How to Grow and Care for Blue Boy Dahlia

The Blue Boy dahlia is a sought-after variety, admired for its consistent blooms and classic form that enhances both gardens and floral arrangements. A point of interest is its name, as no truly blue dahlias exist. The “blue” in its name refers to the cool tones within its petals, which present as shades of lilac, lavender, or mauve, depending on light and soil conditions. This coloration makes it a versatile choice for gardeners.

Characteristics of the Blue Boy Dahlia

Blue Boy is classified as a Formal Decorative dahlia, a group known for its fully double flowerheads with broad, flat, or slightly curved petals. The blooms are substantial, reaching four to six inches in diameter. Its petals are arranged in a regular, pristine pattern, contributing to its formal and symmetrical appearance.

The plant has a full, bushy habit and reaches a mature height of approximately three to four feet. This stature makes it suitable for the middle or back of a border, where its lush, deep green foliage provides a rich backdrop for its flowers.

Planting and Growing Conditions

Plant dahlia tubers after all danger of spring frost has passed and the soil has warmed to at least 60°F. Blue Boy requires a location with full sun, meaning a minimum of six to eight hours of direct sunlight each day. Insufficient light can lead to weaker stems and fewer blooms.

The ideal soil for dahlias is fertile, well-draining, and has a slightly acidic pH. To prepare the planting area, amend the soil with several inches of compost or well-rotted manure. Dig a hole four to six inches deep and place the tuber horizontally with the visible “eye,” or sprout, pointing upward.

After positioning the tuber, cover it with soil, spacing plants one to two feet apart for adequate air circulation. Do not water the tuber immediately after planting. Watering should only commence once green shoots appear, which helps prevent the tuber from rotting before it sprouts.

Ongoing Care and Maintenance

Once your dahlia is established, consistent care will ensure it thrives. Watering should be deep and regular, two to three times per week, depending on your climate. This approach encourages the development of a strong, deep root system, which is more effective than shallow, frequent watering.

Fertilize with a formula that is low in nitrogen and higher in phosphorus and potassium, as high-nitrogen fertilizers promote foliage at the expense of flowers. Begin applying a liquid fertilizer about a month after planting, and continue to feed the plant every few weeks during its growing period.

Given its height and the weight of its blooms, providing support is necessary. Insert a sturdy stake into the ground near the tuber at planting time to avoid damaging the root system. As the plant grows, loosely tie the main stem to the stake. To encourage a bushier plant, “pinch” the central growing tip when the plant is about a foot tall. Deadheading, or removing spent flowers, also signals the plant to produce new blooms.

Overwintering Tubers

In climates where the ground freezes, dahlia tubers must be dug up and stored for the winter. The best time to do this is after the first hard frost has blackened the foliage, which signals the plant to enter dormancy. After the frost, cut the stalks down to a few inches above the ground.

Wait about a week after cutting back the foliage before carefully lifting the tuber clump from the ground with a garden fork. Gently wash away the excess soil and allow the clump to cure, or dry, for several days in a well-ventilated, frost-free location like a garage or shed. This drying period helps prevent rot during storage.

For storage, place the cured tubers in a cardboard box or crate and cover them with a loose medium like vermiculite, peat moss, or wood shavings. This material helps maintain humidity and keeps the tubers from shriveling. Store the box in a cool, dark place where temperatures remain between 40 and 50 degrees Fahrenheit. Check on the tubers periodically to remove any that show signs of rot.