Forcing Perennials for Fall
Fall offers a novel opportunity to bring flowering perennials to market. During this shoulder season, plant selection doesn’t have to be limited to pansies and mums. There is potential to capitalize on the rising interest in perennials, as we’ve discovered with the great success of echinacea ‘Cheyenne Spirit’ and coreopsis UpTick.
The two key factors for successful selling in the fall season have been: 1) Appropriate product selection, and 2) following recipes to schedule perennials to flower for a target ship week, known as forcing perennials. In this article, our goal is to arm you with tools needed to successfully force seed and vegetative perennials for fall sales.
Forcing Seed Perennials
At Kieft Seed, we offer a diverse assortment of seed perennials, including more than two dozen varieties suitable for fall. Varieties with great fall performance in trials conducted by growers as well as our own breeders include a wide range of colors and textures. For example, suitable varieties of coreopsis and gaillardia offer much-desired yellows hues; gaura and heuchera add interesting textures; and dianthus ‘Rockin’ Red’ is a great thriller with bold color. Since forcing requirements for each of these varieties vary, a Fall Forcing Guide has been developed to aid growers (Table 1) and is available online at www.panamseed.com/culture under the perennials tab.
The Fall Forcing Guide lists the perennial series or varieties in our assortment and provides forcing information for items suitable Finish Week 36 to target the Labor Day market. Note that in some classes, only select varieties are suitable for fall production. For example, coreopsis Sunfire and Sunkiss are excellent fall performers, while coreopsis Early Sunrise and Sun Up do not flower profusely under the shorter daylengths of fall, and hence, are not recommended. Similarly, some dianthus series are suitable for fall due to their heat tolerance, while others are not. Please refer to the Fall Forcing Guide for suitability of a specific series or variety.
Since climates across North America vary greatly, certain regional nuances might also need to be considered to fine-tune the product assortment for your specific region. For instance, there are a handful of USDA Hardiness Zone 7 perennials listed in the guide that would not be hardy in some regions. Some climates enable dual-use of perennials as fall décor in containers and as an overwintering variety, if planted in the garden prior to frost. Having this information might appeal to some gardeners. All perennials included in the Fall Forcing Guide are first year flowering and do not need vernalization.
The Fall Forcing Guide gives a suggested sow week, plug size and plug grow weeks for each series or variety. We recommend bulking under short-day photoperiods for echinacea ‘Cheyenne Spirit’ and PowWow, lobelia Starship and rudbeckia Goldsturm. This short-day treatment is an important step to follow for success in the fall, and recommended durations for each series are included. The Fall Forcing Guide also gives finish crop time under natural daylengths and the number of plugs required for numerous pot sizes. As always, please conduct your own trials to determine the input sizes and crop timing that are best suited to your conditions.
Plug & Play Perennial Combos From Seed
Plug & Play Perennial Combos can take your fall seed offering up a notch in container appeal (Figure 1). We currently offer eight Plug & Play Perennial Combos, including six suitable for fall production: Tuscan Sun, Roman Holiday, Paris in Springtime, Amazon Rain Forest, Passion for Pompeii and Sydney Sparkler. The components, planting diagrams and growing information for each of these can be found at www.panamseed.com/plugandplay. For production guidelines of each component, please refer to the Fall Forcing Guide.
Forcing Vegetative Perennials
Many vegetative perennials that do not require vernalization can be reliably scheduled for fall flowering. These include veronica, salvia, achillea, coreopsis, echinacea, leucanthemum and many others. In areas where summer-growing temperatures are excessive, growers may want to consider purchasing a rooted liner from a northern propagator. Also, consider starting fall flowering perennials under 30 to 50 percent shade for the first three weeks until plants are well established to reduce transplant stress.
In our finishing trials in West Grove, Pennsylvania, we consistently see finishing times from a 72-cell liner in the six- to eight-week range. Quality Labor Day–flowering perennials can be planted in Week 28 for a Week 36 finish. Our 2016 scheduling trial results can be found online at www.darwinperennials.com/culture.
Fall is a great time to establish perennials in the garden in regions where USDA Hardiness Zone is 6 or higher. In these areas, plant root systems have time to develop before short days and cold temperatures settle in and therefore overwintering reliability increases. For regions Zone 5 and colder, establishment time is more restricted and perennials planted after mid-August may struggle to establish before frost. In these colder northern regions, perennials serve as wonderful textural and color palette additions to fall porch and patio decorating right alongside mums and other traditional fall flowering plants.
Whether used as new additions to a perennial garden, or colorful accompaniments to porch and patio decorating, perennials provide long-flowering and frost-hardy alternatives for growers, retailers and consumers. New varieties and cultural research provide growers with all the tools necessary for successful fall perennial programs.
Video Library 
