March 2013 Culture

Perennial Solutions: Phlox subulata Early Spring Series By Paul Pilon

Creeping phlox is a widely grown perennial groundcover mostly recognized by the beautiful masses of color it produces in the early spring. It’s hard to beat the stunning display of color as the evergreen carpet wakes up after a long winters rest. Most of the cultivars in production today were also being grown for the last couple of decades as there has been little work to bring improved genetics to the market. However, Bartels Stek (www.bartelsstek.nl) recently introduced the Early Spring collection offering growers earlier bloom times with an excellent growing habit.

The Early Spring series consists of six cultivars ‘Early Spring Blue’, ‘Early Spring Dark Pink’, Early Spring Lavender’, ‘Early Spring Light Pink’, ‘Early Spring Purple’ and ‘Early Spring White’. These cultivars produce impressive displays of color a full two weeks earlier than other Phlox subulata cultivars on the market.

The compact mounds of color reach 4 to 6 inches tall and 12 to 14 inches wide at maturity. The soft, needle-like evergreen foliage is durable and drought resistant once they are established in the landscape. Phlox subulata Early Spring varieties produce an abundance of 3/4-inch star-shaped blooms, which completely cover the entire plant, forming a carpet of color in the early spring. They typically bloom from mid spring to early summer.

Phlox subulata performs well in sunny locations throughout USDA Hardiness Zones 2 to 9. Creeping phlox are commonly used as an attractive groundcover, in bank plantings or as an accent plant in rock gardens. Creeping phlox is suitable for container production and provides loads of flower power in retail displays. In the spring, Phlox subulata provides one of the most striking flower displays which few perennials can rival.

Propagation

The Early Spring series is vegetatively propagated from tip cuttings. For the fullest finished containers, it is best to begin propagation in the late spring (April/May) the year before the containers are to be sold to allow plenty of time for bulking.

Moisten the rooting medium in the liner trays before sticking the unrooted cuttings (URCs). It is not necessary to treat them with rooting compounds prior to sticking. Most propagators stick two cuttings per cell to improve fullness of the liner and performance in the final container. Place the cuttings under a low misting regime for about the first seven to 10 days of propagation.

The misting can gradually be reduced as the cuttings develop new roots. Begin feeding with 100-ppm nitrogen from a water-soluble fertilizer at each irrigation once roots are present. With soil temperatures ranging from 68 to 74° F, the liners take approximately four to five weeks from sticking to become fully rooted and ready for transplanting.

Production

The Early Spring series is suitable for production in small container sizes. Many growers produce Phlox subulata in mum pans or azalea pots which are shallow and wide allowing better drainage than many standard sized containers. When possible, use large liner sizes containing more than one cutting to improve bulking and final plant quality. When planting into large container sizes, it is recommended to plant at least two liner cells per container to properly fill out the pot. For spring blooming, it is best to plant phlox in the late summer.

Creeping phlox prefers to be grown in very porous media (excellent drainage). When transplanting, the growing medium in the pot should be even with the top of the plug. During the bulking phase, it is often beneficial to soft pinch the terminal shoots a couple of times to promote lateral branching.

The Early Spring series should be grown under ‘slightly below average’ watering regimes — keep them slightly moist, but not wet during production. They perform best at light to moderate fertility levels (75 to 12 ppm continuous feed or 150 to 200 ppm as needed) and with slightly acidic pH (5.8 to 6.2). Several growers incorporate low rates of controlled-release fertilizers into the growing mix before planting to effectively provide nutrients to containerized Phlox subulata.

With its slow and prostrate growing habit, it is usually not necessary to control plant height. Usually growers are more concerned with obtaining more growth and bulking rather than trying to reduce it. However, there may be times when some growth regulation is necessary. If height control is required, the plants can be toned using spray applications of daminozide (B-Nine, Dazide) at 2,500 ppm tank-mixed with chlormequat chloride (Cycocel, Citadel) at 1,000 ppm. Under most circumstances, one or two applications of plant growth regulators applied seven days apart should provide adequate height control or toning.

Insects and Diseases

Phlox subulata are susceptible to several insect pests including aphids, leafminers, slugs, spider mites and whiteflies, but rarely do any of these pests become problematic. Creeping phlox are susceptible to numerous diseases including Botrytis, Colletotrichum, downy mildew, Fusarium, Phytopthora, Rhizoctonia and Thielaviopsis. Of these pathogens, Colletotrichum and powdery mildew are the most prevalent. Although the Early Spring collection has increased disease resistance, they still are susceptible to these diseases under certain circumstances. Growers should utilize routine scouting programs to detect the presence of insects and diseases early and to determine if and when control strategies are necessary.

Temperature and Scheduling

Phlox subulata Early Spring series are most commonly grown and marketed in the early spring. To produce the fullest containers with the most bloom, it is very important to bulk creeping phlox in the final container prior to overwintering. The amount of time necessary for bulking varies widely by the size of the container they are grown in.
Provide a minimum of four weeks for 4-inch pots and up to 12 weeks for 1-gallon containers. Using multiple liners in large containers will greatly reduce the amount of time necessary for bulking. Allow at least four weeks from the final pinch until the plants are overwintered.

Flowering occurs sporadically when the plants do not receive a cold treatment. Therefore, provide a minimum of eight weeks of vernalization with temperatures between 35 to 44° F for the best, most uniform flowering. Flower buds are usually visible by the end of the cold period or shortly after they are exposed to warm growing temperatures. Phlox subulata are day-neutral plants and can be grown under any day length after they have been vernalized. Creeping phlox can be forced into flower using a wide range of temperatures. Because they bloom so quickly in the spring, many growers prefer to grow them cool; they will flower in approximately three to four weeks when they are grown at 60° F.

Availability

Unrooted cuttings of Phlox subulata Early Spring series are available from Fides Oro (www.fides-oro.com) through numerous plant brokers. Rooted liners can be acquired from Skagit Gardens Inc. (www.skagitgardens.com) and other reputable propagators.