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Measuring the Marigolds

By Boulder County Master Gardener Mary Marcotte

Garden bed full of marigoldsI’ve always loved the charming lullaby that begins “Inchworm, inchworm, measuring the marigolds…”.

Call me a snob, but this little tune is the only thing I like with regard to marigolds. Many gardeners, however,are picking up packs of marigolds to plant alongside their vegetable starts, touting the flower’s supposed pest-repelling qualities. This spring, in a reputable gardening supply catalog, nearly every picture of veggie gardens features a clump of marigolds. But do marigolds measure up to the purported claims?

According to Iowa State University Extension, marigolds aren’t often bothered by insects and are not prone to fungal diseases like powdery mildew. However, did you know that when it’s hot and dry, spider mites feast heartily on marigolds? From there, it’s a simple hop, skip, and a jump over to the vegetables. Grasshoppers, too, find marigolds quite tasty.

Some gardeners insist that marigolds suppress harmful nematodes in the soil. Nematodes are microscopic round worms that are abundant and naturally occurring in soil. Many nematodes are harmless to plants, and some are even beneficial, parasitizing the likes of blister and Japanese beetle larvae. The nematodes which are destructive to plants, however—such as the root-knot nematode—have not been an issue for Colorado gardeners. They occur in warmer, moister regions of the country where they can be a significant problem.

I’ve also heard gardeners wanting to plant marigolds to deter rabbits and deer. According to Iowa State University Extension, marigolds do not repel rabbits, deer, or other animals. Sometimes, rabbits browse heavily on marigolds. The best safeguard against rabbits is sturdy chicken wire or a fencing of hardware cloth around the vegetable garden.

To be fair, marigolds do attract some beneficial insects (lacewings, ladybeetles, and parasitic wasps) that in turn prey on the bad guys. Simple-flowered marigolds are best for a measured approach to adding pollinator friendly accent colors to your veggie garden.


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