Subseries I.A encompasses minutes of the HSNY's Board of Directors (1915-1926; 1932-1939; 1952-2007), preceded by the Council's minutes (1900-1915, with gaps). Also included are working files for various board committees and initiatives (1900s-early 2000s; scattered).

Subseries I.B contains the HSNY's financial reports for 1959-1974, as well as fundraising benefit material for 1993-1994. It also includes financial reports for the International Flower Show, 1930-1942, and the Garden Index Company, 1933-1934.

Subseries I.C includes the working files of multiple HSNY Executive Directors, among them Alexander Allport, Larry Pardue, David Harrington, Barbara Earnest, and Charles D. Webster, for the 1960s through the 1990s. Because successive administrators absorbed their predecessors' files, it is difficult to attribute documents to a specific creator, so the material is grouped instead by topic (e.g., "Exhibitors," "Special Events," "Trips & Tours," etc.).

Subseries I.D encompasses the administrative files of the HSNY President's office. They are chiefly Millicent Johnson's, who held the title in the 1990s, but possibly include material from others. Like Subseries I.E, these administrative documents are grouped by topic, rather than creator.

The bulk of Subseries I.E regards the 6,000-volume library of botanical books and illustrations bequeathed to the HSNY by lawyer and collector Kenneth K. Mackenzie in 1934. Mackenzie's gift was particularly strong in the works of Swedish botanist and "father of modern taxonomy" Carolus Linnaeus (1707-1778). That portion of the collection--known as the MacKenzie Linnaeana--was acquired by Kansas State University in 1966. The rest of the collection was sold in 1980.

Subseries I.E also includes HSNY guestbooks and visitor logs for exhibits and the library (1933-2010, with large gaps), and material relating to the proposed Lillian Gish Garden in Manhattan. The latter was the brainchild of landscape designer Luther Greene (1910-1987), who in 1980 received approval from Community Board 6 and the Art Commission of the City of New York to plant a garden--with Horticultural Society of New York assistance--honoring actress and longtime Sutton Place resident Lillian Gish (1893-1993) at the foot of East 56th Street. The site, on a platform over the FDR Drive, remained barren since its creation around 1943. Today it has been absorbed by Sutton Place Park.

The subseries includes the Library's ledgers recording its accessions from the 1920s through 1989.

The subseries primarily includes documents related to the periodic meetings of the Library Committee. These documents include the agendas and minutes of the meetings from the 1930s through the late 1980s. Most of these minutes were found in well-ordered binders, into the 1970s. Subsequent to 1974, the files are a mix of minutes and working files related to the meetings. Some of these later files also include documents related to the Library, but not clearly to the Committee. For at least some of the years, the files include summaries of library usage and of accessions.

The subseries includes the subject files of Hort Librarian Katherine Powis. Powis joined Hort in January 1989, and she remained as Librarian into the early 2000s; the files in this subseries date primarily from the 1990s to approximately 2005. Powis previously worked as an Assistant Science Librarian at St. John's University, after earning her Masters degree in Library Science from Queens College in 1986.

Powis's files primarily include various Library administrative matters, especially Library Committee meetings, Library usage statistics, funding (e.g., benefits, grants), donations of books, planning, and bibliographies and other Library resource lists. Some of these administrative files relate to the Library's Archives project (see Subseries II.D) and some concern general Hort administration, such as a copy of an employee handbook and membership lists. The files also include some records related to programs and events, such as the Library's outreach at the annual "New York is Book Country" event, hand-outs for events, program progress reports, and other material.

The subseries includes files related to projects from the 1990s-early 2000s during which time archival material was compiled by the Hort and used to create ready reference resources for internal and external inquiries about the organization. The name Joan Nichols appears often in these files; Joan appears to have been the volunteer primarily responsible for implementing the archives initiative, under the direction of Librarian Katherine Powis. During processing of the collection at N-YHS in 2017, much of the original material compiled was sorted into various series (e.g., Flower Show, Print Matter, etc.). However, some material could not be readily sorted and so was kept together in this subseries. Consequently, the subseries includes a wide range of documents related to Hort's programs and administration. Most of the original material in the subseries dates from the 1980s-2000s, though there are a few earlier original pieces. Much of the subseries includes photocopies of historical documents (e.g., officer lists from annual reports of various years). The date range used in the container list refers to original documents, not the dates of photocopied material.

