Marigolds thrive during the long, hot days of summer. They appreciate deep watering during droughts, but overwatering weakens them. "If you water the beds shallowly every day, the plants won't put their roots down far enough," explains Dam. He cautions that the soil should dictate watering patterns—sandy soil dries out quickly and requires more frequent watering.
While marigolds like heat, too much combined with drought can cause the plants to stop blooming. "This usually happens when a moist spring is followed by four weeks of nothing but hot sun," says Dam. Regular deadheading of spent blooms helps prolong flowering. Choosing late and long-blooming varieties also helps.
Marigolds are relatively free of pests and diseases, but in my garden, slugs love them. Try hand picking, or scatter ash or crushed egg shells around the base of plants.
Dam says his marigolds are starting to attract big, green Japanese beetles, which eat the buds as soon as they open. These insects aren't easy to get rid of but he suggests diatomaceous earth. The powder is dusted on the beetles and plants and attacks their skeletons. Or spray with pyrethrum.
Planting marigolds too close together or watering too heavily can result in mould or a fungus called botrytis blight. Occasionally the plants yellow and die, the result of aster yellow, a disease spread by leaf hoppers and aphids. Remove and destroy affected plants.
Every gardener has a different opinion on what looks best with marigolds. I like to pair orange 'Tangerine Gem' marigolds with trailing blue lobelia in containers. I've also seen garden beds designed with yellow 'Inca' marigolds and bushy blue lobelia. Other gardeners like to use marigolds in hot-colour beds with red salvia or geraniums.
No matter what combination you prefer, there are marigold varieties suited to just about every garden. For the front of a bed, consider T. signata pumila, 'Disco Mix' or cultivars in the Lady, Hero or Janie series. In the midrange, choose from 'Sparky Blend', 'Safari Mix', or the Inca, Solar or Zenith series. Those that do well at the back of the border include 'Cracker Jack', the Gold Coin and Jubilee series.
Totally unmarigold-like are 'Vanilla Cream', 'Snowbird', 'Snowdrift' and 'American White', hybrids that produce creamy white blooms, a radical departure from the golds and maroons associated with the family. Dam discontinued selling 'Vanilla Cream' because he found it inconsistent and unattractive, but Derrick finds it reliable and scentless, a plus for gardeners who dislike the strong pungency typical of most marigolds.