June 2013 Culture

Crop Culture Report: Lavender ‘Sweet Romance’

Lavender has such a strong link in our culture to fragrance and beauty, but making the crossover from long-term to short-term crop has not been easy. ‘Sweet Romance’ from Proven Winners was released to fill the gap of easy-to-produce lavender for traditional annual growers. ‘Sweet Romance’ (Lavandula angustifolia) has deep-blue flowers, requires minimal vernalization, and has a great compact growth and flowering habit, as well as an extended season of flower. Shorter flower stalks mean more room on carts, and the fragrance is outstanding. Keys to success for growers are: manage watering to avoid too much water, the highest light levels, and good air circulation (adequate spacing) in the greenhouse.

Variety Information

Lavender is Mediterranean by nature, so it prefers low humidity, good air flow and cool night temperatures. So growers need to take this into account and space the plants accordingly and order art the correct times of year. Any grower who has experience with lavandula is simply going to find ‘Sweet Romance’ an easier crop to grow. If you have not had experience with growing lavender before, here are a few key things to be thinking about: Use a well-drained potting mix; avoid heavy water-holding mixes. Water in the transplanted liners with a broad spectrum fungicide drench. ‘Sweet Romance’ will still benefit from vernalization; it just needs a lot less. So pay close attention to the vernalization guidelines listed below. To make your life even easier, order your liners in fall and let nature do the work for you. Late summer and fall gives the liners time to bulk up, and you can keep ‘Sweet Romance’ in a minimally heated greenhouse (above 35° F) through the winter. In spring, bring them into a warmer house to grow out, or force them using the lighting regime described below. Last of all, watch your watering and keep these plants on the dry side. Do not fertilize with a constant feed 200 or 300 ppm bedding plant solution — it is WAY too much feed. ‘Sweet Romance’ prefers to be grown using a 50- to 75-ppm concentration.

‘Sweet Romance’ is a simple, value-added crop to produce as long as you follow simple guidelines and avoid doing too much. What everyone wants right? For finishing and retail displays, follow the same basic requirements ­— don’t crowd plants, give them full sun, and do not overwater. Having lavender in bloom in spring while the customers are buying is a big advance in this genus. Start small if you are not familiar with the crop, but take advantage of a fragrant perennial that can help build your spring sales! You can also grow bareroot materials (where available) that have been pre-vernalized.

Cultural/Growing Information

Optimal pH: Between 5.8 and 6.2

Optimal EC: (Using 2:1 extraction method) Between 0.25 and 0.6 (or 1.25 and 2.0 using pour through).

Fertilization recommendations: ‘Sweet Romance’ is a light feeder, only needing 50 to 75 ppm if constant feed, or alternating 100 to 150 ppm with clear water irrigation. Lavandula, like many perennials, do not need high rates of fertilizer. Use a balanced fertilizer with no more than 25 to 30 percent ammonium-based nitrogen. Reduce ammonium levels (in favor of nitrate nitrogen) if you are starting to get too much stretch. Check your water quality with a trusted lab and use fertilizers based on your water quality. Micronutrients should be applied if they are not part of your regular fertilizer.

Growing temperatures: For active growth, 65 to 68° F. Plants can be grown cooler but it extends finish time. A negative DIF to finish the crop by running days 55° F and nights 62 to 65° F can also help to keep plants compact. This will improve overall crop quality.

Light levels: Always high, (more than 5,000 foot-candles) to promote compactness and to accelerate their natural branching capabilities. Lavandula do best in full sun inside the greenhouse and outdoors.

Vernalization: We have produced very nice 41/2-inch plants with no vernalization, just a cool greenhouse after liners have rooted. While vernalization is not required for flowering it is always beneficial; 40° F for at least six weeks (but you can keep them cold longer, up to 10 weeks) will increase the number of flowers and the uniformity of bloom.

Photoperiod: ‘Sweet Romance’ is a long day flowering plant, so you can bring plants into flower earlier in spring with a few simple adjustments in the way of lighting. Start with a larger plant, not a recently planted liner but larger plant material consisting of about 40 leaves on each plant. If the plant has had a vernalization period, you will find it responds better to photoperiodic control.Sixteen hours of daylength extension lighting or a four-hour night interruption (in either case at least 10 foot-candles of light minimum) should continue until there are visible flower buds.

Water requirements: Average, but, if in doubt don’t water, and allow plants to dry slightly (do not dry to wilting stage). Especially under cold low light conditions, be very careful of overwatering. Begin allowing the media to dry between irrigation’s once the roots have formed through the new mix. It is important not to overwater the plants at all stages of production. Avoid overhead watering late in the day or when air circulation is limited.

Planting and timing: Most flower by week 9 or 10, so plan accordingly.
Finish time, 4- to 5-inch:  eight to 10 weeks
Finish time, 6-inch to 1-gallon: 10 to 12 weeks
Finish time, 8-inch: 12 to 16 weeks

Hardiness: Winter hardiness to USDA Zone 5, summer hardiness is most affected by night temperature and humidity.

Pinching and growth regulators: Growth regulators for ‘Sweet Romance’ should not be necessary and will affect flower stalk length, so use care in timing. If you feel PGRs are needed for toning due to low light production conditions, sprays of uniconazole at 4 to 5 ppm can be used or sprays of daminozide at 2,500 ppm or paclobutrazol at 25 to 30 ppm.

Pest and disease management: As with all crops, begin each season with fresh, sterile growing medium and start with a clean, disinfected greenhouse. Disinfectants such as bleach, Greenshield and ZeroTol are all fine. A preventative drench at planting with broad-spectrum fungicide is a great idea.

Insects are not usually a problem, but plants can be affected by aphids or whitefly. Try a preventative drench with Marathon 60WP one to two weeks after transplanting. Rhizoctonia especially in cases of over watering can be controlled with most commercial fungicides like Medallion 50W, Heritage, Contrast 70WSP or Terrachlor 75WP.  

The diseases most likely to infect them include Botrytis, Phytophthora, Pythium, Rhizoctonia, Septoria and Xanthomonas. The most common disease is Phytophthora; symptoms show first above-ground and appear to be an aerial blight (disease begins low on the plant and moves upward). Root rots can be an issue when production conditions are too wet/humid or production space air circulation is low. Simply spacing widely and good water management are the best controls. If chemicals are needed, most broad focus fungicides will work fine.

Where can you find ‘Sweet Romance’? Through your local broker or at these propagation facilities:

EuroAmerican Propagators: www.pweuro.com
Four Star Greenhouse: www.pwfourstar.com
Pleasant View Gardens: www.pvg.com
Walters Gardens: www.waltersgardens.com