How to Grow Calendula From Seed (The Easiest Plant in the Kit)

When to sow calendula seeds

Calendula is an annual, which means it germinates, flowers, sets seed and dies within a single season. That simplicity is what makes it easy: there is no dormancy to break, no cold period to arrange, and no year-two wait.

You have two workable windows. Sow indoors four to six weeks before your last frost date for the earliest possible flowers, or sow directly outdoors once the soil has warmed and frost has passed. Direct sowing is less work and calendula transplants well enough that you are not gaining much by starting early.

In milder regions an autumn sowing overwinters as a small rosette and flowers noticeably earlier the following spring. It is worth trying if your winters are gentle.

1. Four to six weeks before last frost: sow indoors in trays if you want early flowers.
2. After the last frost, once soil has warmed: sow directly where the plants are to grow.
3. Late summer or early autumn, mild regions only: sow for an early display the following year.

How to sow: the one detail that matters

Calendula seed needs darkness to germinate. This is the opposite of several other species in the kit, and it is the single most common reason a tray of calendula disappoints.

Sow at about 6 mm (1/4 inch) and cover the seed properly. Surface-sown calendula, or seed pressed in and left exposed to light, germinates poorly and unevenly. If you are sowing several species at once, this is the one to keep separate in your head.

The seed itself is unmistakable: curved, ridged, greyish-brown and shaped like a small crescent or a curled caterpillar. Nothing else in the kit looks like it, which makes it hard to mix up.

1. Sow 6 mm (1/4 in) deep and cover completely. Darkness is required.
2. Space about 20–30 cm (8–12 in) apart, or thin to that once seedlings are up.
3. Keep the soil moist but not saturated until germination.
4. Expect seedlings in 7–14 days at ordinary room or spring soil temperatures.

Soil, sun and the mistake of being too generous

Calendula grows in ordinary ground and does not want to be fussed over. Full sun gives the best flowering, though it tolerates part shade better than most annuals, and it copes with soil that other plants would sulk in.

Rich soil and heavy feeding produce lush foliage and fewer flowers. If you have been improving a bed for years, calendula will do fine in the poorest corner of it. This is a plant that rewards benign neglect.

It also prefers cooler weather. In hot summers plants often slow down or look tired through the worst of it, then pick up again as temperatures drop in late summer.

Keeping it flowering until frost

Calendula flowers roughly six to eight weeks from sowing, and then it will keep going for months — but only if you keep picking.

The plant's purpose is to set seed. Once it succeeds, flowering slows dramatically. Deadheading, or simply harvesting the flowers, interrupts that and pushes the plant to produce more. A calendula that is picked over every few days will out-flower an unpicked one several times over.

Toward the end of the season, let some heads mature and dry on the plant. Calendula self-seeds freely, and one packet realistically gives you calendula in that bed for years without buying more.

Common problems

Calendula is robust, but three things come up often enough to be worth naming.

Powdery mildew shows up as a grey-white film on leaves, usually in humid conditions or where plants are crowded. Space plants properly, water at the base rather than over the foliage, and remove the worst affected leaves.

Aphids like calendula, which is partly why some gardeners plant it deliberately near vegetables as a decoy. A jet of water or an insecticidal soap handles them, and ladybirds usually arrive on their own.

Leggy, floppy plants generally mean too little light or too much feeding. Neither is fatal, and both are easy to correct next time.

Traditional use, stated carefully

Calendula petals have a long history in European folk practice of being dried and infused into oils and salves, and the plant appears in herbals going back centuries. The flowers are also edible and have been used to colour food.

That history is genuinely interesting. It is not clinical evidence, and nothing on this page should be read as a claim that calendula treats, prevents or cures anything.