Can You Leave Dahlia Bulbs in the Ground Over Winter?

Dahlias are stunning summer bloomers that bring vibrant color to gardens from midsummer into fall. But when winter arrives, many gardeners face the question – should I dig up my dahlia bulbs or can I leave them in the ground?

The answer isn’t straightforward. While some climates allow leaving dahlias in place over winter, other regions can cause the bulbs to rot or freeze. Understanding your specific conditions is key to deciding if in-ground winter storage will work.

The Benefits of Leaving Dahlias in the Ground

Letting your dahlia bulbs remain in the soil all winter offers several potential perks:

• Less work – Avoiding the labor of digging up bulbs and storing them indoors is a major advantage

• Earlier blooms – Dahlias left in place may emerge and flower earlier in spring.

• Bigger plants – Without the disruption of digging, plants can grow larger and produce more flowers.

• No storage issues – You skip any risks of bulbs drying out or rotting in indoor storage.

For many gardeners, the workload reduction alone makes in-ground storage worth considering. But to understand if it’s feasible for your garden, you need to look at the downsides too.

The Risks of Overwintering Dahlias in the Soil

While leaving bulbs in the ground avoids storage problems, it brings its own set of risks:

• Frozen bulbs – If the ground freezes for an extended time, bulbs can freeze and die.

• Rot – Excessive winter moisture can cause bulbs to rot in the ground.

• Rodents/pests – Mice, voles or insects may eat unprotected bulbs over winter.

• No propagation – Without digging bulbs, you lose the chance to divide and propagate more plants.

• Early sprouting – Bulbs may send up growth too early and risk damage from late frosts.

In cold winter climates, these hazards often make in-ground storage unfeasible. But in warmer areas, the risks can be minimized.

Climates Where Leaving Dahlias in the Ground May Work

While specific microclimates matter, generally dahlias can remain in the ground over winter in:

• USDA zones 7-10 – Areas where ground rarely freezes for extended periods.

• Zone 6 – With very well-drained soil and protective mulch, zone 6 is possible in some cases.

• Zone 5 – Only gardens with exceptional drainage and winter insulation stand a chance.

• Sunny spots – Full sun locations have the best odds of success.

• Drier winters – Wet winter soils enhance rot potential.

• Sheltered gardens – Protection from wind and cold is ideal.

Coastal climates often provide the above conditions. And even in colder zones, microclimates may support overwintering. Evaluate your specific garden’s winter character to determine if leaving dahlias in the ground is feasible.

Prepping Dahlias for Overwintering In Place

To give in-ground dahlias their best shot at survival:

• Wait until frost blackens the foliage before cutting back the stalks. Don’t rush the process.

• Chop or mow stalks a few inches above soil level after frost to remove foliage.

• Consider Sanitation Remove any foliage showing signs of disease to prevent spread.

• Apply mulch – Cover bulbs with a deep 8-12 inch layer of straw, leaves, wood chips, or other organic material after a hard frost.

• Check drainage – Ensure beds drain well and don’t puddle. Improve drainage if needed before winter arrives.

• Add insulation – Place another layer such as burlap over the mulch for extra protection in colder climates.

• Use rodent deterrents – Blood meal, hot pepper wax, and metal mesh can help deter pests.

• Select hardy varieties – Some dahlia types, like dinnerplate dahlias, are less cold tolerant.

A bit of prep work in fall can mimic the insulation and protection bulbs would receive in storage. But even with the best preparations, some loss is still possible.

Overwintering Tips From Professional Growers

Looking to experts can provide more guidance on successfully overwintering dahlias in place. Here are tips from growers:

• “Wait as long as possible in fall before cutting back stalks. Let those first few frosts hit.”

• “Scatter a balanced fertilizer over the bed in fall to provide nutrients for next year’s growth.”

• “Cover with plastic sheeting under the mulch for added winter protection in cold climates.”

• “Grow dahlias in raised beds for better drainage over winter.”

