Dahlia Planting & Care Guide

Dahlias are one of the most rewarding flowers you can grow. With a little care and patience, a single tuber can produce dozens of blooms from midsummer until the first frost.

This guide shares a simple overview of dahlia growing practices that work well in colder climates, along with tips we’ve learned while growing dahlias in Alberta.

Every garden is a little different, so think of this guide as a helpful starting point rather than a strict rulebook.

When to Plant Dahlias

Dahlias are frost-sensitive plants and should only be planted after the risk of frost has passed.

For colder climates:

Wait until soil temperatures reach 13–15 °C (55–60 °F)
In many Canadian climates this is late May to early June
Planting into cold soil can cause tubers to rot

Once the soil warms, dahlias grow quickly and vigorously.

Choosing a Planting Location

Dahlias thrive in warm, sunny locations. Choose a site with:

6–8 hours of direct sunlight each day
Well-drained soil
Good air circulation

Avoid planting in areas that remain wet or shaded for long periods.

Preparing the Soil

Healthy soil leads to stronger plants and better blooms. Dahlias prefer:

loose, fertile soil
good drainage
moderate fertility

If you have heavy clay soil, mixing in organic matter can help improve structure and drainage. Gardeners often use:

compost
aged manure
peat moss or coarse sand

How to Plant Dahlia Tubers

Dig a hole 4–6 inches (10–15 cm) deep
Lay the tuber horizontally with the eye facing upward
Cover gently with soil
Space plants 12–24 inches (30–60 cm) apart depending on the variety

Gardeners with smaller growing spaces can still have success planting dahlias as close as 6 inches apart, particularly when growing for cut flowers.

If planting closely, it helps to be mindful of plant height so taller varieties do not shade shorter ones. The expected height for each variety is listed in the product details on every Baby Bird Blooms product page.

Installing stakes or other supports at planting time can prevent accidental root and tuber damage later in the season.

What to Expect After Planting

After planting, dahlia tubers may take 2–8 weeks to emerge depending on soil temperature and weather conditions.

In cooler climates, early growth may appear slow while the tuber focuses on establishing roots underground.

During this time, it is completely normal to see no visible growth above the soil. Once the soil warms and the plant begins actively growing, dahlias often grow quickly and can gain several inches in height in a short period.

Patience early in the season is key.

Watering

Newly planted tubers should not be watered immediately unless the soil is extremely dry. Excess moisture before sprouts appear can cause tubers to rot. Once shoots begin to emerge:

Water deeply 1–2 times per week
Increase watering during hot weather
Ensure soil drains well

Container-grown dahlias may require more frequent watering.

Supporting Your Plants

Many dahlia varieties grow quite tall and benefit from support to keep stems upright throughout the season.

Common support options include:

bamboo stakes
tomato cages
metal garden stakes

For larger garden plantings or rows, many flower farmers use T-posts with horizontal gardening netting. Plants grow naturally through the netting as they mature, which helps keep stems upright and prevents wind damage.

Installing supports early makes plant care much easier later in the season.

Disease & Virus Prevention in Dahlias

There is no cure for common dahlia viruses (such as Dahlia Mosaic Virus) or bacterial galls (crown gall and leafy gall), so prevention is the best protection for your garden.

Start with healthy tubers from local, reputable sources and inspect new plants carefully before planting.

Always use sharp, clean tools when cutting, pinching, deadheading, and harvesting dahlia stems/flowers and when digging or dividing tubers.

Use sharp pruning shears, floral snips, or a pruning knife
Clean and disinfect between plants to prevent the spread of viruses and disease
- always clean tools first, wipe off sap, dirt, and other debris with a damp cloth or paper towel
- disinfect tools between every plant or cut (not just at the end of the day)
- effective disinfectants include:
  - a 10% bleach solution (a 1:9 ratio of 1 part household chlorine bleach to 9 parts water). Soak tools for at least 30-60 seconds, or up to 30 minutes for heavy use. Rinse tools thoroughly with clean water afterward. Make fresh after 24hr, as potency begins to drop the longer it sits. Considered a broad-spectrum disinfectant, but corrosive to metal over repeated use.
  - 70% Ethanol (or Isopropyl Alcohol). Wipe blades thoroughly, dip briefly, or spray - immediate effect, no rinsing afterwards required. While less corrosive and evaporates cleanly, it does evaporate quickly and needs to be reapplied often (i.e., after every cut, not just between plants).
  - Virkon S (2% solution, per label). Mix and soak/dip (or use wipes version); follow label for contact time. Considered a broad-spectrum disinfectant that is also safer on tools and skin, however it is expensive and not as widely available in-stores.

