Lilacs for Florida?

Can Lilacs Really Be Grown in Florida?

For many of us who have spent our childhoods growing up in cold winter climates, one of the fondest memories we hold onto is the gentle wafting of the fragrance of lilacs through the spring gardens of our parents and grandparents. Even though we may have moved to warmer climates later in our lives, where the distinction between fall, winter and spring has become blurred, we still hold dear those nostalgic memories, and wish we could again experience the visual and olfactory delights we remember so vividly.

A few years ago, near the end of my career as Head Gardener of a estate in north central Florida, with more free time and access to unlimited information via the internet, I took up a search for low chill Lilacs. Early on I was encouraged by what I found.

One of my earliest searches turned up work being conducted by Dr. J. Giles Waines, Director of the Botanical Gardens at the University of California at Riverside. Dr Waines was continuing research started by Dr. Louis Erikson, also of UC Riverside, who had been building upon even earlier breeding studies at Descanso Gardens by Walter Lammer. Lammer was the developer of the first low chill Lilacs, hyacinthaflora hybrids. Lammer, Erikson and Waines were trying to increase the number of Lilac cultivars that could be successfully grown and flowered in the warmer, low chill environment of southern California. The hyacinthaflora hybrids eventually formed the basis of the Descanso Gardens lilacs.

The research reports I found, written by Dr Waines, were immediately exciting because they seemed to indicate there were a number of Lilacs that would perform well in warm climates. While it was true that southern California’s climate differed from Florida’s in some respects, the number of winter chill hours experienced at UC Riverside was similar to those experienced here in north Florida.

I immediately contacted Dr Waines and related to him my desire to flower Lilacs in Florida. He generously passed along to me some advice and a list of Lilacs, mostly hyacinthaflora hybrids, that he felt were good candidates for testing.

I was also interested in another Lilac, S. Betsy Ross, which was developed specifically for warm climates, guaranteed to bloom down to USDA Zone 8 and, in addition, had a high tolerance for powdery mildew. It was named and released by Dr Margaret Pooler of the US National Arboretum in July, 2000. Before purchasing the plant, however, I contacted Dr Pooler and asked her opinion. She re-affirmed Betsy Ross’s potential for warm climates and mentioned it had done well in South Carolina. So, I added Betsy Ross to my list.

Probably the most exciting and most promising information came from Descanso Gardens itself, the beneficiary of much of the research conducted by Lammer, Erikson and Waines. Descanso Gardens is located in LaCanada Flintridge, in Los Angeles County, California. The climate of Los Angeles County is variable because of the topography, but is generally mild throughout the year. The average annual high is 75F (average annual range 68F – 85F) and the average annual low is 56F (48F – 66F). Rainfall is low, about 15” per year, occurring mostly in the winter months.

Summers are dry. Winter chill hours range from 56 to 373, depending on location. Descanso Gardens is in AHS Heat Zone 9, Sunset Zone 21 and USDA Zone 9.

The climate of Citrus County, Florida, where I reside and garden, is similar to Los Angeles County. The average annual high is 82F (70F – 91F), the average annual low is 58F (44F – 71F). Rainfall totals and timing are very different, however. Citrus County experiences 51” of rainfall per year, mostly during summer months. Winters are cool and somewhat dry. Citrus County falls in AHS Heat Zone 10, Sunset Zone 26 and USDA Zone 8B-9A. More significant is the number of chill hours Citrus County experiences – about 500 hours in an average winter - higher than Los Angeles County.

These figures gleaned from the literature coupled with Dr Waines’s optimistic outlook for Lilacs here gave me every reason to believe that some Lilacs could be successfully flowered this far south. The only potential problem might be the combination of high heat and humidity of the southeastern US summers. At this point I felt it was necessary to contact the horticultural staff of Descanso Gardens to get their perspective from working directly with the plants. After sending a few e-mails to staff members there, I received a phone call from Wayne Walker, Chief Horticulturist of the Gardens, who was kind enough to discuss Descanso’s collection.

Wayne told me that most of the Lilacs they grew were hyacinthaflora hybrids. He also confirmed their growing zone as USDA Zone 9 and Sunset Zone 21. Wayne felt that drought, coupled with natural chill, forced dormancy and floral bud formation and that he and his staff used those environmental conditions to bring Lilacs into flower each year. To support his theory, he mentioned that when irrigation to the Lilacs was allowed to continue through the winter, and a warmup occurred, the Lilacs could bloom as early as November or December. He also thought the number of chill hours listed for the area was probably correct. Wayne generously agreed to send me a complete list of the Lilacs grown at Descanso Gardens.

Convinced that it was possible to successfully flower Lilacs here in Florida I used Dr Waines’s list and the Descanso list as a starting point, and in the spring of 2009, I purchased several Lilacs and planted them out in my Garden. The Lilacs I started with were S. x hyacinthaflora Angel White, S. x hyacinthaflora Excel, S. x hyacinthaflora Asessippi, S. x hyacinthaflora California Rose, S. x hyacinthaflora Evangeline, S. patula Miss Kim and S. x hyacinthflora Pocahontas. Because it was billed as low chill variety, I also planted out four S. Blue Skies. In the spring of 2010, I planted out one S. Betsy Ross.  Syringa Pocahontas, S. Miss Kim, Blue Skies and S. Betsy Ross stood about three feet tall and one and one half to two feet wide. All the others were younger, multiple trunked, and about one and one half to two feet tall.

The winter of 2009-2010 was colder than average for Citrus County. By the middle of March 735 chill hours had been accumulated, more than 200 above normal. By mid April S. Pocahontas bloomed. Later in the month Miss Kim bloomed as well. None of the other Lilacs bloomed in the spring of 2010.

During the growing season of 2010 all plants received supplemental watering between rain events. North Florida soils are sandy and porous, unable to hold moisture near the surface for more than a few days. During the dry intervals it’s usually hot and humid, very stressful and necessary to provide additional water. This stressful environment took a toll on some of the lilacs. Although Pocahontas had performed well during 2009, adding new branches and foliage, culminating in a bloom early in 2010, it developed branch dieback and was lost by the end of summer. Also lost during 2010 was S. Asessippi.

The winter of 2010-2011 was again colder than average, but less so than the previous year. By mid March Citrus County had received 653 chill hours. All Lilacs had gone dormant over the winter and began to show signs of growth by early March. The first to bloom was S. Betsy Ross. Close behind was Miss Kim, its second consecutive year of bloom. Betsy Ross, about three and one half feet tall, bloomed on five inflorescences. Miss Kim produced more than forty inflorescences. Miss Kim, at more than four feet high is by far the fullest Lilac. As the flowers formed so did new leaves, and both continued to fill out with new growth as the spring progressed.

Syringa Angel White, though it did not bloom, filled out with new foliage quickly and increased in height and width. It also grew well during 2010. All other Lilacs have added new foliage, but slowly.

Although it is too early to declare that Lilacs will definitely grow and flower in North Florida, results so far are encouraging. More time (some Lilacs are still young and not yet fully established) and more average winters will contribute to a better understanding of which Lilacs can be successfully grown here. However, we do know that Miss Kim, Pocahontas and Betsy Ross will flower as far south as Florida USDA Zone 8B-9A (and at least 653 chill hours). Based on the work of pioneers Louis Erikson and Walter Lammer, who developed a tempting list of  low chill varieties, and to the ongoing research being conducted by scientists like Giles Waines of UC and Margeret Pooler of the US National Arboretum, and through careful selection, it may be possible to extend the southern range of flowering Lilacs further than we previously thought.