Extension Spotlight

Marigolds make a great annual bedding plant. They are also very popular and a well-used annual for the vegetable garden. There is certainly a large variety to choose from for adding to your landscape. From the tallest, the African marigolds at three feet tall to some of the shorter marigolds, the dwarfs, only six inches tall. There is a variety of color from creamy white to combinations of orange and red and much more.

Lucky for us, marigolds like full sun and tolerate the heat. They do need well-drained soil and soil that is moist but not wet. They are perfect for edging a bed or planting amongst vegetables. Marigolds do attract beneficial insects such as lacewings, lady beetles and parasitic wasps. These predators do consume a variety of nonbeneficial insects. Lacewings eat aphids, mites and a wide variety of soft-bodied insects. This includes eggs, thrips, mealybugs, immature whiteflies and small caterpillars. Lady beetles eat mostly aphids. They also will eat mites, whiteflies and scale insects. Parasitic wasps eat a lot of insect larvae. They are good at controlling aphids, scale, whiteflies, sawfly larvae, ants, leaf miners and several types of insects. They will parasitize the eggs of European corn borers, tomato hornworms, codling moths, cabbage loopers and imported cabbage worms. Perhaps this answers the question of why marigolds are relatively pest free.

Recent studies including the one published by Backyard Farmer, July 7, 1999 indicates that marigolds contain compounds toxic to root knot and other plant-parasitic nematodes. These nematodes are microscopic round worms that damage plant roots. This leads to reduced yields and poor quality of the vegetable crop. Root nematodes are usually brought in on other plant material coming into the area. Here is brief list of the types of marigolds that can control root nematodes. The most effective varieties are those of French marigolds such as Bolero, Bonita Mixed, Goldie, Gypsy Sunshine, Petite, Petite Harmony, Petite Gold, Scarlet Sophie, Single Gold and Tangerine. For further reading and information on the study and how to utilize this in your garden go to the following link: https://cals.arizona.edu/yavapai/anr/hort/byg/archive/marigoldsandnematodemanagement.html.

Other studies from the University of Hawaii and the University of California states, “Marigold plants produce a number of potentially bioactive compounds, among which α-therthienyl is recognized as one of the most toxic. This sulfur-containing compound is abundant in marigold tissues, including roots. It has nematicidal, insecticidal, fungicidal, antiviral and cytotoxic activities and it is believed to be the main compound responsible for the nematicidal activity of marigold. Thus, nematodes may be killed either by entering the root system of a marigold plant or contacting soil containing marigold’s bioactive compounds.”

If you are interested, you can read more on this study from the University of Hawaii that says bioactive compounds differ in marigold species or Tagetes species and are not found in the same composition, quantity or quality. Here is a link to that study: https://scholarspace.manoa.hawaii.edu/bitstream/10125/12417/PD-35.pdf.

Marigolds are not just another pretty flower. Use them, plant them, but you must deadhead the spent flowers to keep them flowering all through the season.