Plant eryngiums where there is bright light, poor soil and good drainage in order to develop a strong, rigid framework and steely patina.
These plants are good low-maintenance plants for hot dry spaces with good drainage. If grown on damp, heavy soil most eryngiums tend to flop and become a dull, grey-green.
However, eryngiums are very diverse: there are over 240 species worldwide. Try growing one or two sea holly in the driest hot spots you have. Some even do well on clay.
Sea hollies die down completely in winter and, given good drainage, will return every year. An unusual member of the carrot family (Apiaceae). They set down deep tap roots and do not like to be moved once planted. Plants can grow up to 3 feet tall.
- Water sea holly plants deeply, but infrequently during the first season of growth to encourage the tap root to grow deep into the soil (which is the key contributor to sea holly survival during droughts). Otherwise, these plants thrive on benign neglect. In fact, an excessively fertile soil makes plants lanky, so withhold fertilizer.
- Deadheading won’t yield additional blooms. In fact, faded flowers add winter interest long after the first frost occurs, so best to avoid deadheading.
- As common with many blue flowers, sea holly attract butterflies.
The genus Eryngium belongs to the Apiaceae plant family. This family contains edible plants like sweet fennel as well as poisonous plants like the water hemlock. The common denominator of the Apiaceae family is that the plants have hollow stems, and that they produce compound umbels, which are small flowers that radiate from a single stem. From The Spruce