Introduction & History

Alemow is the mysterious rootstock of the tropics — a large-leaved, vigorous citrus species from the Philippines that has carved out a specific niche in lemon production, particularly for Eureka and Lisbon lemons in arid, hot conditions where other rootstocks falter. Known variously as Alemow, Colo, or macrophylla (from its conspicuously large leaves), this species is a paradox: it produces trees of exceptional vigor and early productivity, making it irresistible for commercial lemon growers in California's desert regions and Arizona, yet it carries significant vulnerabilities — poor cold hardiness, tristeza susceptibility, and Phytophthora sensitivity — that limit its use to specific situations. Alemow represents the calculated risk in rootstock selection: where it works, it works brilliantly; where it fails, it fails spectacularly.

History & Origin

Citrus macrophylla is native to the Philippines, where it grows in tropical forests. It was introduced to other tropical and subtropical regions through botanical collections. Its rootstock potential was discovered when researchers observed that lemon varieties grafted on macrophylla produced exceptionally vigorous, early-bearing trees with high yields. This became particularly valuable in California's Coachella Valley and Arizona's desert citrus regions, where the hot, dry climate suits macrophylla rootstock and the lemon industry needed maximum early production.

Botanical Description

A large, vigorous evergreen tree reaching 8–12 m ungrafted — one of the largest-growing citrus species. Leaves are the variety's namesake: very large (12–20 cm, 'macrophylla' = large leaf), dark green, broadly ovate. Thorns are moderate. Flowers are white, tinged purple, large, fragrant. Fruit is large (8–12 cm), rough-skinned, oblong, yellow at maturity, with acidic, moderately juicy flesh. The fruit resembles a rough lemon. The tree's extreme vigor and large leaf size give it a distinctly tropical appearance.

Planting & Cultivation

Used primarily as rootstock for lemons in hot, arid regions. In tropical gardens, can be planted as a specimen tree for its large, ornamental leaves. Space widely (6–8 m) due to extreme vigor. Requires well-drained soil. Not recommended for areas with freezing temperatures or high Phytophthora pressure.

Cultivation

As rootstock, provides: extreme vigor, very early bearing (2–3 years), high lemon yields, excellent performance in hot, arid conditions. The tree's vigor means heavy pruning may be needed to manage size. Irrigate consistently in desert conditions despite drought tolerance. Not recommended for: cold-prone areas, wet soils, regions with severe tristeza virus pressure.

Climate & Cold Protection

The least cold-hardy common rootstock: damaged at approximately -2°C. USDA zones 10a–11 only. Thrives in hot, arid conditions (desert regions). The Philippine tropical origin means poor cold adaptation. This restricts its use to the warmest citrus areas: California deserts, Arizona, tropical regions.

Seasonal Care

Standard lemon cultivation practices for the scion variety. The extreme vigor requires more pruning than trees on other rootstocks. Consistent irrigation in desert conditions.

Cold Protection

The rootstock is very frost-sensitive. In desert regions, cold events are rare but devastating. Protect scion and rootstock from any freezing temperatures.

Seasonal Care Calendar

Propagation

Polyembryonic seeds, easy to grow. Fast-growing seedlings reach budding size quickly. Used in certified nurseries in California and Arizona.

Diseases & Pests

The vulnerabilities: susceptible to tristeza virus (significant limitation), susceptible to Phytophthora root rot (requires well-drained soils), susceptible to citrus exocortis viroid. Moderate nematode resistance. The disease susceptibility profile is the main limitation, restricting macrophylla to situations where its vigor advantage outweighs the disease risks.

Harvesting & Culinary Uses

Not applicable as rootstock. The fruit of ungrafted trees is occasionally used as a sour citrus substitute in cooking.

Culinary Uses

Minimal. Ungrafted tree fruit is occasionally used as a rough lemon substitute. The interest is in what grows above the graft, not the rootstock fruit.

Rootstock Guide

Niche rootstock for lemon production in hot, arid conditions. Advantages: maximum vigor, fastest bearing, high yields, heat tolerance. Disadvantages: tristeza susceptibility, Phytophthora susceptibility, poor cold hardiness. Best for: Eureka and Lisbon lemon in desert regions (California Coachella Valley, Arizona). Not for: cold areas, wet soils, mandarin/orange (typically used only for lemon). The 'speed demon' rootstock.

Container & Companion Growing

Container Growing

Not suitable — far too vigorous.

Companion Planting

Not applicable as rootstock. As a garden tree in tropical regions, its large leaves provide interesting texture contrast with fine-leaved plants.

Common Mistakes to Avoid

Using macrophylla in cold-prone areas where its poor hardiness leads to tree loss. Planting in wet, poorly drained soils where Phytophthora thrives. Using for citrus varieties other than lemon (compatibility may be poor). Failing to manage the extreme vigor with proper pruning.

Frequently Asked Questions