How to Grow Calçots | Soil, pH & Growing Guide

Soil & Growing Conditions

Water: irrigated per traditional practice (Frontiers)

Soil pH range

8 8.6

Span reflects genuine variation between the cited authorities, not a single agreed figure.

Quick Facts

Factor	Value
Soil pH	8 - 8.6
Sunlight	6-6 hours direct sun
Soil texture	loamy, calcareous (Frontiers)
Drainage	well-drained
Lifecycle	biennial, harvested as second-year resprouts
Edible parts	blanched stem shoots

At a Glance

Growth Stages

Stage	BBCH	Notes
Bulb dormancy and replanting	0	Bulbs from the previous season are allowed to remain dormant, then replanted the following late summer (mid-August or late September), at 32,000 plants/ha, 0.3 x 0.75m spacing (Frontiers).
Resprouting	3	Each dormant bulb resprouts into between 1 and more than 25 slender floral shoots (Frontiers) -- the calcots themselves.
Earthing up / blanching	3	As shoots grow, soil is mounded around them to exclude light, keeping the base white and encouraging the shoots to elongate -- the same principle used for leeks (Specialty Produce).
Harvest	8	December (early, sharper) or February (late, sweeter, less fibrous) harvest of the blanched shoots (Frontiers).

Harvest & Storage

When to pick: Harvested at one of two traditional windows: December for a sharper, more pungent early harvest, or February for a sweeter, less fibrous late harvest closer to the ideal calcot profile (Frontiers). Shoots are cut once earthed-up and elongated, with the blanched white base as the prized edible portion.

Diseases

Allium white rot

moderate

Stromatinia cepivora (syn. Sclerotium cepivorum)

Inferred from the species: calcot is Allium cepa, the exact same species as the already-published Onion taxon, which carries this disease. Neither source names a problem specific to the calcot growing method itself.

Pests

Allium leaf miner

low

Phytomyza gymnostoma

Inferred from the species: calcot is Allium cepa, the exact same species as the already-published Onion taxon, which carries this pest. Neither source names a problem specific to the calcot growing method itself.

Calçots, the Catalan Onion Grown to be Grilled

Grown by earthing up

Calcots are second-year onions replanted and earthed up so the shanks blanch long, white and sweet.

Lifted whole

Plants are lifted with their roots in late winter, once the blanched shanks are finger-thick.

Trimmed and bundled

Roots and leaf tips are trimmed and the shanks tied into bundles ready for the fire.

A winter market crop

Calcots reach Catalan markets from late winter into early spring, sold by the bundle.

The calcotada

The whole point of the crop: charred over vine wood, peeled, and dipped in romesco sauce.

References

1. Frontiers in Plant Science (peer-reviewed journal) - Improving the Commercial Value of the 'Calcot' (Allium cepa L.) Landrace: Influence of Genetic and Environmental Factors in Chemical Composition and Sensory Attributes

   Calcots are the immature floral stems of second-year onion resprouts, mainly from the long-day 'Blanca Tardana de Lleida' (BTL) landrace of Allium cepa L. The traditional landrace produces between 1 and more than 25 resprouts ('calcots') per onion bulb, harvested in the plant's second year of growth. Bulb onions are replanted at a density of 32,000 plants per hectare, planting pattern 0.3 x 0.75m, at two possible times: mid-August (early planting) or late September (late planting). Soil: loamy texture, calcareous, between basic and slightly alkaline (pH 8.27-8.61), low organic matter, no electrical conductivity problems recorded. Harvested at two different times: December (early harvest, higher chemical/pungency values) or February (late harvest, sweeter and less fibrous, closer to the ideal sensory profile). Each field managed by farmers using their own customary traditional cultivation techniques for fertilization, irrigation, weed control and pest management -- no standardized disease/pest data given.

2. Specialty Produce -- Tier 2, used only for the earthing-up/blanching technique and EU Protected Geographical Indication status not covered by the Tier-1 journal source, not contradicted by it - Calcot Onions Information and Facts

   Calcots are grown from onion bulbs allowed to remain dormant from the previous season and replanted the following late summer. As the resprouted stalks grow, they are covered with dirt (earthed up) to keep the base white and elongate the shoots -- the same blanching principle used for leeks. Favoured for a mild, sweet flavour and tender texture. Registered with an EU Protected Geographical Indication, certifying they are grown according to traditional methods from their geographical origin in Catalonia, Spain.

2 independent sources are cited for this crop. Where they disagree - soil pH is the clearest case - every figure is preserved rather than averaged into false precision.