Dahlias In Denver: Your Complete High-Altitude Success Guide

ByRimon Chowdhury Updated on

Have you ever strolled through the Denver Botanic Gardens in late summer, seen those spectacular, dinner-plate-sized dahlia blooms, and thought, “There’s no way I could grow those in my own backyard”? That intense sun, the clay soil, the surprise spring snowstorms—it can feel like our Mile High climate is working against us.

I’m here to promise you that it’s not only possible, but deeply rewarding. Growing stunning dahlias in Denver is absolutely achievable for any gardener, and you don’t need a magic green thumb to do it. You just need the right local knowledge.

This comprehensive guide is your roadmap to success. We’ll walk through everything from choosing the perfect varieties for our climate to planting, watering, and the all-important step of saving your tubers for next year. Get ready to fill your garden with breathtaking color!

Why Dahlias are a Perfect Choice for Denver Gardens

It might seem counterintuitive, but dahlias and Denver are a fantastic match. Understanding the benefits of dahlias in Denver can inspire you to give them a try. They aren’t just pretty faces; they are resilient, productive, and perfectly suited to our growing season.

First, they are queens of the late-season garden. Just as some of your early summer flowers begin to fade, dahlias are just getting started, typically hitting their peak from August until our first hard frost. This extends your garden’s beauty well into the fall.

The sheer variety is another huge plus. From tiny, single-petal blooms perfect for pollinators to massive, show-stopping “dinnerplate” varieties, there’s a dahlia for every style and space. They provide an endless supply of cut flowers, allowing you to bring the beauty of your garden indoors all season long.

Finally, embracing sustainable dahlias in Denver is easy. Because you dig up and store the tubers each fall, you’re not buying new plants every year. It’s a wonderful, eco-friendly cycle that saves money and reduces waste. These flowers are a gift that truly keeps on giving.

Getting Started: Choosing the Right Dahlia Varieties

Walking into a nursery or browsing an online catalog can be overwhelming. With thousands of dahlia varieties, where do you even begin? The key is to choose varieties that work well with Denver’s unique conditions.

Consider Our Shorter Season

While we have intense sun, our frost-free growing season can be shorter than in other parts of the country. For guaranteed success, especially for beginners, look for varieties with a shorter “days to maturity” number. Smaller-flowering types like ball, pompon, and collarette dahlias often bloom earlier and more prolifically than the giant dinnerplate varieties.

Don’t worry—you can still grow the big ones! You just need to be patient, as they may not start blooming until late August or even September.

Where to Buy Your Tubers

You have a few great options for sourcing dahlia tubers:

  • Local Garden Centers: Places like Tagawa Gardens or Echter’s will carry tubers in the spring that are known to perform well in our area. This is a great way to support local businesses.
  • Online Specialists: Websites for dahlia farms offer an incredible selection. Just be sure to order early (in winter) as popular varieties sell out fast!
  • Local Flower Clubs: The Colorado Dahlia Society is a fantastic resource and often holds tuber sales in the spring. This is a great way to get locally-acclimated stock and expert advice.
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The Ultimate Dahlias in Denver Care Guide: Planting and Growing

Here it is—your complete roadmap for how to dahlias in Denver. Follow these steps, and you’ll be well on your way to a garden full of incredible blooms. This is a complete dahlias in denver care guide designed for our unique climate.

When to Plant Your Tubers

This is the most critical piece of advice for Denver gardeners: be patient! Our last frost date can be unpredictable. The golden rule here is to plant your dahlia tubers around Mother’s Day, or once the threat of a hard freeze has passed and the soil has warmed to about 60°F.

Planting too early risks rotting the tubers in cold, wet soil. It’s always better to wait a week or two than to plant too soon.

Perfecting Your Soil and Location

Dahlias have two non-negotiable demands: full sun and well-draining soil.

Find a spot in your yard that gets at least 6-8 hours of direct sunlight per day. Morning sun is especially important.

Most of us in the Denver area are blessed with heavy clay soil. To make it dahlia-friendly, you’ll need to amend it. Work a generous amount of compost or other organic matter into the top 8-12 inches of your soil. This improves drainage and provides essential nutrients.

Planting Your Tubers: A Step-by-Step Guide

Ready to get your hands dirty? Don’t worry—this part is simple!

