Dahlia Growing Guide

Planting
Plant your tubers after all danger of frost. The soil temperature should be at least 60 degrees Fahrenheit.
Plant tubers 6” deep in a sunny location at least 12” apart. You may add a ½ to full tablespoon of a balanced granular fertilizer. I like to use Espoma Bio-Tone Starter Plus. Do not water tubers until a sprout is visible above the soil. Excess water can cause tubers to rot.
 
Throughout the Season
Pinching – You can pinch the top of the dahlia plant off to create more blooms. Pinch the dahlia plant when it is 8-10” tall.

Support – Nearly all the dahlias we sell should be supported. You can use a simple garden stake of wood or metal and tie the main stem of the dahlia to the stake. I like to put the stakes in early 6-12” from the tuber. A low tie about 12” up will be enough for 3’ varieties. A second tie will be needed for taller varieties.

Fertilizer – A balanced fertilizer as a liquid or foliar feed during the season will encourage blooms and help create tubers that store better over winter.
Water – Dahlias require regular watering. Give them a thorough soaking at one to two times per week when it does not rain.

Pests – One big win is dahlias are deer resistant! Dahlias do have many common pests. The are enjoyed by many insects including Japanese beetles, thrips, aphids, and cucumber beetles. However, I find if they are planted in a mixed flower bed and regularly watered and fertilized the plants you will enjoy plenty of blooms without any extra pest management.
 
Cutting Flowers
Use sharp snips to cut long stems. Cuting below the next nodes/buds on the plant will result in the plant producing longer stems over time. 
Like all cut flowers, strip the leaves that will be below the water. Place your dahlias in water within 10 minutes of cutting. Replace the water in your vase every 2-3 days.
Dahlia vase life varies greatly by variety. Most of the varieties I grow have a life of 5-7 days.
 
Tuber Storage
If you live in zone 7 or lower you will need to dig your dahlia tuber clumps in the fall and store them over winter. You can wait until the plants have died due to frost / freeze or cut them back near the end of your growing season.
Ideal storage conditions are 45 degrees Fahrenheit and 70% humidity. But most will store fine in a basement or other cool place.

If only storing a few, I recommend storing the whole clump and leaving some dirt on the tuber clump. You can then decide in the spring if you wish to divide the clump.
There is no requirement to divide tubers but you may wish to make more by dividing up the clump. Dahlias have eyes. The concept is similar to eyes on a potato but the eye on a dahlia is only near the stem of the plant. As your tuber clump gets warmer in spring it becomes easier to see the eye or new growth emerging. You may divide your clump into 2 or 4 pieces if it’s easier than dividing individual tubers.

Tuber size has no relation to the health of a tuber or the ability to grow a robust plant. Some varieties commonly produce smaller tubers.
 
Final Thoughts
Remember that many tubers don’t cost more than a potted petunia from a nursery. If the idea of digging and storing tubers is overwhelming, you can choose to treat dahlias as an annual. 

Additional resources:
Floret Dahlia Library – A list of many popular dahlia varieties along with their classifications and features
Longfield Gardens  - Common Pests and Diseases 
Dahlias – Digging, Dividing, and Diseases – Webinar by University of Illinois Extension Horticulture