Grow Time (From Rooted Cutting)
A verbena in a quart container with one pinch per plant (ppp) takes six to seven weeks of grow time. In a gallon container with two ppp, grow time is estimated at 10 to 11 weeks. Verbenas in 12-inch baskets with four to five ppp take 11 to12 weeks of grow time.
Apply 200 to 250 parts per million (ppm) nitrogen (N), using Cal-Mag fertilizers (i.e. 13-2-13,15-5-15,14-4-14, etc.) for more compact growth and neutral pH. Use high ammonium and phosphorus containing fertilizers (i.e.20-10-20, 15-15-15, etc.) for softer growth and to lower pH. Electrical conductivity (E.C.) should be between 2.0 to 2.5 mS/cm (SME), with a pH between 5.8 and 6.2. Avoid letting plants get “bone dry.”
High quality media with good porosity is critical to avoid root rot. Peat-based mixes, like Fafard 2 Mix or 1P Mix, or bark-based mixes, like Fafard 4P Mix or 3B Mix work well.
Verbenas grow best with temperatures between 70 to 75°F during the day and 60 to 65°F at night. When needed, verbenas can tolerate chillier temperatures.
As a general rule, there is a one-pinch minimum, which should occur in propagation. Most Lanai Upright types and trailing verbenas in quart containers usually only require this one pinch. Trailing verbena growing in gallons, baskets, and larger containers should ideally receive a second pinch. The second pinch can occur in propagation if rooting in a large jumbo plug or after transplant of the rooted cutting.
Plant Growth Regulators
Spray with 2500 to 3500 ppm B-Nine plant growth regulator or 5 to 15 ppm Sumagic plant growth regulator to keep plants in check. The key to achieving well-rounded and compact plants without stretching is a drench with Bonzi plant growth regulator at 2 to 3 ppm three to four weeks before finishing. Some growers use 350 to 500 ppm of Florel plant growth regulator early on to improve branching or to substitute for a second pinch.
Insects and Diseases
Thrips and leafminers, as well as thrips-vectored impatiens necrotic spot virus (INSV), can cause problems. Flagship insecticide, Avid miticide/insecticide and Citation insecticide are the proven standards for a successful leafminer control program. Flagship and Avid are also effective in a thrips management program. Many verbena have powdery mildew tolerance, but plants should be scouted regularly under high relative humidity and when there are large fluxuations in day/night temperatures. Palladium, Heritage and Daconil ULTREX insecticides are excellent products to include in a powdery mildew management program.