlot and Bloomquist Alan

And if your dahlias didn’t perform the way you expected the previous season, evaluate whether that nearby fence or overgrown tree is casting more of a shadow than you originally thought.

Last year, I planted dahlias in a raised bed next to my front door. And I packed that raised bed to the BRIM with tubers.

The dahlias in the front half of the raised bed did fantastic. 

The back half, however, grew slowly and bloomed sparingly.

It took me weeks of standing outside my house, in my bathrobe holding my cup of coffee wondering why half the dahlias sucked before I realized that the nearby rhododendron (that I forgot to cut back the year before) had doubled in size and shaded out the back half of the raised bed.

So, how much sun do dahlias really need?

The Internet says that dahlias need at least six to eight hours of sunlight a day in order to bloom decently. If they don’t get enough sun, they don’t bloom well (if at all.)

But I try to plant my dahlias in the places that get the maximum amount of sunlight possible. The sunniest real estate in my garden always goes to my dahlias.

The Internet advises that dahlia prefer morning sun rather than scorching hot afternoon sun (assuming you even have a space that allows you to choose morning or afternoon sun.)

The Pacific Northwest has a lot of cloudy days in the beginning and the end of the season, plus we generally don’t get a sustained amount of 90-degree or hotter days so I don’t worry about super-hot afternoon sun.

Dahlia varieties: Bracken Rose and Thomas Edison

I grow dahlias in two places: at my house, and at my aunt and uncle’s house. My house is a much smaller lot, so my house’s shadow dictates the sun exposure. (The front beds get mostly afternoon sun, the back beds get more morning sun.)

At my aunt and uncle’s house, however, my dahlias are basically growing in a field away from trees and structures. They get A LOT of sun all day long. 

The dahlias at my house grow wonderfully. 

But the dahlias at my aunt and uncle’s grow even better.

So if you live in the Pacific Northwest like I do and have milder summers, stick ‘em where they can sunbathe all day.

Fertilizing: Your Dahlias Are Hungry

I have a confession to make: I have never gotten a soil test. 

*Gasps in flower farmer* 

I know, I KNOW.

I always mean to… I know all the Instagram flower experts tell me I need to do it. 

A soil test has been on the to-do list for literally four years. I didn’t get to it this year, and I probably won’t get to it next year. 

And to be honest, even if I got one, I’d spend hours trying to figure out what it meant, and I’d probably stress out and overthink it, so I finally just took it off my to do list.

Instead, I fertilize my dahlias with all things I know they gobble up all season long.

Dahlias are Hungry Hungry Hippos.

Every year when I plant them, I put a little bone meal into the hole with the dahlia tuber. (Although, some people have complained that critters or pets have dug up their tubers trying to get to the bone meal, so just be aware of that possibility.) 

I’ve recently heard good things from people who plant with bone meal AND blood meal, so I intend on trying that this year as well.

Once in the ground, I then top off the bed with about 1 inch of high quality compost (I avoid compost with cow manure because of possible  weeds or a plant-scorching amount of nitrogen), and mix in Osmose granular fertilizer.

For years, that’s all I did. But I recently started experimenting with mid-season fertilizing. Early in the season, when the green growth starts poking through the dirt, like June, I used high-nitrogen liquid fish fertilizer to give the green growth a boost. Then in mid-July through September, I use a lower-nitrogen fertilizer.

I fertilize by doing a soil soak (meaning I mix the liquid fertilizer into a watering can, or hose attachment, as directed by the bottle) and water the liquid fertilizer/water mix at the base of the plants.

I typically intend to fertilize every other week, but it usually turns into once a month.

When I started doing that, my dahlias EXPLODED with blooms and they churned out an almost overwhelming number of flowers. 

It’s since led to the conclusion that my dahlias are like my youngest son when he was baby: When well-fed, they’re fat and happy.

Water: The thing that will ruin your dahlia season if you don’t preplan

A lot of people worry about overwatering their dahlias so they end up underwatering them.

