In 1993, nearby the Observatory, the Fern garden was planted. It houses a collection of several hundreds of hardy ferns. Throughout the 19th century, ferns and collecting them became popular, especially in the United Kingdom. This period was quite beneficial to the collection of the Hortus, and several of these plants still grow in the garden today.
The collection in the garden mainly focuses on the northern hemisphere as temperate New Zealand is so rich in ferns that it is impossible to show a representative collection Most of the hardy ferns come from Europe, North America and Asia. Some of the plants have been cultivated from spores.
At the end of 2002, the Radbout university in Nijmegen donated a collection of horsetails (Equisetum), which are cultivated in pots. Molecular research now shows that despite their different appearance, they are classified with the ferns. Both collections are part of the Nationale Plantencollectie (National plant collection)