Leaning Pine Arboretum, Mediterranean botanical garden at California Polytechnic State University, San Luis Obispo, United States.

Leaning Pine Arboretum is a five-acre botanical garden in the northern part of the Cal Poly campus in San Luis Obispo County, California, at an elevation of 128 to 139 metres. Its collection is divided into geographic sections: an Entry Garden, Australian, Californian, Chilean, Mediterranean, South African and New Zealand gardens, plus a Dwarf and Unusual Conifer Garden, a Formal Garden with box parterres around a central fountain, a Primitive Garden and a Palm & Aloe Garden.

The arboretum is run by Cal Poly's Horticulture and Crop Science Department on the northern part of the campus, at an elevation of 128 to 139 metres. Its stated mission is to support education, research and public interest in plants used for horticulture and environmentally sound landscape design. In 2022 it received a one-million-dollar donation from a former provost and her husband.

The gardens are grouped by the five Mediterranean-climate regions of the world, and the Chilean Garden sits in the highest part of the five-acre site. In the South African Garden, look for the grape kool aid shrub (Psoralea pinnata) and the sugar bush (Protea repens), whose large flowers carry a strong scent. The Formal Garden contrasts with the rest, with geometric box parterres around a central fountain and clipped evergreens.

The arboretum is accessible most weekdays with no entrance fee, though campus parking may require permits. Morning visits are often the best time to see the plants clearly and enjoy the space with fewer people around.

The grounds feature specialized areas like the Primitive Garden with ancient plant species and a Formal Garden with geometric patterns and tiered fountains. These contrasts show different garden design philosophies and offer visitors varied impressions of gardening styles.