Growing Dahlias

Dahlias are incredibly rewarding — their range of colors, forms, and textures makes them a favorite for home gardeners and flower growers alike. Below you'll find everything you need to grow healthy, productive plants from your tubers — whether you're just starting out or expanding your dahlia collection.

Quick Reference Tips

Plant tubers after the last frost when soil is at least 60°F (15.5°C)
Space 12–18 inches apart
Full sun: 6–8 hours daily
Stake when planting
Do not water until green shoots emerge
Cut blooms when 3/4 open for best vase life
In Zones 3–7, dig and store after first frost

When and How to Plant

We plant our dahlias once the danger of frost has passed and the soil has warmed. Here in Ontario, that usually means mid-to-late May, but always check your local frost dates.

To plant:

Choose a sunny, sheltered spot with well-draining soil
Lay the tuber horizontally, 4 to 6 inches deep, with the eye (or sprout) facing up
Backfill with soil but avoid compacting it
Don’t water at planting—wait until green growth appears

In colder zones (3–7), plant after your region’s last frost. In warmer zones, you may be able to plant earlier.

Choosing the Right Site

Dahlias need sun to thrive. Choose a spot with at least 6 to 8 hours of direct sunlight.

Soil must drain well. If your soil is clay-heavy, amend it with compost and sand. Raised beds work beautifully.

For containers, choose a large pot (at least 14 inches across) with drainage holes. We suggest 1 plant per pot for best bloom performance.

Supporting Your Plants

Most dahlias, especially those over 3 feet tall, need support. We use simple bamboo stakes, but tomato cages or flower netting can also work. Insert your supports at planting time to avoid damaging the tuber later.

As the plant grows, loosely tie the main stem to your stake using soft twine or reusable garden ties.

Watering and Feeding

Hold off on watering until shoots emerge. Overwatering early on can rot tubers. Once established, dahlias prefer deep watering once or twice a week, depending on rainfall and soil.

We feed our dahlias with a low-nitrogen fertilizer (like 5-10-10 or 10-20-20) every 3–4 weeks, starting once plants are about a foot tall. Too much nitrogen = lots of leaves, few flowers.

Pinching and Pruning

Pinch your dahlia when it reaches about 12 inches tall and has 4 sets of true leaves. Use clean pruners to snip the central stem just above a leaf set. This encourages branching, resulting in more blooms on longer, usable stems.

You can also remove side shoots later in the season to focus the plant’s energy on longer stems and better bloom size.

Blooming and Cutting Tips

Dahlias bloom about 8 to 10 weeks after planting. They love to be cut — the more you harvest, the more they bloom.

Cut blooms in early morning or evening when temperatures are cooler. Look for flowers that are about 3/4 open, as dahlias won’t continue to open after being cut.

Strip off lower leaves and place directly into cool water. Dahlias typically last 4–7 days in the vase, depending on the variety and stage of harvest.

End of Season Care

After the first frost blackens the foliage, it’s time to dig your tubers. Cut stems down to 4–6 inches, gently lift the clump with a fork or shovel, and shake off excess soil.

Let the tubers dry for a few days in a cool, dry place out of direct sunlight. Then label them while you still know who’s who.

How to Store Tubers Over Winter

Once tubers are dry, store them in vermiculite, peat moss, or wood shavings in a cardboard box or plastic bin with holes for ventilation. Ideal storage temps are 40–50°F (4–10°C).

We check ours monthly through the winter and remove any that show signs of rot or shriveling.

Come spring, divide large clumps if needed, and you’ll be ready to start the cycle again.

Final Thoughts

We hope this guide helps you feel confident and excited about growing dahlias. They are truly one of the most rewarding flowers you can grow. If you have any questions or want to share your blooms with us, we’d love to hear from you.

Happy planting,
Connie
Petrolia Bloom Co.