How To Grow Dahlias

10 Key Tips to Growing Dahlias Well

Dahlias are vibrant, versatile and rewarding flowers that can enhance any gardeners season. They are not foolproof however. I’ve listed 10 key tips that will help you grow your best dahlias yet!

1. Choose the Right Location

Select a sunny spot in your garden where dahlias can receive at least 6 to 8 hours of direct sunlight each day. Planting in shadier spots will yield you less flowers and make your plants more prone to Powdery Mildew! Ensure the soil is well-draining to prevent bulb rot. Take care to protect your dahlias from rabbits, deer, groundhogs and other wildlife.

2. Prepare the Soil

Dahlias thrive in rich, loamy soil. Test your soil’s pH; ideally, it should be between 6.0 and 7.0. Amend the soil with compost or well-rotted manure to improve its structure and nutrient content. A soil test is your best bet to identify exactly whats missing or abundant in your soil. Too much of one nutrient or mineral could alter your plants ability to take up another nutrient. Home tests are not recommended. Send your sample to a reputable lab for the best results!

3. Select Your Dahlias

There are various dahlia types, including decorative, cactus, pompon, dinnerplate, novelty, ball and waterlily to name a few. Purchase healthy tubers from a reputable source. Choose local or well known flower farms where quality and your satisfaction matter. Some dahlias are better as garden varieties, some better as cut flower varieties. The dahlias you choose should match your intent for growing them. Will they add to the beauty of an existing outdoor garden space? Or will you grow them strictly for bringing the beauty indoors. Your options are endless!

4. Planting Tubers

  • Timing: Plant dahlias in the spring after the last frost and your soil warms to 55°, usually in late April to early May in most regions.

  • Depth: Dig holes approximately 6 to 8 inches deep. Place the tubers (with the “eyes” facing up) in the holes and cover them with loose, enriched soil.

5. Watering

Water the planted tubers once they start to sprout. Newly planted tubers do not have feeder roots to uptake water and are prone to rot if the soil remains wet for extended periods after planting. Pre-sprouting your tubers a month ahead of time can help your plants grow these feeder roots and foliage, diminishing the chances of rot after planting. Once the plants are actively putting on green growth and healthy, keep the soil consistently moist but not soggy. Reduce watering in late fall when the plants begin to harden off for digging and winter storage.

6. Fertilizing

Apply a balanced fertilizer every 4-6 weeks during the growing season. A fertilizer with a higher phosphorus content will promote strong root growth and vibrant blooms. I recommend a fish emulsion such as Neptune’s Harvest Fish and Seaweed Blend, Hi-Brix Molasses as a foliar feed and adding compost every spring to feed your soil. A soil test will be your best tactic to amending your soil for planting. It will tell you what is lacking or abundant in your soil and how to amend.

7. Supporting the Plants

As the dahlias grow taller, they may need support. Use stakes, netting or cages to help keep the plants upright, especially for larger varieties that can become top-heavy. Install stakes at the time you plant your tubers to avoid damage to tubers once the plant is in larger and in active growth.

8. Pest and Disease Management

Regularly inspect your dahlias for aphids, slugs, earwigs and other pests. Use natural remedies to manage infestations. Spraying insecticides, (even if they are approved for organic gardening) can harm the balance and diversity of insects that keep other pests in check. Avoid use chemical fertilizers or sprays. Practice good garden hygiene by removing any diseased plant material and sanitizing floral snips between cuts.

9. Deadheading

Encourage blooming by deadheading spent flowers. This practice helps the plant to focus energy on producing new blooms. If you are growing for cut flowers, cut your flowers deep on their stem to promote longer, vase-worthy stems on the reblooms. Do NOT deadhead if you intend to collect its seeds.

10. Preparing for Winter

After your first hard frost, the foliage will turn black from the freeze. Within a few weeks) cut back the foliage to about 4-6 inches above soil level and dig your tubers. Carefully lift the tubers from the ground using a pitchfork for least amount of tuber disturbance. I clean my tuber clumps of soil and divide before winter storage. Some people store the whole clumps, dirt and all, and divide in the spring. It can be easier to divide in the spring if the eyes are not visible in the fall. I dry my tubers for2- 3 days, label the variety directly on the tuber with a garden marker, then saran wrap each tuber. The wrapped tubers are then placed in dry fine vermiculite in plastic shoe totes at 40° for the rest of winter. I check on them monthly to ensure there is no rot or spoilage.