Longwood Gardens and the Thousand Bloom Chrysanthemum

Using the combination of science and artistry, the fall-blooming chrysanthemum can be grown in a variety of shapes and forms; the most spectacular of these is the thousand bloom chrysanthemum. Pennsylvania is fortunate to be home to Longwood Gardens, considered one of the world's premier horticulture display gardens, and a fall visit to their chrysanthemum festival offers visitors a chance to see this incredible plant.

In 1906, in an effort to save a collection of historic trees from being sold for lumber, Pierre S. duPont bought a farm near Kennett Square, Pennsylvania. Since then, the gardens have grown to 1100 acres and include flower gardens, woodlands, meadows, a large fountain garden, an open-air theater with fountains, an Italian water garden, three tree houses, and a large conservatory with a 10,010 pipe Aeolian organ. While the gardens are beautiful any time of the year, a visit in the fall allows you to immerse yourself in chrysanthemums. The six-week chrysanthemum festival is the most labor-intensive of all of Longwood's featured exhibits. Planning begins two years ahead of time, and growing the mums begins in January. Longwood Gardens has one of the largest collections of rare and specialty chrysanthemums in the United States, with over 180 cultivars representing all 13 classes. Their research team maintains more than 1,500 test tubes containing virus-free mum stock to ensure the continuation of their collection. Mums may be found in the outdoor gardens, but it is in the conservatory that the real magic happens.

The chrysanthemums are displayed in two stages. Beginning at the end of September, the first portion of the festival features blooms that have been forced. The second part of the festival, starting in October and running through mid-November, showcases the natural bloomers. To highlight the forced bloomers, two different techniques, training and grafting, are employed, creating stunning, living showpieces in shapes and forms such as spirals, giant cascading hanging baskets, pagodas, and topiaries.

The showpiece of the festival, a natural bloomer, is the thousand bloom chrysanthemum. A combination of art and science, this plant is created using an ancient technique that originated in China hundreds of years ago and has since expanded into Japan. The goal is to produce a single, extremely large plant with as many uniform blooms as possible, with only a single bloom at the end of each individual branch. Last year's plant, Chrysanthemum x morifolium ‘Susono-no-Hikari’, was Longwood's widest ever, stretching over 12 feet in diameter, showcasing 1366 bright yellow flowers.

Preparation begins 18 months beforehand, in June, when growers start ten stem cuttings that are grown and evaluated as possible plants for the thousand bloom chrysanthemum. Before they are planted in the growing medium, the stems are slit to stimulate more root development, so once the stems are covered with growing medium, new roots will grow. As the plants grow, the stems are pinched to remove each terminal bud. At each pinched stem, two or more new stems will grow along with more buds, creating a fuller plant. These are cared for until December, when two plants are selected as their final choices. This provides twice the chance of a successful outcome. They are carefully chosen based on shape, plant health and vigor, and balance of root-to-shoot growth. At that time, those two mums are transplanted into their final containers. These have been constructed on-site and have an unusual design. Built as a box within a box, dividers inside the planter create a smaller inner box and another mid-sized one. The mums are planted in the inner box, which is filled with special soil that is blended to balance optimal water-holding capacity and air space. This smaller box keeps the soil area small as the plant is growing to stimulate more root development, which is critical to support the nutrition and water needs of the plant. As the plant grows larger, the dividers are removed, and more soil is added. The outside panels of the planter are also removable, so the root development and distribution of soil moisture can be monitored periodically.

While the thousand bloom chrysanthemum is not forced and is allowed to bloom naturally, some adjustments are made to the lighting that, in effect, trick the plant into preventing it from blooming too early during its long growing period.  Mums are short-day bloomers, meaning they are naturally stimulated to bloom as the daylight grows shorter at the end of the summer. To prevent an early bloom, the lights are turned on for a portion of the night so the plant is not stimulated to bloom before it reaches the desired size.

By February, the plants will be large enough for the metal framework they need to support them. Once that is installed, fiberglass support rings are installed monthly, and as the stems grow outward, they are tied down to the rings. Next comes the most labor-intensive stage, disbudding. In mid-September, thousands of flower buds are removed by hand, leaving each stem with only one bud. Disbudding allows all of the plant's energy to go to the terminal buds, creating one large flower on each stem. Once that has been done, working from the top of the plant to the bottom, each flower is wired to a round wire form called a rindai. The rindai supports the flowers, providing precise, even spacing in concentric horizontal rows. Now it's time to transport the thousand bloom chrysanthemum to the conservatory.

Given the time and complexity involved in growing a thousand bloom chrysanthemum, failure is always a possibility. In 2021 and 2022, the plants declined shortly before the start of the festival and were unsuitable for display. The horticulturists determined that the decline was due to a root-borne pathogen. A tremendous amount of research was involved to identify the factors that contributed to the plant's susceptibility and then to create and adapt practices to grow a healthy plant. First, increases were made to the sanitation practices. Looking at the failed plants, it was observed there were more shoots in relation to the number of roots. A large, robust root system is critical to provide the water and nutrition needed to keep the plant healthy and less susceptible to plant pathogens. To create a better balance, alterations were made to the light intensity and night temperatures. The floor temperature was also increased to improve root growth. The watering method was changed and carefully monitored by using a ladle and counting the number of scoops at each irrigation. All of these changes helped produce a successful outcome.

The culmination of hours of hard work, patience, and skill are showcased in this spectacular chrysanthemum. Visiting Longwood Gardens during their chrysanthemum festival provides a chance for visitors to enjoy this remarkable plant.