• “Space bulbs farther apart to prevent crowding issues as bulbs multiply in future years.”

• “Flag plants in fall that you don’t want to keep so you can remove them in spring.”

• “In really cold zones, transplant bulbs into pots and store those in an unheated garage or shed.”

Professional wisdom can boost your success rate when leaving bulbs in the ground. Evaluate the options and decide what fits your conditions.

Spring Care for Overwintered Dahlias

Once spring arrives, overwintered dahlias need some TLC:

• Remove mulch gradually in early spring so bulbs aren’t shocked. Watch for emerging sprouts.

• Check for damage and prune out any dead stalks or insect-infested tubers.

• Divide crowded clumps – Bulbs multiply over seasons and may need division.

• Fertilize with a balanced fertilizer when growth resumes to nourish plants.

• Stake stems as needed and provide seasonal care. Watch for early sprouting.

• Hold off planting other plants immediately over the tubers in case you damage emerging growth.

• Scout for pests like slugs, snails, and earwigs that can attack new growth.

With attentive spring care, your overwintered dahlias will be off to a vigorous start.

Reasons Dahlias Don’t Survive Winter In the Ground

If you lose some or all of your overwintered dahlias, look at these potential causes:

• Excessively wet soils leading to rotting bulbs – improve drainage for next year

• Frozen ground – try mulching heavier or growing in a warmer microclimate

• Rodents or insects – deter pests with blood meal, hot pepper wax, traps, or digging bulbs

• Compacted soil preventing sprouting – cultivate beds to improve soil structure

• Fungal diseases like botrytis – remove infected plant material promptly

• Insufficient mulching – increase mulch depth and ensure full coverage

• Varieties not suited for overwintering – choose hardy dahlia types next season

By diagnosing what may have caused bulb loss, you can make adjustments to improve results going forward. Don’t get discouraged by some failed overwintering attempts – it takes trial and error to get conditions just right.

Should You Take the Risk of Leaving Dahlias in the Ground?

There’s no definitive answer on whether to overwinter dahlias in place. Here are key considerations as you decide:

• Leaving bulbs in the ground succeeds more often in warmer climates with good drainage. Evaluate your winter conditions realistically.

• Accept that you may lose some bulbs and plan for replanting needs in spring.

• Start with overwintering a test batch rather than your whole dahlia collection.

• Be prepared to return to digging and storing bulbs if failures occur multiple seasons in a row.

• Weigh workload now vs. potential disappointment later – there are merits to both options.

By growing in an appropriate climate, prepping beds diligently, and trialing the process cautiously, you can discover if in ground winter storage works for your garden. With extra care and prudent expectations, your dahlias may thrive when left to overwinter in place.

FAQ About Overwintering Dahlia Bulbs In the Ground

Here are answers to some common questions about overwintering dahlia tubers in the soil:

Can you leave dahlia bulbs in pots over winter?

Yes, bulbs in containers can be left in the pots over winter in zones 7+ provided they have excellent drainage. Move pots to a protected area and cover them.

Do you need to cut back dahlia stalks to overwinter in the ground?

Yes, wait until after frost blackens stalks and foliage, then cut back to a few inches above soil level. Removing stalk debris is important.

Is it better to leave dahlias in the ground or dig them up?

There’s no definitive “better” method. In ground can work well in warmer zones but has risks. It’s a personal choice based on your climate and preferences.

Can dahlias be left in the ground for years?

Dahlias can remain in the same garden spot for many years as long as they are healthy, multiply well, and the area doesn’t become overcrowded.

How deep should mulch be over dahlia bulbs left in the ground?

Apply 8-12 inches of an organic mulch like straw, leaves, or wood chips over the bed where bulbs remain in fall.

The option to forgo digging up dahlia bulbs for winter storage is enticing but comes with considerations. By selecting hardy varieties, prepping beds thoroughly, and adjusting practices as needed, you can discover if leaving your dahlias planted in the ground is a viable approach for getting a head start on glorious blooms the following summer.