Verbena is one of those crops that has changed so dramatically over the years that we forget where the crop came from and what advances have been made. Breeding and improvements continue at almost every breeding company; and like most of our industry’s key crops, verbena has a bit of an identity crisis going on when it comes to what growers want and what consumers want.
We are cycling around again to a more grower-driven crop selection process. As a result, you are seeing new varieties with more compact habits and selection for early flowering. These two characteristics are not really beneficial for the homeowner. Compact plants are slower growing usually and more prone to powdery mildew, and early flowering is tightly linked to no repeat flowering. It’s a problem, and all growers should be watching their local university trials to see which plants are the top performers.
The biggest issue by far is powdery mildew and breeding for resistant forms. This is an extremely difficult process as every different region of the country has a different form of powdery mildew, and each form of powdery mildew needs a different type of resistance. It’s complicated. In general, the seed types are more compact and earlier flowering, but you pay for this with a much higher degree of powdery mildew and a very short shelf life at retail.
Growing Tips And Cultural Information For Verbena
Recommended pH: (5.8 to 6.2) Low pH and severe dry down can cause toxicity if supplemental iron has been applied.
EC (2:1 Extraction Method): 0.6 to 0.9
Fertilization Recommendations: 150 to 200 ppm
Production Temperatures: (Note: Lower temperatures can be used as a way to tone and slow growth; however, low temperatures also delay flowering, especially if under low light conditions.)
-Rooting Out: 65°F to 72°F/18°C to 22°C
-Growing On: 65°F to 72°F/18°C to 22°C
-Holding Temperatures: 50°F to 60°F/10°C to 16°C
Light Levels: High. Lower light levels increase stem stretch and reduce branching, as well as the number of flowering stem tips. Higher light levels always give a higher quality crop.
Water Requirements: Moderate to moist. Do not use lack of water to control growth as lower leaves drop when plants are wilted or severely stressed.
Planting and Timing Information: Early spring through fall finish.
-Finish time 4- to 5-inch/4 to 6 weeks
-Finish time: 4.5 inch/4 to 5 weeks
-Finish time 6 inch or gallon/5 to 7 weeks
-Finish time 8 inch/7 to 9 weeks
-Finish time 10- to 12-inch baskets or uprights/8 to 12 weeks
-One pinch at liner planting. Trim back as needed.
-Uniconazole spray to 5 to 10 ppm may be used to keep neighboring pots from growing into each other.
-Growth can be controlled using lower temperatures.
Pest And Disease Management: Powdery mildew can be a problem for verbena. Proper air circulation, humidity control and water management will aid in control and prevention. A routine, preventative spray program is encouraged.
For Growers Of Superbena And Tukana: Since this group of plants can be vigorous, you may want to order a few weeks later if you want to produce the plants in smaller containers. If you are using them in larger pots, like a gallon container, a pinch at transplant will help build a strong chassis for the plant and avoid plants growing together too much. A spray of Uniconazole at 2 to 5 ppm or repeated sprays with the PGR you are most familiar with (as per label instructions) can also be used to control growth. If growing plants for use in mixed containers, they are not so compact that they squeeze out the other plants in the container and will likely not need a pinch or PGR application) in most situations.
For Growers Of Superbena Royale: Since these plants are more compact, they make excellent 4.5-inch production items . However, realize that they still retain quite a bit of vigor and will naturally flower around week 11 to 15 depending on conditions, so order accordingly, and try not to order so early you need to heavily control growth.
Growing With High Light And Good Air Circulation
Regardless of which consumer you are trying to please, the grower or the home gardener, in all respects, the grower who uses high light in production and good air circulation is going to produce the best crops. All verbena need these two aspects to their production for the highest quality. Poor air circulation is an invitation to powdery mildew, which thrives on foliage left wet from irrigation in the evenings and poor air circulation. Verbena can also be toned by cool temperatures in production or moving the plants outside to finish, as long as all danger of frost has passed. Late frosts, even on low temperature-adapted crops, may result in flower delays.