Several of the folders in the subseries with original documents relate to the Hort's public education programs of the 1980s-2000s. Among these were Greenworks (later, GreenHouse), which was vocational training for inmates at Rikers Island; Green Team, which trained at-risk youth in greening projects in public spaces; GreenBranches, which installed gardens around selected branch libraries; Apple Seed, which was an environmental and science education program for the third through sixth grades; and other urban horticulture, community gardening, and related educational programs.

The subseries also holds many files concerning administrative matters. Although much of this is photocopied material, there are several useful original documents, especially from the 1980s, including budget and financial statements, a long range plan, and the results of a member survey.

The latter part of the subseries includes many files related to the archives project itself. These include drafts and notes related to the development of a historical timeline for the Hort, as well as general notes concerning the project and the development of the archives. These files also include preliminary partial finding aids and inventories of records created during the project.

The subseries primarily includes the minutes of the meetings related to the planning of the International Flower Shows for the years 1916 to 1970 (though there were no shows in some years) and for the New York Flower Shows of the 1980s and 1990s. For the years 1942 to 1970 these records include the Board of Directors meeting minutes for International Flower Show, Inc., the corporate body created to organize and run the shows over that period. Prior to 1942, and for the New York Flower Shows, informal committees conducted the planning. These minutes provide insight into the strategic, financial, legal, and other issues surrounding the various Flower Shows.

The subseries also includes various working files and publicity files, especially for the New York Flower Shows. The content of these various files is uneven across the years. The files include floor plans for some of the International Flower Shows of the 1960s, held at the New York Coliseum building; a 1969 memo from Horticultural Society of New York Executive Director Alexander Allport titled "The Future of the International Flower Show," which expressed concerns that would eventually lead to the termination of those shows; publicity packets for the New York shows; sponsor lists; logistical notes; and other items.

This subseries includes bound and loose copies of International Flower Show (IFS) official programs (1913-1970); IFS schedules (1913-1970); Horticultural Society of New York (HSNY) schedule of classes and premiums (1908-1935); HSNY programs/flower show books (1922-1965); HSNY Autumn exhibition programs (1946-1953); HSNY Narcissus & Spring show programs (1936-1958); HSNY Flower Show Schedules (1956-1973); New York Flower Show programs (1985-1996; note that there was no 1994 New York Flower Show); Rockefeller Center Flower Show program (1994); flower show promotional ephemera (1984-1996).

This subseries includes images (i.e., photographic prints, slides, glass lantern slides, negatives, and contact prints) of the International Flower Show (1916-1969), the New York Flower Show (1936-1996, with scrapbooks for the 1988, 1992, 1993, and 1995 shows; note that there was no 1994 New York Flower Show), the Bryant Park Flower Show (1969-1978, with a scrapbook honoring the achievements of Henrietta Sedgwick Lockwood, creator of the Bryant Park Flower Show), and a handful of smaller shows, like the Rockefeller Center Flower Show (1994), Boston Flower Show (1995), and Philadelphia Flower Show (1981, 1998).

This subseries consists of photographs featuring events organized by HSNY. There are images of annual meetings, classes for children and adults, library benefits, staff parties, exhibits and tours. One set of images documents the HSNY's participation in the annual "New York is Book Country" street fair on 5th Avenue from 1996-2002. The subseries also contains 3 folders of slides of various events that were housed together in a binder, in no particular order. These have been kept together. There is also one folder of oversize material.

Most images in this series are dated, and some are captioned; however, for the most part, people in the photos are not identified

This subseries documents HSNY's public outreach gardening and planting programs. The majority of the images are slides of urban community gardens created in neighborhoods lacking access to green space. Also included are photos of the garden at Riker's Island prison, which is part of a job-training program. In addition this subseries features images of the Green Team, an internship program to help people released from prison transition back into their communities. The subseries contains one folder of oversize material.

This subseries is comprised of images of the HSNY's offices, library, archives and collections storage space. It includes many snapshots of staff and volunteers at work. A number of photographs document incidents of water and fire damage to the facilities. There is one folder of oversize material.