Check plants regularly for unusual leaf patterns, distorted growth, or lumps at the base of the plant. If you notice signs of disease, remove the entire plant and dispose of it in the trash (do not compost). Managing pests like aphids and thrips, watering at the base of the plant, and giving dahlias plenty of space for airflow can also help reduce disease risk.

Increasing Bloom Production

A few simple techniques can greatly increase the number of flowers your plants produce.

Pinching

When plants reach 10–12 inches tall, pinch out the central growing tip just above a leaf node. This encourages:

branching
stronger plants
significantly more blooms.

Deadheading

Removing spent flowers encourages the plant to continue producing new buds throughout the season.

Cutting Flowers

Harvesting blooms often also encourages more flowers to form. When cutting, try to cut stems deeply into the plant, which helps encourage longer stems and stronger branching.

Fertilizing

Dahlias appreciate steady feeding throughout the entire growing season (approximately every 3-4 weeks).

Start with a fertilizer that is heavier on nitrogen at the beginning of the season and then by mid-season switching to a fertilizer with less nitrogen and higher levels of phosphorus and potassium to support strong stems and a constant flush of flowers

Both organic and conventional fertilizers can work well depending on your gardening style.

Pre-Sprouting Tubers (recommended but optional)

While pre-sprouting is completely optional, dahlias need at least 120 days of active growth to produce fully developed, mature tubers suitable for winter storage and next year's growth. Pre-sprouting is also a great way to enjoy blooms for longer, especially when growing dahlias in climates with a shorter growing season.

Tubers can be started in:

small pots with potting mix
reusable containers
trays
zip-lock bags with lightly damp material

Keep tubers in a warm, bright location indoors and maintain light moisture — never saturated soil.

If tubers are started indoors, it is important to gradually acclimate young shoots to outdoor conditions before planting outside.

Growing Dahlias in Containers

Dahlias grow very well in containers when given adequate space and consistent watering.

A 12-to-16-inch container is roughly equivalent to a 7-to-10-gallon pot, which works well for many varieties. Shorter or compact varieties can often be grown successfully in 5-gallon containers. Grow bags are also a great option and provide excellent drainage.

Helpful container guidelines:

choose pots that are taller rather than wider
ensure excellent drainage
plant one tuber per container

Because containers dry out faster than garden beds, potted dahlias often require more frequent watering and feeding during the growing season.

Container growing is a great option for gardeners with patios, balconies, or limited garden space.

Common Beginner Mistakes

Many early challenges with dahlias can be avoided with a few simple tips.

Planting too early ➜ Cold soil can cause tubers to rot before growth begins.
Overwatering early in the season ➜ Tubers should remain relatively dry until sprouts appear.
Not providing support ➜ Many dahlias grow tall and benefit from staking or netting.
Too much nitrogen fertilizer ➜ This can produce large leafy plants with fewer flowers.
Expecting immediate growth ➜ Dahlia tubers may take several weeks to emerge, especially in cooler soils.
Forgetting to deadhead ➜ Regular deadheading encourages plants to continue producing blooms throughout the season.

End of Season Care (Cold Climates)

After the first frost blackens the foliage:

Cut stems down to 4–6 inches above the soil.
Carefully dig up the tuber clump.
Allow the clump to dry for several days before storage.

Tubers can be divided in fall after digging and drying or divided in spring before planting.

Overwintering tubers can take a bit of practice, especially in colder climates. There are many different storage methods used by growers, and success can vary depending on temperature and humidity conditions. Gardeners often experiment with different approaches to find what works best in their environment.

The note above is only a very basic overview of storage, and many additional resources are available for gardeners who want to explore tuber storage methods in more detail.

A Note from Baby Bird Blooms

Baby Bird Blooms is a small and growing urban flower farm currently located in Calgary, Alberta. The information in this guide reflects the methods and lessons we’ve learned growing dahlias in our northern climate.

Gardening is rarely perfect — every season brings its own successes, surprises, and challenges. We hope this guide helps you grow beautiful flowers and feel confident experimenting in your own garden.

Thank you for supporting our farm and being part of the journey.

Happy growing!