If you're looking to cultivate an outdoor plant box in cobalt-rich soil, selecting the right plants is crucial. Certain species thrive in heavy metal environments while absorbing excess cobalt, making them perfect for sustainable gardening. Here are the top cobalt-accumulating plants to consider:

1. Alyssum murale – Known for its ability to absorb high levels of cobalt, this flowering plant is both hardy and visually appealing.

2. Crotalaria cobalticola – A legume that naturally grows in cobalt-rich soils, improving soil health while accumulating the metal.

3. Haumaniastrum katangense – A rare but effective cobalt accumulator, ideal for specialized gardening projects.

4. Phyllanthus serpentinus – A tropical plant that tolerates heavy metals and helps detoxify the soil.

5. Ipomoea alpina – A climbing plant that adapts well to cobalt-rich conditions, adding vertical interest to your plant box.

These plants not only enhance your garden's aesthetics but also contribute to eco-friendly soil management. Pair them with organic compost and regular watering for optimal growth. Happy gardening!