Talking Shop: Perennial Potential

Talking Shop: Perennial Potential

Perennials remain popular at retail, with steady to growing demand. Yet growing perennials remains a challenge for many growers, due to perennials having more complex production requirements than annuals. Thanks to breeders’ efforts, each year brings more good, first-year flowering perennial cultivars to market. These first-year flowering cultivars can greatly simplify perennial production.

First-year flowering varieties give growers excellent options for bringing perennials into bloom for specific sales windows easily. Through careful variety selection and understanding a cultivar’s specific keys to flowering, growers can simplify and streamline their perennial production schedules.

Not all first-year flowering perennials are created equal. Many older varieties have long production requirements, taking five months or longer to flower after transplanting plugs. And even when these varieties flower, they may not reach their full potential in terms of flower power or uniformity of flowering. For many ornamental growers, a reasonably quick production schedule and good uniformity are important characteristics for perennial production.

Understanding Photoperiod

Photoperiod is one of the most critical keys to bringing first-year flowering perennials into bloom on schedule. Long-day perennials generally need 14 or more hours of light per day to flower. Day-neutral perennials will flower regardless of day length, but may flower slightly faster under long days. Short-day perennials flower only when under short-day length, generally 12 or fewer hours.

Artificial lighting is an important tool for growers looking to flower long-day perennials for a specific schedule. Under short-day conditions, night break lighting can be used to flower long-day perennials. As little as 10 to 15 footcandles of incandescent light (generally enough to read by) for four hours in the middle of the night is enough to trigger flowering in most long-day perennials. For energy savings, compact fluorescent bulbs can be used in incandescent fixtures with equally effective results.

Growers who have invested in HID lighting systems can extend the day to 16 to 18 hours to create artificial long days. This strategy provides higher light quantity and quality than night-break lighting. It is especially helpful for light accumulating perennials, like Digitalis purpurea. Perennials which accumulate light are similar to zonal geraniums, flowering faster and more uniformly under higher light levels.

Artificial lighting can cause some stretching, particularly with incandescent night break lighting. Once plants have been induced, and flower buds are visible, artificial lighting can be discontinued to help minimize stretch.

Sales Windows

Simply because a cultivar will flower the first year does not mean that it is suitable for finishing in any sales window. Temperature plays an important role in finish quality for perennials, and trying to grow a perennial greatly outside its preferred temperature range can result in poor quality, unsaleable plants. Summer sales windows can be especially challenging, as cool-temperature-loving perennials often bolt quickly, flowering before they fill containers fully.

Day neutral perennials tend to prefer cool growing temperatures (50 to 60°F). Particularly when grown under warm conditions and long days, quality may be poor for many day-neutral perennials. These species include: Arabis, Campanula auriculata, Delphinium, Myosotis, Papaver nudicaule, Primula polyanthus and viola. Avoid growing these perennials above 70°F for best results.

Long-day perennials are generally more tolerant of warm temperatures (60 to 75°F). Examples include Coreopsis grandiflora, echinacea, Phlox paniculata, rudbeckia, Salvia nemorosa and S. x sylvestris.

Vernalized Liners

Remember that perennials which require an overwintering or “vernalization” period can be treated as first-year flowering when growers make use of vernalized liners. A number of propagators supply vernalized liners in a range of sizes. They are generally available only seasonally, due to the cooling process and difficulty keeping liners dormant as temperatures warm up in spring.

Vernalized liners are ideal for finishing non-first-year flowering perennial species, many of which are very popular at retail. Examples include: Aaquilegia, Phlox subulata, Digitalis x mertonensis and heuchera. Remember that photoperiod is still an important flowering trigger, even for vernalized liners.

Here are some suggested long-day summer window perennials. They are all long-day responsive and will finish well at warm temperatures. They can also be finished for spring windows, by using artificial lighting:

- Coreopsis grandiflora ‘Heliot,’ ‘Sunfire’–yellow flowers with red centers, flowering nine to 10 weeks after transplant, earlier than the older ‘Early Sunrise.’

- Hibiscus x hybrida Luna series - naturally compact and well-branched, with large flowers produced eight to 10 weeks after transplant.

- Echinacea purpurea ‘Prairie Splendor’–early blooming with mid-sized habit, flowering 12 to 14 weeks after transplant. Note that Echinacea purpurea seed varieties generally flowers about three to four weeks faster when vernalized.

- Echinacea vegetative hybrids–there are numerous new interspecific hybrids on the market. Most are long-day responsive and flower eight to 10 weeks after transplant.

- Lavandula angustifolia ‘Vicenza Blue’ - compact with fragrant foliage and blue-purple flowers produced 10 weeks after transplant.

- Phlox paniculata Flame series–naturally dwarf series in a good range of colors, flowering 12 to 15 weeks after transplant. Ideal for quart production.

Spring Window Perennials

These varieties are all-day neutral and prefer cool growing conditions. They can also be considered for fall sales windows in many climates:

- Arabis caucasica ‘Snowfix’–compact habit with white flowers, flowering seven to eight weeks after transplant.

- Coreopsis auriculata ‘Nana’ - naturally dwarf cultivar which is day neutral, unlike most coreopsis. Flowers nine to 10 weeks after transplant, about two weeks earlier than the older ‘Early Sunrise.’

- Delphinium grandiflorum Summer series–an excellent, dwarf series with strong, well-branched stems and a wide color range. Flowers seven to nine weeks after transplant.

- Dianthus hybrida ‘Eastern Star’–compact habit with pinkish red flowers produced eight to 10 weeks after flowering. Note that not all cultivars in the Star series are first-year flowering. ‘Neon Star,’ with bright neon pink flowers, will bloom on the same schedule.

- Gaillardia vegetative cultivars - most of the newer vegetative cultivars (‘Fanfare,’ ‘Oranges & Lemons’ and ‘Summer’s Kiss’) are day neutral and often flower easily and early, sometimes before filling out a container, especially when grown under long days. They often require pinching and/or cutting back to produce good pot fill. They typically rebloom two to four weeks after cutting back.

- Viola ‘Etain’–large, creamy yellow with purple flowers are produced six to eight weeks after transplant.

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