Grow Dahlias
HOW TO GROW DAHLIAS
Tips to help your dahlias thrive from tuber to bloom.The key to successful dahlias is warm soil. Plant your tubers after the last frost when the soil is at least 60ºF—usually around the same time you would plant tomatoes. Some gardeners start tubers early indoors in containers and transplant them once the soil warms. If you use this method, use soil without added fertilizer or compost.
Dahlias prefer at least 8 hours of direct sunlight a day. In hot climates, morning sun with afternoon shade works best. We recommend planting tuber in the ground and don't advise planting in pots, containers, or plastic bags.
- Soil Requirements: Dahlias thrive in warm, well-drained soil. Test your soil for any nutrient deficiencies and amend as needed. For heavy, compacted soil, till and add compost, or loosen the soil as best you can.
Plant tubers horizontally, eyes facing up, 4-6" deep, and 18-24" apart. For mass production on a large scale, we make trenches 20" apart and plant tubers every 12". Don't mulch or fertilize until sprouts appear.
Start watering your dahlias once sprouts appear above the soil. Sprinklers or
drip irrigation work best for larger plantings. Frequency and duration: In hot summer months, watering 2-3 times per week for
30-60 minutes per session is typically sufficient. Adjust based on your soil and
weather. If hand watering small gardens, it is better to do less frequent but slower and deeper watering than frequent shallow
watering. Water early in the morning so leaves dry during the day, reducing the
risk of fungal diseases. How often to water depends on:
- Location + Climate: Hot, dry areas need more frequent watering.
- Soil Type: Sandy soil drains quickly and may need more water; clay soil retains moisture longer.
- Temperature: Higher temperatures increase water needs.
Use a low-nitrogen fertilizer when plants reach 6" tall, then monthly until frost. High nitrogen produces lots of leaves but few blooms.
Mulch around dahlias with straw or wood chips to suppress weeds. Avoid use of herbicides near dahlias and control weeds by hoeing, mechanical cultivation or hand weeding.
Pinch the center shoot above the third set of leaves when plants are 8–12” tall to encourage longer, stronger stems and bushier growth.
Staking supports better growth of the plant. Insert stakes when planting or wait until plants are waist-high to avoid root damage.
Cut flowers in the morning when buds aren’t too tight. Use clean, sharp pruners and place stems in water immediately. Change the water daily for longer-lasting blooms. Remove old blooms to encourage new flowers — the more you cut, the more they bloom!
After the first hard frost, cut foliage to 4–6” (to use the stalk as a handle for the clumps). Leave the tubers in the ground for a week for the sprouts/eyes to develop on the tubers. Tubers dug too early are still “green” and will not store, while leaving them in the ground will allow for their skin to harden as it cures, like a potato. If you haven’t experienced a frost by mid-November it’s safe to dig the tubers at that time. Gently dig the tubers about 8” to 10” from the stem, shake off the excess soil carefully and wash off any soil. Allow them to air dry in an area protected from rain and frost for a few days. This air drying toughens the skin of the tuber for winter storage. Be sure to clean up the old foliage from the garden.
Store tubers in a packing material such as slightly dampened peat moss or vermiculite in a paper bag in the basement. Use enough peat moss or vermiculite so the tubers aren’t touching each other. Store in a cool, dry, dark area (temperatures 40-50°F). If you have a lot of tubers to store, we like to use the lawn bags you can buy at the hardware store. Never store the tubers in plastic bags or plastic containers as they require some air flow to avoid rot. Check your tubers once a month throughout the winter months. If you see evidence of rot, they are too wet. If they are shriveled, they are too dry. If you find a rotten tuber remove it immediately so it doesn’t contaminate other tubers. If the tubers are shriveled, mist the peat moss or vermiculite lightly with water. If you have more than one variety, we suggest labeling each tuber. You can write directly on the tuber with permanent marker or use flagging tape if you have a whole bag of one variety.
Dividing your dahlia tubers can be done in the fall or spring. Using a sharp knife, separate healthy tubers from the parent clump. Each tuber must have at least one “eye” or a piece of the crown attached or it will not develop into a blooming plant. You’ll find the eyes at the base of the stem and look like little pink bumps, note that not all individual tubers will have an eye. As long as you have a piece of the stem you’ll most likely have an eye that develops. If the neck of the tuber is broken, you will not have a viable tuber. Think about it like the body of the tuber isn’t connected to the head if the neck is broken, so will not have the brain to tell it to grow. Allow any cut tubers to dry for 24 hours before storing or planting. If you divide in the spring, move the tubers to a warm area for a week to allow the eyes to sprout so they’ll be easier to see.
If you’d like to dive deeper into growing dahlias, we encourage you to connect with your local American Dahlia Society chapter or a nearby gardening or horticulture club—they’re wonderful resources for region-specific advice. Here on our Central Ohio farm, we make decisions based on regular lab analysis of our soil, water, and plant material, which means our methods are tailored to our location and commercial scale. Because every garden is unique, what works for us may not be the best fit for you, so local experts will be the best guides for your specific growing conditions.
Keeping Your Plants Healthy
A healthy garden starts with pest and disease prevention. Insects like aphids and thrips can spread viruses, so regular pest control is essential in helping to prevent problems before they arise.
Many symptoms of disease can also mimic signs of environmental distress: too much or too little water; poor drainage; poor nutrition; or not enough sun can all result in mottled leaves, yellow spots, yellow veining, stunted plants, and twisted foliage.
If you are experiencing any of the issues listed above with your plants, we recommend testing your soil and/or water to determine what conditions you're working with.
You can also try treating with either an insecticide or fungicide to rule out problems caused by pests or fungus. If the new growth on your plants looks healthy, continue with regular treatments as needed.
If You Find a Problem
If you've tested and treated your soil and plants, and your plant is still showing signs of disease, your next steps will depend on what's right for you and your growing practices. The only way to determine whether or not your plant has a disease is to have it examined by a lab, which may not be practical for everyone.
Since we are growing on a commercial scale, we are testing our soil and water regularly, and we send any plants that look symptomatic of disease to a lab to be tested. Over the years, we've had tubers that look like they have crown gall come back with a negative test result, meaning that even a plant showing symptoms of gall tested negative for the disease (see more below).
If Problems Continue
Even with a positive diagnosis, the advice is the same: remove the affected plants and their tubers to eliminate the risk of spreading any disease, and dispose of them in the garbage rather than the compost.
If you can, rotate where you grow your dahlias every few years to prevent bacteria buildup. Be sure to sanitize your tools to avoid spreading bacteria from plant to plant.
Because we are selling our tubers, we cull anything from our plant and tuber stock that looks symptomatic of disease, and each tuber goes through multiple checks between digging time and being packed for an order. Feel free to reach out with any questions or concerns along the way—we are here to help you grow happy, healthy dahlias and tubers.
Oregon State University Lab Results