  1. Dig a hole about 4-6 inches deep.
  2. If you’re growing a tall variety (over 3 feet), now is the best time to put your support stake in the ground, right next to where the tuber will go. Adding it later can damage the tuber clump.
  3. Lay the tuber horizontally in the hole, with the “eye” (the little growth nub where the stalk will emerge) pointing up. If you can’t find the eye, don’t sweat it—it will find its way up!
  4. Cover the tuber with soil, filling the hole completely.
  5. Do not water your tuber after planting. Seriously! Wait until you see the first green sprout emerge from the soil. Watering before this can easily cause the tuber to rot.

Watering Wisely in Our Dry Climate

Once your dahlia has sprouted and is actively growing, it will need consistent moisture. In Denver’s dry air, this is key. The goal is deep, infrequent watering rather than a light daily sprinkle.

Check the soil a few inches down. If it’s dry, it’s time to water. Give the plant a long, deep soak at its base, allowing the water to penetrate far into the root zone. A layer of mulch (like straw or shredded leaves) can do wonders for retaining soil moisture and keeping the roots cool.

Overcoming Common Problems with Dahlias in Denver

Every gardener faces challenges, but knowing what to look for is half the battle. This section addresses the most common problems with dahlias in denver and how to handle them using eco-friendly methods.

Pest Patrol: What to Watch For

Our dry climate can be a haven for certain pests. The most common culprits on dahlias are spider mites and earwigs.

  • Spider Mites: These tiny pests thrive in hot, dry conditions. You’ll notice fine webbing on the underside of leaves. A strong blast of water from the hose can dislodge them. For more serious infestations, insecticidal soap is an effective, eco-friendly option.
  • Earwigs: These critters love to munch on dahlia petals at night, leaving ragged edges. A simple trap can be made by rolling up damp newspaper and placing it near the plants. In the morning, shake the earwigs out into a bucket of soapy water.

Disease Prevention: Powdery Mildew

Powdery mildew, a white, dusty-looking fungus on leaves, can appear during humid spells or when nights are cool. The best defense is good airflow. Don’t overcrowd your plants. If you see it, you can treat it with a simple spray of one part milk to nine parts water. It’s one of the best dahlias in denver best practices to keep your plants healthy.

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The Big Dig: How to Overwinter Dahlia Tubers in Colorado

This is the step that turns you into a true dahlia devotee. To grow dahlias as perennials in Denver, you must dig up the tubers and store them for the winter. Our ground freezes too hard for them to survive.

Timing is Everything: When to Lift Your Tubers

Wait until after the first hard frost has blackened the foliage. This signals the tuber that it’s time to go dormant for the winter. Cut the stalk down to about 4-6 inches.

Cleaning and Curing for Storage

Carefully use a garden fork or shovel to lift the entire tuber clump from the ground, being careful not to break the delicate necks. Gently brush or wash off the excess soil and let the clumps air dry for a day or two in a shady, frost-free place like a garage. You want the skin to be dry to the touch, but the tuber should still feel firm.

Storage Solutions for a Long Winter

The goal is to keep the tubers cool, dark, and with just enough humidity to prevent them from shriveling. A cardboard box or plastic bin with ventilation holes works great. Pack the tubers in a medium like vermiculite, peat moss, or wood shavings. Store the box in a cool, dark place that stays between 40-50°F all winter—an unheated basement or insulated garage is often perfect.

Frequently Asked Questions About Dahlias in Denver

Can I just leave my dahlia tubers in the ground over winter in Denver?

Unfortunately, no. The ground freezes solid in our Zone 5b/6a climate, which will kill the tubers. Digging them up each fall is essential for growing dahlias year after year.

What are the best dahlia varieties for Denver’s shorter growing season?

While most varieties will work, beginners often have great luck with faster-blooming types. Look for smaller decorative, ball, or pompon varieties. ‘Cafe au Lait’ is a famous dinnerplate that does surprisingly well here, but it blooms very late in the season.

Why are my dahlias all leaves and no flowers?

This is a classic sign of too much nitrogen. When you fertilize, use a “bloom booster” formula that is low in nitrogen (the first number) and high in phosphorus and potassium (the second and third numbers). The other common cause is not enough direct sunlight.

Your Denver Dahlia Journey Begins Now

Growing dahlias in Denver isn’t a secret reserved for master gardeners. It’s a joyful process of connecting with the seasons and creating astonishing beauty right in your own yard. You now have all the dahlias in denver tips you need to succeed.

From amending our clay soil to giving them a sunny spot, and from watering deeply to tucking them in for the winter, you are fully equipped. Embrace the challenge, enjoy the process, and prepare for a wave of compliments from your neighbors.

Go forth and grow some joy!

Rimon Chowdhury
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