In Seattle, even us long-time natives forget that every year we basically have little-to-no rain July through late September.

Dahlias NEED consistent watering in order to thrive.

And let me tell you, the BIGGEST lie I hear people tell themselves is that they like hand watering.

Yeah, everyone likes hand watering until: 

• You’re tired.
• It’s hot.
• You’re busy.
• You leave town on vacation.
• You literally forget because your adulting to do list is impossibly long anyway.

My biggest dahlia protip is to figure out an irrigation system for your garden and then put it on a timer. (If you know you don’t have the capacity for an undertaking like that, buy a cheap soaker hose and get an automatic timer.)

You will be happier and your dahlias will be happier. You don’t have to worry about what happens when you go out of town, and you don’t have to worry about forgetting to turn the water on or off.

If you know that an irrigation system won’t work for you and you intend on hand watering, you want to water deeply at least times a week during the summer — and even more on hot streaks.

I usually start watering regularly in June, once the rainy days get more and more rare.

Here’s how to tell if you’re watering enough: Stick your finger in the dirt a day or two after watering. If it’s bone dry, you need more water. If it’s soaking wet, wait a few more days before watering again. (Very scientific, I know.)

Last season, in early August, I noticed one of my dahlia beds looked stunted compared to its neighbors. It was on the same fertilizing schedule and there were not any extra obstacles impacting the amount of sun it received.

For WEEKS, I was confused. 

Finally, I realized there was a leak in the irrigation, which greatly affected the water pressure so the plants were getting about a third of the water that I thought.

 I fixed the leak, and two weeks later those dahlias had caught up to their neighbors.

In summary: Inconsistent watering doesn’t necessarily kill dahlias – but it gives you a mediocre season and you’ll probably hate your plants if you have to go out there daily during a heat wave to keep them from wilting.

So Before You Ask That Dahlia Facebook Group For Advice

Every dahlia season teaches me something new. Last year it was a leaky irrigation line and a rhododendron I forgot I owned. 

Six years in, I still don’t have it all figured out. But I’ve stopped pretending that I need the perfect Instagram growing conditions before I get started.

So if your dahlias are struggling, before you ask Instagram or that dahlia Facebook group (that’s more drama than helpful information anyway) for advice: check the sun, check the water and then check the food. 

Most of the time, it’s one of those three things. 

Your dahlias will do great. And if they don’t,  dont worry, I’ve been there too. So I’ll see you in the garden as I hold my coffee, stare at my dahlias as I wonder what went wrong this time.

West Seattle Flower Farm's Dahlia Sale

Every year, I have a dahlia tuber and cuttings sale. Usually, it's for local pick up only but sometimes in late April, I open up shipping. You can check out all of the varieties I sell here.

👉🏻 Shop dahlias

Quick Answers: Growing Dahlias Successfully

• How much sun do dahlias need?
  
  
• At least 6–8 hours of direct sun (more is usually better if you’re growing in the cloudy Pacific Northwest)
  
  
• How often should I water dahlias?
  
  
• Deep watering 2–3x per week in summer (more in heat), or consistent irrigation
  
  
• What’s the best fertilizer for dahlias?
  
  
• Balanced feeding works well:
  
  
• higher nitrogen early
  
  
• lower nitrogen for blooms later
  
  
• Why aren’t my dahlias blooming?
  
  
• Usually:
  
  
• not enough sun
  
  
• inconsistent watering
  
  
• lack of nutrients
  
  
• Do I need perfect soil to grow dahlias?
  
  
• No
  
  
• But adding compost + some fertilizer will noticeably improve results

Want more hard-earned gardening lessons (and fewer massacres)?

I share what’s working, what’s not, and the occasional very big flower-growing whoopsie like this one in my email newsletter.

If you want honest growing advice, seasonal reminders, and stories from my urban farm, you can join my email list here.

No spam or Instagram perfection. Just flowers, mistakes, and all the lessons they teach (and that I learned the hard way.)