Introduction & History

Carrizo Citrange is the workhorse rootstock of the modern citrus industry — the most widely used citrus rootstock in the world, supporting billions of dollars of commercial citrus production from California to Spain to Australia. This intergeneric hybrid between Washington Navel orange and Poncirus trifoliata was created at the USDA Citrus Research Station in Riverside, California in the early 20th century, part of a systematic effort to develop rootstocks combining the disease resistance of trifoliate orange with the vigor and compatibility of sweet orange. Carrizo's combination of tristeza virus resistance, Phytophthora tolerance, nematode resistance, broad soil adaptability, and good fruit quality induction made it the natural replacement for sour orange rootstock worldwide after tristeza devastated citrus industries in the mid-20th century.

History & Origin

Carrizo citrange was developed at the USDA Date and Citrus Station in Indio/Riverside, California, as one of several citrange (citrus × trifoliate) hybrids. It was selected alongside its sister seedling Troyer citrange from the same cross. For decades, Troyer was the more popular choice, but Carrizo eventually surpassed it due to slightly better nematode resistance and virus tolerance. By the 1970s–80s, Carrizo had become the world's dominant citrus rootstock, a position it largely maintains today. The name 'citrange' was coined by Walter Swingle from 'citrus' + 'orange.'

Botanical Description

A medium-sized, semi-deciduous to evergreen tree reaching 5–7 m if ungrafted. Leaves are unifoliate (single leaflet) but with a noticeable 'winged' petiole hinting at the trifoliate parentage. Thorns are present but moderate. Growth is vigorous and upright. Flowers are white, fragrant. Fruit (if ungrafted) is round, 5–7 cm, with thick rind and bitter, sour, unpalatable flesh — essentially inedible. The tree is intermediate between its parents: more vigorous than Poncirus, more cold-hardy than sweet orange. As rootstock, it is invisible beneath the grafted variety.

Planting & Cultivation

Used exclusively as rootstock. Seeds are sown in certified nurseries, seedlings grown for 12–18 months, then budded with commercial citrus varieties. Home gardeners encounter Carrizo as the rootstock beneath purchased citrus trees. When buying citrus, 'on Carrizo citrange' is one of the most common rootstock specifications. The rootstock is suited to a wide range of soil types (sandy, loamy, clay) and pH conditions (5.0–8.0).

Cultivation

As rootstock, Carrizo provides: vigorous growth (medium to high tree size), excellent Phytophthora resistance, tristeza tolerance, citrus nematode resistance, good cold hardiness transfer, and consistently good fruit quality. Compatible with most commercial citrus varieties: sweet oranges, mandarins, grapefruit, lemons, and limes. Remove rootstock suckers (identifiable by slightly different leaf shape) promptly.

Climate & Cold Protection

Cold-hardy to approximately -10°C ungrafted. As rootstock, transfers significant cold tolerance to the scion. USDA zones 8–11. Performs well across all major citrus-growing regions worldwide. Tolerates heat, drought (once established), and variable humidity.

Seasonal Care

Care follows the scion variety. Monitor graft union annually; remove rootstock suckers immediately. The rootstock's vigor means trees on Carrizo may need more aggressive pruning than those on dwarfing rootstocks.

Cold Protection

The rootstock is cold-hardy to -10°C. Cold protection is determined by the scion variety's tolerance.

Seasonal Care Calendar

Propagation

Grown from seed — polyembryonic, producing uniform nucellar seedlings. Seeds collected from certified Carrizo mother blocks. Sow fresh in fumigated nursery beds. Seedlings reach budding size in 12–18 months. T-budding is the standard grafting method. The most widely propagated citrus rootstock in the world.

Diseases & Pests

Resistant to: tristeza virus, Phytophthora (root rot and gummosis), citrus nematode. Moderately resistant to: citrus blight. Susceptible to: exocortis viroid (use only exocortis-free budwood), some strains of citrus tristeza in severe cases. Overall excellent disease resistance profile.

Harvesting & Culinary Uses

Not applicable — rootstock only. Fruit from rootstock suckers is inedible and should be removed.

Culinary Uses

None — rootstock only.

Rootstock Guide

IS the rootstock standard. Advantages: broad soil adaptability, excellent disease resistance, good vigor, consistent fruit quality, worldwide availability. Disadvantages: can produce overly vigorous trees for small gardens, susceptibility to exocortis viroid, may not dwarf enough for container culture. Best for: commercial orchards, larger home gardens, where standard-sized trees are desired. The 'default' rootstock when no specific need dictates otherwise.

Container & Companion Growing

Container Growing

Not ideal for containers — the vigorous growth produces trees too large for most containers. For container citrus, Flying Dragon trifoliate is the preferred dwarfing rootstock. C-35 citrange (a semi-dwarfing Carrizo-type) is a better choice for large containers.

Companion Planting

Not applicable as rootstock. Companion planting considerations follow the grafted scion variety.

Common Mistakes to Avoid

Failing to remove rootstock suckers, which can outcompete the grafted variety. Using exocortis-infected budwood. Choosing Carrizo when a dwarfing rootstock would be more appropriate for the garden size. Not recognizing Carrizo suckers (slightly different leaf shape from the scion).

Frequently Asked Questions