How to Grow Dahlias in Arizona

Dahlias are one of the most spectacular flowers you can grow in the garden, but here in Arizona they can be a tricky flower to grow.Timing is everything with this flower. We like to think of dahlias as a Goldilocks flower:They dont like cold winter soil tempatures, but they also do not prefer the scorching summer heat (cant blame them).

In the low desert of Arizona, our goal is to take advantage of the short window between winter's coldest temperatures and the intense heat of summer. For us, that means planting dahlias Outside in late February for blooms in April, May, and early June.

In this article we are going to talk about when to start your dahlia plants, and best practices for growing them. 

When to Plant Dahlias in Arizona

Dahlias have a short season here in the low desert, so giving them the biggest head start is essential to for best blooms in your garden. We like to start dahlias indoors in January to transplant outside after your last frost. We are in zone 9b our typically last frost date is February 15th. 

Start indoors: January

Plant: Mid-Late February
Active Growth: March–April
Primary Bloom Season: April - Early June

Starting your Dahlia plants

Dahlias can be started in three different ways: from seed, cuttings, or tubers. Each method has its own advantages depending on what you want to grow.

Dahlias from Seed: Growing dahlias from seed is an inexpensive and fun way to grow lots of plants. Unlike tubers and cuttings, seedlings are genetically unique, so the flowers may not look exactly like the parent plant. This makes seeds especially exciting if you enjoy experimenting with new colors, shapes, and flower forms. They area easy to start from seed and are a great way to learn how to grow dahlias. 

Dahlias from Cuttings: Cuttings are taken from actively growing dahlia plants and rooted to create new plants. Because they are clones of the parent plant, they will produce the same variety and flower characteristics. Cuttings are a great option when you want a specific variety without starting with a large tuber. 

Dahlias from Tubers: Tubers are the most traditional way to grow dahlias. Each tuber contains the stored energy the plant needs to quickly establish itself, making this one of the easiest and fastest methods. Tubers produce a genetically identical plant to the parent, so you know exactly what color and flower form you're getting. They can also be dug and saved at the end of the season to grow again the following year.

What is our favoirte way to grow dahlias?

Cuttings!

Why We Grow Dahlias from Cuttings

We prefer growing many of our dahlias from rooted cuttings because they arrive as young plants that are already actively growing. Unlike a dormant tuber that first needs to sprout and establish roots, a rooted cutting has a head start on the growing season. Once planted, it can quickly establish itself and begin putting on new growth.

This head start is especially valuable in Arizona's short spring growing window, where we want our dahlias to grow and flower before the intense summer heat arrives. Starting with actively growing cuttings can help us achieve earlier blooms than we typically get from newly planted tubers, while still producing the exact dahlia variety we want.

Can you still start them from tubers? Absolutely! I would recommend starting them indoors 4-6 weeks before transplanting outside. Tubers can be large, so starting them in a 6" or 1 gallon nursery pot may be recommended. Do not over water tubers before they start to grow, as they are prone to rot if over watered. 

Choosing a Planting Location

We like to plant dahlias in the ground or in containers that receive 6-8+ hours of direct sunlight. Afternoon shade is always appreciated when temperatures soar about 90 degrees. 

Avoid locations surrounded by excessive reflected heat, such as against west-facing block walls, gravel landscapes, or other areas that become extremely hot in late spring. 

If you are growing them for the first time, consider growing them in a containers and moving them around as spring temperatures heat up. 

 Soil

Dahlias perform best in rich, fertile, well-draining soil.

Arizona's native soil can be heavy and alkaline, so improving the planting area before planting your dahlias can make a significant difference. We recomend planting your dahlias in good well draining soil, with plenty of organic matter. 

The most important thing is drainage. Dahlias can rot when they remain wet for extended periods. Planting them in containers will give them excelent drainage if you have heavy clay soil. Raised beds are also a great spot to plant your dahlias. 

