How To Prepare Your Soil For Planting Dahlias

Some plants can handle any growing condition, but Dahlias really need the right conditions to produce the outstanding blooms they’re known for. With a well-prepared soil bed, your Dahlias will create beautiful growth very quickly. Follow these steps for success! 

• Dahlias prefer rich and well-drained soil. Loose, nutrient-rich soil will feed tubers and encourage strong root growth. Soil must be well-draining, because Dahlias like plenty of water, but soggy soil will cause tubers to rot. Dahlias are great for sandy, loamy, or acidic soil.
• If you’re starting with clay soil, dry soil, or compacted soil, it will be important to make sure that you properly prepare your planting area in order to see growth and blooms. If you have challenging soil, or if you live in an area with heavy rainfall, you may want to consider growing Dahlias in berms or raised beds to create optimal conditions.
• Enrich your soil with compost work in a good organic fertilizer before planting. Look for a fertilizer that’s low in nitrogen, to encourage blooms and not too much leafy growth. Organic material will feed your Dahlias, and help the soil to retain moisture as needed for the plants.

When To Plant Dahlias

Plant dahlias when the threat of frost has passed. If that’s not until late May or early June where you live, you can start dahlias indoors, 4-6 weeks before your last frost date. In containers, lay tubers on their sides with the stems up and cover with 2 inches of soil. Wait until you see new growth breaking through to water. Then, they can be transplanted outside when it’s warm enough.

How To Plant Dahlia Tubers

1. First, prepare your soil as outlined above. Don’t skip this step! Preparation is the key to success.

2. Dig holes for planting. 

• Spacing may vary based on your varieties however dahlias grow well with 14  - 18” between each tuber. The largest varieties of Dinner Plate Dahlias will do best with wider spacing to allow for foliage and flowers to grow. 
• Holes should be relatively shallow and wide enough for tubers to be spread out, like fingers. Tubers for large varieties like Dinner Plate should be about 6 inches deep, while smaller varieties can be about 4 inches deep. 

3. Plant tubers.

• Place tubers so that the crown (where the tubers connect) is a few inches below the surface of the soil. If there are buds, or ‘eyes’ on the tubers, place those facing up - that’s where stems will grow. 
• Gently backfill soil around the tubers so that they are completely covered by a few inches of soil. There is typically some stem material at the top of the tubers, and if so, the stem can be at or just below the surface of the soil. 

4. Staking

• For Dahlias with large flowers, and generally those growing 3 feet or taller, we recommend staking when you plant. 

5. Watering

• Once planted, give tubers a thorough soak to remove any air pockets and encourage root growth. Until they sprout, Dahlia tubers don’t need much water. 

Growing & Care For Dahlias Throughout The Season

Pinching

Dahlias require the one-time task of pinching off the tops once the tubers have sprouted and formed leaves. Wait until three sets of leaves appear, and then top the stem just above the highest set of leaves. This pruning tactic encourages the plant to grow more branches, thus creating more blooms.

Growth Habit

Dahlias grow quickly, producing bush plants and flowering in the first season. 

Watering Dahlias

Water regularly, and try to keep your foliage dry. Avoid overwatering, as soggy soil can lead to rotting tubers. We recommend less frequent, but deep watering. 

It’s best to let the soil dry out between watering, as soggy soil can easily cause tubers to rot (remember - that’s why good soil preparation is so important). Water thoroughly about once per week until Dahlias sprout. 

Once you see top growth, water as needed when soil has dried out. As the plant starts to grow and temperatures increase with the start of summer, you may need to water more often. If you’re experiencing regular rainfall, you may not need to water if your soil is not drying out. 

When watering, keep water near the soil surface, and avoid getting leaves wet to help prevent diseases. Water slowly and deeply to give the soil a thorough soak.

Fertilizing Dahlias

Look for a fertilizer that is high in potassium (K) and phosphorus (P) but low in nitrogen (N). Potassium and Phosporous encourage bud growth and flowering. Check your NPK (Nitrogen-Phosporous-Potassium) levels in your fertilizer before you purchase. Expert growers recommend formulas such as 5-10-10, 10-20-20, or even 0-0-10. Fertilizing dahlias just a couple of times can make a big difference to the flower yield. Add when planting, and once a month at most before flowering begins.