How to Grow Marigolds

Choose the right marigold

Most garden marigolds belong to one of three groups, and they behave differently enough that it pays to know which one you’re buying.

African marigolds (Tagetes erecta), also called American marigolds, are the tall ones. They have big double flowers up to 4 or 5 inches across and grow 10 to 36 inches tall, and Penn State puts the tallest at 3 to 4 feet. They are the slowest to bloom, usually flowering from midsummer to frost, and storms can knock the tall ones over.

French marigolds (T. patula) are compact and bushy, 6 to 18 inches tall, with flowers up to 2 inches across. They bloom longer than African types and stand up better to rain, which makes them the better choice for humid, stormy climates. UF/IFAS says French marigolds do well year-round in Florida, while African types are best for spring there.

Signet marigolds (T. tenuifolia) are small, lacy plants that get covered in single flowers and have a lemony scent. They make good edging and window-box plants.

Triploid or “mule” marigolds are African-French crosses that cannot set seed, so they keep blooming through hot weather. The catch is that only about half their seed germinates, so sow extra.

Extension services name varieties that have done well in their own states. In Iowa, Iowa State suggests the Inca and Perfection series (African), ‘Queen Sophia’ and ‘Golden Gate’ (French), and ‘Golden Gem’ and ‘Lemon Gem’ (signet). For South Carolina, Clemson points to the ‘Big Duck’ African hybrids for heat tolerance and the 7-inch ‘Hot Pak’ French series for heat and humidity. Mississippi State found the Giant series to be an excellent cut flower on the Mississippi coast.

Where to plant

Pick a spot in full sun with well-drained soil. Marigolds grow in almost any soil, but they do best in moderately fertile loam with a pH of about 5.5 to 7.0. Clemson warns that below pH 5.5 the leaves can develop a bronze speckling caused by manganese or iron toxicity, so lime acidic soils according to a soil test. Wet, poorly drained ground leads to stem rot.

Work some organic matter into the top 6 inches of soil before planting. If you don’t have a soil test, mix in a slow-release fertilizer made for annuals at planting time and leave it at that.

Planting from seed or transplants

Marigolds are one of the easiest flowers to grow from seed. You can sow them directly once the soil has warmed and frost danger is over. Cover the seed about 1/4 inch deep and keep the soil moist. In warm soil, sprouts appear in 4 to 7 days. Mississippi State gives 75 to 80°F as the outdoor germination range.

For earlier flowers, start seed indoors at 70 to 75°F. Recommended lead times vary: Mississippi State uses 4 weeks, Iowa State 6, and Clemson 4 to 6, with 8 weeks for African types because they take longest to bloom. Harden seedlings off before planting them out after the last frost. The dates for your zone above show both windows.

Spacing depends on type. Clemson and Penn State space French and signet marigolds 8 to 10 inches apart (Iowa State allows 6 to 9), and African marigolds 12 to 16 inches apart, up to 18 inches for the tallest varieties. Crowded plants hold moisture in their foliage and get more disease.

Water and feeding

Water well at planting and keep the soil evenly moist for the first couple of weeks. Once the plants are established, they need about 1 inch of water a week. When rain falls short, water deeply once a week and let the soil dry slightly in between. Water at the base, not over the foliage. Mulch between plants holds moisture and keeps weeds down.

Go light on fertilizer. Nitrogen produces leaves at the expense of flowers, so use a balanced product or one with a higher middle (phosphorus) number.

Pinching, deadheading and staking

Once young plants are established, pinch out the growing tips so they branch and stay compact. Through the season, remove spent flowers to keep new ones coming. Stake tall African marigolds, or plant them where a fence or sturdier neighbors can shelter them, so summer storms don’t flatten them.

Expect a lull in the South during peak July-August heat. Mississippi State notes that plants can stall and bloom less for a while, then pick up again as temperatures ease. If signet marigolds slow down in midsummer, Clemson suggests shearing them back by one-third to push a fresh flush when the weather cools.

Common problems

• Spider mites: worst in hot, dry weather. Leaves look stippled and may show fine webbing. Hose the foliage often or use insecticidal soap.
• Aster yellows: yellowed, distorted growth, sometimes with leafy tufts where flowers should be. Leafhoppers spread it and there is no cure, so pull affected plants and throw them out rather than composting them.
• Powdery mildew and gray mold (Botrytis): these show up in shade, crowding and wet, humid weather. Grow in sun, space properly and water at the soil line.
• Slugs, leafminers, aphids, whiteflies, thrips and grasshoppers: occasional pests. Check plants regularly and act early.
• Stem and root rot: a sign of poorly drained soil.

What marigolds do (and don’t do) for pests

Marigolds are famous as a pest repellent, and the evidence only partly backs that up. Iowa State reports that research found marigolds don’t reduce insect damage on vegetable crops. Clemson notes that some insects are actually attracted to them.

Nematodes are where marigolds really help, but only when they’re used a particular way. Some French and African marigolds produce a root chemical that suppresses root-knot nematodes. Penn State’s method is to plant a thick stand in spring, grow it for several months, and then till or dig the plants into the soil. Clemson names the French cultivars ‘Tangerine’ and ‘Single Gold’ as resistant to several root-knot nematode species. Marigolds scattered among tomatoes or other crops do not protect them.

Cutting and drying

Cut marigolds for the vase when the flowers are just starting to open. Strip any leaves that would sit underwater and put the stems in water right away. Mississippi State holds cut stems at 36 to 41°F and finds they last a week or more without any preservative. To dry them, cut perfect blooms, strip the leaves and hang the stems upside down until they are dry.