Evergreen plants survive an unfavorable cold or dry period with full foliage, while other plants discard all their foliage to avoid dry damage. In the narrower sense, the term "evergreen plant" is used here for non leaf-shedding broadleaved trees and lianas. The plants are found in cool to warm (sub-)oceanic, Mediterranean and tropical rainforest climates, which are characterized by year-round humidity and the absence of severe frosts. From the point of view of the plants, this means that no period of severe physiological drought stress takes place above or below ground for the duration of the year.
In this area of the outdoor garden, the selection of plants must be limited to species whose adult stage nevertheless tolerates the local winter frosts down to –20 °C. The nearby Baltic Sea as well as the neighboring stream on the grounds of the Botanical Garden have a favorable effect here, mitigating the weather extremes by increasing humidity and weakening dry heat.