Fertilizing Dahlias

Dahlias are vigorous growers and benefit from regular feeding throughout their relatively short Arizona growing season.

Start fertilizing once the plants are actively growing. We like to use a liquid fertilizer weekly as well as a granular fertilizer at time of planting. 

Use a balanced fertilizer such as Jack Classic 20-20-20 early in the season and transition toward a fertilizer designed to encourage flowering as buds begin developing.

Pinching Dahlias

For bushier plants and more flowers, pinch your dahlias when they are approximately 8–12 inches tall and have developed several sets of leaves.

Remove the growing tip just above a set of leaves.

It can feel counterproductive to cut a perfectly healthy young plant, but pinching encourages the plant to branch and produce additional flowering stems.

Supporting Your Plants

Many cut-flower dahlias can grow several feet tall and become top-heavy once they begin producing flowers.

Install stakes, netting, tomato cages, or another support system early in the season rather than waiting until the plants begin falling over.

Arizona spring winds can be surprisingly strong, making support especially important for tall varieties.

In containers we like to use stakes and tie the dahlias to them for a seamless support that is easier to hide. 

Dahlia Bloom Season in Arizona

When planted in late February, we typically begin seeing flowers in April.

The plants really come into their own during April and May, when temperatures are warm but haven't yet reached the extremes of summer.

Blooming can continue into early June, but performance begins declining as nighttime and daytime temperatures rise.

This is why planting early is so important.

If you wait until April to plant your tubers, you may end up with beautiful plants just as temperatures become too hot for good flower production.

Cutting Dahlia Flowers

Dahlias make exceptional cut flowers, and harvesting them regularly actually encourages the plants to continue producing.

Unlike some flowers, dahlias do not open significantly after being cut, so harvest flowers when they are nearly or completely open.

Cut stems deeply into the plant whenever possible. This encourages longer, stronger stems on future growth.

Harvest during the cooler parts of the day—preferably early in the morning—and immediately place the stems into clean water.

What Happens When Arizona Gets Hot?

This is where growing dahlias in Arizona differs dramatically from growing them in cooler climates.

Dahlias simply aren't designed for our extreme summer temperatures.

Once temperatures begin consistently climbing above 100°F, plants may:

• Slow or stop producing flowers
• Produce smaller or misshapen blooms
• Develop shorter stems
• Show leaf scorch
• Wilt during the afternoon
• Begin declining altogether

Rather than fighting the plant's natural response, we treat spring as our primary dahlia season.

Think of dahlias as a spring crop in the low desert, rather than a traditional summer flower.

Can You Grow Dahlias Again in Fall?

Potentially!

Arizona's long warm fall gives us another period of dahlia-friendly temperatures. However, timing a fall crop can be more challenging because plants must establish while temperatures are still extremely hot.

If you're experimenting with fall dahlias, afternoon shade and careful irrigation become especially important.

For the most reliable results, we recommend focusing on the late-February planting and spring bloom cycle first.

The Secret to Growing Dahlias in Arizona

Growing dahlias successfully in Arizona really comes down to timing.

Don't follow the traditional advice that treats dahlias as a summer flower.

Here in the low desert, we want to get them planted early enough that they can grow, flower, and put on their show before our extreme summer heat arrives.

Planting in late February gives us that perfect Goldilocks window—after the worst of winter's cold but before the worst of summer's heat.

Get the timing right, give them rich soil, consistent water, plenty of sunlight, and a little protection from our harshest afternoon sun, and you can enjoy an incredible flush of dahlias throughout April, May, and into early June.

Favorite varieties:

Karma Bi-color Bronze

Tall cut flower variety reaching 4-5' in height. Perfect addition to the back of the boarder garden. This variety is a deep coral to peach tone as it ages.

Miss Mandy:

Lighter in color than the Karma bi-color bronze, that makes the perfect pastel touch to the container garden. This variety reaches only 18-24" in height making it great for any small pot or container garden.