Failure is a big part of gardening, especially in the unusual conditions we have on the High Line. Growing plants in 15- 18" inches of constructed soil on a bridge that passes over streets and buildings presents unique challenges. By observing plants in the wild we can form an idea of how they will perform in our garden. However, just because a plant thrives in our region does not mean it will thrive here in the park. Soil, topography, sunlight and hydrology all affect how a plant grows – how big it gets, how long it lives, and how it competes with its neighbors. If we pay close attention to these conditions, we can get a sense of whether we can give a species what it needs. We've learned that no matter how beautiful a plant might be and how well it might fit aesthetically in the garden, it may not be worth planting if we have to alter existing conditions to keep it happy.
Soil nutrient levels, pH, and depth are some of the first things to consider when deciding whether to introduce a new species. In the poor soils along roadsides and train tracks, you'll often see swathes of native little bluestem grass ( Schizachyrium scoparium) standing perfectly upright into the winter. In our soils, which are regularly irrigated and rich in nutrients and organic matter, the little bluestem tends to flop, making for an unattractive autumn display. To account for the difference between our conditions and those of this grass's wild habitat, we've switched to the 'Standing Ovation' cultivar which has a stiffer habit.
In some areas of our wetland planting – casually referred to as the bog – we plan to alter conditions in order to create niches for species like Virginia marsh St. John's wort ( Triadenum virginicum) and handsome Harry (Rhexia virginica). These smaller perennials were crowded out by graceful cattail (Typha laxmannii) and giant horsetail (Equisetum hymale). While both St. John's wort (Triadenum virginicum) and handsome Harry (Rhexia virginica) grow well in the rich soils of our "bog", these conditions favor the larger more aggressive plants. To help the smaller plants compete we will create niches where they have the advantage. We'll add sand in some areas to reduce nutrient levels. We may also propagate and plant sphagnum moss, which has the capacity to lower pH. By mimicking their tough natural habitats, we hope to give our smaller wetland perennials the upper hand and control the spread of some of the larger species.
like giant horsetail (Equisetum hyemale). The horsetail stems shown here will reach a height of about 3'.
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