When we hear the word “desert” we usually imagine Sahara or Kara-Kum with their scorching sand-dunes devoid of any vegetation. But the soil of stony deserts of Central and South America is very rich in all necessary salts for cacti. Though its contains very little amount of humus, water dissolves salts and the plant can absorb them.
But if rains are extremely rare here, where does water comes from? Plentiful dews, falling at night and flowing down between ribs of cacti, the night fogs accumulating on prickly stalks – this is a poor water diet of desert types of cactus growing in Mexico, Peru, and Ecuador.
Roots of many cacti of these places are radish-shaped and are capable to save water within, or ramify widely near the surface. To reduce moisture evaporation, cacti aspire to curtail the area of the stalk surface. That’s why they have either spherical or a short cylindrical form.
Desert cactus types are not afraid of burning sun: some of them have thick and dense thin skin, which becomes flat and “hides” in the ground for the period of droughts; some have high sharp ribs causing shade; others are covered with dense prickles or setae, looking like a brush.
For their correct development desert types of cactus require much sun, soil containing little humus and careful watering. They can easily die because of water stagnation in the ground even during summer heat.