How to Grow Calçots

At a Glance

Quick Facts

Factor	Value
Soil texture	loamy, calcareous (Frontiers)
Drainage	well-drained
Lifecycle	biennial, harvested as second-year resprouts
Edible parts	blanched stem shoots

Soil & Growing Conditions

Water: irrigated per traditional practice (Frontiers)

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)

Likely rather than confirmed: calcot is Allium cepa, the exact same species as the cultivated onion, which carries this disease. Neither source names a problem specific to the calcot growing method itself.

Pests

Allium leaf miner

low

Phytomyza gymnostoma

Likely rather than confirmed: calcot is Allium cepa, the exact same species as the cultivated onion, which carries this pest. Neither source names a problem specific to the calcot growing method itself.

What the research guides add

A calçot is a blanched onion shoot, and the Protected Geographical Indication description is the clearest account of how it is grown.

• The PGI calçots come exclusively from shoots of Allium bulbs of the variety Blanca Grande Tardía de Lérida. (Foods and Wines from Spain)
• The process begins when white onion seeds are sown in October, November and December. (Foods and Wines from Spain)
• As the shoots grow, the plants are earthed up to blanch the base, the part that is eaten. (Foods and Wines from Spain)
• Plant density is approximately 0.5 × 0.3 m, and 4 to 7 calçots are obtained from each bulb. (Foods and Wines from Spain)

Sources for this section

• Foods and Wines from Spain (Calçot de Valls PGI): Calçot de Valls PGI

Section researched and checked on 25 October 2026 by the SoilCommander Editorial Team. How we check facts: editorial policy.

Sources

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. Plants For A Future (PFAF) - Allium cepa

   PFAF entry for Allium cepa. Fetched and parsed directly for the USDA hardiness rating.

3. Specialty Produce - Calcot Onions Information and Facts

   A secondary gardening reference rather than a university or horticultural authority, used only for the earthing-up/blanching technique and EU Protected Geographical Indication status not covered by the peer-reviewed journal source, not contradicted by it. 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.

These 3 sources are specific to this region. The full list of 3 sources behind this guide (Frontiers in Plant Science (peer-reviewed journal), Plants For A Future (PFAF), Specialty Produce) is in the references of our UK guide to calçots; they describe the plant itself, which is the same wherever it grows.