How to Grow Calendula in Australia

Calendula (Calendula officinalis), also called pot marigold or English marigold, is a daisy-family annual (Asteraceae) grown for cut flowers, edible petals and companion planting. It is not a Tagetes marigold: the French and African marigolds are a separate genus from the American tropics, while calendula comes from the Mediterranean. It flowers through the cool months when little else does, and the usual mistake is sowing it into the heat.

Three mistakes that matter

1. Sowing the seed too shallow. Calendula seed needs darkness to germinate, so seed left near the surface often fails to come up. Sow it 12 to 15 mm deep, cover it well and keep the soil moist until seedlings appear.
2. Sowing into the heat. Plants prefer cool weather and often stop flowering in strong heat. A late spring sowing in a warm zone can finish almost as soon as it starts. Sow in the windows set out in When to plant.
3. Leaving faded flowers on the plant. Spent flowers set seed, the plant flowers less, and seedlings spring up all over the bed. Remove each flower as it fades, as set out under Deadheading.

When to plant

Seed comes up in 7 to 21 days in soil between 10°C and 24°C, and plants flower best through autumn, winter and spring. Most zones have two windows: sow in autumn for winter flowers, and again from late winter for spring colour.

In frosty gardens, finish autumn sowings by about Anzac Day so plants are well grown before the hard frosts arrive.

Site, soil and setup

Grow calendula in full sun or half sun, in any reasonably fertile, well-drained soil. It copes with poor soil and needs little more than compost, and a pH of 6 to 7 suits it.

Calendula fits a rotation as a cool-season filler, following summer crops in autumn and handing the bed back in late spring.

Container growing

Give each plant a pot at least 20 cm wide and 20 cm deep, about 5 L, filled with fresh potting mix. The dwarf 'Fiesta Gitana Mix', 30 to 35 cm tall, and 'Pink Surprise', about 40 cm, suit pots best.

• Watering: water whenever the surface of the mix feels dry, and never leave the pot standing in a saucer of water.
• Feeding: once seedlings have true leaves, water in worm casting liquid diluted to the colour of weak tea, fortnightly.
• Position: full sun or half sun, such as a north-facing step or courtyard.

Sowing Seeds

Sow calendula direct where it is to flower, or raise seedlings in punnets and plant them out.

Starting under cover

• Sow seed 12 to 15 mm deep in punnets of seed raising mix and cover it well.
• Keep the mix moist but never wet; seedlings appear in 7 to 21 days.
• Plant out once seedlings stand 5 to 7 cm tall.
• Harden off seedlings first (a week or so of longer spells outdoors each day, so they toughen up to sun and wind).

Sowing direct

• Sow a few seeds per spot, 12 to 15 mm deep and 30 to 50 cm apart, then water in gently.
• Thin to the strongest seedling at each spot once the true leaves appear.

Care by growth stage

Steady water and a light hand with feeding carry calendula from seed to flower. Weeks count from sowing.

If growth stalls in poor soil, a light dose of all-purpose controlled release granular (NPK around 14-5-10), scratched into the soil, can help.

Deadheading

Snip or pull off each flower as it fades, matching the method to the plant's habit.

• Dwarf types: pull or snip off each flower of 'Fiesta Gitana Mix' the day after it fades.
• Tall types: cut spent flowers of 'Pacific Beauty Mix' and 'Ball's Improved Orange' back to a leaf. Picking long stems for the vase does the same job.
• Mildewed plants: take off the worst leaves along with the spent flowers.
• Late in the season: leave a few flowers to ripen if you want seed or self-sown seedlings.

Companion planting

Calendula flowers are rich in pollen and nectar, so a few plants through the vegie patch bring in beneficial insects.

Grows well with

• Vegetable beds in autumn and winter: the flowers feed beneficial insects through the cool months.
• Sweet alyssum (Lobularia maritima): another cool-season flower, so the pair keep colour and nectar in the garden through winter.

Keep apart

• Sowthistle (Sonchus oleraceus), capeweed (Arctotheca calendula) and cobbler's pegs (Bidens pilosa): weeds that host tomato spotted wilt virus and the thrips that carry it.
• Beds of small, slow seedlings: self-sown calendula can crowd them out.

Harvesting Flowers

Pick flowers at full bloom, once every petal has opened out.

• Snip or snap off the whole flower head, then pull the petals free for the kitchen.
• For the vase, cut the longest stem you can with clean secateurs.
• Keep picking: plants usually flower again within about two weeks.
• Keep watering steadily through the picking weeks.

To dry the flowers, spread them in a well-ventilated spot out of direct sun for 1 to 5 days. Store them in an airtight jar in a cool, dark cupboard. Scatter fresh petals over salads, or use dried petals to colour rice, butter and cheese in place of saffron.

Common problems

Seedlings collapse at soil level. Damping off (Pythium species and Rhizoctonia solani) rots young stems and roots, most often in wet seed raising mix or soil. Read more

Flowers stay shut. Calendula flowers open and close with the sun, so closed flowers on a dull day are normal.

Seedlings everywhere. Calendula self-seeds readily and can become weedy where spent flowers are left on (see Deadheading).

Pests and diseases

Snails threaten seedlings first, then sap-suckers and leaf diseases take over as plants grow.

Common garden snail (Cornu aspersum). Snails and slugs graze tender leaves at night and can strip a row of young seedlings. Read more

Aphids (family Aphididae). These small sap-suckers favour calendula's soft growth, crinkling or curling the leaves and leaving sticky honeydew. Read more

Tomato spotted wilt virus (Orthotospovirus tomatomaculae). Calendula is among the ornamentals that suffer major losses to it in Australia. Thrips such as western flower thrips (Frankliniella occidentalis) spread it, leaving ringspots, mottling and line patterns on leaves, and infected plants cannot be cured. Read more

Powdery mildew (Erysiphe and Podosphaera species). White powdery patches spread across the leaves, most often in autumn and in damp, humid weather. Read more

Prevention first

• Hunt snails and slugs by torchlight while plants are small.
• Check shoot tips weekly, and hose aphids off with a firm jet of water.
• Leave room for air to move between plants, and water at the base rather than over the leaves.
• Pull out and bin any plant with ringspots or mottling, and keep weeds down around the bed.

Tips

1. In warm gardens, try 'Pacific Beauty Mix', a strain reported to handle heat better than most.
2. Move self-sown seedlings to where you want them while they are small, and give spare ones to the chooks.
3. Save seed from your best plants once the heads are fully ripe and dry.
4. Check with your local council about calendula's weed potential if your garden borders bushland.