How to Fertilize Dahlias

Dahlias bloom in many forms, both plain and fancy.

Dahlias bloom in many sizes, forms and colors, from little pompoms to giant "dinner plate" types that grow to a foot or more in diameter. Dahlias are heavy feeders, and monthly feeding encourages bigger blooms. Although they need regular fertilization, they don't like a lot of nitrogen, which causes excessive green growth at the expense of flowers and may cause weak stems as well. Compost and manure aren't essential to grow dahlias, but these amendments add nitrogen to the soil slowly and also help the soil hold moisture.

Things You'll Need

• Compost or well-rotted manure (optional)
• 5-10-15, 5-10-10 or other low-nitrogen fertilizer
• Shovel or cultivating tool

Instructions

Before Planting

1. Spread compost or manure evenly over the planting bed, if desired. To give the plants the full benefit of soil amendments, work them into the bed about a month before planting.

2. Spread 5-10-15 or 5-10-10 fertilizer on top of the manure at the rate of about 2 lbs. per 100 square feet.

3. Work the amendments into the soil with a shovel or cultivating tool. Work to a depth of 8 to 10 inches.

During the Growing Season

1. Fertilize monthly using the amount of fertilizer recommended on the product label. Carefully work the fertilizer into the top layer of soil, no more than in inch deep.

2. Water slowly, allowing the soil to absorb as much water as possible without running off.

3. Fertilize for the last time around Aug. 15.

Tips & Warnings

• Don't cultivate deeply around dahlias. They have shallow roots that are easily damaged.

References

• Ohio State University Extension; Growing Dahlias; Jack Kerrigan
• University of Minnesota Extension; Growing Dahlias; Paul E. Read
• Washington State University Extension; Dhalias; Donna Black