Why choose Forner-Alcaide 5 (FA5)?
Technical analysis
It draws its strength from its two parents: the hardiness of Poncirus and the limestone tolerance of the Cleopatra mandarin. Unlike other hybrids, it actively manages the soil "Triangle of Death" (limestone, clay, salt) by acidifying its roots to absorb iron and by excluding salt from the leaves. It induces strong dormancy (semi-deciduous), protecting the tree against frosts down to 3°F (−16°C).
Point of caution
Although semi-dwarfing (ideal for small gardens), it induces early bearing. You will need to support this early productivity with suitable nutrition in the first few years.
Quick comparison
More tolerant of calcareous soils than the C35 citrange or the Citrumelo.
More cold-hardy than the bitter orange: 3°F (−16°C) vs. 14°F (−10°C).
More compact than Volkameriana (ideal for container growing).
Our conclusion
The FA5 is the modern "all-terrain" rootstock. It is the ideal compromise if you want the cold hardiness of Poncirus without its strict soil pH requirements.