A cactarium or cactuario (from Latin, cactarium ) is a garden dedicated to the planting of cactus. Although they generally specialize in collecting cacti, they can also include other desert plants such as sabla, agaves or crassulaceae, although then we would be talking about a xeriscaping.
The cactus are succulent plants native to the American continent, typical of arid environments. They require dry conditions and therefore, in many countries, the collections are kept in greenhouses that protect from the rains. Due to their low need for water, they are a sustainable landscaping option . 
Cactariums also tend to host plants from other botanical families, native to the desert regions of the world.
A cactus garden is a garden for the cultivation and display with many types of cacti. Cacti, due to their unusual appearance for Europeans, attracted the attention of the first European colonizers of Americas and were brought to Europe as ornamental plants already in the 16th century.
The first known collection of cacti was collected in the second half of the 16th century by the pharmacist Morgan in London. Popularity of these plants constantly grew, which was also facilitated by the biological characteristics of many cacti - unpretentiousness to watering  and dry air (the latter is essential for room culture), easy vegetative reproduction. Also, indoor types of cacti, in particular Rebutia, in the summer can be moved in it pot in the garden. In Botanical Gardens of many European countries as well as in private greenhouses, significant collections has been accumulated.