The black hawthorn is a Feng Shui compatible plant when facing East. The plant's blossoming nature resonates with the Feng Shui Wood element associated with East, expressing growth and new beginnings. Its dark hue is associated with mystery and introspection, encouraging personal growth. However, individual interpretations of Feng Shui may vary.

Northern sea oats, known for its upright bearing and naturally flowing energy, might serve as a propitious element should it be placed in the Southeast of your space. As per Feng Shui maxims, the Southeast traditionally symbolizes wealth and prosperity. Northern sea oats's inherent vibrancy falls in concord with this narrative, theoretically aiding in the flow of positive energy related to affluence. However, readers' individual experiences may differ depending on a constellation of other factors at play.

The green-winged orchid signifies resilience and adaptability, making it compatible for Southwest-facing areas. This same region, in Feng Shui, relates to relationships and motherhood, which resonates with the orchid's enduring properties, subtly enhancing these aspects of life.

The yellow margin orchid boasts a delightful harmony with a North-facing positioning. As water symbolizes the Northern direction in Feng Shui, such an alignment may benefit from the yellow margin orchid's manifestation of prosperity—a feature associated with its vibrant, golden hue. Yet, interpretations may vary, ensuring every practitioner can engage in their personal resonance with the plant.

The common vervain plant is deemed suitable for North-facing areas, according to Feng Shui principles. This is majorly attributed to its 'water' energy that aligns seamlessly with the symbol of 'water' often tied to the Northern direction in Feng Shui. However, planetary forces can be unique in each scenario, leading to different degrees of compatibility based on personal context.

The red huckleberry is subtly compatible with the North direction according to Feng Shui principles, surmised from its vibrant red berries which cultivate a soothing ambiance. The North direction, often linked with the element of water, and red, representative of Fire, suggests an equilibrium perhaps present here. Nonetheless, interpretations may vary based on personal insights and intuition.

In Feng Shui, the barley aligns with tranquility, nourishment, and resilience. It could bestow an energy of calm stability when situated in the Northeast direction. This placement has been associated with the earth element, reflecting the barley's inherent link to soil and sustenance. As always, individual results may vary, and the effect is subject to the unique interaction of energies in your environment. Therefore, it's recommended to consult a Feng Shui professional for personalized advice.

The pigeon pea harmonizes well with the Southwest-facing direction. This is due to its robust and woody nature, which relates symbolically to the Earth element that governs the Southwest according to Feng Shui principles. However, each individual's energy may result in unique interactions.