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Marigolds want at least six hours of direct sun, and eight is better. In four hours of sun the plant survives but stretches, the stems go soft, the flowers come thin and pale, and the whole thing leans towards the brightest gap. Shade also keeps the foliage damp for longer in the morning, which is the single biggest driver of the gray mold that ruins the big African heads.
If a plant in the ground is clearly in the wrong place, marigolds transplant well even in flower as long as you take a generous rootball and water it in hard. Lift it in the evening, cut the open flowers off, and it will be growing again within a week.
Water the soil, never the flowers
Water deeply and then let the top inch (2.5 cm) of soil dry before you water again. Marigolds have a dense fibrous root system that recovers from a mild wilt without lasting damage, so erring dry is far safer than keeping the soil constantly wet. Roots that sit in wet soil rot at the collar and the plant goes over in an afternoon with no warning.
Aim the can at the base of the plant. Water sitting inside a double marigold flower cannot evaporate out of the packed petals, and that trapped moisture is where flower rot starts. If you use a sprinkler, run it in the morning so the heads dry by midday.
In pots the rules change. A twelve inch (30 cm) container of marigolds in high summer may need water every day, because the plant is transpiring hard in full sun and the roots have nowhere else to go. Check by weight rather than by the surface, which dries misleadingly fast.
| Situation | How often | What to watch |
|---|---|---|
| In the ground, established | Deeply once a week in dry spells | Wilting at midday that recovers by evening is normal |
| In the ground, just planted | Every two or three days for two weeks | Keep the rootball itself damp, not just the soil around it |
| Container in full sun | Daily in high summer | Lift the pot to judge weight; the surface lies |
| Cool wet spell | Stop entirely | Look for collapse at the base, which means collar rot |
Feed less than you think
Marigolds flower best in poor to average soil. Rich ground or a regular high nitrogen feed gives you a big soft dark green plant with hardly any flowers, and that is the most common complaint about marigolds in a well tended vegetable garden where the soil has been manured for the crops.
In the ground, plants in reasonable soil need nothing at all for the whole season. In containers the compost runs out of nutrients after about six weeks, so give a liquid feed low in nitrogen and higher in potassium every two or three weeks from then on. Tomato feed at half strength is exactly the right balance.
If a plant is already all leaf and no flower, stop feeding completely, cut it back by a third, and wait. It will usually come into flower three weeks later once the nitrogen surge has been used up.
Soft dark foliage, thick stems, wide leaf spacing and few buds is a nitrogen picture, not a disease. Note which beds do this to your marigolds and you will know next year which ones need no feed at all.
Deadhead through the whole season
Deadheading is what keeps a marigold flowering until frost. Every head that is allowed to set seed shifts the plant towards ripening that seed and away from making new buds, and a French type left alone for three weeks in midsummer visibly slows down and starts to look tired.
Take the spent head off with the stalk, not just the petals. Follow the flower stem down to the first pair of leaves or the first side shoot and pinch or snip there. Leaving a bare inch of stalk gives you a stub that dies back and gives gray mold a foothold, and it looks untidy for weeks.
Do it every three or four days in high summer and it takes two minutes per plant. Do it once a month and it becomes a chore that fills a bucket. A big African type with heavy heads is the one that suffers most, because a rain soaked spent pompon holds water like a sponge against the stem.
- Learn what a spent head looks like The petals dull and pull inwards, the back of the head swells and goes pale green, and the whole thing feels dry and papery rather than springy. Take it then, before the seed sets.
- Cut back to a leaf joint Trace the stem down to the first pair of leaves below the flower and cut just above them. New shoots break from that joint within a week and each carries its own bud.
- Leave a few heads at the end From late summer, stop deadheading a couple of the best plants so the heads can dry on the plant for seed. Mark those plants so you do not tidy them up by habit.
Support and tidy the big types
African marigolds carry very heavy heads on hollow stems, and a summer downpour will lay a three foot plant flat overnight. A single cane behind the main stem, tied loosely once at eighteen inches (45 cm), is enough. Put it in when you plant, not after the plant has gone over, because pushing a cane through an established root system does real damage.
French and signet types need no support but do need air. Thin out any stems that cross into the middle of a congested plant in midsummer. Opening the center keeps the foliage dry and prevents the mildew and mold that follow humid nights.
Keep the ground under the plants clear of fallen petals. A wet mat of dead petals against the stems is where both slugs and stem rot get established, and it is the easiest thing in the whole marigold year to prevent.
Record which plants needed staking and how tall they actually got. Packet heights are optimistic in rich soil and short in poor soil, and your own note from last year is a better guide than either.