How to Grow Calendulas | Complete Growing Guide

At a Glance

Quick Facts

Factor	Value
Soil pH	6 - 7
Sunlight	4-8 hours direct sun
Germination temp	16C
Minimum survivable temp	-15C
Drainage	Well-drained; light, poor, free-draining soil tolerated (RHS). USU: moderately nutrient-rich, tolerates a wide range.
Lifecycle	Hardy annual (RHS also lists a biennial habit). Genuinely distinct from the Tagetes marigolds already in this catalogue (French/Aztec marigold, Signet marigold) -- Calendula and Tagetes share the common name "marigold" but are different genera. RHS rates it H5, hardy throughout most UK regions even in severe winters (-15 to -10C). Flowers from summer through early autumn (RHS).
Edible parts	flowers, leaves

Soil & Growing Conditions

Soil pH range

6 7

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

Growth Stages

Stage	BBCH	Notes
Sowing	0	RHS: sow direct in spring (or autumn), 0.5cm deep into finely prepared soil, thinned to 23cm apart; sow at 2-3 week intervals for a continuous display. USU: sow 1/4in deep once soil temperature reaches 60F, germinates in 1-2 weeks; thin seedlings to 8-12in apart in the row.
Establishment care	3	USU: supply 1-1.5in of water a week in mid-summer for optimal growth, though the plant can survive low-water conditions; side-dress every month with a complete soluble fertilizer for optimal bloom.
Flowering and companion planting	6	Deadhead regularly and pinch out terminal shoots to encourage bushy growth and prolong flowering (RHS; USU); USU gives a concrete number -- plants re-bloom in about 2 weeks after deadheading. USU: often planted around tomatoes and potatoes as a companion, acting as a trap crop that draws aphids, whiteflies and thrips away with its sticky sap. Self-seeds readily year to year (RHS).
Harvest	8	USU: pick the complete flower head at full bloom; dry in 1-5 days in a ventilated area away from sunlight. RHS: flowers good for cutting, petals edible, used both in cooking and by herbalists for skincare; USU adds the leaves are also edible, often added to salads.

Harvest & Storage

When to pick: USU: pick the complete flower head at full bloom; plants re-bloom in about 2 weeks after deadheading. RHS: flowers good for cutting.

Storage

USU: dry flowers in 1-5 days in a ventilated area away from sunlight.

Diseases

Powdery mildew

low

Named by both RHS and USU ("powdery mildew(s)").

Calendula virus diseases (unspecified/unidentified)

low

RHS names "a virus" without further detail -- recorded at unspecified level rather than inventing a named virus.

Pests

Glasshouse whitefly

low

Trialeurodes vaporariorum

Named directly by USU.

Aphids

low

Aphididae (various spp.)

Named by both RHS and USU.

Calendula Photo Gallery

A bushy plant

A bushy calendula plant with orange flowers.

Bee pollination

A bee pollinating a calendula flower.

A flower close-up

Close-up of a single calendula flower.

In a garden bed

Calendula plants growing in a garden bed.

A double-flowered variety

A double-flowered orange calendula variety.

A pale double variety

A pale double-flowered calendula variety.

A young plant

A young calendula plant with early flowers.

A single flower

A single calendula flower against foliage.

Multiple blooms

Multiple double-flowered calendula blooms on a bush.

References

1. Royal Horticultural Society - Calendula officinalis (common marigold)

   Soil: chalk, loam, sand; well-drained; light, poor, free-draining soil tolerated; pH acid, alkaline or neutral. Sun/aspect: full sun or partial shade, any aspect; exposed or sheltered. Size: 0.1-0.5m height/spread, matures within 1-2 years. Hardiness H5 (-15 to -10C, hardy throughout most UK regions even in severe winters). Sowing: direct in spring, 0.5cm deep into finely prepared soil, thin to 23cm apart; sow at 2-3 week intervals for a continuous display; also sown in situ in autumn. Care: deadhead regularly to prolong flowering; pinch out terminal shoots to encourage bushy growth; self-seeds year to year. Uses: good for cutting, edible petals, used by herbalists for skincare products; flowers summer through early autumn. Pests: may be susceptible to aphids. Diseases: may be susceptible to powdery mildews and a virus.

2. Utah State University Extension - How to Grow Calendula in Your Garden

   Site/soil: well-drained, moderately nutrient-rich, pH 6-7, tolerates a wide range, suits most Utah soils. Spacing: thin to 8-12in apart in the row. Sowing: 1/4in deep once soil temperature reaches 60F, germinates in 1-2 weeks; grown from seed or transplants after frost danger passes. Water: 1-1.5in per week in mid-summer for optimal growth, though it can survive low-water conditions. Fertilizing: side-dress every month with a complete soluble fertilizer for optimal bloom. Harvest: pick the complete flower head at full bloom; plants re-bloom in about 2 weeks after deadheading; flowers dry in 1-5 days in a ventilated area away from sunlight. Companion planting: often planted around tomatoes and potatoes to help deter insect pests, acting as a trap crop that draws aphids, whiteflies and thrips with its sticky sap. Pests: whiteflies and aphids, controlled with a hard stream of water or regular insecticidal soap. Diseases: powdery mildew, managed with good air circulation, controlled irrigation, and removing infested plant parts.

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.