Dahlia tubers start arriving in the mail as early as February but most areas have frost risks into late spring. So what should you do with dahlia tubers in the weeks or months before you can plant them outside? Proper care in spring will give your dahlias the best start.
Storing Tubers Until Planting
If tubers arrive more than 4-6 weeks before your outdoor planting date you’ll need to store them properly
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Keep tubers in a cool, dark location like a basement, garage, or cellar. Temperatures should stay above freezing but as cool as possible.
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Leave tubers in their shipping bags but open or cut the bags for airflow. Avoid excess moisture buildup.
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Check tubers occasionally for sprouting. Some varieties start sprouting earlier than others.
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Once sprouts are 1-2 inches long, move tubers to warmth and light to strengthen sprouts.
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Discard any tubers that are mushy or rotting to prevent disease spread.
With cool storage, most dahlia tubers can be kept dormant for 2-3 months from arrival until planting. Just monitor for premature sprouting.
Potting Up Tubers
An alternative to cool storage is to pot up the tubers in containers:
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Use pots 4-6 inches wide. Terra cotta pots work well to moderate moisture and promote airflow.
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Use a well-draining potting mix, not dense garden soil. A blend with compost, perlite, and vermiculite is ideal.
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Plant tubers horizontally, 3-4 inches deep, with the eye or sprout end facing up. Cover completely.
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Water sparingly at first, just to settle soil. Allow the potting mix to dry out slightly between waterings.
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Place potted tubers in a warm area above 70°F with at least 8 hours of light. This encourages sprout development.
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Fertilize lightly with a balanced liquid fertilizer once sprouts emerge.
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Transition to full sun 1-2 weeks before planting outdoors.
Follow these tips and potted dahlia tubers will grow strong root systems and foliage ready for transplanting into the garden.
When to Plant Dahlia Tubers Outside
Dahlias require consistently warm soil temperatures to thrive. Most varieties grow best with:
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Minimum soil temperature of 60°F at 4 inch depth
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Nighttime temperatures reliably above 50°F
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No frost in the forecast
Across most of the U.S., these conditions are reached between:
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Zones 8-10: February to March
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Zones 6-7: April
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Zones 5-4: Mid to late May
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Zones 3-1: Early to mid June
Track soil temperatures in your area and plant dahlias 1-2 weeks after soils have warmed sufficiently.
How to Plant Dahlias Outside
When the time comes to move your sprouted tubers or potted plants into the garden:
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Select a site with full sun – at least 8 hours of direct light daily.
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Prepare soil well by mixing in compost, aged manure, and organic granular fertilizer.
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Work soil to a crumbly texture. Dahlias need good drainage.
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Dig holes 6 inches deep and 18-24 inches apart.
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Place sprouted tubers horizontally, 4-6 inches deep. Cover with soil.
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For potted tubers, plant the entire pot contents to avoid disturbing roots.
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Water thoroughly after planting and as needed to establish plants.
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Stake taller varieties to support heavy blooms.
Follow these spring care tips, and your treasured dahlia tubers will reward you with vigorous growth and spectacular late summer flowers.
##What to Do If Planting Gets Delayed
Weather or life events may prevent planting dahlias on schedule. Here are some options if planting gets pushed back:
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Keep sprouted tubers in pots and move to partial shade. Limit water to reduce growth.
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Plant in containers outdoors in a sheltered area, then transplant into garden later.
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Check tubers for rotting and discard affected ones to prevent spread.
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Allow sprouts and stems to dry and detach from the tuber. Re-store dormant tubers.
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Keep un-sprouted tubers dormant in cool storage for up to 10-12 weeks total.
While not ideal, dahlias are forgiving if planting is delayed a few weeks. Just provide the best care possible in the interim.
Avoiding Common Problems
With proper spring care, you can avoid several issues:
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Rotting tubers – Caused by excess moisture in storage or at planting. Discard affected tubers immediately.
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Weak sprouts – Due to insufficient light and warmth after sprouting. Move to bright location.
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Leggy growth – From too much warmth before planting. Reduce temperatures or light duration.
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Poor transplant survival – Due to planting too early while soil is cold. Wait until soils warm sufficiently.
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Flowering delays – From inadequate sunlight or overfeeding nitrogen. Improve light exposure and reduce fertilizer.
Key Tips for Dahlia Tubers in Spring
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Store dormant tubers in cool, dark conditions until sprouting begins.
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Pot up sprouted tubers in well-draining mix; grow on in warm area with adequate light.
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Plant outdoors only once nighttime temperatures stay above 50°F and soil warms to 60°F.
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Prevent rotting, weak growth, legginess, and other issues with proper care.
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Be prepared to adjust timing if planting gets delayed by weather or other factors.
Treating your tubers correctly in spring will give your dahlias the healthiest start and lead to thriving, floriferous plants all season long.
Caring for Dahlias in Pots
I find dahlias don’t need any special treatment. I put them in pots at the end of winter and keep them in the greenhouse until there is a chance of frost. Around April, I move them outside into pretty pots for the summer. Depending on the variety, they begin flowering June/July.
Dahlias in the ground
In order to keep dahlias flowering for longer, you have to keep dead-heading and picking them. I like to cut a few to show off around the house and give them to Lenny the tortoise as afternoon snacks. If you pick the plant often, it will keep giving you bright, healthy flowers all summer long, sometimes until late October and, if it’s been a really mild fall, November.
I leave the tubers in the ground all winter after the plants drop their blooms and start to die. The Dahlia bushes in the ground are safe in beds close to the house, so I leave the leaves to wilt and die where they are and let them overwinter that way. The bush will then provide cover and protection for the tuber and hibernating wildlife. I wont cut back until Spring to prepare for the growing season.
Mulching with woodchip further helps to retain moisture and feed and protect the tubers in the ground. I add a fresh layer to my beds every Spring.
In my experience, Dahlias benefit greatly from being staked. Since their flower heads tend to be heavy, stake the plant’s main stems to keep them straight and make the stems look their best.
Planting dahlias in pots
Dividing Dahlias! ✂️ // Garden Answer
FAQ
How to prepare dahlia tubers for spring?
How do you wake up dahlia tubers?
Should I soak dahlia tubers before planting?
What happens if you don’t divide dahlia tubers?
How do you plant dahlia tubers?
There are many different ways to plant dahlia tubers. You can plant the tubers directly into the ground, or into pots. If planting into the ground you can grow them in rows, like we do at our flower farm, or plant them in a sunny spot in your garden.
Do dahlia tubers dry out?
In our damp climate, dahlia tubers take a long time to dry out, so when separating dahlia tubers in spring, they have had a chance to dry out for months in our garage. Sometimes dividing dahlia tubers in the spring takes more muscle power. If the dahlias are in a large clump, dividing can be tricky.
When should I Divide dahlia tubers?
During spring, before you plant the overwintered root mass, is when to divide dahlia tubers. If you divide when you pull the roots for overwintering, you may find they are not viable in spring, so wait a bit before splitting dahlia tubers. This is because each tuber must have an eye or growth bud that is viable.
How do you care for dahlia tubers?
Care of tubers starts with proper treatment during the growing season. While most dahlias start producing tubers in the spring, the roots do not mature until late in the growing season. Before digging, go through the garden and throw away any weak stock.