This subseries contains images that were used to illustrate various HNSY publications, including the newsletter. Some images are mounted to boards, with notes indicating crop marks and other editing instructions.

The subseries primarily includes images that emphasize plants, either as individual specimens or in an aesthetic context, such as with gardens, landscape architecture, interiors, topiaries, or floral displays. The subseries includes many images associated with international or domestic United States locations; while these images often emphasize plants they also include commercially-produced souvenir images of built structures and general tourist travel snapshots. While many of the images have some basic level of identification, most lack a more detailed context and few seem to relate to identifiable Horticultural Society activities (see subseries V.A. for those). Most of the images seem to date from the 1960s to early 1980s, but there are earlier and later views. The formats in the subseries include glass plate lantern slides (4-1/2" x 3-1/2"), 35mm slides, transparencies, photographic prints (mostly black and white), and negatives.

Although much of the subseries has a certain degree of randomness to it and ambiguity as to context, several portions are well-defined and substantive. These include a captioned photograph album of World War I scenes of troop movements and trench warfare with their related destruction of trees in France (1917); lantern slides of Mrs. Louis Levy's azalea and rock garden in Dobbs Ferry, NY; a photograph album documenting a trip to Japan (1967); sets of educational slides concerning sowing and repotting and turfgrass diseases; images by recognized photographers Ralph Bailey of House & Garden and Bruce Cratsley; an organized set of slides depicting seasonal wildflowers; and two photograph albums of cacti cultivated by Richard Weiler.

The subseries includes periodical publications issued over time by the Hort that, generally, had its membership as the principal audience. The content and titles of these changed somewhat over time, but generally included information about organizational matters, such as upcoming events, and horticulture-related short articles and book reviews. Following is a general summary of the content of the titles in the subseries:

Memoirs: Three volumes that include the papers read at conferences organized by Hort in 1902, 1907, and 1926.

Journal: This ran from April 1906 to July 1924. It Includes annual reports, proceedings of Hort meetings, reports on the various flower exhibitions, library accessions, committee reports, and papers/lectures on horticultural matters. It was replaced by the Year Book.

Year Book: Started in May 1925, replacing the Journal. It includes annual reports, lectures/papers, flower show reports, accessions, etc. For the first few Year Books, the period covered is roughly August to May of the following year. In 1927, publication shifted to a calendar year basis. These appear to have ended in 1940, though a Year Book was published in 1951 to commemorate the events of 1950, the Hort's 50th anniversary year.

Monthly Bulletin / Bulletin: The Bulletin appears to have started about January 1930. It started as a small pamphlet with short announcements concerning upcoming meetings and events/programs, new members, and accessions. By the early 1930s, it expanded to include lists of awards given for exhibits at the monthly meetings. By 1933, it further expanded to include transcripts or summaries of lectures. By 1934, a glossy version appeared, with increasing numbers of photographs. In Feb 1942, the Bulletin started presenting annual reports for the prior year, fully replacing the Year Book. The Monthly Bulletin ended in 1947, going to quarterly in 1948. It ceased publication with the first quarter 1950.

News: It started in January 1951, replacing the Bulletin. Slimmed down from the Bulletin and much more casual, the News no longer included annual reports or articles, but focused on announcements, award winners, accessions, and basic membership information, though over time the content got more expansive. It was produced irregularly and ended in early 1957.

Bulletin: Reintroducing the former title and replacing the News, the new Bulletin included both basic announcements and short articles, including book reviews. Starting in 1957, the Bulletin continued until 1973, though by 1970 it had been scaled down in size and scope. An announcement-oriented Member Newsletter started in late 1969, overlapping with the Bulletin through 1973. After 1973, the Member Newsletter (with the title shortened to just Newsletter in 1983) continued; the latest copy held by the subseries dates from 1998. The subseries holds a set of cards that represent an index to the Bulletin for the years 1958-1962.

Garden was a bi-monthly publication of The Garden Society, a division of the NY Botanical Garden. Subscriptions to Garden were a benefit of membership in one of the institutions comprising The Garden Society, of which Hort was one. The bulk of the magazine content was common to all institutions, but some front pages were content specific to Hort. The content was horticulture-related and was not concerned with Hort organizational and event matters.The subseries holds issues from 1977-1984 and 1986.