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Herbs, Flowers & Specialty CropsDahlias Planting Calendar
Dahlias are tender tubers that frost will kill. Timing is a matter of waiting for settled, warm weather, planting with a stake, and then digging and storing tubers after the first hard freeze.
Key points
- Plant tubers after frost danger passes and the soil has warmed.
- Set tubers eye up about six inches deep and add a stake at planting.
- Pinch for branching and cut flowers often.
- Lift after a hard freeze, dry and store in a cool, dry, ventilated place.
When should you plant dahlia tubers?
Oregon State University Extension advises planting after frost risk has passed and the soil has warmed, which it says usually falls between April 15 and June 1 in Oregon, depending on location, and suggests Mother's Day or the time you set out tomatoes as a rule of thumb.
Those dates are for Oregon. In other regions, use your own average last frost from the National Weather Service or your county extension office, and wait for the soil to warm. Planting into cold, wet soil risks rot.
If you want earlier bloom, you can pot tubers indoors a few weeks before the last frost and move them out when frost danger has passed. Keep pots in a bright spot and avoid overwatering.
How deep and how far apart should you plant them?
The Oregon State guide places tubers eye side up, about six inches deep, and two to three feet apart. It suggests covering with two to three inches of soil at first and gradually backfilling as shoots emerge.
Spacing gives plants room to fill out and air to move through, which reduces disease. Check the variety description, since tall and compact types differ.
If tubers are shriveled or soft when you unpack them, ask the seller about them. Firm tubers with an eye produce the best plants.
Why stake dahlias at planting time?
Place a sturdy stake beside each hole at planting, on the side where the eye will emerge, so you do not damage the tuber later. Tie stems to the stake as they grow, using soft ties.
Large flowering types get heavy and topple in wind and rain. Setting supports early is far easier than adding them after plants are tall.
- Set the stake before covering the tuber.
- Use soft ties.
- Raise ties as plants grow.
- Check supports before storms.
What soil and site do dahlias need?
Dahlias need full sun and a well-drained site. The Oregon State source recommends compost or well-rotted manure or other organic matter in the planting area and a soil test to find nutrient gaps, with a preferred pH of about 6. Use your test results and local recommendations, since nutrient management rules vary by state.
Water deeply during dry spells but avoid soggy soil. Do not water heavily until shoots emerge, since tubers can rot before they sprout.
- Choose full sun.
- Add organic matter and test the soil.
- Do not water heavily before shoots emerge.
- Keep plants evenly moist once growing.
How do you pinch and cut dahlias?
Pinch the main stem above a few sets of leaves when plants are about a foot tall to encourage branching and more flowers. Cut flowers regularly, since removing blooms prompts more.
Cut stems in the cool of the morning, and place them in water at once. Remove spent flowers promptly.
Disbudding, or removing side buds, gives larger flowers on fewer stems. Whether you do this depends on the type of flower you want.
How do you lift and store dahlia tubers?
After a hard freeze, Oregon State advises cutting stalks to about six inches and digging the tubers. Wash off soil, let them dry for about a day in a sheltered space and avoid bare concrete, which wicks moisture. Separate clumps so each tuber has an eye, and store in newspaper-lined boxes layered in vermiculite or sawdust.
In mild regions, tubers may overwinter in the ground with mulch. Ask your extension office what works locally, and check stored tubers during winter for rot or shriveling.
Label tubers by variety before storage, because they look alike when dry. Check them monthly through winter.
- Cut stalks to about six inches after a hard freeze.
- Dry tubers for about a day in a sheltered spot.
- Divide clumps so each tuber has an eye.
- Store in a cool, dry, ventilated place and check monthly.
What problems should you watch for?
Slugs on young shoots, aphids, spider mites and fungal problems are common. Spacing, clean-up and morning watering reduce them. Ask your extension office to identify problems before treating.
If you consider a pesticide, the label is the law, pre-harvest intervals apply and applicator licensing varies by state. Dahlias attract pollinators, so protect them.
Rotate planting sites when you can, and clean tools between plants to reduce the spread of problems.
- Space plants for air movement.
- Water at the base.
- Check for slugs on young shoots.
- Ask extension to identify problems before treating.
Timing at a glance
| Item | Window | Caveat |
|---|---|---|
| Dahlia tubers in Oregon, as reported by Oregon State University Extension | Plant after frost risk passes and soil warms, usually between April 15 and June 1 depending on location | Source guidance for Oregon; other regions should use their own last frost date. |
Sources and further reading
Last reviewed: November 2026. Educational information, ranges only. Confirm timing with your county extension office.