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Marigolds are half hardy annuals, so the whole year is bracketed by frost at both ends. They cannot go out until the last spring frost has passed and they are killed by the first autumn one, and everything in between is a single long flowering run if you keep the seed heads off.
From sowing to first flower takes roughly seven to nine weeks for French and signet types and nine to eleven for the tall African ones. Work backwards from your last frost date rather than fixing on a calendar month, and the same plan works in either hemisphere.
| Point in the season | Main job | The judgement to make |
|---|---|---|
| 6 weeks before last frost | Sow indoors at 70F (21C) | Only start this early if you have real light, or plants will draw |
| 4 weeks before last frost | Pot up and pinch at 4 true leaves | Pinch French and signet; decide for African |
| 2 weeks before last frost | Harden off over 7 to 10 days | Increase outdoor time gradually; bring in on cold nights |
| After the last frost | Plant out at final spacing | Soil above 65F (18C); slug patrol for the first fortnight |
| Early summer | First flowers, start deadheading | Deadhead to a leaf joint every 3 or 4 days |
| Midsummer | Feed containers, thin congested centers | No nitrogen in the ground; open plants up for air |
| Late summer | Cut back leggy plants by a third | Stop deadheading marked plants for seed |
| Early autumn | Collect dried seed heads | Base of the head must be brown and papery |
| First frost | Clear the plants | Compost sound material, bin anything moldy |
Spring: raising plants that are not drawn
The whole spring stage is a race between the plant's growth and the light you can give it. Sowing six weeks before your last frost is about right on a bright windowsill or under lights. Without good light, sow four weeks before instead: a stocky small plant beats a tall pale one every time, and it will overtake it within a month of planting out.
Pot on at three or four true leaves, pinch at four, and keep the plants cooler once they are up, around 60 to 65F (15 to 18C), which slows extension without slowing root growth. Then harden off properly over seven to ten days, starting with a sheltered hour and building to a full night outside. Marigolds moved straight from a warm sill to open ground stall for two or three weeks and can scorch.
Early summer: the fortnight that decides the year
Plant out once the last frost has passed and the soil is above 65F (18C). Space French types eight inches (20 cm) apart, signets eight to ten, and African types twelve to eighteen inches (30 to 45 cm) with a cane already in place. Water in hard so the rootball itself is soaked, not just the surface around it.
The two weeks after planting out are when most losses happen, and almost all of them are slugs. Clear mulch and weeds a hand's width back from every stem, water in the morning rather than the evening, and go out with a torch an hour after dark on the first two nights. After that the plants are tough enough to look after themselves.
First flowers open a few weeks later. From the first spent head onwards, deadheading becomes the main job and stays that way until autumn.
Note the date you planted out, the date of the first open flower, and how many plants you lost in the first fortnight. Those three numbers tell you next year whether to sow earlier, plant out larger, or take slugs more seriously.
Midsummer to autumn: keeping it going
By midsummer a well grown marigold is flowering hard, and the work is deadheading every three or four days, feeding containers with a low nitrogen liquid feed every two or three weeks, and watering deeply rather than often. Plants in the ground in reasonable soil need no feed at all.
In late summer, plants that have gone leggy and bare in the middle respond well to being cut back by a third to just above leaf joints. They break within a week and give one more strong flush that carries through to frost. At the same time, mark two or three good plants and stop deadheading them so the heads can dry for seed.
Early autumn is seed collecting, and it needs three or four weeks of drying on the plant after the last flowers open, so leave enough time before frost. Once frost blackens the plants, pull them, compost anything sound, and bin any head that showed gray mold rather than composting the spores back into the garden.
- Deadhead on a fixed rhythm Every three or four days in high summer, cutting back to the first pair of leaves below the flower. This one habit is what keeps a marigold in flower until frost.
- Cut back once in late summer Take a third off every stem on plants that have gone thin and woody in the center. Expect the next flush about three weeks later.
- Mark seed plants before you forget Tie string round the plants you are saving seed from at the same time you do the late summer cut back, and leave those uncut.
- Clear before the ground gets wet Frosted marigold stems collapse into a wet mat that shelters slugs over winter. Pulling them the week after the first frost removes that shelter.