A weed is simply a plant that a particular gardener does not want in a particular place. The designation of “weed” depends on circumstances. A plant that might behave perfectly well in one set of conditions or among one set of companions can become a menace in a different situation. The High Line’s gardeners spend much of their time weeding out seedlings of plants that we cultivate here in the park to keep them from overrunning their neighbors. As our interns and seasonal gardeners learn when they rotate through the different sections of the park, one gardener may be nursing seedlings of a certain species along, while another gardener might be pulling out every last seedling of the same species. Weeding is largely based on the proportions of different plants in the original design and how well they compete with one another.
Adaptations like prolific seed production, fast growth rates, and the early development of strong roots give plants a competitive advantage and can make them challenging to control in the garden. Fast-growing and freely self-seeding vines like virgin’s bower (Clematis virginiana) and Virginia creeper (Parthenocissus quinquefolia) can be nuisances, requiring regular management from the gardeners. Seedlings of heath aster (Symphiotrichum ericoides) and Korean feather grass (Calamagrostis arundinacea) turn up everywhere, but can easily be pulled, unlike like the abundant and deeply-rooted seedlings of northern sea oats (Chasmanthium latifolium) and thread-leaf bluestar (Amsonia hubrichtii).
Seeds and spores also arrive from the surrounding area, carried by wind, birds and nursery pots. Copper leaf (Acalypha rhomboidea), smart weed (Polygonum pensylvanicum) yellow wood sorrel (Oxalis stricta), and violets (Viola sp.) are common throughout the High Line. While we remove most of the plants that seed in, some of these species have been good fits for the garden. If a new arrival complements the colors and textures of the surrounding plants and fills a void in the planting, we may integrate it into the design. For example, we kept the sensitive fern (Onoclea sensibilis) because this beautiful northeastern native thrived in a difficult spot, where many of the other species have suffered from grub damage.
Others arrivals, like the common reed (Phragmites australis) cannot be eradicated, despite our best efforts. An invasive species in North America, common reed spreads by both seeds and rhizomes (underground organs that can produce new shoots). The plant can regenerate from a piece of rhizome left in the soil. Common reed disrupts healthy ecosystems and forms monotypic stands in highly disturbed and polluted areas like the New Jersey Meadowlands. Given the chance, it would completely dominate the bog on the High Line.
Common reed is one of several invasive species present in the park, all of which have the capacity to wreak havoc in the garden. Invasives like multiflora rose (Rosa multiflora), lesser celadine (Ficaria verna) and oriental bittersweet (Celastrus orbiculatus) have adaptations that help them outcompete other plants. We are lucky to have enough gardeners to keep ahead of these invasive species. The High Line horticulture team weeds the entire park by hand. Lacking adequate staff, many institutions have to fall back on synthetic herbicides when the most pernicious species invade.
Plants that have been labeled weeds range from native species that may actually have garden value to highly aggressive invasive species that can overrun a garden. Evaluating how a plant functions in a particular context helps the High Line horticulture team develop management plans and priorities for the many species that arrive and spread throughout the park. We focus our energy on removing true threats, then weeding unwanted species and editing cultivated species. By observing how new arrivals behave, we have also discovered some wonderful additions for the gardens.
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TD Bank is the Presenting Green Sponsor of the High Line.