How to Grow Black Radishes Canada | Complete Growing Guide

At a Glance

Quick Facts

Soil & Growing Conditions

Water: moist but well-drained, moisture-retentive (RHS)

Growth Stages

Harvest & Storage

When to pick: Harvest in autumn, before the first frost; takes two to three times longer to mature than common red radish (RHS, Nature & Garden).

Diseases

Pests

Black Radish, Sowing to Harvest

Black skin, white flesh

Black Radish is a formal botanical variety of the already-published Radish, Raphanus sativus var. niger -- defined by its tough black or brownish skin over pungent white flesh.

An ancient heritage variety

The German label reads "Schwarzer Winterrettich" (black winter radish) -- Raphanus sativus var. niger -- one of the oldest named radish types still grown today.

Two to three times slower to mature

Nature & Garden: black radish takes roughly two to three times longer to mature than common red radish -- RHS classes it as a late-maturing heritage type.

Harvested before the first frost

RHS and Nature & Garden agree: harvest in autumn, before the first frost -- this root shows the round form typical of the 'Black Spanish Round' type.

Go easy on the nitrogen

Nature & Garden warns against excess organic material or high-nitrogen feed, which pushes leafy growth like this at the expense of the root below ground.

References

1. Nature & Garden -- Tier 2, used only for sowing depth/spacing/timing detail RHS's cultivar page does not cover, not contradicted by it - Black radish - sowing, growing, properties

   Sow directly where the plants are to grow, in furrows 1/2 to 1 inch (2-3cm) deep, from May to September/October depending on climate. Space 2-4 inches (5-10cm) apart, further for larger radishes. Soil pH ideally 5.9-6.8, well-drained and loamy, rich in organic matter, 6-8 hours of sun daily. Takes about two to three times longer to mature than common red radish; harvest before the first frost. Avoid excess organic material, manure or high-nitrogen fertiliser, which encourages lush foliage at the expense of the root.

2. RHS (Royal Horticultural Society) - Raphanus sativus 'Black Spanish Round'

   Late-maturing heritage variety with round black skin and white interior flesh. Hardiness H2 (tolerates low temperatures but cannot survive freezing, 1-5C minimum). Full sun. Soil: chalk, clay, loam or sand; moist but well-drained; acid, alkaline or neutral pH; moisture-retentive soil that isn't overly acidic. Maximum height up to 10cm, spread 0.1-0.5m. Time to maturity 1 year (grown as an annual biennial). Quick to harvest and fits well into limited garden spaces. Harvest available in autumn, reflecting its late-maturing classification. Grow from seed. No pruning needed. PESTS: susceptible to slugs, snails, and flea beetles. DISEASES: may develop brassica downy mildew -- named directly for this variety, not inferred.

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.