Growing Dahlias

How to Grow Dahlias from Tubers

Dahlias are stunning, long-blooming flowers that produce from mid-summer to fall. Whether you’re a beginner or an experienced gardener, the tips below will guide you in adding vibrant colours and breathtaking blooms to your garden!

What is a Dahlia Tuber?

A dahlia tuber is the underground storage organ of a dahlia plant. It's a swollen, fleshy root that stores nutrients and energy for the plant, allowing it to grow and bloom. Dahlia tubers are planted in the soil, and from them, the plant produces stems, leaves, and flowers. Each tuber can grow into a full dahlia plant when properly planted and cared for. Depending on your growing zone, they are typically dug up in the fall and stored over winter in cooler climates, then replanted in the spring for new growth.

When to Plant Dahlias

Dahlia tubers should be planted after the danger of frost has passed and the soil has warmed to at least 15°C. In most regions, this is mid-to-late spring (around May for zones 5-6). If you want earlier blooms, you can pre-sprout or start tubers indoors a few weeks before planting them outside.

Where to Plant Dahlias

Dahlias thrive in:

• Full sun - At least 6-8 hours of direct sunlight per day.
• Well-drained soil - Avoid clay-heavy or soggy soil. Sandy loam is best.
• Good air circulation - Space plants 12-18 inches apart for better airflow and disease prevention.

How to Pre-Sprout Dahlia Tubers

Pre-sprouting helps tubers establish quicker and can give you earlier blooms.

Steps to Pre-Sprout Dahlias:

1. Choose a shallow tray or container with drainage holes.

2. Fill with slightly damp potting mix or peat moss (not too wet, or tubers may rot).

3. Place tubers horizontally with the “eye” facing up

4. Keep in a warm place (15-21°C) with indirect light.

5. Check for sprouts in 2-4 weeks. Once shoots appear, they’re ready for planting.

How to Plant Dahlia Tubers Directly in the Garden

If you prefer to plant tubers directly into the garden, follow these steps:

1. Wait until after the last frost and soil is (15°C).

2. Dig a hole 4-6 inches deep and place the tuber horizontally with the eye facing up.  We plant tubers with a tablespoon of Blood Meal in the bottom of every hole. We apply fertilizer throughout the season as needed. 

3. Do NOT water after planting - tubers can rot if the soil is too wet before sprouting.

4. Once shoots emerge (in about 2-4 weeks), start watering deeply once a week.

5. Stake tall varieties early to avoid damaging roots later.

How to Start Dahlia Tubers Indoors

Starting dahlias in pots indoors gives you a head start on the season.

Steps to Start Dahlias Indoors:

1. Choose a 1 gallon pot with drainage holes.

2. Use well-draining potting mix.

3. Plant tuber 2 inches deep with the eye facing up.

4. Keep in a warm, sunny location (or under grow lights).

5. Water sparingly until shoots appear, then increase watering.

6. Harden off plants before transplanting outdoors by gradually exposing them to outdoor conditions over a week.

How to Care for Dahlia Plants

• Watering – Deeply water 1-3 times per week (or as needed), allowing soil to dry slightly between waterings. 
• Fertilizing – The common advice for dahlias is to use a high-nitrogen fertilizer until mid-season, but to reduce nitrogen towards the end of the season.
• Staking – Tall varieties (3 feet or taller) need support. Use stakes, bailing twine or netting to prevent stems from breaking.
• Pinching – When your plant has 3-4 sets of leaves (8-12" tall), give them a hard pinch by cutting the stem. This encourages bushier growth, more blooms and increases overall stem length.
• Deadheading – Regularly remove spent flowers to encourage continuous blooming.

When to Harvest Dahlia Blooms

• Harvest when flowers are almost fully open – they don’t open much once after they've been harvested.
• Cut in the morning or evening for best vase life.
• Use sharp scissors or pruners and cut stems at an angle.
• Place immediately in fresh water and let them hydrate for a few hours before arranging.
• For the longest vase life (5-7 days), change water daily and trim stems every other day.

When to Dig Up Dahlia Tubers

Since dahlias are not winter-hardy in cold climates (zones 3-7), tubers must be dug up before freezing temperatures.

Steps for Digging Up Tubers:

1. Wait until the first frost blackens the foliage.

2. Cut back stems to 4-6 inches above the ground.

3. Carefully dig up tubers with a garden fork, avoiding damage.

4. Wash off excess soil and let tubers dry in a cool, airy place for 24-48 hours. Divide tubers if you wish to increase your dahlia stock. 

5. Store in a cool (4-10°C), place in peat moss, or vermiculite. We use vermiculite.

6. Check occasionally for rot or shriveling, adjusting storage conditions as needed.

If stored properly, tubers will be ready to plant again next spring!

Growing dahlias is rewarding and provides months of beautiful blooms. Whether you’re planting directly in the garden, starting indoors, or pre-sprouting, following these steps will help you enjoy a stunning dahlia display all season long! Let’s grow dahlias together!