BioCycle July 2005, Vol. 46, No. 7, p. 59
With a long-term goal of avoiding pesticides, compost tea is used as a tool to keep plants healthy – allowing over 5,000 baseball games to be played from spring to fall and ornamentals to bloom in the gardens.
Matthew Brown

IN 2003, The Central Park Conservancy began brewing compost tea and applying it to selected lawns, planting beds, and trees. Since that time, we have carefully monitored our ‘trials’ on compost tea. Overall, we have seen only minor disease and pest outbreaks on both the applied areas and their respective controls, but due to the brevity of our study, our data are still inconclusive and their outcomes have yet to be seen. For this article, we will focus on two examples in the Park: The North Meadow, a large turf field, and in the Conservatory Garden, several ornamental flower beds.
Luckily, the main component of our compost tea is produced right here in the park. Most people do not realize that the Conservancy has been composting leaves and woodchips on a large scale for the past 20 years inside the park. All of the leaves that aren’t mulched into the lawns, and the wood chips produced from maintaining the trees, are brought to a two and a half acre composting site. The composting operation has become more sophisticated over time as we have focused on increasing turning frequency of the windrows and on streamlining the screening operations. This helps us better manage the in-flow of fresh material and out-flow of finished product. Because we are in an urban center, you can only imagine some of the “treasures” we find during the screening process such as a tricycle, hockey sticks, and plenty of discarded clothing! Once we have screened out all of these “treasures”, 100 percent of the finished product goes out into the field for use in lawn renovations, topdressing, and landscape restorations.
We brew our compost tea solution by combining the leaf mold and older wood chips from our compost pile with a small portion of higher nitrogen compost from a fish and plant blend produced elsewhere. The three composts are put in a fine mesh sack and allowed to steep in heavily aerated water for three to four days. In addition to the composts, we also add about a dozen carefully researched ingredients that have been shown either to enhance bioactivity within the tea and/or to enhance bioactivity in the soil. Some of these ingredients include humic acid (we use several different mines for redundancy but also to diversify parent material), dehydrated fish emulsion, pulverized kelp (again, several different varieties from different oceans to maximize micronutrient content), pulverized crab shells, in-house produced worm castings, and molasses. Much of the research in compost tea and sources for the ingredients are from the agriculture sector; adopting these ingredients for use in an urban setting has been a process that has connected us with many alternative resources and suppliers.
TESTING TEAS FOR QUALITY CONTROL
Our teas are tested as often as possible to check fungal, bacterial, protozoa and nematode populations and to ensure some level of quality control. To date, we have never produced statistically similar results from two different teas, even using identical amounts of each ingredient. Our approach is to utilize these teas that contain diverse populations of bacteria, fungi, and microbes both in soil and on plant leaves to promote plant vigor and health. We believe that this diversity might be more advantageous than applying the exact same teas to a given area, if we were even able to produce them. This methodology, however, is more intuitive than scientific.
So far, we are seeing some positive results: North Meadow West is our largest field (6 acres) where some 5000 baseball and softball games are played from spring through fall, followed by about 500 soccer games from late fall until the lawn is closed for winter. The soil that supports this predominantly Kentucky bluegrass lawn is a poorly drained, silt loam. We apply compost tea to this field every week. In the last two years, there have been only two relatively minor separate outbreaks of disease. The first was a spring outbreak of leaf spot and rust, which are considered standard diseases during a rainy spring, and the second was a late june leaf spot and rhizoctonia. We only intervened with a pesticide for the late June outbreak because it had started to spread rapidly. In the spring leaf spot and rust case, the disease subsided without any intervention.
Every year in the Conservatory Garden – an ornamental garden located in the north end of the park – we plant about 21,000 tulip bulbs in four beds during the fall for a dazzling spring display. At the end of the tulip flowering in late spring, the bulbs are removed and chrysanthemums are planted in their place. The four beds are divided into two parts in this experiment: Two receiving tea on a monthly basis and the other two receiving only water. We chose to treat this area with compost tea because of minor Botrytis outbreaks in the past on the tulips. So far, the Botrytis has not reemerged, and there have been no other noticeable differences in all four beds. This year, we lost about 100 bulbs from all four beds combined, with the majority coming from a control bed. The preliminary pathology results are showing that it is most likely from mites and not Botrytis. From an IPM approach, losing 0.47 percent of the total “crop” is not any loss at all, but one worth noting. Even for ornamentals this is an extremely low number of bulbs lost.
LOW LEVELS OF DISEASE AND PESTS
Are the low levels of disease and pests in both the turf and planting beds due to the compost tea? It is hard to say. Both have been treated with pesticides in past years, so then there is the question of how much residual protection we’re getting. As far as the turf goes, maybe it has been a lot of luck and good weather? Nevertheless, a long-term outlook is required for trials like these before any conclusions can be made.
The science community is only beginning to seriously research, evaluate, and fully understand compost teas. It is difficult to scientifically study compost tea because there are so many variable factors at every step of the process. Evaluating its effectiveness is only one piece of the puzzle. Finding out what the teas modes of action are, how each ingredient contributes to its composition, and exactly what species perform beneficial functions are essential to understanding compost teas completely. Maybe then we can start drawing some concrete conclusions about the benefits of compost tea in the Park.
The philosophy of the Conservancy is not to look at compost tea as the only tool needed to keep the plants healthy, but rather to view compost tea as a part of a larger program – one that includes daily disease and insect scouting, ongoing trainings and other education for horticulture staff, and careful nutrient monitoring. The Conservancy has a strong, long-term commitment to exploring compost tea as well as other alternatives to pesticides; utilizing this program, we hope, will keep Central Park clean, green, and healthy.
Matthew Brown is with the Central Park Conservancy’s Soil and Water Health Lab based in New York City. He can be e-mailed at mbrown@centralparknyc.org.